<%BANNER%>

Use and effects of diploid pollenizers for triploid watermelon [Citrullus lanatus (Thunberg) Matsumura and Nakai] production

University of Florida Institutional Repository

PAGE 1

1 USE AND EFFECTS OF DIPLOID POLL ENIZERS FOR TRIPLOID WATERMELON [ Citrullus lanatus (Thunberg) Matsumura and Nakai] PRODUCTION By JOSHUA HERBERT FREEMAN A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2007

PAGE 2

2 2007 Joshua Herbert Freeman

PAGE 3

3 To my wife Lindsey for the sacrifices she has made for me to be here, and to my parents for their unyielding support.

PAGE 4

4 ACKNOWLEDGMENTS Foremost, I thank my advisor, Dr. Stephen Ol son for giving me the opportunity to pursue this degree and for his personal and professional guidance. I also tha nk the members of my committee for the time they have dedicated and the knowledge and guidance they have provided. Special thanks go to Dr. Eric Simonne and Dr. Bill Stall for their professional guidance and willingness to help me with any aspect of my car eer. I greatly appreciate the field and office staff at NFREC who helped throughout my dissert ation. Special thanks go to Dr. Powell Smith for planting a seed in my mind that has led me to where I am today. None of this would have been possible if not for the sacrifices that my wife Lindsey has made, putting her career on hold in order to support our family dur ing this time. She has been the strong foundation that has kept me sane and kept me on point. I will be forever grateful to my parents, Linda and Herb Freeman for their re lentless support and cons tant prayer. I would also like to thank my grandparents, Lurie Go ff and Blake Freeman for their support of me in anything I do. I thank God every day for blessi ng me with the mind a nd body that have allowed me to do this and for the family that has suppor ted me. I also thank God for putting me where I need to be when I need to be there. I hope I have made my wife, my family and my God proud.

PAGE 5

5 TABLE OF CONTENTS page ACKNOWLEDGMENTS...............................................................................................................4 LIST OF TABLES................................................................................................................. ..........7 LIST OF FIGURES................................................................................................................ .........8 ABSTRACT............................................................................................................................... ......9 CHAPTER 1 INTRODUCTION..................................................................................................................11 2 REVEW OF THE LITERATURE..........................................................................................13 Review of Diploid Watermelon..............................................................................................13 Taxonomy and Botany....................................................................................................13 Watermelon Production Practices...................................................................................15 Watermelon Production Statistics...................................................................................18 Review of Triploid Watermelon.............................................................................................19 Background Information.................................................................................................19 Seedless Watermelon Market Share................................................................................20 Triploid Seedless Watermelon Production......................................................................21 Pollinator Activity and Preference..................................................................................26 Pollen Effects................................................................................................................. ..27 Competition.................................................................................................................... .30 3 CHARACTERISTICS OF DIPLOID POLL ENIZERS FOR USE IN TRIPLOID WATERMELON PRODUCTION.........................................................................................32 Introduction................................................................................................................... ..........32 Materials and Methods.......................................................................................................... .32 Results........................................................................................................................ .............34 Discussion..................................................................................................................... ..........36 4 POLLEN VIABILITY OF DIPLOID WA TERMELON POLLENIZER CULTIVARS.......40 Introduction................................................................................................................... ..........40 Materials and Methods.......................................................................................................... .40 Results........................................................................................................................ .............42 Discussion..................................................................................................................... ..........42

PAGE 6

6 5 DIPLOID WATERMELON POLLENIZER CULTIVARS EXHIBIT VARYING DEGREES OF PERFORMANCE WITH RE SPECT TO TRIPLOID WATERMELON YIELD.......................................................................................................................... ..........46 Introduction................................................................................................................... ..........46 Materials and Methods.......................................................................................................... .46 Results........................................................................................................................ .............49 Discussion..................................................................................................................... ..........50 6 COMPETITIVE AFFECT OF IN-ROW DIPLOID WATERMELON POLLENIZERS ON TRIPLOID WATERMELON YIELD.............................................................................57 Introduction................................................................................................................... ..........57 Materials and Methods.......................................................................................................... .57 Results........................................................................................................................ .............58 Discussion..................................................................................................................... ..........59 7 VARIABILITY IN WATERMELON FLOW ER ATTRACTIVENESS TO INSECT POLLINATORS.................................................................................................................... .63 Introduction................................................................................................................... ..........63 Materials and Methods.......................................................................................................... .63 Results........................................................................................................................ .............64 Discussion..................................................................................................................... ..........66 8 VARIABILITY IN POLLEN PROD UCTION BY DIPLOID WATERMELON POLLENIZERS.................................................................................................................... ..72 Introduction................................................................................................................... ..........72 Materials and Methods.......................................................................................................... .72 Results........................................................................................................................ .............73 Discussion..................................................................................................................... ..........74 LIST OF REFERENCES............................................................................................................. ..77 BIOGRAPHICAL SKETCH.........................................................................................................84

PAGE 7

7 LIST OF TABLES Table page 3-1 Analysis of variance for pollenizer fruit weight and fruit per plant at Quincy and Live Oak FL during 2005..................................................................................................37 3-2 Interaction effect of loca tion and watermelon pollenizer cu ltivars on fruit per plant at Quincy and Live Oak FL during 2005...............................................................................37 3-3 Main effects for pollenizer fruit weig hts combined over experiments conducted in Quincy and Live Oak, FL, during 2005.............................................................................38 4-1 Analysis of variance for pollen viability of watermelon pollenizer cultivars tested during the Spring and Fall of 2006 at Quincy, FL.............................................................44 4-2 Influence of diploid watermelon pollenizer cultivar on pollen viability at Quincy, FL during the Spring and Fall of 2006....................................................................................45 5-1 Pollenizer cultivar effect on Tri-X 313 yield at Blackvi lle, SC during 2005..................54 5-2 Pollenizer cultivar effect on Supercrisp watermelon yield and average fruit weight at Blackville, SC, Citra, FL, and Quincy, FL during 2006................................................54 5-3 Pollenizer cultivar effect on soluble solids concentration of seedless watermelons at Blackville, SC during 2005 and Citra, FL Quincy, FL, and Blackville, SC during 2006........................................................................................................................... .........55 5-4 Pollenizer cultivar effect on hollowheart disorder in Supercrisp watermelon at Quincy, FL, and Blackville, SC combined with Citra, FL during 2006. Means are to be compared within the same column................................................................................56 5-5 Seed sources for various pollenizer cultivars used during 2005 and 2006........................56 6-1 Influence of pollenizer cultivar and spacing on triploid watermelon yield during 2006........................................................................................................................... .........62 8-1 Pollen production by four diploid waterm elon pollenizer cultivars at Quincy, FL during the Fall of 2006.......................................................................................................76

PAGE 8

8 LIST OF FIGURES Figure page 3-1 Pollenizer staminate flower counts comb ined over Quincy and Live Oak, FL, during 2005. Means not followed by the same le tter are significantly different at ( P 0.05) by Duncans Multiple Range Test.....................................................................................39 5-1 Field diagram for pollenizer experiments at Blackville, S.C., Citra, FL., and Quincy, FL. in 2005 and 2006. Columns represent i ndividual rows. The same design was used for replications three and four...................................................................................52 5-2 Individual three-row plot design for pollenizer experiments at Blackville, S.C., Citra, FL, and Quincy, FL in 2005 and 2006. Plot shown is using a pollenizer recommended to be planted at a 1: 3 pollenizer to seedless ratio.......................................53 7-1 Influence of cultivar on pollinator visitation to staminate watermelon flowers at Quincy, FL, Spring 2006. Visitation means are to be compared within sample date. Means not followed by the same letter are significantly different at P 0.05..................68 7-2 Interaction effect of cultivar and time on pollinator visitation to staminate watermelon flowers at Quincy, FL, on 23 May, 2006. Visitation means are to be compared within sample time. Means not followed by the same letter are significantly different at P 0.05......................................................................................69 7-3 Influence of cultivar on pollinator visitation to staminate watermelon flowers at Quincy, FL, Fall 2006. Visitation means are to be compared within sample date. Means not followed by the same letter are significantly different at P 0.05..................70 7-4 Interaction effect of cultivar and time on pollinator visitation to staminate watermelon flowers at Quincy, FL, on 23 Sept., 2006. Visitation means are to be compared within sample time. Means not followed by the same letter are significantly different at P 0.05......................................................................................71

PAGE 9

9 Abstract of Dissertation Pres ented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy USE AND EFFECTS OF DIPLOID POLL ENIZERS FOR TRIPLOID WATERMELON [Citrullus lanatus (Thunberg) Matsumura and Nakai] PRODUCTION By Joshua Herbert Freeman May 2007 Chair: Stephen M. Olson Major: Horticultural Science The use of in-row pollenizers has become popula r because it allows a greater number of triploid plants to be planted per hectare. Mul tiple in-row pollenizer cultivars are available but it is unclear if any exhibit superior performance with respect to trip loid watermelon yield and if so, what varietal characteristics contribu te to a pollenizer s performance. Field trials were conducted during the Spring and Fall of 2005 and 2006 at various locations in FL. and S.C. to determine the pe rformance of various pollenizers and also what contributed to their success. Of the in-row polleni zers that were tested, Sidekick resulted in the greatest triploid watermelon yields. Yields from plots polleni zed by Patron, SP-1, Jenny, and Mickylee were not significantly lower. The use of Compa nion resulted in significantly lower yields than plots pollenized Sid ekick, Patron, SP-1, and Jenny. Pollen viability can vary between cultivars of a plant species and the pollen viability of four pollenizer cultivars was evaluated. Poor pol len viability from a pollenizer could result in increased fruit abortions and lower yield. No significant differences in pollen viability were detected between pollenizer cultivars tested. Th e production of staminat e flowers is a crucial factor for pollenizers as there must be adequate pollen flow during triploid watermelon fruit set. Flower production for Companion, Jenny, Mickylee, and SP-1 was recorded and

PAGE 10

10 Companion produced as many flow ers as Jenny or Mickylee throughout most of the season. The flowering period of Companion does appear to be shorter than other cultivars. Pollinator preference was examined between Companion, Mickylee, and SP-1 and Companion was found to be the least attractive of the three. The lack of pollinator visitation to Companion appears to be the greatest contri butor to its poor performance. Mickylee is an attractive option to use as a pollenizer because of its lower seed costs. However, Mickylee has a growth habit that is more vigorous than most other pollenizers. Studies comparing SP-1 and Mickylee show ed that the Mickylee competed more with associated triploid plants and reduced yield. Factors affecting pollenizer performance the most appear to be pollinator pref erence, staminate flower produc tion, and competitive effect on associated triploids.

PAGE 11

11 CHAPTER 1 INTRODUCTION Seedless watermelons now account for 78% of th e watermelons sold in the United States. Triploid watermelon plants produce seedless fruits however; they do not produce sufficient viable pollen which is necessary for fruit set. To achieve optimal seedless watermelon yields, rows of diploid watermelon cultivars are planted in the same field as the tr iploids. These diploid cultivars account for 20 to 33% of the watermel on plants per hectare. With low demand for seeded watermelons, it has become less desirable to maintain this much hectarage in diploid plants. Diploid cultivars (pol lenizers) designed to be plante d within the row of triploid watermelons are now available. The use of th ese in-row pollenizers requ ires no dedicated space for the pollenizer plants, thus allowing for an incr ease in triploid plants per hectare. When inrow pollenizers first became available there we re few options, now there are 11 commercially available cultivars. Using in-ro w pollenizers is a new concept a nd most of the in-row pollenizer cultivars have been on the market less than tw o years. The performance of in-row pollenizer cultivars has not been demonstrat ed, however earlier studies have re ported differences in triploid watermelon yields due to pollenizer cultivar. It is suspected that the similar results will be observed with in-row pollenizers. Available in-row pollenizers have diverse phe notypes and variable plant characteristics and it is unclear how these may eff ect the cultivars performance. Characteristics such as flower production, pollen production, pollen viability, attr activeness to pollinators, and plant vigor could have a marked effect on how triploid plants in association with the pollenizers will yield. Pollenizer seed/plant costs are highly variable and it is unclear whet her the more expensive pollenizers will provide for greater seedless watermelon yields.

PAGE 12

12 The aim of this body of work is to determin e how well in-row pollenizers perform and how their varietal characteristics influence their performance.

PAGE 13

13 CHAPTER 2 REVEW OF THE LITERATURE Review of Diploid Watermelon Taxonomy and Botany The watermelon [ Citrullus lanatus (Thunberg) Matsumura & Na kai] was originally described in Africa as Mamordica lanata by Carl Thunberg in 1794 (Hara, 1969). Schrader proposed Citrullus vulgaris in 1836 which was commonly used until lanatus was accepted as the oldest specific epithet. Hara revealed the original description in 1969 that was published by Matsumura and Nakai in 1920 and watermelon has since been designated as Citrullus lanatus (Thunberg) Matsumura & Nakai (Hara, 1969). Watermelon is a dicotyledonous angiosperm in the order Violales and family Cucurbitaceae (Kartesz, 2006). The cen ter of origin for the species is believed to be in southern Africa, where it was first described by T hunberg. David Livingstone reported seeing watermelons growing wild in the Kalahari De sert in 1857 (Wehner, 2006). Watermelon is a warm-season, herbaceous vining annual with angular stems that may reach 9 m long (Wehner, 2006). There are also genotypes that exhibit a bush or dwarf growth habit (due to shorter internodes) that have shorter stems a nd are less branched. The main stem or crown of the plant develops from the seedling stem and may have few to many lateral branches develop depending on genotype. Most watermelon genotypes have pinnately lobed leaves with three to five pairs of lobes and are born singly on the stem (McCreig ht, 1996). Cultivars have been developed that have a nearly entire leaf which is due to a ge ne mutation (Wehner, 2006). Branched tendrils are produced at each node. Watermelon is a monoecious plant with imperfect flowers that are born singly at the leaf axil (Wehner, 2006). Watermel on flowers are small in comparison with other cucurbits such as those in the genera Cucurbita and are born on short peduncles. When plants

PAGE 14

14 reach sexual maturity, staminate (m ale) flowers are produced first a nd for a period of time before pistillate (female) flowers ar e produced. Generally, staminate flowers have three anthers and pistillate flowers have three stigmatal lobes. Pi stillate flowers have inferior ovaries which vary in size and shape depending on genotype. St aminate flowers are only open for one day and pistillate flowers are only receptive for one day. The corollas, stamens and pistils of watermelon flowers are all yellow. Watermelons are entomophilous plants that are primarily pollinated in cultivation by honeybee ( Apis mellifera L.) (Maynard, 2001). Watermelon entomophily is a symbiotic relationship between the insect and plant as pl ants receive pollination and bees obtain pollen (which is the only protein source for honeybees) and nectar. Pollination is facilitated by the production of a sticky substance on the surface of the pollen grains called pollenkitt. Pollenkitt enables adherence to floral visitors in order to disseminate pollen and is primarily seen in entomophilous angiosperms (Dobson et al., 1996). Pollenkitt is comprised mostly of lipids which also play a role in attraction of pollinat ors (Dobson, 1988; Pernal and Currie, 2002). Poor pollination may result in fruit abortion or misshap en fruit which is unmarketable (Rubatzky and Yamaguchi, 1997; Stanghellini et al., 1997; Walters, 2005). Watermelon fruit is a specialized berry with thick skin (rind) known as a pepo (Rubatzky and Yamaguchi, 1997). Watermelon rind thickness is dependent on genotype and can be very thin to thick depending on the in tended use of the watermelon. The edible portion of watermelon is the endocarp, although rind a nd seeds can and are consumed in certain geographic areas. Watermelon fruit are highly variable in size, shape, and color, and although all three are genetically determined, size can be altered th rough production practice s. Watermelons may range from cylindrical to round a nd may be from two to over 90 kg at maturity (Wehner, 2006).

PAGE 15

15 The largest watermelon recorded was 119 kg (Wehne r, 2006). Most cultivars that are currently grown commercially in the U.S. range from 5.5 to 9.0 kg. Consumer preference has changed gradually over time and large fruit (> 11.3 kg) that were once prefe rred are now virtually unacceptable in most of the U.S. market. Average maturity for watermelon fruit is 80 days from transplant and 110 days from seed. Watermelon s eeds are variable in size shape, and color but are usually flattened, teardrop shaped and brow n to black in color (Robinson and DeckerWalters, 1997). Optimum temperatures for s eed germination range form 29.4-32.3C (Olson et al., 2006). Watermelon plants are in tolerant to frost and grow best when the average temperature is above 21.1C (Rubatzky andYamaguchi, 1997). Watermelon Production Practices Growing watermelons and producing optimal yields is dependent on many factors including fertilization, ir rigation, soil management and other cultural prac tices (Hochmuth et al., 2001a). The pH of the soil can greatly infl uence nutrient availabi lity and crop growth. Watermelon plants can tolerate a range of pH va lues from 5.5 to 7.5 but 6.0 to 6.5 is optimum (Hochmuth et al., 2001a). Various forms of lime can be used to correct acidic soil pH, which is common in the highly weathered soils of the south east. Calcium is important in the growth and development of watermelon because it is necessary to maintain the struct ural integrity of cell walls. Inadequate calcium in developing watermelon fruit can l ead to a disorder known as blossom-end rot (BER) (Taylor and Locascio, 2004). Blossom-end rot occurs when tissue at the blossom-end of the fruit begins to collapse. This collapse is visualized as necrotic areas at the blossom-end which allow pathogens to enter the fruit and eventually leads to decay. Although BER is a calcium deficiency, factors such as in adequate or inconsiste nt irrigation, elemental competition, high salinity, high temperature a nd high or low transpiration may induce the problem (Taylor and Locacsio, 2004).

PAGE 16

16 Other elements such as nitrogen, phosphorus potassium, magnesium, and micro-nutrients are also necessary for adequate fruit growth a nd plant development (Hoc hmuth et al., 2001a). The amount of these elements needed may vary by soil type and location. Soil testing should be performed in order to understand what the crop requirements are at a given location. Nitrogen, phosphorus, and potassium are generally the thre e most limiting nutrients and recommendations for the maximum amounts of nutrient addition for watermelon production in Florida are 168N72.2P-140K kg/ha (Olson et al., 2006). Irrigation amounts and frequencies required by the crop can vary depending on soil type, its water holding capacity, and environmental conditions (Rubatzky a nd Yamaguchi, 1997). A minimum of 93 cm of water per hectare is requir ed to successfully grow watermelons (Rubatzky and Yamaguchi, 1997). Irrigation frequencies are important because some portions of growth and development require more water and are more sensitive to moisture stress than others. Water deficit during flowering a nd early fruit growth can have a greater negative impact on watermelon yield than water stress during other growth periods (Erdem and Yuksel, 2003). Watermelon fruit growth and development is triggered by hormones produced by developing seeds, which are depe ndent on pollen transfer from st aminate to pistillate flowers (Rubatzky and Yamaguchi, 1997). Pollination can be a yield limiting factor in watermelon production and in many areas, poll ination by feral honeybees is no longer reliable due to the recent introduction of two parasitic mite species [ Acarapis woodi (Rennie) and Varroa jacobsoni (Oudemans)] (Delaplane and Mayer, 2000). Thes e mites have reduced feral and domesticated honeybee colonies by 90% and 30% respectivel y (Stanghellini et al., 1998; Ambrose, 1997; Harbo and Hoopinger, 1997). The reduction of feral honeybee populations necessitates the introduction of domesticated honeybees in large hectarage, high density plantings. Commercial

PAGE 17

17 pollinators are available for rent or purchase and honeybees are the most readily available. Recommendations vary from one to five hives pe r hectare, which is dependent on hive strength (Olson et al., 2006). Adlerz (1966) reported th at in diploid watermel on, a minimum of eight honeybee visits and 1000 pollen grains per pistilla te flower were necessary for fruit set. Stanghellini (1997) reported similar findings of a minimum six visits per flower in diploid watermelon. Visitation rates lower than this resulted in significantly greate r fruit abortion rates (Stanghellini, 1997). Cultural practices used in watermelon producti on have changed over the years but the ones having the most effect are the use of polyethyl ene mulch and drip irrigation. Traditionally watermelons were grown on bare ground with either overhead or seep irrigation. The use of drip irrigation decreases the amount of water used and increases the use efficiency (Smajstrla et al., 2002). It also allows growers to target fertilizer applications directly to the plants through the use of soluble fertilizer that is pumped through the drip tape (Clark et al., 2005). The use of polyethylene mulch has many advantages includ ing earliness, increased yields, increased profitability, irrigation and fertil izer retention, weed suppression, and fruit protection (Lu et al., 2003; Hochmuth et al., 2001b; Sa nders et al., 1999; Lamont, 1993; Bryan, 1966). By covering the ground with black polyethylene mulch, soil te mperatures are raised which increases early plant growth rate and thus early yield. Mulc h has been shown to decrease harvest time in the spring as much as a month (Bryan, 1966). The earliness of the crop may greatly influence the profitability by allowing producer s to enter the market before other producers or producing regions. The use of polyethylene mulch has al so allowed for the adoption of soil fumigants which are essential for profitable commercial production in certain areas. The use of greenhouse-grown containerized watermelon seedlings has also increased which is due mostly to

PAGE 18

18 increased seed prices and the benefit of signifi cantly greater early yi elds (Nettles, 1963). Implementing polyethylene mulch and the use of transplants has incr eased the success of producers in Florida, Georgia, and South Carolina as it allows them to enter the market before the July 4th holiday. Generally, watermelon movement in the U.S. is greater and the price is higher before this holiday (USDA, 2006). These three states accounted for 42% of the watermelon hectarage in the U.S. in 2005 (USDA-NASS, 2006). Watermelon plant spacing has changed over the y ears; most likely due to adoption of other cultural practices that make production more efficient and a decrease in size preference by consumers (Hochmuth et al., 2001a). Current recommendations for watermelon spacing range from 1.1 to 2.7 m per plant (Daniello, 2003, Olson et al, 2006). Recent research has shown that greater yields per hectare may be achieved on pol yethylene mulch with sp acings as small as 1.0 m per plant (Goreta et al., 2005; Sanders et al., 1999). Plant sp acing is also dependent on plant architecture, as some genotypes have a more vigor ous growth habit than others (Edelstein and Nerson, 2002; Kultur et al., 2001; Reiners and Riggs, 1997). Watermelon Production Statistics Watermelons are grown throughout the world in tropical and subtropical climates. World watermelon production has ranged from 81 billion kg in 2001 to 93.2 billion kg in 2004 (Arney et al., 2006). The worlds largest producer of watermelons is China which usually accounts for over half of the world production (A rney et al., 2006). The U.S. ge nerally ranks fourth in world production and produces on average 1.8 b illion kg (Arney et al., 2006). Florida consistently ranks am ong the top three watermelon-pr oducing states in the nation in both hectares harvested and crop value and pr oduces about 20% of the watermelons grown in the United States (USDA, 2005). Over the last five years, Florida harvested on average ten thousand hectares of watermelons annually worth an average of 72.1 million dollars. In Florida,

PAGE 19

19 watermelons account for 3.9 % of the cash receipts fo r vegetables and 0.91% of the cash receipts for agriculture (USDA, 2002). A lthough watermelon hectarage in th e U.S. has declined over the last five years, total production has remained stable as a result of increased production per hectare. One factor that has changed is th e types of watermelons that are being produced. Review of Triploid Watermelon Background Information Triploid seedless watermelon was first desc ribed in the United States in 1951 based on work that had been conducted in Japan si nce 1939 (Maynard and Elmstrom, 1992; Kihara, 1951). Seedless watermelons are produced by watermelon plants th at are genetically triploid (3n). Watermelon plants are naturally diploid (2n). Triploid plants are grown from triploid seed which is produced by crossing a tetraploid (4n) fe male parent with a diploid male parent. The female parent is produced by treating a diploid seed ling with colchicine, a ch emical that binds to tubulin and inhibits the formation and activity of microtubules in pl ant cells. This inhibits the separation of chromosomes during mitosis whic h doubles the number of chromosomes in the plant and creates a tetraploid (Wehner, 2006). Th e triploid offspring ar e sterile which is why fruits produced by these plants have no seeds. Fruit growth and enlargem ent in watermelons is signaled by hormones produced by developing seeds. Since there are no developing seeds in triploid fruit, these developmental signals are obtained from pollen tube growth and ovule fertilization (Rhodes et al., 1997; Robinson and Decker-Walters 1997; Maynard and Elmstrom, 1992). Ovules abort shortly after fertilization but may remain in the flesh as small rudimentary white seeds (Maynard and Elmstrom, 1992; Kihara 1951). Though fruit growth and development in triploids is signa led by pollen tube grow th, triploid plants produce little if any viable pollen (Rhodes et al., 1997; Robinson and Decker-Walters, 1997; Ma ynard and Elmstrom,

PAGE 20

20 1992). A diploid watermelon cultivar must be plan ted in close proximity to the triploid to provide sufficient viable pollen. This diploi d plant is referred to as a pollenizer. The first hybrid triploid watermelon cultivar s produced by Kihara were finished in 1951 (Wehner, 2006). Triploid watermelon cultivars ha ve been commercially available for nearly 35 years but interest from consumers and growers remained low until the late 20th century. There was little interest in early trip loid cultivars due to erratic and poor performance in the field and high seed costs as compared to diploid cultivar s (Maynard and Elmstrom, 1992). Seed for early triploid cultivars were quot ed at $135 per 1000 seed which was 900 times higher than hybrid diploid cultivars at the time (M aynard and Elmstrom, 1992). Reluctance in adoption of triploids may have also been due to the necessity of using transplants and the increased input costs associated with them. A survey of over 1300 pe ople conducted in 1992 indicated that while 74% knew of seedless watermelons only 31% had ev er purchased one (Wiemann, 1992). Marr and Gast (1991) surveyed consumers and indicated that they were willing to pay 50% more for seedless watermelons and that there was no differential preferen ce between taste of seeded and seedless. The authors suggested that the response seen was on appearance alone as participants were shown cut fruit of both types. In 1990, Karst (1990) estimated that 5% of the U.S. watermelon market was seedless but they had the potential to gain up to 50% market share. Since this time, seedless watermelons have gain ed popularity in the marketplace and also with watermelon growers. Cultivars that would be c onsidered modern cultivars became commercially available in the early 1990s and several are still considered in dustry standards today (Maynard and Elmstrom, 1992). Seedless Watermelon Market Share Before 2002, watermelon market data was not separated into seedless and seeded categories so it is difficult to loca te accurate statistics on the produc tion of either. To date, there

PAGE 21

21 is still no separation of the production area grown in the U.S. but there are now reliable data on seedless and seeded watermelons sold in the U.S. Seedless watermelons accounted for 78% of the watermelons sold in the U.S. in 2006 whic h is up from 50% of the U.S. market in 2002 (USDA, 2006). The portion of Floridas waterm elon production that is triploid has increased from 42% in 2002 to 79% in 2006 (USDA, 2006). There is some incentive for growers to produce seedless watermelons because they typi cally receive 4.5 to 11.0 cents per kg premium and it has become increasingly harder to market seeded watermelons since their market share has decreased (USDA, 2006). Triploid Seedless Watermelon Production The cultural practices used in triploid seedless watermelon production are similar to diploid production with respect to plant spacing, fertilization, and ir rigation. Average maturity is also similar between the two. Grow th habit of triploids is similar to diploids but there are also genotypes that exhibit compact grow th and plant spacing may need to be altered to produce fruits of desirable size. Triploid seed are more difficult to germinate th an diploids and require precise environmental conditions. While diploid cultivars may germinate in as low as 12.7 C, triploid seed will not germinate below 26.6 C and optim um temperature is between 29.4 C and 32.2 F (Hochmuth et al., 2001a). Seed coat adherenc e is also a problem with triploids and may negatively affect seedling growth. To avoid this, seeds must be planted with the radicle end up at 45 to 90 (Maynard and Elmstrom, 1992; Ma ynard, 1989). With these requirements and the high cost of triploid s eed, the use of transplants in spring tr iploid production is necessary as soil temperatures are too cold for direct seeding. Pollination is also a necessity in triploid plants and the introduction of domesticated pollinators, such as honeybees or bumblebees, ma y be more important in triploid production (Walters, 2005). Stanghellini (1997) and Alderz (1966) both reported that pistillate diploid

PAGE 22

22 flowers required a minimum of six to eight hone ybee visits for optimal fruit set and visitation rates lower than this significantly increas ed fruit abortion. Walters (2005) conducted experiments on triploid watermelons in which ho neybee visitations were controlled in order to determine the number of visits n ecessary for optimal fruit set. Research plots contained a 33% pollenizer ratio in order to mimic commercial production. Findings sugg ested that between 16 and 24 honeybee visits were required to achieve maximum seedless watermelon fruit set. These visitation numbers are two to four times higher than what is needed in diploid plants and it was suggested that this is due to a dilution of viable diploid pollen w ith non-viable triploid pollen. The most crucial difference between diploid a nd triploid production systems is the addition of the diploid pollenizer in the triploid field. Kihara (1951) s uggested that one diploid plant should provide enough pollen to achieve adequate fru it set in four to five triploid plants. By these recommendations, 16 to 20% of the plants per hectare should be diploid. Until 2001, there were no scientific data on which pollenizer ra tio would maximize seedless watermelon yield. Maynard and Elmstrom (1992) indicated that a po llenizer ratio of 33% ha d produced acceptable seedless yields and other s ources recommended ratios of 20 to 33% (Robinson and DeckerWalters, 1997; Rubatzky and Yamaguchi, 1997) The method for introducing diploid watermelons into the field at this time was to pl ant solid rows of diploid plants between rows of triploid plants. The diploid cultivar must be di fferent than the triploid in size, shape, or rind pattern in order to facilitate efficient harvest. NeSmith and Duval (2001) used distance of a triploid row from a pollenizer row to make in ferences on pollenizer frequencies. Genesis triploid was used and Ferrari was used as the pollenizer. Their results showed the greatest seedless yields in rows 3.0 m from the pollenizer row with yields in rows farther away declining. Yield estimates produced by NeSmith and Duval (2001) suggested that the greatest seedless

PAGE 23

23 watermelon yield per hectare woul d be achieved with a 1:4 polleni zer to seedless ratio when 1.5 m between-row spacing is used. In this scenario, pistillate triploid flow ers would never be more than 3.8 m away from a staminate diploid flower. Fiacchino and Walters (2003) conducted the same type of experiment but used isolated fields with different pollenizer ratios. The plot design used by Fiacchino and Walters more closely resembled a commercial watermelon field. Plots consisted of raised, plastic mulched beds with 1.5 m between-row spacing. This experi ment also used dedicated rows of pollenizers at ratios of 11, 20, and 33%. In this study, multiple pollenizer cultivars were used to determine if cultivar, as well as frequency, had an effect on s eedless watermelon yield. Millionaire triploid was used and Crimson Sweet and Fiesta were used as pollenizers. Fiacchino and Walters (2003) found plots containing a 33% pollenizer ratio did not have gr eater yield than those with 20%, but both 20 and 33% plots had greater seedless yields than th e plots with an 11% pollenizer ratio. Though there was no difference in yield betw een the 20 and 33% plots, a field with 20% pollenizer ratio would have grea ter seedless watermelon yield on a per hectare basis due to a higher number of triploid plants. These resear chers also reported a significant difference in seedless yield between the two pollenizer cult ivars used, with plots pollenized by Crimson Sweet having greater yield. When Fiesta wa s used as a pollenizer cultivar there was significantly greater hollow heart disorder present in the seedless watermelons. Previous to Fiacchino and Walters (2003), pollenizer choice was based on marketing concerns and not how it affected the triploid crop. In this st udy, watermelon yields per hectare were greatest in plots where pistillate trip loid flowers never exceeded 3.8 m away from a staminate diploid flower, which is in agreement with Nesmith and Duval (2001).

PAGE 24

24 The consensus between Nesmith and Duval (2001) and Fiacchino and Walters (2003) reinforced the non-scientific recommendations of Maynard and Elmstrom (1992) who suggested that a 1:2 pollenizer to triploid ratio. The maximum distance between pistillate triploid and staminate diploid flowers was never greater than 3.9 or 4.5 m because 2.75 and 3.0 m betweenrow spacings were used (Maynard and Elms trom, 1989, 1992). This research was conducted when seedless watermelons held less than 50% of the U.S. market so the production scheme of using dedicated pollenizer rows allowed producers to be diversified in the marketplace. During the early years of commercial seedless produc tion, it may have been more economically beneficial for growers to grow at a 1:1 pollenizer to triploid ratio as seedless melons held such a small market share. With the growth in popular ity of seedless watermelons and their increased market share, it has become less desirable to grow seeded watermelons. Under previous triploid production schemes, as much as a third of a gr owers hectarage needed to be in diploid watermelons. A new cultural management system has recen tly been developed that allows for an increase in the number of triploid plants per he ctare. New diploid cultivars have been developed specifically for the role of pollenizer and thes e cultivars, commonly called special pollenizers, are designed to be planted with in the row of triplo id plants without changing in-row spacing. Special pollenizer cultivars became available in the early 2000s and were used on large hectarage beginning in 2004. As there is no dedicated space for the pollenize r, triploid plants can be planted at 100% stand. Common practices are to punch plant hol es and transplant the field solid with triploid seedlings then go back through the field and tran splant pollenizers between triploid seedlings at the appropriate de nsity. Diploid cultivars produce flowers sooner than triploid cultivars so transplanting the pollenizer seve ral days later may more closely synchronize

PAGE 25

25 blooming in the two types of plants (Freeman and Olson, 2007). This system of pollenizer arrangement increases triploid plant numbers by 20 to 33% per hectare, thus increasing the number of seedless fruits harves ted per hectare. Most of th ese pollenizer cultivars are not intended to be harvested which, allows for harves t of only seedless fruit. This can avoid the confusion of having multiple types of harvestabl e watermelons in the field and the added labor costs of multiple harvests. Though most special pollenizers were not in tended to be harvested, the following cultivars produce marketable fruit: Jenny, Minipol, P innacle, Polimore. Any small fruited diploid cultivar could be used as a pollenizer if it produc es adequate staminate flowers and pollen. Some producers may have a ma rket for the seeded pollenizer fruits and may be able to benefit economically by using one of these cultivars. There are two different types of special polle nizer cultivars available; highly branched plants with reduced foliage and thin vines or short inter-node bush-type plants. The thin-vine types have foliage and vines that are smalle r than standard watermelon plants by varying degrees. These types also exhibit some degr ee of increased branching which increases the number of terminals and therefor e the number of male flowers pr oduced. The reduction in vine and foliage size is intended to reduce the nega tive effects that may occur when decreasing the area per plant by introducing the pollenizer in-ro w. Thin-vine special pollenizers currently available are: Increase (Southwestern Seed s), Jenny (Nunhems US A, Inc., Acampo, CA), Minipol (Hazera Seeds, Inc., Coconut Creek, FL ), Patron (Zeraim Gedera Seed Co, Ltd., Palm Desert, CA), Pinnacle (Southwestern Vegetable Seed, LLC., Casa Grande, AZ), Polimore (Hazera Seeds, Inc., Coconut Cree k, FL), Sidekick (Harris Moran Seed Co., Modesto, CA), SP-1 (Syngenta Seeds, Inc., Bois e, ID), SP-4 (Syngenta Seeds, Inc., Boise, ID). The bush-type pollenizers have a comp act growth habit with short internodes and a

PAGE 26

26 branching pattern more similar to standard wate rmelons. These cultivars also have a nearly entire leaf with highly reduced lobes. Bush-type pollenizer s currently available are Companion (Seminis, Inc., Oxnard, CA) and Stud (Abbott and Cobb, Inc., Feasterville, PA). Most fruits produced by speci al pollenizers are small and usually weigh less than 2.5 kg (Freeman and Olson, 2007). Special pollenizer cultiv ars produce fruits with one of two types of rind patterns, solid grey to light green or light gr een with a dark green stripe, and vary in shape from round to oblong and blocky. As with the dedicated-row pollenizer arrangement, a pollenizer cultivar that has fruits easily distinguish able from the seedless fruits should be chosen. Most special pollenizer fruits are substantially smaller than medium and large seedless fruits which aides in their distinction. However, wh en personal size seedless watermelons (< 3.2 kg) are produced, a cultivar with a di stinct rind should be chosen as separation based on size may not be possible. The thin-vine pollenizers are r ecommended to be planted at a 1:3 pollenizer to triploid ratio while the bush-type cultivars are recomme nded at a 1:2 pollenizer to triploid ratio. Pollinator Activity and Preference Cultivated watermelon crops require pol lination and domesticated honeybees ( Apis mellifera L.) are the most important pollinator (Fr ee, 1993). Walters (2005) illustrated that increased honeybee visitation to pi stillate triploid flowers is required for fruit set due to the dilution of viable diploid polle n with non-viable triploid polle n. Both triploid and diploid watermelon plants produce visually similar stamin ate flowers and triploid flowers produce pollen although it is not viable. Honeybee foraging habits are cont rolled by both visual and olf actory cues but it is unlikely that they can visually distingui sh between triploid and diploid flowers (Butler, 1951; von Frishch 1967). These cues are processed during pre-a lighting inspection and determine whether the flower will be foraged. It has been shown that floral structures such as petals, sepals,

PAGE 27

27 gynoecium, and pollen have distinct volatile emi ssions that are species and genotype specific (Dobson et al., 1996; Dobson, 1991; Dobson et al., 1987). The volatiles from pollen (which are derived from pollenkitt) are the mo st important factors when honeybees decide to forage a flower or not (Pernal and Currie, 2002). Although a hier archy of pollen preference was shown by Olsen et al. (1979), no differences we re observed between the species used by Pernal and Currie (2002). The olfactory cues from pollen also appe ar to be quantitative and decreasing emissions throughout the day indicate less reward to foragers (Dobson et al., 1996). It has been suggested that pollen odor may be distinct between ma le-fertile and malesterile flowers of the same species (Dobson et al., 1996). Preference for male-fertile over malesterile potato flowers has been shown in bum blebee which may have been due to pollen odor (Arndt et al., 1990; Batra, 1993). Wolf et al. (1999) conducted pollinator preference experiments in which honeybees were placed in a fi eld with two watermelon cultivars, one Citrullus colocynthis accession and one C. colocynthis x C. lanatus hybrid BAG, with the number of visitations being recorded. Significantly great er bee visitation was seen in the watermelon cultivar BAG and the C. colocynthis accession, neither of which had nectar volume, pollen quantity, or flower size th at was different from the other geno types tested. Wolf et al. (1999) found a positive correlation between honeybee visitation and sugar concentration of nectar which is what greater visitation was attr ibuted to. This conclusion is in contrast to Pernal and Currie (2002) who illustrated that pollen odor was more important than forage quality for honeybees. Pollen Effects Triploid seedless watermelon fruit growth a nd development is dependent on pollination of the pistillate triploid flowers with viable diploid pollen (Kih ara, 1951; Maynard and Elmstrom, 1992). It has been shown in othe r genera that genotype can have a significant effect on pollen viability and that variations in viability can affect the re productive success of the individual

PAGE 28

28 receiving the pollen. Parzies et al. (2005) repor ted significant differences in pollen viability within and between species of barley however, these differences were only evident after the pollen was subjected to incubation treatments. Th ese results indicate more of a difference in pollen longevity as oppo sed to viability. Fortescue and Turner (2004) investigated the pollen viability within and among multiple banana species and among ploidy levels within a single species. This st udy reported significant differences in pollen viability between species, w ithin species, between ploidy levels within a single species, and within ploidy levels of a sing le species. The differences in pollen viability were as great as 100% between cultivars of the same ploidy level and same species (Fortescue and Turner, 2004). Pollen source has been inve stigated in mandarin orange and significant effects were reported on fruit quality parameters Vithanage (1991) inve stigated the pollen donor effects on Ellendale mandarin using six different pollenizers. Vithanage reported that fruit weights of Ellendale were significantly greater when Murcott and Emperor were used as pollenizers. Wallace and Lee (1999) conducted experiments in which Ellenor mandarin was pollinated by Murcott, Imperial, and Ellenor. This study found that fruits from Ellenor had significantly greater size and su gar content when Murcott was used as a pollenizer. Lavi et al. (1996) reported significant differences in po llen viability among cultiv ars of macadamia but found no correlation between pollen viab ility and fruitle t retention. Nikkanen et al. (2000) illustrate d that pollen viability within Picea abies was significantly effected by individual po llen donor and germination conditions, and that there was an interaction between these two factors. These results show that individuals of the same species, within a geographic area, may require specific environmenta l conditions for reproduc tive success. Brevis et al. (2006) reported signifi cant differences in pollen viability among rabbiteye blueberry

PAGE 29

29 cultivars, although all cultivars had a high averag e viability. This study suggested that while pollen viability was statistically significant, it may not be biologically significant and is not thought to contribute to reproduc tive failure in blueberry. Polle n viability data presented by Brevis et al. (2006) was similar to previous findings in rabbiteye and southern highbush blueberry (Cockerham and Galle ta, 1976; Lang and Parrie, 1992). There is only one published study on pollen viab ility in the family Cucurbitaceae. Nepi and Pacini (1993) investigated various asp ects of pollination in a single cultivar of Cucurbita pepo They reported that average pollen viability at anthesis was 92% which decreased to 75% within 6 h and further decreased to 20% at 11 h after anthesis. This decrease in viability was attributed to dehydration of the pollen grain. There is no published data on pollen viability of watermelon cultivars. Variation in pollen production has been reported between gene ra and among species of the same genera in the Poaceae, and among species of the same genera in the Cupressaceae (Hidalgo et al., 1999; Prieto-Baen a et al., 2003). In diploid wate rmelon, Stanghellini and Schultheis (2005) investigated 27 cultivars and found significan t differences in production of pollen grains per flower and pollen grains per plant. Polle n production ranged from 134,206 grains per plant per day for Jamboree to 264,589 grains per plant per day for Summer Flavor 800. The time period over which diploid cultivars pr oduce pollen may be as important as the amount of pollen produced. Diploid watermelon cultivars begin to produce staminate flowers about seven days before triploid plants begin to flower and it is essential that the diploids continue producing staminate flowers throughout triploid fruit set (Fr eeman and Olson, 2007). Significant differences in total staminate flower production, as well as fl owering longevity, have been reported in diploid watermelon cultiv ars (Freeman and Olson, 2007; Stanghellini and

PAGE 30

30 Schultheis, 2005). Greater staminate flower an d pollen production by a diploid cultivar may improve its performance as a pollenizer by reducing the dilution effect of viable pollen that is created by triploid plants. Competition Competition has been defined as the negative interaction between two organisms (Connell, 1990). In plants, this competition is for light, water, nutrients, and space, and can be interspecific (between two species) or in tra-specific (between individuals of the same species). Interspecific competition from weed species as well as intra-specific competition from neighboring crop plants can reduce the surviv ability of plants and the yiel d and quality of plant products (Firbank and Watkinson, 1990). Intra-specific competition in cropping systems is regulated by planting density which is intended to maximi ze production per unit area. Maximum production per unit area occurs when plant population and yield per plant are in correct proportions. Experimental models have shown that plant yiel ds increase with plant density to a maximum point and then plateau or declin e as density continues to increas e (Holliday, 1960). Intra-specific competition and plant density can also be used as tools to manipulate yield parameters such as size distribution of fruit (Mot senbocker and Arancibia, 2002; Reiners and Riggs, 1999; Sanders et al., 1999). Intra-specific competition of crop plants is investigated through studies that examine the effect of planting density or sp atial arrangement on crop yield. In vining cucurbits such as muskmelon ( Cucumis melo L.), pumpkin ( Cucurbita pepo L.), and watermelon, it has been shown that increasing plant density increases total yield but decrea ses yield per plant (Ban et al., 2006; Duthie et al., 1999a; Duthie et al., 199b; Goreta et al., 2005; Kultur et al., 2001; Maynard and Scott, 1998; Reiners and Riggs, 1999, 1997; Sande rs et al., 1999). The increases in yields per unit area reported in these studies were due to increased fruit numbers per unit area.

PAGE 31

31 Although the use of in-row diploi d pollenizers has increased, it has not been determined if the increased competition on neighboring triploid plants will be deleterious. When planted at a 1:3 pollenizer to triploid ratio, the pollenizer will directly impact 2/ 3 of the plants per hectare by decreasing in-row spacing by 1/4. This would re duce area per plant from 2.2 m to 1.6 m for plants grown on 2.4 m between-row spacing a nd 0.9 m in-row spacing. Though reduced, this area is still greater than th e 1.0 m per plant which has b een shown to produce greatest watermelon yields per hectare (Goreta et al., 200 5; Sanders et al., 1999). Results from other studies in watermelon do not provide insight as the phenotype of the polle nizer and triploid are different. As pollenizer growth will not impact a ll triploid plants per hectare, the appropriate study to investigate pollenizer competition effect is the neighborhood (area of influence) study in which the performance of a singl e individual is measured as a function of distance from the competitor (Radosevich and Roush, 1990).

PAGE 32

32 CHAPTER 3 CHARACTERISTICS OF DIPLOID POLL ENIZERS FOR USE IN TRIPLOID WATERMELON PRODUCTION Introduction With triploid seedless watermelons now occ upying 78% of the United States market, it is suspected that the use of in-ro w pollenizer cultivars will increa se (USDA, 2006). There are no published studies that compare important charact eristics of diploid wate rmelon pollenizers such as staminate flower production, flowering peri od, and fruit production. Pollenizer flower production may be a strong indicator of how a cu ltivar will perform and flowering period is critical to the type of production system the po llenizer is used in. Using a pollenizer cultivar with low fruit production and eas ily distinguishable fruit could also increase efficiency in harvesting operations. The objectives of this study were to determine staminate flower production, flowering period, and qu antity and size of fruit produc tion of several commercially available diploid pollenizers. Materials and Methods Experiments were conducted at the North Flor ida Research and Education Center, Quincy, FL, and the North Florida Research and Educatio n Center-Suwannee Valley, Live Oak, FL. In Quincy, the soil type was a Norfolk Loamy Fine Sand (fine-loamy, kaolinitic, thermic, Typic Kandiudults) and in Live Oak the soil was a Lakeland fine sand (thermic, coated Typic Quartzipsamments). At both locations, the expe riment was arranged as a randomized complete block design with four replica tions. Transplants were produced in a greenhouse at Quincy in expanded polystyrene flats of the inverted pyramid design which were 3.75 3.75 6.25 cm using soil-less media. Prior to the laying of the mulch, pre-plant fertilizer was applied at recommended rates and incorporated into the soil (Olson et al., 2004). All fertilizer was applied pre-plant in Quincy and one-fourth was applied pr e-plant in Live Oak. Weekly fertigation was

PAGE 33

33 used to apply the remainder of the fertilizer in Live Oak. Watermelon plants were irrigated as needed. On 1 Apr. 2005, 5-week-old seedlings of SP1, Companion, Jenny, and Mickylee were transplanted into raised beds fumigated w ith methyl bromide and chloropicrin (67/33) and covered with black polyethylene mulch. In Live Oak, plots consisted of two rows; beds were 0.6 m wide by 10 m long on 2.1 m centers, with in-row spacing of one meter. Pollenizer cultivars were planted with the triploid cultivar Tri-X 313. A polle nizer plant was planted at the beginning and end of each plot, and between every th ird and fourth Tri-X 313 plant in the plot. Plots at Live Oak consisted of 18 triploid plants and eight pollenizers. In Quincy, plots consisted of two rows; beds were 0.9 m wide by 13.2 m long on 2.4 m centers, with an in-row spacing of one meter. Tri-X 313 was also used in Qu incy and placement and spacing of pollenizer cultivars were the same as for Live Oak. Plots at Quincy consisted of 24 triploid plants and 10 pollenizers. Plants were sampled after the onset of male flowering by pollenizer cultivars, and data were collected twice a week at both locations. On ce 70% of pollenizer plants in each plot had at least one open male flower (f lowering threshold), the plot was considered to have begun flowering. Numbers of male flowers per plant were recorded from the beginning of flowering (29 Apr.) until the end of the fruit set period (3 June). Early season flower counts were obtained by counting open male flowers on all pollenizer plants in each plot. However, after plants began to vine heavily (making flower counting difficu lt), flower counts were obtained from a single row in each plot. Fruit from polleni zers were harvested at or n ear maturity and weighed on two dates per location. Tri-X 313 was not harveste d for yield and only serv ed to provide intraspecific competition for the pollenizers. Wit hout this competition, growth habit of the

PAGE 34

34 pollenizers would be different a nd not reflect flower counts that would be seen under commercial production conditions. Statistical analysis was performed using the GLM procedures of SAS (SAS Institute, Inc., Cary, NC). For statistical analysis, location wa s added and the experiment was analyzed as a factorial experiment with two f actors, location and cultivar. If an interaction was present, LSMEANS analysis and LSD were was used to explain results, otherwise means separation was performed using Duncans multiple range test. Results The first pollenizer cultivar to reach the thre shold for flowering in all plots was SP-1, on 2 May, 2005 in Quincy. All cultivars had reach ed the flowering threshold by 10 May and 12 May for Quincy and Live Oak, respectively. Pe ak fruit set by Tri-X 313 began 14 May and ended 3 June at both locations. By 1 June, T ri-X 313 had set all commercially harvestable fruit, and by 10 June, mature Tri-X 313 melons were present at both locations. Location did not significantly affect male flower counts, and there was no significant interaction between location and cultivar ( P > 0.05). Data were combined over locations and analyzed. On 29 Apr., SP-1 produced 0.65 flowers pe r plant (fpp), which was not significantly different from Companion or Mickylee whic h had 0.65 and 0.21 fpp, respec tively (Fig. 3-1). Jenny had 0.12 fpp which was significantly lower th an that of Companion or SP-1, but not Mickylee. On 3 May, SP-1 had 0.73 fpp whic h was greater than Companion at 0.52 fpp or Jenny at 0.38 fpp. Mickylee had 0.25 fpp wh ich was significantly lower than that of Companion or SP-1, but not Jenny. On 9 May, Jenny had 1.95 fpp which was greater than Companion at 1.00 fpp. However, fpp for Jenny was not different than SP-1 or Mickylee, which were 1.65 and 1.50 fpp, respectively. On 13 May, SP-1 had 6.36 fpp which was not different than Jenny at 5.76 fpp or Mickylee at5.52 fpp, howe ver, SP-1 was significantly

PAGE 35

35 higher than Companion, 4.75 fpp. On 16 Ma y (Tri-X 313 had begun producing female flowers), SP-1 had greater flow er counts compared to the other pollenizer cultivars; SP-1 had 9.72 fpp compared to 7.88, 7.56, and 7.5 fpp for Mickylee, Companion or Jenny, respectively. This trend conti nued throughout the remainder of th e season as most mid (16 May) to late (1 June) season male flower counts s howed that Companion, Jenny, and Mickylee had similar numbers of flowers but were less than SP-1. Flower numbers increased and peaked on 26 May when SP-1 had 35.5 fpp which was greater than Companion, Mickylee, and Jenny which had 14.50, 13.80 and 12.80 fpp, respectively. Analysis of pollenizer fruit counts per plot i ndicated a significant lo cation effect and an interaction between location and cultivar (Table 31). Distribution of fruit per plant by cultivars was slightly different at the two locations (Table 3-2). At Quinc y, fruit set was greater for SP-1, with 5.8 melons per plant (mpp) compared to all other cultivar s. Companion set the least number of fruit, with 1.8 mpp, which was le ss than Jenny at 4.3 m pp or Mickylee at3.7 mpp. At Live Oak, Jenny produced 3.4 mpp a nd SP-1 produced 3.3 mpp, which were greater than Mickylee at 1.7 mpp or Companion at 1.2 mpp. The interaction between cultivar and location is due to the different rankings of fr uit production by cultivar at each location. In Quincy, fruit production by Jenny and Mickyle e were not significan tly different, however both produced less fruit than SP1. At Live Oak, fruit produc tion by SP-1 and Jenny were not significantly different but both produced more fruit than Mickylee. At Quincy, Mickylee produced more fruit than Companion but at Li ve Oak fruit production was similar between the two. Data analysis indicated that lo cation had a significant effect on pollenizer fruit weight, and that fruit weights in Live Oak (avg. = 2.80 kg) we re lower than those at Quincy (avg. = 3.06 kg)

PAGE 36

36 ( P 0.05). There was no interaction between loca tion and cultivar. Mickylee had the highest fruit weight, 4.34 kg/fruit, whic h was higher than for Compani on or Jenny which were 2.61 and 2.56 kg/fruit, respectively (Table 3-3). SP-1 had the lowest fruit weight at 2.21 kg/fruit, which was less ( P 0.05) than of all othe r pollenizer cultivars. Discussion SP-1 and Companion produces non-edible fruits while Jenny and Mickylee produce edible melons. When used as pollenizers, fru it production is not desirabl e because melons from pollenizers can confuse the harvestin g process (with mixing of seeded and seedless fruit) as well as hinder harvesters from moving efficientl y through the field. Companion and Mickylee produce easily distinguishable melons based on the grey to pale green color and no rind pattern. SP-1 produces a light green melon with very thin light green broken stripes while Jenny produces melons that have a medium green b ackground with dark green stripes. All four pollenizer cultivars would be easily distinguisha ble by size from most commercial melons, other than personal-size seedless watermelons wh ich generally weigh between 1.8 and 2.2 kg. All four pollenizers had male flowers pr esent during peak seedless watermelon fruit setting. Results were similar to Dittmar et al (2005) with SP-1 produc ing significantly more male flowers than Companion, Jenny, or M ickylee. Although flower production by SP-1 was highest other cultivars may also provide more than enough pollen to accomplish optimal seedless watermelon fruit set. Stanghellini and Schultheis (2005) reported that pollen production is also variable between diploid watermel on cultivars so flower production may not be completely indicative of a cultiv ars male reproductive output. All cultivars appear to be viable options for use as pollenizers in triploid wa termelon production as all were producing male flowers during fruit set of seedless watermelons.

PAGE 37

37 Table 3-1. Analysis of variance for pollenizer fruit weight and fru it per plant at Quincy and Live Oak FL during 2005. Source df MS P -value Fruit weight Replication 3 0.10217 0.848 Location 1 2.67961 0.015 Cultivar 3 35.3234 <0.0001 Location*Cultivar 3 0.17825 0.708 Error 21 0.38212 Fruit per plant Replication 3 0.33208 0.207 Location 1 17.7012 <0.0001 Cultivar 3 14.2712 <0.0001 Location*Cultivar 3 1.75791 0.0006 Error 21 0.20113 Table 3-2. Interaction effect of location and watermelon pollenizer cultivars on fruit per plant at Quincy and Live Oak FL during 2005. Location cultivar Fruit (no./plant) Quincy SP-1 5.8 Jenny 4.3 ** Mickylee 3.7 NS Companion 1.8 ** Live Oak Jenny 3.4 SP-1 3.3 NS Mickylee 1.7 ** Companion 1.2 NS NS, *, ** non-significant, or significant at P < 0.05 or P < 0.01, Least Squares Means analysis.

PAGE 38

38 Table 3-3. Main effects for pollenizer fruit weights combined over experiments conducted in Quincy and Live Oak, FL, during 2005. Cultivar Avg fruit wt (kg) Mickylee 4.34 az Companion 2.61 b Jenny 2.56 b SP-1 2.21 c z Means followed by the same letter are not significantly different at ( P 0.05) by Duncans multiple range test.

PAGE 39

39 a a a a a a a a b b b b b b b b b b b b b b b 0 5 10 15 20 25 30 35 40 29-Apr3-May9-May13-May16-May 19-May23-May26-May30-May3-Jun Sampling DateNumber of Male Flowers Per Plant SP-1 Companion Jenny Mickylee Figure 3-1. Pollenizer staminate flower counts combined over Quincy and Live Oak, FL, during 2005. Means followed by the same letter are not signifi cantly different at ( P 0.05) by Duncans multiple range test.

PAGE 40

40 CHAPTER 4 POLLEN VIABILITY OF DIPLOID WA TERMELON POLLENIZER CULTIVARS Introduction Pollen produced by diploid watermelon pollenizers is important because it is necessary for fruit set and flesh fill in associated triploid watermelon crops (Kihara, 1951; Maynard and Elmstrom, 1992). Viable pollen produced by polle nizers is diluted with non-viable triploid pollen which increases pollinator visitation rate s required by pistillate triploid flowers. Pollenizers with poor pollen viability could furt her increase required visi tation from pollinators and reduce stigmatal area available to viable po llen; both of which coul d have negative effects on seedless watermelon yield and quality. Significant differences in pollen viability have been reported between cultivars of the same species in several genera. The objective of this project was to determine pollen viability of four polleni zer cultivars to investigate possible effects on performance. Materials and Methods On 3 Apr. and 1 Aug. 2006, 4-week old waterm elon seedlings were transplanted into raised beds. The beds were covered with bl ack polyethylene mulch in the spring and white polyethylene mulch in the fall. Experiments were performed at the North Florida Research and Education Center (NFREC) in Quincy, FL. Soil type present at NFREC is Norfolk loamy sand (fine-loamy, kaolinitic, thermi c Typic Kandiudults). Experimental design both seasons was a randomized complete block with four replica tions. Four diploid pollenizer cultivars, Companion, Jenny, Mickylee, and SP-1, were used to determine pollen viability. Experimental plots were 4.57 m long with an in-row spacing of 0.91 m and between-row spacing of 2.43 m. Three seedlings were planted in each plot. Fertil ization, irrigati on, and pesticide

PAGE 41

41 application practices recommended by the Univ ersity of Florida In stitute of Food and Agricultural Sciences were followed (Olson et al., 2006). Sampling was initiated on 17 May and samples were taken on 24 May and 31 May in the spring. Sampling was initiated on 31 Aug. and samp les were taken on 7 Sept. and 14 Sept. in the fall. Sampling was initiated when other triploid watermelons at NFREC th at were transplanted on the same dates began to set fruit. The samp ling period was scheduled to mimic peak fruit set in triploid watermelons. The fruit set in this ti me frame would be the majority of the fruit that would be available for commercial harves ting schemes that are typical for FL. On sampling dates, watermelon flowers were rem oved from the plant befo re anthesis. This was to insure that pollinator s would not remove pollen and an adequate supply would be available for analysis. Three flowers were rem oved from each plot and placed into plastic cups and covered to exclude pollinators. Flowers were taken to the lab and allowed to open. After anther dehiscence had occurred (v erified with a hand lens) sample analysis was initiated. Pollen was removed from the anthers and placed on a sl ide. Viability was determined using the diaminobenzidine (DAB) protocol for peroxidase activity in pollen (Dafni et al., 2005). Rodriguez-Riano and Dafni (2000) compared the results of four vital dyes versus pollen germination results and illustrate d the superiority of peroxidase tests over other commonly used vital dyes. This test utilizes a dye that creates a color differen tial between viable and non-viable pollen. Four 100 pollen grain sub-samples were an alyzed from each plot using a compound microscope. A pollen grain was considered viable if it had turned dark brown or black. All pollen samples were analyzed on the same day pollen was collected. It is important with watermelon pollen that the pollen be thoroughly mixed with the dye on the slide in order to have

PAGE 42

42 adequate contact between the polle n grains and dye. If large cl umps of pollen are not broken up, dye may not infiltrate the pollen and false negatives may be observed. On each sample date heat killed pollen (two h at 80C) was used to check the efficacy of the dye. New dye was prepared for each sample date. A square-root transforma tion was performed on the data and analysis of variance and means separation (Duncans multiple range test) were performed using the GLM procedures of SAS (SAS In stitute Inc., Cary, NC) Results There were no sampling dates in either seas on where pollenizer cultivar had a significant ( P 0.05) effect on pollen viability (Table 4-1) There was also no significant interaction between pollenizer cultivar and sampling date (Table 4-1). In the spring trial, sampling date had a significant ( P 0.05) effect on pollen viability with 31 May having greater average viability than 24, or 17 May (Table 4-2). Pollen viab ility on 31 May was 98.6% wh ich was significantly greater than 97.4 or 97% for 17 May and 24 May, respectively. The average pollen viability over all cultivars and all dates for spring and fall were 97.7 and 97.9%, respectively. There was very little variation with in the data and the coefficient of vari ation was never higher than 0.84%. Discussion The results of this study illustrate that there is no significant variation in pollen viability within the cultivars tested and that pollen viab ility is high and changes very little if any throughout the growing season, at leas t not within the critical period of triploid fruit set. The sample date in the spring with higher viability is more likely due to environmental conditions than cultivar characteristics. Freeman ( 2007) observed that seedless watermelon yield was significantly lower when Companion was used as a pollenizer versus Jenny or SP-1. The results of this study suggest that pollen viability was not a contributing factor in the varying degrees of performance of these pollenizers. Fact ors such as floral attractiveness to pollinators,

PAGE 43

43 timing and total production of staminate flowers, and pollen production may be more important characteristics of pollenizers. The small amount of variation in pollen viabilit y between the cultivars tested suggests that there may be little within the spec ies or at least in cultivated va rieties. Nepi and Pacini (1993) reported that the pollen viability of Greyzini ( Cucurbita pepo L.) averaged 92% which is similar to the findings of this study. Pollen viabil ity appears to play no role in the performance of the pollenizers tested and may not be an importa nt characteristic of pol lenizer cultivars.

PAGE 44

44 Table 4-1. Analysis of varian ce for pollen viability of watermelon pollenizer cultivars tested during the Spring and Fall of 2006 at Quincy, FL. Source df MS P -value Spring Sampling Date 2 0.02827 0.003 Replication 3 0.00410 0.410 Cultivar 3 0.00856 0.124 Date*Cultivar 6 0.00281 0.669 Error 33 0.00415 Fall Sampling Date 2 0.00302 0.367 Replication 3 0.00290 0.408 Cultivar 3 0.00281 0.422 Date*Cultivar 6 0.00257 0.519 Error 33 0.00292

PAGE 45

45 Table 4-2. Influence of diploid watermelon polleni zer cultivar on pollen viability at Quincy, FL during the Spring and Fall of 2006. Pollen viability Pollenizer Cultivar 17 May 24 May 31 May 31 Aug. 7 Sept. 14 Sept. Mickylee 97.8 NS z 98.0 NS z 98.7 NS z 97.4 NS z 98.2 NS z 97.8 NS z Companion 97.4 97.2 99.2 97.6 98.1 98.8 Jenny 97.3 97.2 98.3 97.8 97.7 97.0 SP-1 97.2 95.5 98.1 97.9 98.7 97.6 Date Means 97.4 b y 97.0 b 98.6 a 97.7 NS y 98.2 97.8 z P = 0.05 Means are compared w ithin the same column. y P = 0.05 Means from the same season are compared within the row.

PAGE 46

46 CHAPTER 5 DIPLOID WATERMELON POLLENIZER CULTI VARS EXHIBIT VARYING DEGREES OF PERFORMANCE WITH RESPECT TO TRIPLOID WATERMELON YIELD Introduction With seeded watermelons only holding about 20% of the U.S. market, there is interest in using pollenizers that do not require dedicated field space (USDA, 2006). Traditionally pollenizers occupied 20-33% of th e land area in a field. New polleni zers have been developed to be planted in-row with triploid plants without altering spacing. There are now multiple in-row pollenizer cultivars available that exhibit varying growth habits. Previous research has reported differences in production and timing of staminate flowers by pollenizer cultivars. The seed costs of in-row pollenizers are greater than open-pollinated and hybrid diploids and most in-row pollenizers are not intended to be harvested. Ther e is interest in using open-pollinated cultivars in-row to reduce input costs but it is unclear if acceptable yields will result. These experiments were conducted to determine if there was a diffe rence in performance between in-row pollenizer cultivars and if a standard open-pollinated cultivar could be used in-row with similar success. Materials and Methods These experiments were performed at one location (Blackville, SC) in 2005 and three locations (Blackville, SC, Citra, FL, Quincy, FL) in 2006. The experimental design used was a randomized complete block with four replications. Experimental plots consisted of three raised bed rows that were spaced 2.43 m center-to-cente r and covered with black polyethylene mulch. Watermelon plants were spaced 0.91 m in-row. Rep lications consisted of three rows 116 m long with a 7.62 m buffer between replications. A diag ram of the experimental layout is shown in Figures 5-1 and 5-2. The two outsi de rows were planted with Tri-X Palomar and the interior row was planted with Tri-X 313 in 2005 and S upercrisp in 2006. In 2005, pollenizer cultivars used were Jenny, Mickylee, a nd SP-1 with Tri-X Palomar as a control. In 2006, the

PAGE 47

47 pollenizer cultivars used were Companion, Jenny, Mickylee, Patron, Pinnacle, Sidekick, and SP-1 with Tri-X Palomar as a c ontrol. Pollenizer seed sources are listed in table 5-5. In order to reduce pollen contaminatio n from neighboring plots, an eight plant buffer (7.3 m) of Tri-X Palomar was planted in the cent er row between each plot (Figure 5-2). It has been demonstrated that distance from a diploid pollenizer of 6.0 m or greater will greatly reduce the triploid fruit set (NeSmith and Duval, 2001) Tri-X Palomar was chosen as the buffer cultivar and control plot po llenizer because it does not produce viable pollen and its rind coloration is distin ctly different than the harvested cult ivars, Tri-X 313 and Supercrisp. Eight triploid watermelon plants were transplanted into each plot including the control or check plot. Three plants of a pollenizer cultivar were planted in each plot except the control plot where TriX Palomar was planted in place of a pollenizer. Control plots were in place in order to observe if pollen was moving from plot to plot. Jenny, Mickylee, Pat ron, Pinnacle, Sidekick, and SP-1 were planted at a 1:3 pol lenizer to triploid ratio while Companion was planted at a 1:2 pollenizer to triploid ratio. These ratios are recommended by pr oducers of the various pollenizers. Three plants of the 1:3 ratio polleni zers, and four plants of the 1:2 ratio pollenizer were included in each plot in the same row as the harvested watermelon. Soil type at the Edisto Research and Educa tion Center (EREC) in Blackville, SC was Dothan loamy sand (fine-loamy, kaolinitic, thermic Plinthic Kandiudults). Soil type at the North Florida Research and Education Center (NFREC ) in Quincy, FL was Norfolk loamy sand (fineloamy, kaolinitic, thermic Typic Kandiudults). Soil type at the Plant Science Research and Education Unit (PSREU) in Citra, FL was Hague sand (loamy, siliceous, semiactive, hyperthermic Arenic Hapludalfs). Drip tapes (1.89 lmin.-1/30.48 m at 68 kPa; 30.48 cm emitter spacing) were laid under and concurrently with the polyethylene mulch. Beds were fumigated

PAGE 48

48 with methyl bromide/chloropicr in 67:33 at a rate of 448 kgha-1 broadcast at EREC in 2005, and PSREU and NFREC in 2006. Fertilizer r ecommendations for EREC were 156N-0P-130.2K kgha-1 in 2005 and 2006 (Franklin, 1998). Fertili zer recommendations for PSREU and NFREC were 168N-48P-140.2K kgha-1 and 183.6N-24P-152.3K kgha-1, respectively (Olson et al., 2006). All fertility recommendations were based on soil test results. Four-week-old watermelon plants were transplanted at EREC on 27 Apr ., 2005 and 17 Apr., 2006. Four-week-old seedlings were transplanted at PSREU and NFREC on 21 Mar. and 3 Apr., 2006, respectively. Plots were sprayed with fungicides and inse cticides as recomme nded (Olson et al., 2006, Sanders et al., 2006). Pesticide applications we re timed so that there was minimal effect on pollinators. One honeybee ( Apis mellifera L.) hive was located near the center of each replication at Citra and Quincy, FL in 2006 whil e at Blackville, SC in both years a grouping of twenty honeybee hives was maintained 300 ft. north of test plots. At all locations in 2005 and 2006, watermelons were harvested once per week fo r three weeks. At the last harvest, all marketable melons were harvested. The center of each fruit was sampled for total soluble solids using a hand-held refractometer. Hollow hear t measurements were taken by measuring the length and width of hollow cavities in watermelons that had been cut longitudinally from stem end to blossom end. Soluble solids and hollow hear t data were taken from three melons per plot during the first harvest at all locations in 2006. Soluble solids data were taken from three watermelons per plot during the first harvest at Blackville, SC in 2005 but no hollow heart data were taken. Yield and soluble solids data from 2005, and hollow-heart data from 2006 were analyzed using the GLM procedures and means separation was accomplished using Duncans multiple range test in the SAS system (SAS Institute, Inc., Cary, NC). In 2006, there were multiple

PAGE 49

49 locations and as location was not of primary inte rest in this study, locat ion was set as a random effect. The MIXED procedure was used to an alyze cultivar effect on fruit yield (kgha-1, fruit/ha, and kg/fruit) and soluble solids. This allows for greater infere nce of the results and how they may relate to many locations as compared with se tting location as a fixed effect (Cushman et al., 2003; Schabenberger and Pierce, 2002). Polleni zer cultivar was set as a fixed effect and location, replication, and locati on by cultivar interaction were set as random effects. Results Treatments with pollenizer cultivars had significantly greater yield of triploid watermelons at all locations and in both years compared to the check (Tables 5-1 & 52). In addition there were significant differences among pollenizer cul tivars in 2006 (Table 5-2). There were no significant differences in triploid watermelon yi elds among pollenizer cultivars in 2005 (Table 51). In 2006, plants pollenized by Sidekick yielded 65,242 kgha-1 but were not significantly different than plants pollenized by Patron, SP-1, Jenny, or M ickylee which yielded 63,677, 61,766, 61,751, and 59,599 kgha-1, respectively (Table 5-2) Plants pollenized by Companion had the lowe st yields at 49,976 kgha-1, which were significantly lower than those pollenized by Jenny, SP-1, Pat ron or Sidekick but not signi ficantly different than plants pollenized by Pinnacle or Mic kylee which yielded 53,333 and 59,599 kgha-1, respectively. Plots containing Pinnacle had significantly lower yields than those containing Sidekick but were not significantly different than plots containing Mickylee SP-1, Jenny or Patron (Table 5-2). Pollenizers had a sign ificant effect on number of triploid watermelons compared to the check. All plots with pollenizer cultivars had significantly greater numbers of melons per hectare than the control plots at all locations in both years (Tables 5-1 & 5-2). There were no significant differences in fruit production betw een the pollenizer cultivars in 2005 and 2006. In 2006, plants pollenized by Patron produced 9,616 fruit/ha which was not significantly greater

PAGE 50

50 than Companion which produced 7,565 fruit/ha. Po llenizer cultivars had a significant effect on average triploid watermelon fruit weight in 2006, but not in 2005 (Tables 5-1 & 5-2). Pollenizer cultivars did not have a significant effect on solu ble solids in both year s (Table 5-3). In 2006, pollenizer cultivars did not have a significant effect on hollowheart at the Citra, FL and Blackville, SC locations (Table 5-4). Pollenizer cultivars did ha ve a significant effect on hollow heart at Quincy, FL with all plots with polleni zers having significantly less hollow heart in the triploid watermelons when compared with th e control plots (Table 5-4). There were no significant differences in hollow heart inci dence between pollenizer cultivars. Discussion This research shows that some pollenizer cultiv ars tested can be exp ected to perform better than other cultivars, and do so at diverse locations. Similar results were reported by Fiacchino and Walters (2003) in which triploid watermel on yields were significan tly different due to pollenizer cultivar used. The only cultivar that showed questionable performance was Companion. Due to its growth and flowering habit it may not produce en ough staminate flowers and pollen at the end of fruit setting in the triploid crop. Companion is a short internode plant that becomes overgrown by triploid plants near the end of the season wh ich may lead to staminat e flowers that are not readily detectable by pollinators. Differences in staminate flower production by pollenizer cultivars have been reported however, it does not appear that flower production is the determining factor of a pollenizers perfor mance (Dittmar et al., 2005; Freeman and Olson, 2007). In both of these studies, SP-1 produced greater numbers of st aminate flowers when compared to Jenny or Mickylee, however, da ta presented here indicates no difference in triploid watermelon yields betw een these pollenizer cultivars. Pollenizers must be able to continue growing and producing flower s throughout the production cycle.

PAGE 51

51 There were significant differences in severity of hollow heart at Quincy between plots containing pollenizer cultivars a nd the control but not between the pollenizers. Unfortunately, this does not help to elucidate the cause of hollow heart as it may have been caused by reduced pollination in control plots or excessive growth of the few existing watermelons. The incidence of hollow heart at Blackville, SC and Citra, FL was low overall and this may be why there was no effect by the pollenizers. The experimental design was successful in reducing pollen flow out of experimental plots as indicate d by minimal fruit set in control plots. This experimental design spaced the triploid watermelon fr om a pollenizer cultivar by 7.3 m. NeSmith and Duval (2001) illustrated that when distance of a triploid from a pollenizer was six meters or greater, triploid fruit numbers diminished substantially. Triploid pistillate flowers (Tri-X Palomar) in plot buffers served to filter viable diploid polle n before pollinators entered another plot. Of the cultivars tested, it app ears that the pollenizers Jenny, Mickylee, Patron, Pinnacle, Sidekick, and SP1 would be good choices. Some of the tested pollenizers (Mickylee, Jenny, Pinnacle) can be harvested and sold if the grower has a market for seeded watermelons. If growers have a strong market fo r seeded melons then there may be no reason to plant pollenizers in-row. The pollenizers costs va ry greatly, so this must also be taken into consideration. Of the pollenizer cultivars that were shown to perfor m adequately (Jenny, Mickylee, Patron, Pinnacle, Sidekick, SP-1), se lection should be based on seed/plant cost and distinctness between pollenizer and market melon.

PAGE 52

52 Replication 1 Replication 2 Plot 1 Plot 1 Plot 2 Plot 2 Plot 3 Plot 3 Plot 4 Plot 4 Plot 5 Plot 5 Plot 6 Plot 6 Plot 7 Plot 7 B U F F E R Plot 8 B U F F E R 7.6 m Drive Row B U F F E R Plot 8 B U F F E R Figure 5-1. Field diagram for po llenizer experiments at Blackvill e, SC, Citra, FL, and Quincy, FL in 2005 and 2006. Columns represent i ndividual rows. The same design was used for replications three and four.

PAGE 53

53 Tri-X Palomar Tri-X Palomar Tri-X Palomar Tri-X Palomar Data melon Pollenizer Data melon Data melon Data melon Pollenizer Data melon Data melon Data melon Pollenizer Data melon Tri-X Palomar Tri-X Palomar Tri-X Palomar B U F F E R Tri-X Palomar B U F F E R Figure 5-2. Individual three-row plot design for pollenizer experime nts at Blackville, SC, Citra, FL, and Quincy, FL in 2005 and 2006. Plot shown is using a pollenizer recommended to be planted at a 1:3 pollenizer to seedless ratio.

PAGE 54

54 Table 5-1. Pollenizer cultivar effect on Tri -X 313 yield at Blac kville, SC during 2005 Pollenizer cultivar Yield (kgha-1) z Fruit (no./ha) z Avg wt (kg/fruit) Jenny 67,565 a y 9,386 a y 7.6 NS SP-1 63,944 a 9,666 a 6.9 Mickylee 61,759 a 8,966 a 7.0 Tri-X Palomar x 10,494 b 1,400 b 8.7 z Yield estimates are based on plant popu lations of 4483 plants per hectare. y Means with the same letter are not significantly different at ( P 0.05) by Duncans multiple range test. x Triploid cultivar serving as check against pollen contamination from neighboring plots. Table 5-2. Pollenizer cultivar effect on Supercri sp watermelon yield and average fruit weight at Blackville, SC, Citra, FL, and Quincy, FL during 2006. Pollenizer cultivar Yield (kgha-1) z Fruit (no./ha) z Avg wt (kg/fruit) Sidekick 65,242 a 9,386 a 7.3 a b Patron 63,677 a b 9,616 a 7.0 b SP-1 61,766 a b 9,106 a 7.0 b Jenny 61,751 a b 9,195 a 6.9 b Mickylee 59,599 a b c 9,106 a 6.7 b Pinnacle 53,333 b c 7,845 a 7.2 a b Companion 49,976 c 7,565 a 6.9 b Tri-X Palomar y 8,545 d 1,074 b 7.8 a LSD x 10,494 2,116 0.7 z Yield estimates are based on plant popu lations of 4483 plants per hectare. y Triploid cultivar serving as check against pollen contamination from neighboring plots. x P = 0.05

PAGE 55

55 Table 5-3. Pollenizer cultivar effect on soluble solids concentration of seedless watermelons at Blackville, SC during 2005 and Citra, FL Quincy, FL, and Blackville, SC during 2006. Soluble solids concentration (%) Pollenizer cultivar Blackville, SC 2005 Combined locations 2006 Sidekick 12.2 NS Patron 12.1 SP-1 11.0 NS z 12.3 Jenny 11.6 12.3 Mickylee 11.2 12.3 Pinnacle 12.1 Companion 12.4 Tri-X Palomar y 11.6 12.2 LSD x 0.7 z Means with the same letter ar e not significantly different at ( P 0.05) by Duncans multiple range test. y Triploid cultivar serving as check against pollen contamination from neighboring plots. x P = 0.05

PAGE 56

56 Table 5-4. Pollenizer cultivar effect on hollowheart disorder in Supercrisp watermelon at Quincy, FL, and Blackville, SC combined with Citra, FL during 2006. Means are to be compared within the same column. Hollowheart area (cm) Pollenizer cultivar Quincy, FL Blackville, SC & Citra, FL Tri-X Palomar z 187.0 a y 4.7 NS Patron 73.3 b 12.2 Jenny 70.2 b 5.8 Sidekick 68.2 b 9.7 Companion 58.1 b 3.3 Mickylee 54.7 b 2.6 SP-1 53.5 b 15.7 Pinnacle 37.5 b 10.7 z Triploid cultivar serving as check against pollen contamination from neighboring plots y Means with the same letter are not significantly different at ( P 0.05) by Duncans multiple range test. Table 5-5. Seed sources for various po llenizer cultivars used during 2005 and 2006. Pollenizer cultivar Company Patron Zeraim Gedera Seed Co., Ltd. (Palm Desert, CA) Jenny Nunhems USA, Inc. (Acampo, CA) Sidekick Harris Moran Seed Co. (Modesto, CA) Companion Seminis Vegetable Seed, Inc. (Oxnard, CA) MickyLee Many sources SP-1 Syngenta Seeds, Inc.(Boise, ID) Pinnacle Southwestern Vegetable Seed, LLC. (Casa Grande, AZ.)

PAGE 57

57 CHAPTER 6 COMPETITIVE EFFECT OF IN-ROW DIPLOID WATERMELON POLLENIZERS ON TRIPLOID WATERMELON YIELD Introduction Due to the high cost of in-row diploid pollenizer seed, there is intere st in using standard watermelon cultivars in-row. One cultivar that is being evaluated for in-row use is Mickylee which produces an easily distingu ishable fruit, a crucial characte ristic for diploid pollenizers. Most in-row pollenizer cultivars have reduced folia ge in order to compete less with triploid plants. Mickylee is an attract ive option as a pollenizer because of the low seed costs but it is unclear whether the more vigorous growth ha bit will negatively impact seedless watermelon yields. The objective of this study was to determin e if pollenizer growth habit and pollenizer to triploid spacing would have an effect on triploid watermelon yield. Materials and Methods Experiments were conducted at the North Florida Research and Education Center (NFREC) in Quincy, FL. and the Plant Science Re search and Education Un it (PSREU) in Citra, FL. in the Spring of 2006 and also at NFREC in the Fall of 2006. Soil type at NFREC was Norfolk loamy sand (fine-loamy, kaolinitic, thermic Typic Kandiudults) and at PSREU was Hague sand (loamy, siliceous, semiactive, hyperthe rmic Arenic Hapludalfs). At NFREC (spring and fall) all fertilizer was incorporated pre-plant at a rate of 183.6N-24P-152.3K kgha-1. At PSREU two thirds of the fertilizer was a pplied pre-plant and the remainder of the recommendation was fulfilled through weekly fertig ation. Total fertilizer applied at PSREU was 168N-48P-140.2K kgha-1. Fertilization was based on soil test results and University of Florida recommendations (Olson et al., 2006). At bot h locations, irrigation wa s provided through drip tape (1.89 lmin.-1/30.48 m at 68 kPa; 30.48 cm emitter spaci ng) which was laid concurrently with black polyethylene mulch in the spring and with white on black polyethylene mulch in the

PAGE 58

58 fall. Soil was fumigated at plastic laying with me thyl bromide/chloropicrin 67:33 at a rate of 448 kgha-1. Beds were spaced 2.43 m center-to-center. Experimental design was a factorial with four replications and tw o factors, pollenizer cultivar and in-row spacing. In-row spacings be tween one pollenizer plant and one triploid plant were 0.2, 0.4, 0.6, 0.8, and 1.0 m. Plots consiste d of six pairs (one po llenizer, one triploid) of plants with equal pollenizer to triploid spacin gs. Each pair of plants was spaced 1.0 m in-row from the next pair. On 21 Mar., 3 Apr., a nd 1 Aug., 4-week old watermelon seedlings were transplanted. Sugarheart triploid was used al ong with Mickylee (sta ndard vining habit) and SP-1 (reduced foliage, thin-vines) as pollenizers Harvests of spring trials were made on 8 and 19 June at PSREU and on 21 and 28 June, and 7 Ju ly at NFREC. Fall harvests were on 11 and 25 Oct. Insecticides and fungicide s were applied as needed to main tain plant health (Olson et al., 2006). Groupings of honey bee ( Apis mellifera L.) hives were placed in close proximity to all experiments. The GLM procedures of SAS (SAS In stitute, Inc., Cary, NC) were used to analyze the effects of pollenizer cultiv ar on Sugarheart watermelon yi eld and interactions between pollenizer cultivar and spacing. The GLM procedures were also used to analyze the polynomial effects of pollenizer to triploid spacing. Results Pollenizer cultivar and plant spacing had significant effects on seedless watermelon yield at Citra and Quincy ( P 0.05) in the spring but not at Quincy in the fall ( P > 0.05). Cultivar and plant spacing had significant effects on fruits pe r plant (fpp) at both lo cations in the spring, however, the significance at Citra for cultivar and plant spacing were P = 0.0983 and P = 0.0633, respectively. Plant spacing had significant linear effect s on seedless watermelon yield and fpp at both locations in the spring (Table 61). No significant effects on average watermelon weight were observed in any of the experiments. Cultivar and plant spacing had no effect on

PAGE 59

59 seedless watermelon yield or yield components at Quincy in the fall. No significant interaction effects were observed between cultivar and pl ant spacing. A significan t interaction between location and pollenizer cultivar was detected in the spring therefore locations will be presented separately. Seedless watermelon yields from plants paired with Mickylee at Citra and Quincy were 24.6 and 33.5 kg/plant, respectively. Yi elds from plants paired with SP-1 at Citra and Quincy were 27.7 and 43.3 kg/plant, respectively, which we re significantly greater than yields from plants paired with Mickylee. At Quincy, pl ants paired with Mic kylee produced 3.74 fpp which was significantly lower than 4.85 fpp produced by plants paired with SP-1. At Citra, plants paired with Mickylee produced 3.68 f pp which was lower than 4.04 fpp produced by plants paired with SP-1; however th is was only statistically significant at P = 0.10 Seedless watermelon yields and fpp increased linearly with increased spacing at both locations in the spring. Yiel ds from plots with 0.2 m in-row spacings were 22.1 and 32.0 kg/plant at Citra and Quincy, respectively. Yi elds from plots with 1.0 m in-row spacing were 30.8 kg/plant at Citra and 47.8 kg/plant at Quincy. Discussion These results appear to indicat e that the vigorous growth habit of pollenizer Mickylee negatively impacted yield of the triploid cultivar Sugarheart compared to the reduced foliage of pollenizer SP-1. Seedless wate rmelon yields (kg/plant) from plants paired with Mickylee yielded 11.4 and 22.4% less than plants paired with SP-1 at Citra and Quincy, respectively. At current pollenizer ratios recommended by seed producers, pollenizer competition could affect two thirds of the triploid plants per hectare. These yield reductions can be expected at all in-row spacings as there was no interaction between cultiv ar and spacing. Extrapolations of yield to a per hectare basis were not performed because it is unclear how many pollenizer plants would be

PAGE 60

60 necessary at these plant populations which ranged from 10,089 plantsha-1 at the closest spacings to 2,017 plantsha-1 at the widest. There was also no yield data from plants that were considered to be unaffected by pollenizer compe tition. During the fall experiment at Quincy, there was a severe outbreak of gummy stem blight ( Didymella bryoniae (Auersw.) Rehm) which was not controlled by the weekly fungicide applications. This no doubt reduced seedless watermelon yields which affected the statistical outcome. The trends in fruit yield and fr uit number observed in this stu dy are similar to other reports in watermelon where increased pl ant population, and thus increas ed competition, changes yield through fruit number and not average fruit mass (B rinen et al., 1979; Duth ie et al., 1999a, 1999b; NeSmith, 1993). Competition studies investigati ng weed species effect on watermelon yield have also shown increasing competition lowers wa termelon yield as a function of fruit number and not fruit size (Buker et al., 2003; Monks and Schultheis, 1998). The results from this project are not in ag reement with Freeman (2007) who evaluated the performance of in-row pollenizers and found no diffe rence in seedless watermelon yield between plots containing Mickylee or SP-1. The experimental desi gn used was intended to compare pollenizer cultivars as a function of pollen provi ded by each cultivar and not its competitive effect. This study collected yield data by plot wh ich does not provide insight into pollenizer to triploid competition as some plants were located directly beside pollenizers and some were not. It is unclear why a significant reduction in yield caused by Mic kylee in this study is not in agreement with the results reported by Freeman (2007).

PAGE 61

61 Mickylee is an attractive option as a pollenizer because of the low seed costs. However, the results of this study indicat e that seedless watermelon yiel ds and fruits per plant will significantly decrease when Mickylee is used as a pollenizer as compared with SP-1 regardless of in-row spacing.

PAGE 62

62Table 6-1. Influence of pollenizer cultivar a nd spacing on triploid watermelon yield during 2006. Location Citra, FL Spring 2006 Quincy, FL Spring 2006 Quincy, FL Fall 2006 Treatment Fruit (no./plant) Yield (kg/plant) Avg. wt. (kg/fruit) Fruit (no./plant) Yield (kg/plant) Avg. wt. (kg/fruit) Fruit (no./plant) Yield (kg/plant) Avg. wt. (kg/fruit) Cultivar SP-1 4.04 27.7 6.8 4.85 43.4 8.8 3.04 19.0 6.2 Mickylee 3.68 24.5 6.7 3.74 33.5 8.8 2.85 17.4 6.0 Significance ** NS *** *** NS NS NS NS Spacing (m) 0.2 3.33 22.1 6.5 3.57 32.0 8.9 2.98 18.2 6.0 0.4 3.68 24.9 6.7 3.46 29.7 8.4 2.85 17.5 6.0 0.6 3.92 26.3 6.7 4.52 40.4 8.8 2.86 18.4 6.4 0.8 4.02 26.6 6.7 4.85 43.9 9.0 3.18 19.3 6.0 1.0 4.35 30.8 7.1 5.28 47.8 9.0 2.86 17.6 6.1 Significance L*** L*** NS L*** L*** NS NS NS NS NS, *, **, *** Non-significant or significant at P 0.10, 0.05 or 0.01, respectively.

PAGE 63

63 CHAPTER 7 VARIABILITY IN WATERMELON FLOW ER ATTRACTIVENESS TO INSECT POLLINATORS Introduction In a field that is producing seedless waterm elons, there must be both diploid and triploid plants (Kihara, 1951; Maynard and Elmstrom, 1992). For fruit set to occur in triploid plants, pollen must be moved from the stam inate diploid flower to the pistil late triploid flower. Triploid and diploid plants produce staminat e flowers which bear pollen, how ever, triploid pollen is nonviable. It is unlikely that inse ct pollinators can visually distin guish between the two and foraging of staminate triploid flowers dilutes the flow of viable pollen within a fiel d. If staminate flowers produced by the diploid pollenizer are more attractive than triploid staminate flowers, a greater proportion of viable pollen could be moved by pollinators which may lead to greater reproductive success in triploid fruits. The floral attractiveness of a polleni zer could also impact its performance. The objective of this study was to determine the fl oral attractiveness of staminate flowers of three pollenizer cultivars and one triploid cultivar. Materials and Methods Field experiments were conducted at the Nort h Florida Research and Education Center (NFREC) in Quincy, FL. during the Spring and Fall of 2006. Soil type at NFREC is Norfolk loamy sand (fine-loamy, kaoliniti c, thermic, Typic Kandiudults). The experimental design was a randomized complete block with eight replicatio ns. Experimental plots were 4.57 m long with in-row spacing of 0.46 m and between row spacing of 4.9 m. The experime nt consisted of two rows 73.2 m long. On 3 Apr. and 1 Aug. 2006, 4-week old watermelon seedlings were transplanted into raised beds covered with black polyethylene mulch in the spring and white on black polyethylene mulch in the fall. Three waterm elon plants were transplanted into each plot. Number of pollinator visitations was recorded for four watermelon cultivars, Companion,

PAGE 64

64 Intruder, Mickylee and SP-1. Three cultivars are diploid polle nizers and one (Intruder) is a triploid. Fertilization, irri gation, and pesticide application practices recommended by the University of Florida Institute of Food and Agri cultural Sciences were followed (Olson et al., 2006). A grouping of two honeybee ( Apis mellifera L.) hives was placed near the center of the experiment. Sampling was performed on five occasions in the spring and three in the fall. Sampling started when plants began to produce staminate and pistillate flowers. On sampling dates, sampling was initiated at anthesis. Five stam inate flowers were chosen in each plot and visitations from honeybees and bumblebees ( Bombus spp. Cresson) were counted for two minutes. Three to four sampling repetitions were performed on each sampling date and are referred to as sampling time. Previous research has illustrated an intera ction between cultivar attractiveness and sampling time, for this reason sampling times were kept succinct and sampling time was considered a main effect. Two indivi duals recorded visitations in order to keep repetition time under 45 minutes. Analysis of variance was performed using the GLM procedures of SAS (SAS Instit ute, Inc., Cary, NC) to determ ine significance of main and interaction effects and Duncans multiple ra nge test was used for means separation. Results Watermelon cultivar and sampling time had a significant effect ( P 0.05) on floral visitation by insect pollinators on six of eight sa mpling dates. Cultivar or sampling time did not influence pollinator visitation on 11 May or 29 Sept. Significant interactions ( P 0.05) between time and cultivar were detected on 23 May and 22 Sept. Visitation of a diploid cultivar was significantly greater than the triploid cu ltivar on six of eight sampling dates. On 16 May, SP-1 had 2.4 visi ts per plot (vpp) which was significantly greater than Mickylee, Companion, or Intruder which had 1.1, 1.0, and 0.8 vpp, respectively (Fig. 7-1).

PAGE 65

65 Pollinator visitation of Mickylee, Companion, or Intruder was not significantly different. Pollinator visitations to Mickylee and SP-1 were 2.9 vpp which was significantly greater than Companion or Intruder which had 1.5 and 1.0 vpp, respectively, on 19 May. An interaction between sampling time and cultivar occurred on 23 May. During th e first sampling time, SP-1 had 4.2 vpp which was not significantly greater th an Companion or Mickylee which had 3.0 and 2.75 vpp, respectively (Fig. 7-2). However, a ll three cultivars had significantly greater visitation than Intruder at 0.3 vpp. During the second sampling time, Mickylee had 5.5 vpp which was not significantly differe nt than SP-1 at 2.8 vpp but was significantly greater than Intruder and Companion at 1.5 and 1.3 vpp, respect ively. Visitation of S P-1, Intruder, and Companion were not significantly different. There were no significant differences between cultivars during the third and fourth sampling times. On 25 May, Mickylee had 2.8 vpp which was significantly greater than SP-1, C ompanion, or Intruder at 1.8, 1.4 and 0.4 vpp, respectively (Fig. 7-1). SP-1 and Companion were not signi ficantly different but both had greater visitation than Intruder. On 15 Sept, SP-1 had 7.7 vpp which was greater than Mickylee, Intruder or Companion at 6.1, 5.8, and 3.7 vpp, respectively (Fi g. 7-3). Mickylee and Intruder were not significantly different but both ha d greater visitation than Compa nion. An interaction between sampling time and cultivar occurred on 22 Sept. During the first sampling time, SP-1 had 2.7 vpp which was not greater than Mickylee at 1.8 vpp but was greater than Companion and Intruder at 0.7 and 0.5 vpp, respectively (Fig. 7-4). Mickylee, Companion, and Intruder were not significantly different. During the s econd sampling time, SP-1 had 6.8 vpp which was similar to Mickylee at 5.2 vpp and both had great er visitation than Companion or Intruder which had 2.3 and 2.1 vpp, respectively. Compani on and Intruder were not significantly

PAGE 66

66 different. There was no significan t difference between cultivars during the third sampling time. On 29 Sept. main effects did not influence pollinator visitation (Fig. 7-3). No data were taken from Companion on 29 Sept. because it had cea sed producing staminate flowers. Complete floral visitation data are shown in figures 7-1 7-4. Discussion Either Mickylee, SP-1, or both received greater floral vi sitation than Companion or Intruder. Previous research as shown that staminate flower produc tion by SP-1 is greater than that of Mickylee or Companion which were similar (Freeman and Olson, 2007). The number of flowers that were used in sampling was held constant in order to determine the relative attractiveness of each cultivars staminate flow er. This research illustrates differential attractiveness between cultivars and ploidy levels. Visitation at the whole plant level for SP-1 could be higher than the other cultivars due to greater numbers of staminate flowers but a staminate flower produced by SP-1 is not necessa rily more attractive th an a staminate flower produced by Mickylee. Other researchers have reported differences in pollinator visitation between watermelon cultivars and between Citrullus lanatus and Citrullus colocynthis which was attributed to nectar sugar concentration (Wol f et al., 1999). It has been shown that floral volatiles emitted from pollen are the most important close-range cue during foraging by honeybees, however; visual stimuli are important long-range cues (Per nal and Currie, 2002). Companion has a nearly entire leaf with reduced lobes and produces staminate flowers with short peduncles. These factors tend to obstruct the view of Companions staminate flowers which may be why Companion was generally vi sited less than SP-1 and Mickylee. A diploid watermelon cultivar was preferred over the triploid on sampling dates where cultivar affected pollinator vi sitation. Triploid watermelon plants produce mostly non-viable, aborted pollen which may be covered with less pollenkitt than viable pollen. Pollenkitt produces

PAGE 67

67 volatiles that are important in foraging decisions of pollinators. These volatiles are an indicator of pollen reward that is avai lable in a flower and reduced volatile emissions may indicate reduced reward (Dobson et al., 1996). A reductio n in pollenkitt produced in triploid staminate flowers could represent reduced reward and resu lt in flowers that are less attractive to pollinators. Previous research has shown that Bombus spp. preferentially foraged potato flowers that produced viable pollen over ones produci ng non-viable pollen wh ich may be due to differences in volatile em issions (Batra, 1993). When the performance of multiple diploid wa termelon pollenizer cultivars were compared, triploid watermelon yields from plots pollenized by Companion were significantly less than plots pollenized by SP-1 or Mic kylee. The lower preference of Companion may lead to less viable pollen transported by pollinators and thus le ss fruit on triploid plants. A diploid pollenizer cultivar with staminate flowers which are more attractive than triploid staminate flowers could increase the movement of viable pollen within a field and possibly increase seedless watermelon yield.

PAGE 68

68 b a a b b b a a b ns c b b 0 0.5 1 1.5 2 2.5 3 3.5 5/11/065/16/065/19/065/25/06Sampling DateVisits/plot (visits per 5 flowers per 2 min) SP-1 Companion Mickylee Intruder Figure 7-1. Influence of cultivar on pollinator visitation to staminate watermelon flowers at Quincy, FL., Spring 2006. Visit ation means are to be compared within sampling date. Means foll owed by the same letter are not significantly different at P 0.05.

PAGE 69

69 a ab a b ns a a ns b b 0 1 2 3 4 5 6 Time 1Time 2Time 3Time 4Sample TimeVisits/plot (visits per 5 flowers per 2 min) SP-1 Companion Mickylee Intruder Figure 7-2. Interaction of cultivar and time on pollinator vis itation to staminate watermelon flowers at Quincy, FL., on 23 Ma y, 2006. Visitation means are to be compared within sampling time. Means followed by the same letter are not significantly different at P 0.05.

PAGE 70

70 ns b a b c 0 1 2 3 4 5 6 7 8 9 9/15/069/29/06Sampling DateVisits/plot (visits per 5 flowers per 2 min) Mickylee SP-1 Intruder Companion Figure 7-3. Influence of cultivar on pollinator visitation to staminate watermelon flowers at Quincy, FL., Fall 2006. Visitat ion means are to be compared within sampling date. Means followe d by the same letter are not significantly different at P 0.05.

PAGE 71

71 ab a a a b b ns b b 0 1 2 3 4 5 6 7 8 Time 1Time 2Time 3Sampling TimeVisits/plot (visits per 5 flowers per 2 min) Mickylee SP-1 Intruder Companion Figure 7-4. Interaction of cultivar and time on pollinator vis itation to staminate watermelon flowers at Quincy, FL., on 23 Se pt., 2006. Visitation means are to be compared within sampling time. Means followed by the same letter are not significantly different at P 0.05.

PAGE 72

72 CHAPTER 8 VARIABILITY IN POLLEN PRODUCTION BY DIPLOID WATERMELON POLLENIZERS Introduction Pollen produced by diploid watermelon pollenizers is necessary for fruit set and flesh fill in associated triploid watermelon crops (Kih ara, 1951; Maynard and Elmstrom, 1992). Viable pollen produced by pollenizers is diluted with non-viable triploid pollen which increases pollinator visitation rates required by pistillate trip loid flowers. It is important that there be adequate viable diploid pollen moved throughout a field and polleni zers that produce the greatest amounts of pollen may perform bette r with respect to triploid watermelon yield. Significant differences in pollen production have been report ed between cultivars of diploid watermelon as well as in other plant species. The objective of this project was to determine the amount of pollen produced by four pollenizer cultivars to investigate possible effects on pollenizer performance. Materials and Methods Experiments were conducted at the North Florida Research and Education Center (NFREC) in Quincy, FL during the fall of 2006. Soil type at NFREC is Norfolk loamy sand (fine-loamy, kaolinitic, thermi c, Typic Kandiudults). The expe rimental design was a randomized complete block with four replications. Expe rimental plots were 4.57 m long with in-row spacing of 0.91 m and between row spacing of 2.43 m. On 1 Aug. 2006, 4-week old watermelon seedlings were transplanted into raised beds covered with white on black polyethylene mulch. Beds were fumigated with methyl bromide/ chloropicrin 67:33 at a rate of 448 kgha-1 broadcast. Three seedlings were planted in each plot. Fe rtilization, irrigation, a nd pesticide application practices recommended by the Univer sity of Florida Institute of Food and Agricultural Sciences were followed (Olson et al., 2006).

PAGE 73

73 Sampling was initiated on 31 Aug. with additional samples taken on 8 Sept. and 14 Sept. On sampling dates, watermelon flowers were re moved before anthesis, placed into plastic containers and covered to exclude pollinators. Two flowers per cultivar were analyzed from each replication. Flowers were allowed to open and anther dehiscence was verified before flowers were processed. Flower petals were excised with a razor blade and peduncles were removed before flowers were placed into separa te vials containing 5 mL of a solution of 70:30 ethanol/ethyl acetate mixture. This solution serv ed to preserve the polle n and also to remove pollenkitt from the exterior of the pollen grains. The removal of pollenkitt was necessary to obtain uniform pollen distribution in the liquid media. Sample vi als were sonicated in a waterbath sonicator to remove all pollen from anther s. After the anthers and any other remaining floral structures were removed, vials were sonicated again to ensure the removal of all pollenkitt. Three 50 L sub-samples were taken from each vial and pollen grains were counted on a grided microscope slide. Sub-sample values were th en extrapolated to obtain total number of pollen grains per flower. Pollen sub-sample counts were averaged for each flower. Analysis of variance was performed using the GLM procedures of SAS (SAS Institute Inc., Cary, N.C.) and means separation was performed using Duncans multiple range test. Results Pollenizer cultivar and sampling date had significant effects ( P 0.05) on pollen production per flower. Th ere was no significant ( P > 0.05) interaction between cultivar and sampling date. On 31 Aug., Mickylee produce d 49,975 pollen grains per flower (gpf) which was not significantly greater than Companion at 44,800 gpf but both were greater than SP-1 and Jamboree at 37,813 and 36,700 gpf, respec tively (Table 1). Pollen production by Companion was not significantly greater than SP-1 or Jamboree. On 8 Sept., Companion

PAGE 74

74 produced 62,275 gpf which was not significantly great er than Mickylee at 60,250 gpf or SP-1 at 53.138 gpf but was greater than Jamboree at 44,975 gpf. Pollen prod uction by SP-1 and Jamboree were not significan tly different on 8 Sept. On 14 Sept., Mickylee produced 58,900 gpf which was significantly great er than Companion, Jambo ree, and SP-1 at 50,825, 48,475, and 42,250, respectively. Seasonal averages for pollen production are shown inTable 1. Discussion The results of this study illustrate that the amount of pollen produced by diploid watermelon plants differs by cultivar and also changes throughout the season. Pooled data for pollen production illustrates that Mickylee a nd Companion produce significantly greater amounts of pollen per flower than SP-1 or Jam boree. However, the po llen output per flower may not accurately represent the pollen output per plant. Previous research on flower production by pollenizers illustrated that SP-1 produced significantly greater numbers of staminate flowers when compared to Mickylee or Compani on (Freeman and Olson, 2007). The increased production of staminate flowers by SP-1 may re sult in greater pollen output per plant when compared with the other cultivars. The trend observed was that pollen production st arts low, increases and then decreases as the season progresses. These results are in cont rast the Stanghellini and Schultheis (2005) who reported that sampling day did not affect pollen production per flower. However, the duration of sampling used by Stanghellini and Schultheis (2 005) was not stated and flowers sampled over a shorter time frame may not exhib it the variation observed here. As watermelon plants begin to branch and produce flowers on secondary terminal s, it has been observed that flower size decreases. The decrease in flower size appa rently correlates with the decrease in pollen production per flower. Although pollen production per flower may decrease as the season

PAGE 75

75 progresses, it is likely that pollen production pe r plant will increase to a point as the number of staminate flowers produced increases. In theory, pollenizers that produce the greate st amount of pollen co uld outperform other pollenizers with lower pollen output. Greater pol len output by a pollenizer may also facilitate the reduction in pollenizer plant numbers used per unit area. However, other experimental results suggest that pollen producti on alone is not a reliable indi cator of pollenizer performance as the use of SP-1 resulted in significantly gr eater triploid watermelon yield when compared to the use of Companion. There are many factor s that influence the pe rformance of diploid watermelon pollenizers and pollen production is likely a strong contributor. Howerver, it is not a reliable factor on which to judge a pollenizers potential.

PAGE 76

76 Table 8-1. Pollen production by four diploid watermelon polleni zer cultivars at Quincy, FL during the Fall of 2006. Pollen grains per flower Cultivar 31 Aug. 8 Sept. 14 Sept. Combined Mickylee 49,775 a z 60,250 a z 58,900 a z 56,308 a z Companion 44,800 a b 62,275 a 50,825 b 52,633 a SP-1 37,813 b 53,138 a b 42,550 c 44,500 b Jamboree 36,700 b 44,975 b 48,475 b c 43,383 b z Means followed by the same lette r are not significantly different at P 0.05 by Duncans multiple range test.

PAGE 77

77 LIST OF REFERENCES Adlerz, W.C. 1966. Honey bee visit numbers and watermelon pollination. J. Econ. Entomol. 59:28-30. Ambrose, J.T. 1997. The importance of honey bees in North Carolina. N.C. Coop. Ext. Serv. Beekeeping Note #1A. Arndt, G.C., J.L. Rueda, H.M. Kidane-Maria m, and S.J. Peloquin. 1990. Pollen fertility in relation to open pollinated tr ue seed production in potatoe s. Amer. Potato J. 67:499-505. Arney, M., S.R. Fore, and R. Brancucci 2006. Watermelon reference book. National Watermelon Promotion Board. Orlando, Fla. Ban, D., S. Goreta, and J. Borosic. 2006. Plan t spacing and cultivar affect melon growth and yield components. Scientia Hort. 109:238-243. Batra, S.W.T. 1993. Male-fertile potato flower s are selectively buzz-pollinated only by Bombus terricola Kirby in upstate New York. J. Kansas Ent. Soc. 66:252-254. Brevis, P.A., D.S. NeSmith, H.Y. Wetzstein, D.B. Hausman. 2006. Production and viability of pollen and pollen-ovule ratios in four rabbiteye blueberry cultivars. J. Amer. Soc. Hort. Sci. 131:181-184 Brinen, G.H., S.J. Locascio, and G.W. Elmstrom. 1979. Plant and row spacing, mulch, and fertilizer rate effects on watermelon produc tion. J. Amer. Soc. Hort. Sci. 104:725-726. Bryan, H.H. 1966. Effect of plastic mulch on the yield of several vege table crops in North Florida. Proc. Fla. St ate Hort. Soc. 79:139-146. Buker, R.S., W.M. Stall, S.M. Olson, D.G. Schilling. 2003. Season-long interference of yellow nutsedge ( Cyperus esculentus ) with direct-seeded and transplanted watermelon ( Citrullus lanatus ). Weed Tech. 17:751-754. Butler, C.G. 1951. The importance of perfume in the discovery of food by the worker honeybee (Apis mellifera L.). Proceedings of the R oyal Society of London, Series B, 138:403-413. Clark, G.A., D.Z. Haman, and F.S. Zazueta. 2005. In jection of chemicals into irrigation systems: rates, volumes, and injection periods. Un iv. Fl. Coop. Ext. Serv. BUL250. 9 Dec. 2006. (http://edis.ifas.ufl.edu/AE116 ) Cockerham, L.E. and G.J. Galleta. 1976. A survey of pollen characteristic s in certain Vaccinium species. J. Amer. Soc. Hort. Sci. 101:671-676. Connell, J. H. 1990. Apparent versus "real" compet ition in plants, p. 9-23. In: J.B. Grace and D. Tilman (eds.) Perspectives on Plant Competition. Academic Press. New York.

PAGE 78

78 Cushman, K.E., D.H. Nagel, T.E. Morgan, P. D. Gerard. 2004. Plant popul ationaffects pumpkin yield components. HortTechnology 14:326-331. Dafni, A., M. Neppi, and E. Pacini. 2005. Polle n and stigma biology, p. 83-147. In A. Dafni., P.G. Kevan and B. Husband (eds.) Practical Pollination Biology. Enviroquest, Cambridge, Canada. Daniello, F.J. 2003. Watermelon. Tex. Coop. Ext. Horticulture Crop Guide Series. 10 Dec. 2006. (http://aggiehorticulture.t amu.edu/extension/vegetable/cropguides/watermelon.html ) Delaplane, K.S., and D.F. Mayer. 2000. Crop po llination by bees. CAB Intl., Wallingford, U.K. Dittmar, P.J., J.R. Schultheis, and D.W. Monks. 2005. Characterization of the growth and development of commercially available watermelon pollenizers. HortScience 40:872 (abstr.) Dobson, H.E.M. 1988. Survey of pollen and pollenkitt lipids Chemical cues to flower visitors? American Journal of Botany 75:170-182. Dobson, H.E.M. 1991. Pollen and flower fragra nces in pollination. Acta. Hort. 288:313-320. Dobson, H.E.M., J. Bergstrom, G. Bergstrom, a nd I. Groth. 1987. Pollen and flower volatiles in two Rosa species. Phytochemistry 26:3171-3173 Dobson, H.E.M., I. Groth, and G. Bergstrom. 1996. Pollen advertisement: Chemical contrasts between whole-flower and pollen odors. American Journal of Botany 83:877-885. Duthie, J.A., B.W. Roberts, J.V. Edelson, a nd J.W. Shrefler. 1999a. Plant density-dependent variation in density, freq uency, and size of watermelon fruits. Crop Sci. 39:412-417 Duthie, J.A., J.W. Shrefler, B.W. Roberts, and J.V. Edelson. 1999b. Plant density-dependent variation in marketable yiel d, fruit biomass, and marketable fraction in watermelon. Crop Sci. 39:406-412. Edelstein, M. and H. Nerson. 2002. Genotype and plant density affect watermelon grown for seed consumption. HortScience 37:981-983. Erdem, Y. and A.N. Yuksel. 2003. Yield response of watermelon to irrigation shortage. Sci. Hort. 98:365-383. Fiacchino, D.C. and S.A. Walters 2003. Influence of diploid polle nizer frequencies ontriploid watermelon quality and yi elds. HortTechnology 13:58-61. Firbank, L.G. and A.R. Watkinson. 1990. On the e ffects of competition: from monocultures to mixtures, p. 165-192. In: J.B. Grace and D. Tilman (eds.) Perspectives on Plant Competition. Academic Press. New York.

PAGE 79

79 Fortescue, J.A. and D.W. Tu rner. 2004. Pollen fertility in Musa : viability in cultivars grown in southern Australia. Australian J. of Agr. Res. 55:1085-1091 Franklin, R. 1998. Nutrient management for S outh Carolina. Clemson Univ. Coop. Ext. Serv. Extension Circular 476. Free, J.B. 1993. Insect pollination of crops, 2nd ed. Academic, London. Freeman, J.H. 2007. Use and effects of diploid pollenizers for triploid watermelon [Citrullus lanatus (Thunberg) Ma tsumura & Nakai] production. Univ. FL., Gainesville, PhD Diss. 46-56. Freeman, J.H. and S.M. Olson. 2007. Characteristic s of watermelon pollenizer cultivars for use in triploid production. Int. J. Veg. Sci. In Press von Frisch, K. 1967. The Dance Language and Orie ntation of Bees. Belknap Press. Cambridge, Ma. Gillaspy, G., H. Bendavid, W. Gruissem. 1993. Fruits a developmental perspective. Plant Cell 5:1439-1451. Goreta, S., S. Perica, G. Dumicic, L. Bu can, and K. Zanic. 2005. Growth and yield of watermelon on polyethylene mulch with different spacings and nitrogen rates. HortScience 40:366-369. Hara, H. 1969. The correct authors name for Citrullus lanatus (Cucurbitaceae). Taxon 18:346347. Harbo, J.R. and R.A. Hoopinger. 1997. Honey bees (Hymenoptera: Apidae) in the United States that express resistance to Varroa jacobsoni (Mesostigmata: Varroidae). J. Econ. Entomol. 90:893-898. Hidalgo, P.J., C. Galan, and E. Domingu ez. 1999. Pollen production in the genus Cupressus Grana 38:296-300. Hochmuth, G.J, E. Kee, T.K. Hartz, F.J. Dainello, and J.E. Motes. 2001. Cultural management, p. 78-97. In: D.N. Maynard (ed.) Watermelons characteristics, production and marketing. ASHS Press. Alexandria, VA. Hochmuth, G.J., R.C. Hochmuth, and S.M. Olson. 2001. Polyethylene mulching for early vegetable production in north Fl orida. Univ. Fla. Coop. Ext. Serv. Circular 805. 9 Dec. 2006. (http://edis.if as.ufl.edu/CV213 ) Holiday, R. 1960. Plant population a nd crop yield. Nature 186:22-24 Karst, T. 1990. Seedless watermelon sure to grow. The Grower 23:61.

PAGE 80

80 Kartesz, J.K. 2006. PLANTS profile for Citrullus lanatus U.S. Dept. Agric. NRCS. 3 Dec. 2006. (http://plants.usda.gov/ja va/profile?symbol=CILA3 ). Kihara, H. 1951. Triploid watermelons. Proc. Amer. Soc. Hort. Sci. 58:217-230. Kultur, F., H.C. Harrison, and J.E. Staub. 2001. Spacing and genotype affect fruit sugar concentration, yield, and fruit size of muskmelon. HortScience 36:274-278. Lamont, W.J., Jr. 1993. Plastic mulches for th e production of vegetable crops. HortTechnology 3:35-39. Lang, G.A. and E.J. Parrie. 1992. Pollen viab ility and vigor in hybr id southern highbush blueberries ( Vaccinium corymbosum L. x spp.). HortScience 27:425-427. Lavi, U., S. Nachman, I. Barucis, D. Gaash, A. Kadman. 1996. The effect of pollen donors and pollen viability on fruitlet drop in Macadamia integrifolia (Maiden & Betche). Tropic. Agric. 73:249-251. Lu, W., J.V. Edelson, J.A. Duthie, and B.W. Roberts. 2003. A comparis on ofyield between high and low intensity management for three watermelon cultivars.HortScience 38:351-356. Marr, C.W. and K.L.B. Gast. 1991. Reactions by c onsumers in a farmers market to prices for seedless watermelon and ratings of eating quality. HortTechnology 1:105-106. Maynard, D.N. 2001 An introduction to the watermelon, p. 9-20. In: D.N. Maynard (ed.) Watermelons characteristics, production a nd marketing. ASHS Press. Alexandria, VA. Maynard, D.N. 1989. Triploid watermelon seed orientation affects seedcoat adherence on emerged cotyledons. HortScience 24:603-604. Maynard, D.N. 1992. Growing seedless watermelon. Univ. Fla. Coop. Ext. Serv. Fact sheet HS687. 12 Oct. 2006. (http://edis.ifas.ufl.edu/CV006 ) Maynard, D.N. and G.W. Elmstrom 1989. Evaluation of triploid watermelon cultivars in central and southwest Florida. Proc. Fl a. State Hort. Soc. 102:313-319. Maynard, D.N. and G.W. Elmstrom. 1992. Trip loid watermelon production practices and varieties. Acta Hort. 318:169-173. Maynard, E.T. and W.D. Scott. 1998. Plant spac ing affects yield of Superstar muskmelon. HortScience 33:52-54. McCreight, J.D. 1998. Botany and culture, p. 2-6. In: T.A. Zitter, D.L. Hopkins, and C.E. Thomas (eds.) Compendium of cucurb it diseases. APS Press. St. Paul, MN. Monks, D.W. and J.R. Schultheis. 1998. Critica l weed free period for large crabgrass ( Digitaria sanguinalis ) in transplanted watermelon. Weed Sci. 46:530-532.

PAGE 81

81 Motsenbocker, C.E. and R.A. Arancibia. 2002. In-row spacing influences triploidwatermelon yield and crop value. HortTechnology 12:437-440. Nepi, M. and E. Pacini. 1993. Pollination, polle n viability and pistil receptivity in Cucurbita pepo Annals of Botany. 72:527-536. NeSmith, D.S. 1993. Plant spacing influences watermelon yield and yield components. HortScience 28:885-887. NeSmith, S. and J. Duval. 2001. Fruit set of triplo id watermelon as a function of distance from a diploid pollenizer. HortScience 36:60-61. Nettles, V.F. 1963. Planting and mulching studies w ith cucurbits. Proc. Fla. State Hort. Soc. 76:178-182. Nikkanen, T., T. Aronen, H. Hggman, and M. Ve nlinen. 2000. Variation in pollen viability among Picea abies genotypes potential for unequal pate rnal success. Theor. Appl. Genet. 101:511-518. Olsen, L., R. Hoopinger, and E.C. Martin. 1979. Pollen preferences of honeybees sited on four cultivated crops. J. Ap icultural Res. 18:196-200. Olson, S.M., E.H. Simonne, W.M. Stall, P.D. R oberts, S.E. Webb, T.G. Taylor, and S.A. Smith. 2006. Cucurbit production in Flor ida, p. 191-237. In: S. M. Olson and E. H. Simonne (eds.) Vegetable production handbook for Florid a. Univ. Fla. Coop. Ext. Serv. and Vance Publishing. Lenexa, KS. Parzies, H.K., F. Schnaithmann, and H.H. Geiger. 2005. Pollen viability of Hordeum spp genotypes with different flowering ch aracteristics. E uphytica 145:229-235. Pernal, S.F and R.W. Currie. 2002. Discriminatio n and preferences for pollen-based cues by foraging honeybees, Apis mellifera L. Animal Behaviour 63:369-390. Prieto-Baena, J.C., P.J. Hidalgo, E. Dominguez, and C. Galan. 2003. Pollen production in the Poaceae family. Grana 42:153-160. Radosevich, S.R. and M.L. Roush. 1990. The role of competition in agriculture, p. 341-363. In: J.B. Grace and D. Tilman (eds.) Perspectives on Plant Competition. Academic Press. New York. Reiners, S. and D.I.M. Riggs. 1997. Plant spacing a nd variety affect pumpkin yield and fruit size but supplemental nitrogen doe s not. HortScience 32:1037-1039. Reiners, S. and D.I.M. Riggs. 1999. Plant popula tion affects yield and fruit size of pumpkin. HortScience 34:1076-1078. Rhodes, B., K.B. Gruene, and W.M. Hood. 1997. Honey bees waste time on triploid male flowers. Cucurbit Genet. Coop. Rpt. 20:45.

PAGE 82

82 Robinson, R.W. and D.S. Decker-Walters. 1997. Cucurbits. CAB Intl., Wallingford, U.K. Rodriguez-Riano, T. and A. Dafni. 2000. A new pr ocedure to asses pollen viability. Sex. Plant Reprod. 12:241-244. Rubatzky, V.E. and M. Yamaguchi. 1997. World vegetables, 2nd ed. Chapman & Hall Publ., New York. Sanders, D.C. (ed.), J.M. Kemble, E.J. Sikora, R.L. Hassell, G. Miller, T. Keinath, J.K. Norsworthy, P. Smith, G.E. Boyhan, W.T. Kelley, D.B. Langston, A.S. Culpepper, A.S. Sparks, J.E. Boudreaux, J.M. Cannon, D.H. Na gel, R.G. Snyder, D. Ingram, M.R. Williams, B.O. Layton, J.D. Byrd, M.W. Sha nkle, A. Rankins, R.B. Batts, M.E. Clough, N.G. Creamer, J.M. Davis, W.R. Jester, D. W. Monks, L.M. Reyes, J.R. Schultheis, A. Thornton, G.T. Roberson, K.A. Sorensen, J.F. Walgenbach, D.B. Orr, D.R. Tarpy, C.W. Averre, M.A. Cubeta, K. Ivors, G.J. Holmes, K.M. Jennings, F.J. Louws, D.F. Ritchie, C.R. Crozier, G.D. Hoyt, D.N. Maynard, R.S. Mylavarape, and H.J. Savoy. 2006. Vegetable crop guidelines for the southeastern U.S. Vance Publ. Corp., Lincolnshire, Ill., in cooperation with the N.C. Veg. Growers Assn., Raleigh, N.C. Sanders, D.C., J.D. Cure, and J.R. Schultheis. 1999. Yield response of watermelon to planting density, planting pattern, and polyeth ylene mulch. HortScience 34:1221-1223. Schabenberger, O. and F.J. Pierce. 2002. Contemporar y statistical models for the plant and soil sciences. CRC Press. Boca Raton, Fla. Smajstrla, A.J., B.J. Bowman, G.A. Clark, D.Z. Haman, D.S. Harrison, F.T. Izuno, D.J. Pitts, and F.S. Zazueta. 2002. Efficiencies of florida ag ricultural irrigation systems. Univ. Fl. Coop. Ext. Serv. Fact Sheet BUL247. 10 Dec. 2006. (http://edis.ifas.ufl.edu/AE110 ) Stanghellini, M.S., J.T. Ambrose, and J.R. Schultheis. 1997. The effects of honey bee and bumble bee pollination on fruit set and abor tion of cucumber and watermelon. Amer. Bee J. 137:386-391. Stanghellini, M.S., J.T. Ambrose, and J.R. Schultheis. 1998. Seed production in watermelon: a comparison between two commercially avai lable pollinators. HortScience 33:28-30. Stanghellini, M.S. and J.R. Schultheis. 2005. Ge notypic variability in staminate flower and pollen grain production of diploid watermelons. HortScience 40:752-755. Taylor, M.D. and S.J. Locascio. 2004. Blossom-e nd rot: a calcium deficiency. J. Plant. Nutr. 27:123-139. U.S. Department of Agriculture. 2006. National wa termelon report. U.S. Dept. Agr. Agricultural Marketing Service. Thomasville, Ga. 15 Dec. 2006 (http://www.ams.usda.gov ) U.S. Department of Agriculture. 2005. Quick stats. U.S. Dept. Agr. Natl. Agr. Statistics Serv. Washington, D.C. 12 Dec. 2006. (http://www.nass.usda.gov/QuickStats/ Create_Federal_All.jsp )

PAGE 83

83 U.S. Department of Agriculture. 2002. Census of agriculture. U.S. Dept. Ag r. Fla. Ag. Statistics Serv. Tallahassee, Fla. 8 Dec. 2006. (http://www.nass.usda.g ov/Statistics_by_State/ Florida/index.asp ) Vithanage, V. 1991. Effect of different pollen parents on seediness and quality of Ellendale tangor. Scientia Hort. 48:253-260. Wallace, H.M. and L.S. Lee. 1999. Pollen source, fruit set and xenia in mandarins. J. Hort. Sci. Biotechnology 74:82-86 Walters, S.A. 2005. Honey bee pollination requirem ents for triploid watermelon. HortScience 40:1268-1270. Wehner, T.C. 2006. Watermelon crop inform ation taxonomy, morphology, physiology. Hort. Sci. Dept. NCSU. 16 Dec. 2006 (http://cuke.hort.ncsu.edu/cuc urbit/wmelon/wmelonmain.html ) Wiemann, S. (ed.) 1992. The Packer Fresh Trends Vance Publishing Corp., Lincolnshire, IL Wolf, S., Y. Lensky, and N. Paldi. 1999. Genetic variability in flow er attractiveness to honeybees ( Apis mellifera L.) within the genus Citrullus HortScience 34:860-86

PAGE 84

84 BIOGRAPHICAL SKETCH Joshua Herbert Freeman was born on October 24, 1980 to Linda and Herbert Freeman of Columbia, S.C. He first became interested in ag riculture while working on cattle farm near his home. After graduating from Ridge View High School he attended Clemson University where earned a bachelors degree in entomology. In the fall of 2002, he enrolled in the University of Florida and pursued a doctor of plant medicine degree. His caree r aspirations changed and in the fall of 2004, he began working on doctorate of philosophy in horticultural science at the University of Florida.


Permanent Link: http://ufdc.ufl.edu/UFE0019763/00001

Material Information

Title: Use and effects of diploid pollenizers for triploid watermelon Citrullus lanatus (Thunberg) Matsumura and Nakai production
Physical Description: 84 p.
Language: English
Creator: Freeman, Joshua Herbert ( Dissertant )
Olson, Stephen M. ( Thesis advisor )
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2007
Copyright Date: 2007

Subjects

Subjects / Keywords: Horticultural Science thesis, Ph. D.   ( local )
Dissertations, Academic -- UF -- Horticulture   ( local )
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
theses   ( marcgt )

Notes

Abstract: The use of in-row pollenizers has become popular because it allows a greater number of triploid plants to be planted per hectare. Multiple in-row pollenizer cultivars are available but it is unclear if any exhibit superior performance with respect to triploid watermelon yield and if so, what varietal characteristics contribute to a pollenizer’s performance. Field trials were conducted during the Spring and Fall of 2005 and 2006 at various locations in FL. and S.C. to determine the performance of various pollenizers and also what contributed to their success. Of the in-row pollenizers that were tested, ‘Sidekick’ resulted in the greatest triploid watermelon yields. Yields from plots pollenized by ‘Patron’, ‘SP-1’, ‘Jenny’, and ‘Mickylee’ were not significantly lower. The use of ‘Companion’ resulted in significantly lower yields than plots pollenized ‘Sidekick’, ‘Patron’, ‘SP-1’, and ‘Jenny’. Pollen viability can vary between cultivars of a plant species and the pollen viability of four pollenizer cultivars was evaluated. Poor pollen viability from a pollenizer could result in increased fruit abortions and lower yield. No significant differences in pollen viability were detected between pollenizer cultivars tested. The production of staminate flowers is a crucial factor for pollenizers as there must be adequate pollen flow during triploid watermelon fruit set. Flower production for ‘Companion’, ‘Jenny’, ‘Mickylee’, and ‘SP-1’ was recorded and ‘Companion’ produced as many flowers as ‘Jenny’ or ‘Mickylee’ throughout most of the season. The flowering period of ‘Companion’ does appear to be shorter than other cultivars. Pollinator preference was examined between ‘Companion’, ‘Mickylee’, and ‘SP-1’ and ‘Companion’ was found to be the least attractive of the three. The lack of pollinator visitation to ‘Companion’ appears to be the greatest contributor to its poor performance. ‘Mickylee’ is an attractive option to use as a pollenizer because of its lower seed costs. However, ‘Mickylee’ has a growth habit that is more vigorous than most other pollenizers. Studies comparing ‘SP-1’ and ‘Mickylee’ showed that the ‘Mickylee’ competed more with associated triploid plants and reduced yield. Factors affecting pollenizer performance the most appear to be pollinator preference, staminate flower production, and competitive effect on associated triploids.
Subject: diploid, seeded, seedless, special, triploid
General Note: Title from title page of source document.
General Note: Document formatted into pages; contains 84 pages.
General Note: Includes vita.
Thesis: Thesis (Ph. D.)--University of Florida, 2007.
Bibliography: Includes bibliographical references.
General Note: Text (Electronic thesis) in PDF format.

Record Information

Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
System ID: UFE0019763:00001

Permanent Link: http://ufdc.ufl.edu/UFE0019763/00001

Material Information

Title: Use and effects of diploid pollenizers for triploid watermelon Citrullus lanatus (Thunberg) Matsumura and Nakai production
Physical Description: 84 p.
Language: English
Creator: Freeman, Joshua Herbert ( Dissertant )
Olson, Stephen M. ( Thesis advisor )
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2007
Copyright Date: 2007

Subjects

Subjects / Keywords: Horticultural Science thesis, Ph. D.   ( local )
Dissertations, Academic -- UF -- Horticulture   ( local )
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
theses   ( marcgt )

Notes

Abstract: The use of in-row pollenizers has become popular because it allows a greater number of triploid plants to be planted per hectare. Multiple in-row pollenizer cultivars are available but it is unclear if any exhibit superior performance with respect to triploid watermelon yield and if so, what varietal characteristics contribute to a pollenizer’s performance. Field trials were conducted during the Spring and Fall of 2005 and 2006 at various locations in FL. and S.C. to determine the performance of various pollenizers and also what contributed to their success. Of the in-row pollenizers that were tested, ‘Sidekick’ resulted in the greatest triploid watermelon yields. Yields from plots pollenized by ‘Patron’, ‘SP-1’, ‘Jenny’, and ‘Mickylee’ were not significantly lower. The use of ‘Companion’ resulted in significantly lower yields than plots pollenized ‘Sidekick’, ‘Patron’, ‘SP-1’, and ‘Jenny’. Pollen viability can vary between cultivars of a plant species and the pollen viability of four pollenizer cultivars was evaluated. Poor pollen viability from a pollenizer could result in increased fruit abortions and lower yield. No significant differences in pollen viability were detected between pollenizer cultivars tested. The production of staminate flowers is a crucial factor for pollenizers as there must be adequate pollen flow during triploid watermelon fruit set. Flower production for ‘Companion’, ‘Jenny’, ‘Mickylee’, and ‘SP-1’ was recorded and ‘Companion’ produced as many flowers as ‘Jenny’ or ‘Mickylee’ throughout most of the season. The flowering period of ‘Companion’ does appear to be shorter than other cultivars. Pollinator preference was examined between ‘Companion’, ‘Mickylee’, and ‘SP-1’ and ‘Companion’ was found to be the least attractive of the three. The lack of pollinator visitation to ‘Companion’ appears to be the greatest contributor to its poor performance. ‘Mickylee’ is an attractive option to use as a pollenizer because of its lower seed costs. However, ‘Mickylee’ has a growth habit that is more vigorous than most other pollenizers. Studies comparing ‘SP-1’ and ‘Mickylee’ showed that the ‘Mickylee’ competed more with associated triploid plants and reduced yield. Factors affecting pollenizer performance the most appear to be pollinator preference, staminate flower production, and competitive effect on associated triploids.
Subject: diploid, seeded, seedless, special, triploid
General Note: Title from title page of source document.
General Note: Document formatted into pages; contains 84 pages.
General Note: Includes vita.
Thesis: Thesis (Ph. D.)--University of Florida, 2007.
Bibliography: Includes bibliographical references.
General Note: Text (Electronic thesis) in PDF format.

Record Information

Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
System ID: UFE0019763:00001


This item has the following downloads:


Full Text





USE AND EFFECTS OF DIPLOID POLLENIZERS FOR TRIPLOID WATERMELON
[Citrullus lan2atus (Thunberg) Matsumura and Nakai] PRODUCTION




















By

JOSHUA HERBERT FREEMAN


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA

2007





































O 2007 Joshua Herbert Freeman


































To my wife Lindsey for the sacrifices she has made for me to be here, and to my parents for their
unyielding support.









ACKNOWLEDGMENTS

Foremost, I thank my advisor, Dr. Stephen Olson for giving me the opportunity to pursue

this degree and for his personal and professional guidance. I also thank the members of my

committee for the time they have dedicated and the knowledge and guidance they have provided.

Special thanks go to Dr. Eric Simonne and Dr. Bill Stall for their professional guidance and

willingness to help me with any aspect of my career. I greatly appreciate the field and office

staff at NFREC who helped throughout my dissertation. Special thanks go to Dr. Powell Smith

for planting a seed in my mind that has led me to where I am today.

None of this would have been possible if not for the sacrifices that my wife Lindsey has

made, putting her career on hold in order to support our family during this time. She has been

the strong foundation that has kept me sane and kept me on point. I will be forever grateful to

my parents, Linda and Herb Freeman for their relentless support and constant prayer. I would

also like to thank my grandparents, Lurie Goff and Blake Freeman for their support of me in

anything I do. I thank God every day for blessing me with the mind and body that have allowed

me to do this and for the family that has supported me. I also thank God for putting me where I

need to be when I need to be there. I hope I have made my wife, my family and my God proud.












TABLE OF CONTENTS




page

ACKNOWLEDGMENTS .............. ...............4.....


LIST OF TABLES ........._..... ...............7....__........


LIST OF FIGURES .............. ...............8.....


AB S TRAC T ......_ ................. ............_........9


CHAPTER


1 INTRODUCTION ................. ...............11.......... ......


2 REVEW OF THE LITERATURE. ............. ...... ...............13..


Review of Diploid Watermelon ............_...... ...............13...
Taxonomy and Bot any .............. ............... 13....
Watermelon Production Practices .............. ...............15....
Watermelon Production Statistics .............. ...............18....
Review of Triploid Watermelon ................. ...............19................
Background Information .............. ...............19....
Seedless Watermelon Market Share ................. ...............20................

Triploid Seedless Watermelon Production ................. ...............21.......__.....
Pollinator Activity and Preference .............. ...............26....
Pollen Effects............... ...............27

Com petition ................. ...............30........ ......

3 CHARACTERISTICS OF DIPLOID POLLENIZERS FOR USE IN TRIPLOID
WATERMELON PRODUCTION ............_...... ...............32...


Introducti on ............. ...... ._ ...............32...
Materials and Methods .............. ...............32....
Re sults............. ...... ._ ...............34...
Discussion ............. ...... ._ ...............36...


4 POLLEN VIABILITY OF DIPLOID WATERMELON POLLENIZER CULTIVARS.......40


Introducti on ..........._.. ....._. ._ ...............40.....
Materials and Methods .............. ...............40....
Re sults.............._ ...... ...............42.....
Discussion .............._ ....... ...............42.....













5 DIPLOID WATERMELON POLLENIZER CULTIVARS EXHIBIT VARYING
DEGREES OF PERFORMANCE WITH RESPECT TO TRIPLOID WATERMELON
Y IELD .............. ...............46....


Introducti on ............. ..... .. ...............46...
M materials and M ethods .............. ...............46....
Re sults............. ..... ...............49...
Discussion ............. ..... ...............50...


6 COMPETITIVE AFFECT OF IN-ROW DIPLOID WATERMELON POLLENIZERS
ON TRIPLOID WATERMELON YIELD ....._ .....___ .........__ ............5


Introducti on ............. ..... .._ ...............57....
M materials and M ethods .............. ...............57....
Re sults............. ...... ...............58....
Discussion ............. ...... ._ ...............59....


7 VARIABILITY IN WATERMELON FLOWER ATTRACTIVENESS TO INSECT
POLLINATORS .............. ...............63....


Introducti on ................. ...............63.................
M materials and M ethods .............. ...............63....
Re sults ................ ...............64.................
Discussion ................. ...............66.................


8 VARIABILITY IN POLLEN PRODUCTION BY DIPLOID WATERMELON
POLLENIZ ERS ............. ...... ._ ...............72...


Introducti on ........._.__....... ._ __ ...............72....
M materials and M ethods .............. ...............72....
Re sults........._.__....... .__ ...............73....
Discussion ........._.__....... .__ ...............74....


LIST OF REFERENCE S ........._.__....... .__. ...............77...


BIOGRAPHICAL SKETCH .............. ...............84....










LIST OF TABLES


Table page

3-1 Analysis of variance for pollenizer fruit weight and fruit per plant at Quincy and
Live Oak FL during 2005. ............. ...............37.....

3-2 Interaction effect of location and watermelon pollenizer cultivars on fruit per plant at
Quincy and Live Oak FL during 2005. ............. ...............37.....

3-3 Main effects for pollenizer fruit weights combined over experiments conducted in
Quincy and Live Oak, FL, during 2005. ............. ...............38.....

4-1 Analysis of variance for pollen viability of watermelon pollenizer cultivars tested
during the Spring and Fall of 2006 at Quincy, FL. .............. ...............44....

4-2 Influence of diploid watermelon pollenizer cultivar on pollen viability at Quincy, FL
during the Spring and Fall of 2006. ........._ ....__ ......_ .....__ ............45

5-1 Pollenizer cultivar effect on 'Tri-X 313' yield at Blackville, SC during 2005..................54

5-2 Pollenizer cultivar effect on Supercrisp' watermelon yield and average fruit weight
at Blackville, SC, Citra, FL, and Quincy, FL during 2006. ............... ...................5

5-3 Pollenizer cultivar effect on soluble solids concentration of seedless watermelons at
Blackville, SC during 2005 and Citra, FL, Quincy, FL, and Blackville, SC during
2006............... ...............55..

5-4 Pollenizer cultivar effect on hollowheart disorder in Supercrisp' watermelon at
Quincy, FL, and Blackville, SC combined with Citra, FL during 2006. Means are to
be compared within the same column ................. ...............56...............

5-5 Seed sources for various pollenizer cultivars used during 2005 and 2006. .......................56

6-1 Influence of pollenizer cultivar and spacing on triploid watermelon yield during
2006............... ...............62..

8-1 Pollen production by four diploid watermelon pollenizer cultivars at Quincy, FL
during the Fall of 2006. ........... ..... .._ ...............76..










LIST OF FIGURES


Figure page

3-1 Pollenizer staminate flower counts combined over Quincy and Live Oak, FL, during
2005. Means not followed by the same letter are significantly different at (P < 0.05)
by Duncan's Multiple Range Test. ............. ...............39.....

5-1 Field diagram for pollenizer experiments at Blackville, S.C., Citra, FL., and Quincy,
FL. in 2005 and 2006. Columns represent individual rows. The same design was
used for replications three and four. ............. ...............52.....

5-2 Individual three-row plot design for pollenizer experiments at Blackville, S.C., Citra,
FL, and Quincy, FL in 2005 and 2006. Plot shown is using a pollenizer
recommended to be planted at a 1:3 pollenizer to seedless ratio ................... ...............53

7-1 Influence of cultivar on pollinator visitation to staminate watermelon flowers at
Quincy, FL, Spring 2006. Visitation means are to be compared within sample date.
Means not followed by the same letter are significantly different at P I 0.05. .................68

7-2 Interaction effect of cultivar and time on pollinator visitation to staminate
watermelon flowers at Quincy, FL, on 23 May, 2006. Visitation means are to be
compared within sample time. Means not followed by the same letter are
signify cantly different at P I 0.05. ............. ...............69.....

7-3 Influence of cultivar on pollinator visitation to staminate watermelon flowers at
Quincy, FL, Fall 2006. Visitation means are to be compared within sample date.
Means not followed by the same letter are significantly different at P I 0.05. .................70

7-4 Interaction effect of cultivar and time on pollinator visitation to staminate
watermelon flowers at Quincy, FL, on 23 Sept., 2006. Visitation means are to be
compared within sample time. Means not followed by the same letter are
significantly different at P I 0.05. ............. ...............71.....









Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

USE AND EFFECTS OF DIPLOID POLLENIZERS FOR TRIPLOID WATERMELON
[Citrullus lanatus (Thunberg) Matsumura and Nakai] PRODUCTION

By

Joshua Herbert Freeman

May 2007

Chair: Stephen M. Olson
Major: Horticultural Science

The use of in-row pollenizers has become popular because it allows a greater number of

triploid plants to be planted per hectare. Multiple in-row pollenizer cultivars are available but it

is unclear if any exhibit superior performance with respect to triploid watermelon yield and if so,

what varietal characteristics contribute to a pollenizer' s performance.

Field trials were conducted during the Spring and Fall of 2005 and 2006 at various

locations in FL. and S.C. to determine the performance of various pollenizers and also what

contributed to their success. Of the in-row pollenizers that were tested, Sidekick' resulted in the

greatest triploid watermelon yields. Yields from plots pollenized by 'Patron', 'SP-1', 'Jenny',

and 'Mickylee' were not significantly lower. The use of 'Companion' resulted in significantly

lower yields than plots pollenized 'Sidekick', 'Patron', 'SP-1', and 'Jenny'.

Pollen viability can vary between cultivars of a plant species and the pollen viability of

four pollenizer cultivars was evaluated. Poor pollen viability from a pollenizer could result in

increased fruit abortions and lower yield. No significant differences in pollen viability were

detected between pollenizer cultivars tested. The production of staminate flowers is a crucial

factor for pollenizers as there must be adequate pollen flow during triploid watermelon fruit set.

Flower production for 'Companion', 'Jenny', 'Mickylee', and 'SP-1' was recorded and










'Companion' produced as many flowers as 'Jenny' or 'Mickylee' throughout most of the season.

The flowering period of 'Companion' does appear to be shorter than other cultivars. Pollinator

preference was examined between 'Companion', 'Mickylee', and 'SP-1' and 'Companion' was

found to be the least attractive of the three. The lack of pollinator visitation to 'Companion'

appears to be the greatest contributor to its poor performance.

'Mickylee' is an attractive option to use as a pollenizer because of its lower seed costs.

However, 'Mickylee' has a growth habit that is more vigorous than most other pollenizers.

Studies comparing 'SP-1' and 'Mickylee' showed that the 'Mickylee' competed more with

associated triploid plants and reduced yield. Factors affecting pollenizer performance the most

appear to be pollinator preference, staminate flower production, and competitive effect on

associated triploids.









CHAPTER 1
INTTRODUCTION

Seedless watermelons now account for 78% of the watermelons sold in the United States.

Triploid watermelon plants produce seedless fruits however; they do not produce sufficient

viable pollen which is necessary for fruit set. To achieve optimal seedless watermelon yields,

rows of diploid watermelon cultivars are planted in the same field as the triploids. These diploid

cultivars account for 20 to 33% of the watermelon plants per hectare. With low demand for

seeded watermelons, it has become less desirable to maintain this much hectarage in diploid

plants. Diploid cultivars (pollenizers) designed to be planted within the row of triploid

watermelons are now available. The use of these in-row pollenizers requires no dedicated space

for the pollenizer plants, thus allowing for an increase in triploid plants per hectare. When in-

row pollenizers first became available there were few options, now there are 11 commercially

available cultivars. Using in-row pollenizers is a new concept and most of the in-row pollenizer

cultivars have been on the market less than two years. The performance of in-row pollenizer

cultivars has not been demonstrated, however earlier studies have reported differences in triploid

watermelon yields due to pollenizer cultivar. It is suspected that the similar results will be

observed with in-row pollenizers.

Available in-row pollenizers have diverse phenotypes and variable plant characteristics

and it is unclear how these may effect the cultivar' s performance. Characteristics such as flower

production, pollen production, pollen viability, attractiveness to pollinators, and plant vigor

could have a marked effect on how triploid plants in association with the pollenizers will yield.

Pollenizer seed/plant costs are highly variable and it is unclear whether the more expensive

pollenizers will provide for greater seedless watermelon yields.









The aim of this body of work is to determine how well in-row pollenizers perform and how

their varietal characteristics influence their performance.









CHAPTER 2
REVIEW OF THE LITERATURE

Review of Diploid Watermelon

Taxonomy and Botany

The watermelon [Citrullus lan2atus (Thunberg) Matsumura & Nakai] was originally

described in Africa as Mamordica lanata by Carl Thunberg in 1794 (Hara, 1969). Schrader

proposed Citrullus vulgaris in 1836 which was commonly used until lan2atus was accepted as the

oldest specific epithet. Hara revealed the original description in 1969 that was published by

Matsumura and Nakai in 1920 and watermelon has since been designated as Citrullus lan2atus

(Thunberg) Matsumura & Nakai (Hara, 1969).

Watermelon is a dicotyledonous angiosperm in the order Violales and family

Cucurbitaceae (Kartesz, 2006). The center of origin for the species is believed to be in southern

Africa, where it was first described by Thunberg. David Livingstone reported seeing

watermelons growing wild in the Kalahari Desert in 1857 (Wehner, 2006). Watermelon is a

warm-season, herbaceous vining annual with angular stems that may reach 9 m long (Wehner,

2006). There are also genotypes that exhibit a bush or dwarf growth habit (due to shorter inter-

nodes) that have shorter stems and are less branched. The main stem or crown of the plant

develops from the seedling stem and may have few to many lateral branches develop depending

on genotype. Most watermelon genotypes have pinnately lobed leaves with three to five pairs of

lobes and are born singly on the stem (McCreight, 1996). Cultivars have been developed that

have a nearly entire leaf which is due to a gene mutation (Wehner, 2006). Branched tendrils are

produced at each node. Watermelon is a monoecious plant with imperfect flowers that are born

singly at the leaf axil (Wehner, 2006). Watermelon flowers are small in comparison with other

cucurbits such as those in the genera Cucurbita and are born on short peduncles. When plants









reach sexual maturity, staminate (male) flowers are produced first and for a period of time before

pistillate (female) flowers are produced. Generally, staminate flowers have three anthers and

pistillate flowers have three stigmatal lobes. Pistillate flowers have inferior ovaries which vary

in size and shape depending on genotype. Staminate flowers are only open for one day and

pistillate flowers are only receptive for one day. The corollas, stamens and pistils of watermelon

flowers are all yellow.

Watermelons are entomophilous plants that are primarily pollinated in cultivation by

honeybee (Apis mellifera L.) (Maynard, 2001). Watermelon entomophily is a symbiotic

relationship between the insect and plant as plants receive pollination and bees obtain pollen

(which is the only protein source for honeybees) and nectar. Pollination is facilitated by the

production of a sticky substance on the surface of the pollen grains called pollenkitt. Pollenkitt

enables adherence to floral visitors in order to disseminate pollen and is primarily seen in

entomophilous angiosperms (Dobson et al., 1996). Pollenkitt is comprised mostly of lipids

which also play a role in attraction of pollinators (Dobson, 1988; Pernal and Currie, 2002). Poor

pollination may result in fruit abortion or misshapen fruit which is unmarketable (Rubatzky and

Yamaguchi, 1997; Stanghellini et al., 1997; Walters, 2005).

Watermelon fruit is a specialized berry with thick skin (rind) known as a pepo (Rubatzky

and Yamaguchi, 1997). Watermelon rind thickness is dependent on genotype and can be very

thin to thick depending on the intended use of the watermelon. The edible portion of watermelon

is the endocarp, although rind and seeds can and are consumed in certain geographic areas.

Watermelon fruit are highly variable in size, shape, and color, and although all three are

genetically determined, size can be altered through production practices. Watermelons may

range from cylindrical to round and may be from two to over 90 kg at maturity (Wehner, 2006).









The largest watermelon recorded was 119 kg (Wehner, 2006). Most cultivars that are currently

grown commercially in the U.S. range from 5.5 to 9.0 kg. Consumer preference has changed

gradually over time and large fruit (> 11.3 kg) that were once preferred are now virtually

unacceptable in most of the U.S. market. Average maturity for watermelon fruit is 80 days from

transplant and 110 days from seed. Watermelon seeds are variable in size, shape, and color but

are usually flattened, teardrop shaped and brown to black in color (Robinson and Decker-

Walters, 1997). Optimum temperatures for seed germination range form 29.4-32.30C (Olson et

al., 2006). Watermelon plants are intolerant to frost and grow best when the average temperature

is above 21.10C (Rubatzky andYamaguchi, 1997).

Watermelon Production Practices

Growing watermelons and producing optimal yields is dependent on many factors

including fertilization, irrigation, soil management, and other cultural practices (Hochmuth et al.,

2001a). The pH of the soil can greatly influence nutrient availability and crop growth.

Watermelon plants can tolerate a range of pH values from 5.5 to 7.5 but 6.0 to 6.5 is optimum

(Hochmuth et al., 2001a). Various forms of lime can be used to correct acidic soil pH, which is

common in the highly weathered soils of the southeast. Calcium is important in the growth and

development of watermelon because it is necessary to maintain the structural integrity of cell

walls. Inadequate calcium in developing watermelon fruit can lead to a disorder known as

blossom-end rot (BER) (Taylor and Locascio, 2004). Blossom-end rot occurs when tissue at the

blossom-end of the fruit begins to collapse. This collapse is visualized as necrotic areas at the

blossom-end which allow pathogens to enter the fruit and eventually leads to decay. Although

BER is a calcium deficiency, factors such as inadequate or inconsistent irrigation, elemental

competition, high salinity, high temperature and high or low transpiration may induce the

problem (Taylor and Locacsio, 2004).









Other elements such as nitrogen, phosphorus, potassium, magnesium, and micro-nutrients

are also necessary for adequate fruit growth and plant development (Hochmuth et al., 2001a).

The amount of these elements needed may vary by soil type and location. Soil testing should be

performed in order to understand what the crop requirements are at a given location. Nitrogen,

phosphorus, and potassium are generally the three most limiting nutrients and recommendations

for the maximum amounts of nutrient addition for watermelon production in Florida are 168N-

72.2P-140K kg/ha (Olson et al., 2006).

Irrigation amounts and frequencies required by the crop can vary depending on soil type,

its water holding capacity, and environmental conditions (Rubatzky and Yamaguchi, 1997). A

minimum of 93 cm of water per hectare is required to successfully grow watermelons (Rubatzky

and Yamaguchi, 1997). Irrigation frequencies are important because some portions of growth

and development require more water and are more sensitive to moisture stress than others.

Water deficit during flowering and early fruit growth can have a greater negative impact on

watermelon yield than water stress during other growth periods (Erdem and Yuksel, 2003).

Watermelon fruit growth and development is triggered by hormones produced by

developing seeds, which are dependent on pollen transfer from staminate to pistillate flowers

(Rubatzky and Yamaguchi, 1997). Pollination can be a yield limiting factor in watermelon

production and in many areas, pollination by feral honeybees is no longer reliable due to the

recent introduction of two parasitic mite species [Acarapis woodi (Rennie) and Varroa jacobsoni

(Oudemans)] (Delaplane and Mayer, 2000). These mites have reduced feral and domesticated

honeybee colonies by 90% and 30% respectively (Stanghellini et al., 1998; Ambrose, 1997;

Harbo and Hoopinger, 1997). The reduction of feral honeybee populations necessitates the

introduction of domesticated honeybees in large hectarage, high density plantings. Commercial









pollinators are available for rent or purchase and honeybees are the most readily available.

Recommendations vary from one to five hives per hectare, which is dependent on hive strength

(Olson et al., 2006). Adlerz (1966) reported that in diploid watermelon, a minimum of eight

honeybee visits and 1000 pollen grains per pistillate flower were necessary for fruit set.

Stanghellini (1997) reported similar findings of a minimum six visits per flower in diploid

watermelon. Visitation rates lower than this resulted in significantly greater fruit abortion rates

(Stanghellini, 1997).

Cultural practices used in watermelon production have changed over the years but the ones

having the most effect are the use of polyethylene mulch and drip irrigation. Traditionally

watermelons were grown on bare ground with either overhead or seep irrigation. The use of drip

irrigation decreases the amount of water used and increases the use efficiency (Smaj strla et al.,

2002). It also allows growers to target fertilizer applications directly to the plants through the

use of soluble fertilizer that is pumped through the drip tape (Clark et al., 2005). The use of

polyethylene mulch has many advantages including earliness, increased yields, increased

profitability, irrigation and fertilizer retention, weed suppression, and fruit protection (Lu et al.,

2003; Hochmuth et al., 2001b; Sanders et al., 1999; Lamont, 1993; Bryan, 1966). By covering

the ground with black polyethylene mulch, soil temperatures are raised which increases early

plant growth rate and thus early yield. Mulch has been shown to decrease harvest time in the

spring as much as a month (Bryan, 1966). The earliness of the crop may greatly influence the

profitability by allowing producers to enter the market before other producers or producing

regions. The use of polyethylene mulch has also allowed for the adoption of soil fumigants

which are essential for profitable commercial production in certain areas. The use of

greenhouse-grown containerized watermelon seedlings has also increased which is due mostly to









increased seed prices and the benefit of significantly greater early yields (Nettles, 1963).

Implementing polyethylene mulch and the use of transplants has increased the success of

producers in Florida, Georgia, and South Carolina as it allows them to enter the market before

the July 4th holiday. Generally, watermelon movement in the U.S. is greater and the price is

higher before this holiday (USDA, 2006). These three states accounted for 42% of the

watermelon hectarage in the U.S. in 2005 (USDA-NASS, 2006).

Watermelon plant spacing has changed over the years; most likely due to adoption of other

cultural practices that make production more efficient and a decrease in size preference by

consumers (Hochmuth et al., 2001a). Current recommendations for watermelon spacing range

from 1.1 to 2.7 m2 per plant (Daniello, 2003, Olson et. al, 2006). Recent research has shown that

greater yields per hectare may be achieved on polyethylene mulch with spacings as small as 1.0

m2 per plant (Goreta et al., 2005; Sanders et al., 1999). Plant spacing is also dependent on plant

architecture, as some genotypes have a more vigorous growth habit than others (Edelstein and

Nerson, 2002; Kultur et al., 2001; Reiners and Riggs, 1997).

Watermelon Production Statistics

Watermelons are grown throughout the world in tropical and subtropical climates. World

watermelon production has ranged from 81 billion kg in 2001 to 93.2 billion kg in 2004 (Arney

et al., 2006). The world's largest producer of watermelons is China which usually accounts for

over half of the world production (Arney et al., 2006). The U. S. generally ranks fourth in world

production and produces on average 1.8 billion kg (Arney et al., 2006).

Florida consistently ranks among the top three watermelon-producing states in the nation

in both hectares harvested and crop value and produces about 20% of the watermelons grown in

the United States (USDA, 2005). Over the last five years, Florida harvested on average ten

thousand hectares of watermelons annually worth an average of 72. 1 million dollars. In Florida,









watermelons account for 3.9 % of the cash receipts for vegetables and 0.91% of the cash receipts

for agriculture (USDA, 2002). Although watermelon hectarage in the U.S. has declined over the

last five years, total production has remained stable as a result of increased production per

hectare. One factor that has changed is the types of watermelons that are being produced.

Review of Triploid Watermelon

Background Information

Triploid seedless watermelon was first described in the United States in 1951 based on

work that had been conducted in Japan since 1939 (Maynard and Elmstrom, 1992; Kihara,

1951). Seedless watermelons are produced by watermelon plants that are genetically triploid

(3n). Watermelon plants are naturally diploid (2n). Triploid plants are grown from triploid seed

which is produced by crossing a tetraploid (4n) female parent with a diploid male parent. The

female parent is produced by treating a diploid seedling with colchicine, a chemical that binds to

tubulin and inhibits the formation and activity of microtubules in plant cells. This inhibits the

separation of chromosomes during mitosis which doubles the number of chromosomes in the

plant and creates a tetraploid (Wehner, 2006). The triploid offspring are sterile which is why

fruits produced by these plants have no seeds. Fruit growth and enlargement in watermelons is

signaled by hormones produced by developing seeds. Since there are no developing seeds in

triploid fruit, these developmental signals are obtained from pollen tube growth and ovule

fertilization (Rhodes et al., 1997; Robinson and Decker-Walters, 1997; Maynard and Elmstrom,

1992). Ovules abort shortly after fertilization but may remain in the flesh as small rudimentary

white seeds (Maynard and Elmstrom, 1992; Kihara 1951). Though fruit growth and

development in triploids is signaled by pollen tube growth, triploid plants produce little if any

viable pollen (Rhodes et al., 1997; Robinson and Decker-Walters, 1997; Maynard and Elmstrom,









1992). A diploid watermelon cultivar must be planted in close proximity to the triploid to

provide sufficient viable pollen. This diploid plant is referred to as a pollenizer.

The first hybrid triploid watermelon cultivars produced by Kihara were finished in 1951

(Wehner, 2006). Triploid watermelon cultivars have been commercially available for nearly 35

years but interest from consumers and growers remained low until the late 20th century. There

was little interest in early triploid cultivars due to erratic and poor performance in the field and

high seed costs as compared to diploid cultivars (Maynard and Elmstrom, 1992). Seed for early

triploid cultivars were quoted at $135 per 1000 seed which was 900 times higher than hybrid

diploid cultivars at the time (Maynard and Elmstrom, 1992). Reluctance in adoption of triploids

may have also been due to the necessity of using transplants and the increased input costs

associated with them. A survey of over 1300 people conducted in 1992 indicated that while 74%

knew of seedless watermelons only 31% had ever purchased one (Wiemann, 1992). Marr and

Gast (1991) surveyed consumers and indicated that they were willing to pay 50% more for

seedless watermelons and that there was no differential preference between taste of seeded and

seedless. The authors suggested that the response seen was on appearance alone as participants

were shown cut fruit of both types. In 1990, Karst (1990) estimated that 5% of the U.S.

watermelon market was seedless but they had the potential to gain up to 50% market share.

Since this time, seedless watermelons have gained popularity in the marketplace and also with

watermelon growers. Cultivars that would be considered modern cultivars became commercially

available in the early 1990s and several are still considered industry standards today (Maynard

and Elmstrom, 1992).

Seedless Watermelon Market Share

Before 2002, watermelon market data was not separated into seedless and seeded

categories so it is difficult to locate accurate statistics on the production of either. To date, there









is still no separation of the production area grown in the U. S. but there are now reliable data on

seedless and seeded watermelons sold in the U.S. Seedless watermelons accounted for 78% of

the watermelons sold in the U. S. in 2006 which is up from 50% of the U. S. market in 2002

(USDA, 2006). The portion of Florida' s watermelon production that is triploid has increased

from 42% in 2002 to 79% in 2006 (USDA, 2006). There is some incentive for growers to

produce seedless watermelons because they typically receive 4.5 to 11.0 cents per kg premium

and it has become increasingly harder to market seeded watermelons since their market share has

decreased (USDA, 2006).

Triploid Seedless Watermelon Production

The cultural practices used in triploid seedless watermelon production are similar to

diploid production with respect to plant spacing, fertilization, and irrigation. Average maturity is

also similar between the two. Growth habit of triploids is similar to diploids but there are also

genotypes that exhibit compact growth and plant spacing may need to be altered to produce fruits

of desirable size. Triploid seed are more difficult to germinate than diploids and require precise

environmental conditions. While diploid cultivars may germinate in as low as 12.7 OC, triploid

seed will not germinate below 26.6 OC and optimum temperature is between 29.4 OC and 32.2 OF

(Hochmuth et al., 2001a). Seed coat adherence is also a problem with triploids and may

negatively affect seedling growth. To avoid this, seeds must be planted with the radicle end up

at 450 to 900 (Maynard and Elmstrom, 1992; Maynard, 1989). With these requirements and the

high cost of triploid seed, the use of transplants in spring triploid production is necessary as soil

temperatures are too cold for direct seeding.

Pollination is also a necessity in triploid plants and the introduction of domesticated

pollinators, such as honeybees or bumblebees, may be more important in triploid production

(Walters, 2005). Stanghellini (1997) and Alderz (1966) both reported that pistillate diploid









flowers required a minimum of six to eight honeybee visits for optimal fruit set and visitation

rates lower than this significantly increased fruit abortion. Walters (2005) conducted

experiments on triploid watermelons in which honeybee visitations were controlled in order to

determine the number of visits necessary for optimal fruit set. Research plots contained a 33%

pollenizer ratio in order to mimic commercial production. Findings suggested that between 16

and 24 honeybee visits were required to achieve maximum seedless watermelon fruit set. These

visitation numbers are two to four times higher than what is needed in diploid plants and it was

suggested that this is due to a dilution of viable diploid pollen with non-viable triploid pollen.

The most crucial difference between diploid and triploid production systems is the addition

of the diploid pollenizer in the triploid field. Kihara (195 1) suggested that one diploid plant

should provide enough pollen to achieve adequate fruit set in four to five triploid plants. By

these recommendations, 16 to 20% of the plants per hectare should be diploid. Until 2001, there

were no scientific data on which pollenizer ratio would maximize seedless watermelon yield.

Maynard and Elmstrom (1992) indicated that a pollenizer ratio of 33% had produced acceptable

seedless yields and other sources recommended ratios of 20 to 33% (Robinson and Decker-

Walters, 1997; Rubatzky and Yamaguchi, 1997). The method for introducing diploid

watermelons into the field at this time was to plant solid rows of diploid plants between rows of

triploid plants. The diploid cultivar must be different than the triploid in size, shape, or rind

pattern in order to facilitate efficient harvest. NeSmith and Duval (2001) used distance of a

triploid row from a pollenizer row to make inferences on pollenizer frequencies. 'Genesis'

triploid was used and 'Ferrari' was used as the pollenizer. Their results showed the greatest

seedless yields in rows 3.0 m from the pollenizer row with yields in rows farther away declining.

Yield estimates produced by NeSmith and Duval (2001) suggested that the greatest seedless









watermelon yield per hectare would be achieved with a 1:4 pollenizer to seedless ratio when 1.5

m between-row spacing is used. In this scenario, pistillate triploid flowers would never be more

than 3.8 m away from a staminate diploid flower.

Fiacchino and Walters (2003) conducted the same type of experiment but used isolated

fields with different pollenizer ratios. The plot design used by Fiacchino and Walters more

closely resembled a commercial watermelon field. Plots consisted of raised, plastic mulched

beds with 1.5 m between-row spacing. This experiment also used dedicated rows of pollenizers

at ratios of 11, 20, and 33%. In this study, multiple pollenizer cultivars were used to determine if

cultivar, as well as frequency, had an effect on seedless watermelon yield. 'Millionaire' triploid

was used and 'Crimson Sweet' and 'Fiesta' were used as pollenizers. Fiacchino and Walters

(2003) found plots containing a 33% pollenizer ratio did not have greater yield than those with

20%, but both 20 and 33% plots had greater seedless yields than the plots with an 11% pollenizer

ratio. Though there was no difference in yield between the 20 and 33% plots, a field with 20%

pollenizer ratio would have greater seedless watermelon yield on a per hectare basis due to a

higher number of triploid plants. These researchers also reported a significant difference in

seedless yield between the two pollenizer cultivars used, with plots pollenized by 'Crimson

Sweet' having greater yield. When 'Fiesta' was used as a pollenizer cultivar there was

significantly greater hollow heart disorder present in the seedless watermelons.

Previous to Fiacchino and Walters (2003), pollenizer choice was based on marketing

concerns and not how it affected the triploid crop. In this study, watermelon yields per hectare

were greatest in plots where pistillate triploid flowers never exceeded 3.8 m away from a

staminate diploid flower, which is in agreement with Nesmith and Duval (2001).









The consensus between Nesmith and Duval (2001) and Fiacchino and Walters (2003)

reinforced the non-scientific recommendations of Maynard and Elmstrom (1992) who suggested

that a 1:2 pollenizer to triploid ratio. The maximum distance between pistillate triploid and

staminate diploid flowers was never greater than 3.9 or 4.5 m because 2.75 and 3.0 m between-

row spacing's were used (Maynard and Elmstrom, 1989, 1992). This research was conducted

when seedless watermelons held less than 50% of the U. S. market so the production scheme of

using dedicated pollenizer rows allowed producers to be diversified in the marketplace. During

the early years of commercial seedless production, it may have been more economically

beneficial for growers to grow at a 1:1 pollenizer to triploid ratio as seedless melons held such a

small market share. With the growth in popularity of seedless watermelons and their increased

market share, it has become less desirable to grow seeded watermelons. Under previous triploid

production schemes, as much as a third of a grower' s hectarage needed to be in diploid

watermelons.

A new cultural management system has recently been developed that allows for an

increase in the number of triploid plants per hectare. New diploid cultivars have been developed

specifically for the role of pollenizer and these cultivars, commonly called special pollenizers,

are designed to be planted within the row of triploid plants without changing in-row spacing.

Special pollenizer cultivars became available in the early 2000s and were used on large hectarage

beginning in 2004. As there is no dedicated space for the pollenizer, triploid plants can be

planted at 100% stand. Common practices are to punch plant holes and transplant the field solid

with triploid seedlings then go back through the field and transplant pollenizers between triploid

seedlings at the appropriate density. Diploid cultivars produce flowers sooner than triploid

cultivars so transplanting the pollenizer several days later may more closely synchronize









blooming in the two types of plants (Freeman and Olson, 2007). This system of pollenizer

arrangement increases triploid plant numbers by 20 to 33% per hectare, thus increasing the

number of seedless fruits harvested per hectare. Most of these pollenizer cultivars are not

intended to be harvested which, allows for harvest of only seedless fruit. This can avoid the

confusion of having multiple types of harvestable watermelons in the field and the added labor

costs of multiple harvests. Though most special pollenizers were not intended to be harvested,

the following cultivars produce marketable fruit: 'Jenny', 'Minipol', 'Pinnacle', 'Polimore'.

Any small fruited diploid cultivar could be used as a pollenizer if it produces adequate staminate

flowers and pollen. Some producers may have a market for the seeded pollenizer fruits and may

be able to benefit economically by using one of these cultivars.

There are two different types of special pollenizer cultivars available; highly branched

plants with reduced foliage and thin vines or short inter-node bush-type plants. The thin-vine

types have foliage and vines that are smaller than standard watermelon plants by varying

degrees. These types also exhibit some degree of increased branching which increases the

number of terminals and therefore the number of male flowers produced. The reduction in vine

and foliage size is intended to reduce the negative effects that may occur when decreasing the

area per plant by introducing the pollenizer in-row. Thin-vine special pollenizers currently

available are: 'Increase' (Southwestern Seeds), 'Jenny' (Nunhems USA, Inc., Acampo, CA),

'Minipol' (Hazera Seeds, Inc., Coconut Creek, FL), 'Patron' (Zeraim Gedera Seed Co, Ltd.,

Palm Desert, CA), 'Pinnacle' (Southwestern Vegetable Seed, LLC., Casa Grande, AZ),

'Polimore' (Hazera Seeds, Inc., Coconut Creek, FL), 'Sidekick' (Harris Moran Seed Co.,

Modesto, CA), 'SP-1' (Syngenta Seeds, Inc., Boise, ID), 'SP-4' (Syngenta Seeds, Inc., Boise,

ID). The bush-type pollenizers have a compact growth habit with short internodes and a









branching pattern more similar to standard watermelons. These cultivars also have a nearly

entire leaf with highly reduced lobes. Bush-type pollenizers currently available are 'Companion'

(Seminis, Inc., Oxnard, CA) and 'Stud' (Abbott and Cobb, Inc., Feasterville, PA).

Most fruits produced by special pollenizers are small and usually weigh less than 2.5 kg

(Freeman and Olson, 2007). Special pollenizer cultivars produce fruits with one of two types of

rind patterns, solid grey to light green or light green with a dark green stripe, and vary in shape

from round to oblong and blocky. As with the dedicated-row pollenizer arrangement, a

pollenizer cultivar that has fruits easily distinguishable from the seedless fruits should be chosen.

Most special pollenizer fruits are substantially smaller than medium and large seedless fruits

which aides in their distinction. However, when personal size seedless watermelons (< 3.2 kg)

are produced, a cultivar with a distinct rind should be chosen as separation based on size may not

be possible. The thin-vine pollenizers are recommended to be planted at a 1:3 pollenizer to

triploid ratio while the bush-type cultivars are recommended at a 1:2 pollenizer to triploid ratio.

Pollinator Activity and Preference

Cultivated watermelon crops require pollination and domesticated honeybees (Apis

mellifera L.) are the most important pollinator (Free, 1993). Walters (2005) illustrated that

increased honeybee visitation to pistillate triploid flowers is required for fruit set due to the

dilution of viable diploid pollen with non-viable triploid pollen. Both triploid and diploid

watermelon plants produce visually similar staminate flowers and triploid flowers produce pollen

although it is not viable.

Honeybee foraging habits are controlled by both visual and olfactory cues but it is unlikely

that they can visually distinguish between triploid and diploid flowers (Butler, 1951; von Frishch

1967). These cues are processed during pre-alighting inspection and determine whether the

flower will be foraged. It has been shown that floral structures such as petals, sepals,










gynoecium, and pollen have distinct volatile emissions that are species and genotype specific

(Dobson et al., 1996; Dobson, 1991; Dobson et al., 1987). The volatiles from pollen (which are

derived from pollenkitt) are the most important factors when honeybees decide to forage a flower

or not (Pernal and Currie, 2002). Although a hierarchy of pollen preference was shown by Olsen

et al. (1979), no differences were observed between the species used by Pernal and Currie

(2002). The olfactory cues from pollen also appear to be quantitative and decreasing emissions

throughout the day indicate less reward to foragers (Dobson et al., 1996).

It has been suggested that pollen odor may be distinct between male-fertile and male-

sterile flowers of the same species (Dobson et al., 1996). Preference for male-fertile over male-

sterile potato flowers has been shown in bumblebee which may have been due to pollen odor

(Arndt et al., 1990; Batra, 1993). Wolf et al. (1999) conducted pollinator preference experiments

in which honeybees were placed in a Hield with two watermelon cultivars, one Citrulhts

colocynthis accession and one C. colocynthis x C. lan2atus hybrid 'BAG', with the number of

visitations being recorded. Significantly greater bee visitation was seen in the watermelon

cultivar BAG and the C. colocynthis accession, neither of which had nectar volume, pollen

quantity, or flower size that was different from the other genotypes tested. Wolf et al. (1999)

found a positive correlation between honeybee visitation and sugar concentration of nectar which

is what greater visitation was attributed to. This conclusion is in contrast to Pernal and Currie

(2002) who illustrated that pollen odor was more important than forage quality for honeybees.

Pollen Effects

Triploid seedless watermelon fruit growth and development is dependent on pollination of

the pistillate triploid flowers with viable diploid pollen (Kihara, 1951; Maynard and Elmstrom,

1992). It has been shown in other genera that genotype can have a significant effect on pollen

viability and that variations in viability can affect the reproductive success of the individual









receiving the pollen. Parties et al. (2005) reported significant differences in pollen viability

within and between species of barley however, these differences were only evident after the

pollen was subj ected to incubation treatments. These results indicate more of a difference in

pollen longevity as opposed to viability.

Fortescue and Turner (2004) investigated the pollen viability within and among multiple

banana species and among ploidy levels within a single species. This study reported significant

differences in pollen viability between species, within species, between ploidy levels within a

single species, and within ploidy levels of a single species. The differences in pollen viability

were as great as 100% between cultivars of the same ploidy level and same species (Fortescue

and Turner, 2004). Pollen source has been investigated in mandarin orange and significant

effects were reported on fruit quality parameters. Vithanage (1991) investigated the pollen donor

effects on 'Ellendale' mandarin using six different pollenizers. Vithanage reported that fruit

weights of 'Ellendale' were significantly greater when 'Murcott' and 'Emperor' were used as

pollenizers. Wallace and Lee (1999) conducted experiments in which 'Ellenor' mandarin was

pollinated by 'Murcott', 'Imperial', and 'Ellenor'. This study found that fruits from 'Ellenor'

had significantly greater size and sugar content when 'Murcott' was used as a pollenizer. Lavi et

al. (1996) reported significant differences in pollen viability among cultivars of macadamia but

found no correlation between pollen viability and fruitlet retention.

Nikkanen et al. (2000) illustrated that pollen viability within Picea abies was significantly

effected by individual pollen donor and germination conditions, and that there was an interaction

between these two factors. These results show that individuals of the same species, within a

geographic area, may require specific environmental conditions for reproductive success. Brevis

et al. (2006) reported significant differences in pollen viability among rabbiteve blueberry









cultivars, although all cultivars had a high average viability. This study suggested that while

pollen viability was statistically significant, it may not be biologically significant and is not

thought to contribute to reproductive failure in blueberry. Pollen viability data presented by

Brevis et al. (2006) was similar to previous findings in rabbiteve and southern highbush

blueberry (Cockerham and Galleta, 1976; Lang and Parrie, 1992).

There is only one published study on pollen viability in the family Cucurbitaceae. Nepi

and Pacini (1993) investigated various aspects of pollination in a single cultivar of Cucurbita

pepo. They reported that average pollen viability at anthesis was 92% which decreased to 75%

within 6 h and further decreased to 20% at 11 h after anthesis. This decrease in viability was

attributed to dehydration of the pollen grain. There is no published data on pollen viability of

watermelon cultivars.

Variation in pollen production has been reported between genera and among species of the

same genera in the Poaceae, and among species of the same genera in the Cupressaceae (Hidalgo

et al., 1999; Prieto-Baena et al., 2003). In diploid watermelon, Stanghellini and Schultheis

(2005) investigated 27 cultivars and found significant differences in production of pollen grains

per flower and pollen grains per plant. Pollen production ranged from 134,206 grains per plant

per day for 'Jamboree' to 264,589 grains per plant per day for 'Summer Flavor 800'.

The time period over which diploid cultivars produce pollen may be as important as the

amount of pollen produced. Diploid watermelon cultivars begin to produce staminate flowers

about seven days before triploid plants begin to flower and it is essential that the diploids

continue producing staminate flowers throughout triploid fruit set (Freeman and Olson, 2007).

Significant differences in total staminate flower production, as well as flowering longevity, have

been reported in diploid watermelon cultivars (Freeman and Olson, 2007; Stanghellini and









Schultheis, 2005). Greater staminate flower and pollen production by a diploid cultivar may

improve its performance as a pollenizer by reducing the dilution effect of viable pollen that is

created by triploid plants.

Competition

Competition has been defined as the negative interaction between two organisms (Connell,

1990). In plants, this competition is for light, water, nutrients, and space, and can be inter-

specifie (between two species) or intra-specific (between individuals of the same species). Inter-

specific competition from weed species as well as intra-specific competition from neighboring

crop plants can reduce the survivability of plants and the yield and quality of plant products

(Firbank and Watkinson, 1990). Intra-specific competition in cropping systems is regulated by

planting density which is intended to maximize production per unit area. Maximum production

per unit area occurs when plant population and yield per plant are in correct proportions.

Experimental models have shown that plant yields increase with plant density to a maximum

point and then plateau or decline as density continues to increase (Holliday, 1960). Intra-specific

competition and plant density can also be used as tools to manipulate yield parameters such as

size distribution of fruit (Motsenbocker and Arancibia, 2002; Reiners and Riggs, 1999; Sanders

et al., 1999).

Intra-specific competition of crop plants is investigated through studies that examine the

effect of planting density or spatial arrangement on crop yield. In vining cucurbits such as

muskmelon (Cucumis melo L.), pumpkin (Cucurbitapepo L.), and watermelon, it has been

shown that increasing plant density increases total yield but decreases yield per plant (Ban et al.,

2006; Duthie et al., 1999a; Duthie et al., 199b; Goreta et al., 2005; Kultur et al., 2001; Maynard

and Scott, 1998; Reiners and Riggs, 1999, 1997; Sanders et al., 1999). The increases in yields

per unit area reported in these studies were due to increased fruit numbers per unit area.









Although the use of in-row diploid pollenizers has increased, it has not been determined if the

increased competition on neighboring triploid plants will be deleterious. When planted at a 1:3

pollenizer to triploid ratio, the pollenizer will directly impact 2/3 of the plants per hectare by

decreasing in-row spacing by 1/4. This would reduce area per plant from 2.2 m2 to 1.6 m2 foT

plants grown on 2.4 m between-row spacing and 0.9 m in-row spacing. Though reduced, this

area is still greater than the 1.0 m2 per plant which has been shown to produce greatest

watermelon yields per hectare (Goreta et al., 2005; Sanders et al., 1999). Results from other

studies in watermelon do not provide insight as the phenotype of the pollenizer and triploid are

different. As pollenizer growth will not impact all triploid plants per hectare, the appropriate

study to investigate pollenizer competition effect is the neighborhood (area of influence) study in

which the performance of a single individual is measured as a function of distance from the

competitor (Radosevich and Roush, 1990).









CHAPTER 3
CHARACTERISTICS OF DIPLOID POLLENIZERS FOR USE IN TRIPLOID
WATERMELON PRODUCTION

Introduction

With triploid seedless watermelons now occupying 78% of the United States market, it is

suspected that the use of in-row pollenizer cultivars will increase (USDA, 2006). There are no

published studies that compare important characteristics of diploid watermelon pollenizers such

as staminate flower production, flowering period, and fruit production. Pollenizer flower

production may be a strong indicator of how a cultivar will perform and flowering period is

critical to the type of production system the pollenizer is used in. Using a pollenizer cultivar

with low fruit production and easily distinguishable fruit could also increase efficiency in

harvesting operations. The objectives of this study were to determine staminate flower

production, flowering period, and quantity and size of fruit production of several commercially

available diploid pollenizers.

Materials and Methods

Experiments were conducted at the North Florida Research and Education Center, Quincy,

FL, and the North Florida Research and Education Center-Suwannee Valley, Live Oak, FL. In

Quincy, the soil type was a Norfolk Loamy Fine Sand (fine-loamy, kaolinitic, thermic, Typic

Kandiudults) and in Live Oak the soil was a Lakeland fine sand (thermic, coated Typic

Quartzipsamments). At both locations, the experiment was arranged as a randomized complete

block design with four replications. Transplants were produced in a greenhouse at Quincy in

expanded polystyrene flats of the inverted pyramid design which were 3.75 x 3.75 x 6.25 cm

using soil-less media. Prior to the laying of the mulch, pre-plant fertilizer was applied at

recommended rates and incorporated into the soil (Olson et al., 2004). All fertilizer was applied

pre-plant in Quincy and one-fourth was applied pre-plant in Live Oak. Weekly fertigation was










used to apply the remainder of the fertilizer in Live Oak. Watermelon plants were irrigated as

needed.

On 1 Apr. 2005, 5-week-old seedlings of 'SP-1', 'Companion', 'Jenny', and 'Mickylee'

were transplanted into raised beds fumigated with methyl bromide and chloropicrin (67/33) and

covered with black polyethylene mulch. In Live Oak, plots consisted of two rows; beds were 0.6

m wide by 10 m long on 2. 1 m centers, with in-row spacing of one meter. Pollenizer cultivars

were planted with the triploid cultivar 'Tri-X 313'. A pollenizer plant was planted at the

beginning and end of each plot, and between every third and fourth 'Tri-X 313' plant in the plot.

Plots at Live Oak consisted of 18 triploid plants and eight pollenizers. In Quincy, plots consisted

of two rows; beds were 0.9 m wide by 13.2 m long on 2.4 m centers, with an in-row spacing of

one meter. 'Tri-X 3 13' was also used in Quincy and placement and spacing of pollenizer

cultivars were the same as for Live Oak. Plots at Quincy consisted of 24 triploid plants and 10

pollenizers.

Plants were sampled after the onset of male flowering by pollenizer cultivars, and data

were collected twice a week at both locations. Once 70% of pollenizer plants in each plot had at

least one open male flower (flowering threshold), the plot was considered to have begun

flowering. Numbers of male flowers per plant were recorded from the beginning of flowering

(29 Apr.) until the end of the fruit set period (3 June). Early season flower counts were obtained

by counting open male flowers on all pollenizer plants in each plot. However, after plants began

to vine heavily (making flower counting difficult), flower counts were obtained from a single

row in each plot. Fruit from pollenizers were harvested at or near maturity and weighed on two

dates per location. 'Tri-X 313' was not harvested for yield and only served to provide intra-

specific competition for the pollenizers. Without this competition, growth habit of the










pollenizers would be different and not reflect flower counts that would be seen under commercial

production conditions.

Statistical analysis was performed using the GLM procedures of SAS (SAS Institute, Inc.,

Cary, NC). For statistical analysis, location was added and the experiment was analyzed as a

factorial experiment with two factors, location and cultivar. If an interaction was present,

LSMEANS analysis and LSD were was used to explain results, otherwise means separation was

performed using Duncan's multiple range test.

Results

The first pollenizer cultivar to reach the threshold for flowering in all plots was SP-1', on

2 May, 2005 in Quincy. All cultivars had reached the flowering threshold by 10 May and 12

May for Quincy and Live Oak, respectively. Peak fruit set by 'Tri-X 313' began 14 May and

ended 3 June at both locations. By 1 June, 'Tri-X 313' had set all commercially harvestable

fruit, and by 10 June, mature 'Tri-X 313' melons were present at both locations. Location did

not significantly affect male flower counts, and there was no significant interaction between

location and cultivar (P > 0.05). Data were combined over locations and analyzed.

On 29 Apr., SP-1' produced 0.65 flowers per plant (fpp), which was not significantly

different from 'Companion' or 'Mickylee' which had 0.65 and 0.21 fpp, respectively (Fig. 3-1).

'Jenny' had 0. 12 fpp which was significantly lower than that of 'Companion' or 'SP-1', but not

'Mickylee'. On 3 May, 'SP-1' had 0.73 fpp which was greater than 'Companion' at 0.52 fpp or

'Jenny' at 0.38 fpp. 'Mickylee' had 0.25 fpp which was significantly lower than that of

'Companion' or 'SP-1', but not 'Jenny'. On 9 May, 'Jenny' had 1.95 fpp which was greater than

'Companion' at 1.00 fpp. However, fpp for 'Jenny' was not different than 'SP-1' or 'Mickylee',

which were 1.65 and 1.50 fpp, respectively. On 13 May, 'SP-1' had 6.36 fpp which was not

different than 'Jenny' at 5.76 fpp or 'Mickylee' at5.52 fpp, however, 'SP-1' was significantly










higher than 'Companion', 4.75 fpp. On 16 May ('Tri-X 313' had begun producing female

flowers), 'SP-1' had greater flower counts compared to the other pollenizer cultivars; 'SP-1' had

9.72 fpp compared to 7.88, 7.56, and 7.5 fpp for 'Mickylee', 'Companion' or 'Jenny',

respectively. This trend continued throughout the remainder of the season as most mid (16 May)

to late (1 June) season male flower counts showed that 'Companion', 'Jenny', and 'Mickylee'

had similar numbers of flowers but were less than 'SP-1'. Flower numbers increased and peaked

on 26 May when 'SP-1' had 35.5 fpp which was greater than 'Companion', 'Mickylee', and

'Jenny' which had 14.50, 13.80 and 12.80 fpp, respectively.

Analysis of pollenizer fruit counts per plot indicated a significant location effect and an

interaction between location and cultivar (Table 3-1). Distribution of fruit per plant by cultivars

was slightly different at the two locations (Table 3-2). At Quincy, fruit set was greater for

'SP-1', with 5.8 melons per plant (mpp) compared to all other cultivars. 'Companion' set the

least number of fruit, with 1.8 mpp, which was less than 'Jenny' at 4.3 mpp or 'Mickylee' at3.7

mpp. At Live Oak, 'Jenny' produced 3.4 mpp and 'SP-1' produced 3.3 mpp, which were greater

than 'Mickylee' at 1.7 mpp or 'Companion' at 1.2 mpp. The interaction between cultivar and

location is due to the different rankings of fruit production by cultivar at each location. In

Quincy, fruit production by 'Jenny' and 'Mickylee' were not significantly different, however

both produced less fruit than 'SP-1'. At Live Oak, fruit production by 'SP-1' and 'Jenny' were

not significantly different but both produced more fruit than 'Mickylee'. At Quincy, 'Mickylee'

produced more fruit than 'Companion' but at Live Oak fruit production was similar between the

two.

Data analysis indicated that location had a significant effect on pollenizer fruit weight, and

that fruit weights in Live Oak (avg. = 2.80 kg) were lower than those at Quincy (avg. = 3.06 kg)










(P < 0.05). There was no interaction between location and cultivar. 'Mickylee' had the highest

fruit weight, 4.34 kg/fruit, which was higher than for 'Companion' or 'Jenny' which were 2.61

and 2.56 kg/fruit, respectively (Table 3-3). 'SP-1' had the lowest fruit weight at 2.21 kg/fruit,

which was less (P < 0.05) than of all other pollenizer cultivars.

Discussion

'SP-1' and 'Companion' produces non-edible fruits while 'Jenny' and 'Mickylee' produce

edible melons. When used as pollenizers, fruit production is not desirable because melons from

pollenizers can confuse the harvesting process (with mixing of seeded and seedless fruit) as well

as hinder harvesters from moving efficiently through the field. 'Companion' and 'Mickylee'

produce easily distinguishable melons based on the grey to pale green color and no rind pattern.

'SP-1' produces a light green melon with very thin light green broken stripes while 'Jenny'

produces melons that have a medium green background with dark green stripes. All four

pollenizer cultivars would be easily distinguishable by size from most commercial melons, other

than personal-size seedless watermelons which generally weigh between 1.8 and 2.2 kg.

All four pollenizers had male flowers present during peak seedless watermelon fruit

setting. Results were similar to Dittmar et al. (2005) with 'SP-1' producing significantly more

male flowers than 'Companion', 'Jenny', or 'Mickylee'. Although flower production by 'SP-1'

was highest other cultivars may also provide more than enough pollen to accomplish optimal

seedless watermelon fruit set. Stanghellini and Schultheis (2005) reported that pollen production

is also variable between diploid watermelon cultivars so flower production may not be

completely indicative of a cultivars male reproductive output. All cultivars appear to be viable

options for use as pollenizers in triploid watermelon production as all were producing male

flowers during fruit set of seedless watermelons.









Table 3-1. Analysis of variance for pollenizer fruit weight and fruit per plant at Quincy and Live
Oak FL during 2005.
Source df MS P-value

Fruit weight

Replication 3 0.10217 0.848
Location 1 2.67961 0.015
Cultivar 3 35.3234 <0.0001
Location*Cultivar 3 0.17825 0.708
Error 21 0.38212

Fruit per plant

Replication 3 0.33208 0.207
Location 1 17.7012 <0.0001
Cultivar 3 14.2712 <0.0001
Location*Cultivar 3 1.75791 0.0006
Error 21 0.20113


Table 3-2. Interaction effect of location and watermelon pollenizer cultivars on fruit per plant at
Quincy and Live Oak FL during 2005.
Location x cultivar Fruit (no./plant)
Quincy SP-1 5.8
Jenny 4.3 **
Mickylee 3.7 Ns
Companion 1.8 **
Live Oak Jenny 3.4
SP-1 3.3 Ns
Mickylee 1.7 **
Companion 1.2 Ns
Ns, *,** non-si nificant, or si nificant at P<0.05 or P<0.01, Least S uares Means anal sis.












Table 3-3. Main effects for pollenizer fruit weights combined over experiments conducted in
Quincy and Live Oak, FL, during 2005.
Cultivar Avg fruit wt (kg)
Mickylee 4.34 az
Companion 2.61 b
Jenny 2.56 b
SP-1 2.21 c
z Means followed by the same letter are not significantly different at (P < 0.05) by
Duncan's multiple range test.
















35



30



S25


S20


-* SP-1
-M-Co mpa union
- -Jenny
-M- Mickylee


a7


b b b
b
b


29-Apr 3-May 9-May 13-May 16-May 19-May 23-May 26-May 30-May 3-Jun
Sampling Date


Figure 3-1. Pollenizer staminate flower counts combined over Quincy and Live Oak<, FL, during 2005. Means followed by the same
letter are not significantly different at (P <0.05) by Duncan' s multiple range test.









CHAPTER 4
POLLEN VIABILITY OF DIPLOID WATERMELON POLLENIZER CULTIVARS

Introduction

Pollen produced by diploid watermelon pollenizers is important because it is necessary for

fruit set and flesh fill in associated triploid watermelon crops (Kihara, 1951; Maynard and

Elmstrom, 1992). Viable pollen produced by pollenizers is diluted with non-viable triploid

pollen which increases pollinator visitation rates required by pistillate triploid flowers.

Pollenizers with poor pollen viability could further increase required visitation from pollinators

and reduce stigmatal area available to viable pollen; both of which could have negative effects

on seedless watermelon yield and quality. Significant differences in pollen viability have been

reported between cultivars of the same species in several genera. The objective of this project

was to determine pollen viability of four pollenizer cultivars to investigate possible effects on

performance .

Materials and Methods

On 3 Apr. and 1 Aug. 2006, 4-week old watermelon seedlings were transplanted into

raised beds. The beds were covered with black polyethylene mulch in the spring and white

polyethylene mulch in the fall. Experiments were performed at the North Florida Research and

Education Center (NFREC) in Quincy, FL. Soil type present at NFREC is Norfolk loamy sand

(fine-loamy, kaolinitic, thermic Typic Kandiudults). Experimental design both seasons was a

randomized complete block with four replications. Four diploid pollenizer cultivars,

'Companion', 'Jenny', 'Mickylee', and 'SP-1', were used to determine pollen viability.

Experimental plots were 4.57 m long with an in-row spacing of 0.91 m and between-row spacing

of 2.43 m. Three seedlings were planted in each plot. Fertilization, irrigation, and pesticide









application practices recommended by the University of Florida Institute of Food and

Agricultural Sciences were followed (Olson et al., 2006).

Sampling was initiated on 17 May and samples were taken on 24 May and 31 May in the

spring. Sampling was initiated on 31 Aug. and samples were taken on 7 Sept. and 14 Sept. in the

fall. Sampling was initiated when other triploid watermelons at NFREC that were transplanted

on the same dates began to set fruit. The sampling period was scheduled to mimic peak fruit set

in triploid watermelons. The fruit set in this time frame would be the maj ority of the fruit that

would be available for commercial harvesting schemes that are typical for FL.

On sampling dates, watermelon flowers were removed from the plant before anthesis. This

was to insure that pollinators would not remove pollen and an adequate supply would be

available for analysis. Three flowers were removed from each plot and placed into plastic cups

and covered to exclude pollinators. Flowers were taken to the lab and allowed to open. After

anther dehiscence had occurred (verified with a hand lens) sample analysis was initiated. Pollen

was removed from the anthers and placed on a slide. Viability was determined using the

diaminobenzidine (DAB) protocol for peroxidase activity in pollen (Dafni et al., 2005).

Rodriguez-Riano and Dafni (2000) compared the results of four vital dyes versus pollen

germination results and illustrated the superiority of peroxidase tests over other commonly used

vital dyes. This test utilizes a dye that creates a color differential between viable and non-viable

pollen.

Four 100 pollen grain sub-samples were analyzed from each plot using a compound

microscope. A pollen grain was considered viable if it had turned dark brown or black. All

pollen samples were analyzed on the same day pollen was collected. It is important with

watermelon pollen that the pollen be thoroughly mixed with the dye on the slide in order to have










adequate contact between the pollen grains and dye. If large clumps of pollen are not broken up,

dye may not infiltrate the pollen and false negatives may be observed. On each sample date heat

killed pollen (two h at 800C) was used to check the efficacy of the dye. New dye was prepared

for each sample date. A square-root transformation was performed on the data and analysis of

variance and means separation (Duncan's multiple range test) were performed using the GLM

procedures of SAS (SAS Institute Inc., Cary, NC)

Results

There were no sampling dates in either season where pollenizer cultivar had a significant

(P < 0.05) effect on pollen viability (Table 4-1). There was also no significant interaction

between pollenizer cultivar and sampling date (Table 4-1). In the spring trial, sampling date had

a significant (P < 0.05) effect on pollen viability with 31 May having greater average viability

than 24, or 17 May (Table 4-2). Pollen viability on 31 May was 98.6% which was significantly

greater than 97.4 or 97% for 17 May and 24 May, respectively. The average pollen viability

over all cultivars and all dates for spring and fall were 97.7 and 97.9%, respectively. There was

very little variation within the data and the coefficient of variation was never higher than 0.84%.

Discussion

The results of this study illustrate that there is no significant variation in pollen viability

within the cultivars tested and that pollen viability is high and changes very little if any

throughout the growing season, at least not within the critical period of triploid fruit set. The

sample date in the spring with higher viability is more likely due to environmental conditions

than cultivar characteristics. Freeman (2007) observed that seedless watermelon yield was

significantly lower when 'Companion' was used as a pollenizer versus 'Jenny' or 'SP-1'. The

results of this study suggest that pollen viability was not a contributing factor in the varying

degrees of performance of these pollenizers. Factors such as floral attractiveness to pollinators,









timing and total production of staminate flowers, and pollen production may be more important

characteristics of pollenizers.

The small amount of variation in pollen viability between the cultivars tested suggests that

there may be little within the species or at least in cultivated varieties. Nepi and Pacini (1993)

reported that the pollen viability of 'Greyzini' (Cucurbita pepo L.) averaged 92% which is

similar to the findings of this study. Pollen viability appears to play no role in the performance

of the pollenizers tested and may not be an important characteristic of pollenizer cultivars.












Table 4-1. Analysis of variance for pollen viability of watermelon pollenizer cultivars tested
during the Spring and Fall of 2006 at Quincy, FL.
Source df MS P-value

Spring

Sampling Date 2 0.02827 0.003
Replication 3 0.00410 0.410
Cultivar 3 0.00856 0.124
Date* Cultivar 6 0.00281 0.669
Error 33 0.00415

Fall

Sampling Date 2 0.00302 0.367
Replication 3 0.00290 0.408
Cultivar 3 0.00281 0.422
Date* Cultivar 6 0.00257 0.519
Error 33 0.00292












Table 4-2. Influence of diploid watermelon pollenizer cultivar on pollen viability at Quincy, FL
during the Spring and Fall of 2006.
Pollen viability
Pollenizer
Cultvar 17 May 24 May 31 May 31 Aug. 7 Sept. 14 Sept.
Mikyee 97.8 Nsz 98.0 Nsz 98.7 Nsz 97.4 Nsz 98.2 Nsz 97.8 N
Companion 97.4 97.2 99.2 97.6 98.1 98.8
Jenny 97.3 97.2 98.3 97.8 97.7 97.0
SP-1 97.2 95.5 98.1 97.9 98.7 97.6
Date Means 97.4 b Y 97.0 b 98.6 a 97.7 NS y 98.2 97.8
z P = 0.05 Means are compared within the same column. Y P = 0.05 Means from the same
season are compared within the row.









CHAPTER 5
DIPLOID WATERMELON POLLENIZER CULTIVARS EXHIBIT VARYING DEGREES OF
PERFORMANCE WITH RESPECT TO TRIPLOID WATERMELON YIELD

Introduction

With seeded watermelons only holding about 20% of the U. S. market, there is interest in

using pollenizers that do not require dedicated field space (USDA, 2006). Traditionally

pollenizers occupied 20-33% of the land area in a field. New pollenizers have been developed to

be planted in-row with triploid plants without altering spacing. There are now multiple in-row

pollenizer cultivars available that exhibit varying growth habits. Previous research has reported

differences in production and timing of staminate flowers by pollenizer cultivars. The seed costs

of in-row pollenizers are greater than open-pollinated and hybrid diploids and most in-row

pollenizers are not intended to be harvested. There is interest in using open-pollinated cultivars

in-row to reduce input costs but it is unclear if acceptable yields will result. These experiments

were conducted to determine if there was a difference in performance between in-row pollenizer

cultivars and if a standard open-pollinated cultivar could be used in-row with similar success.

Materials and Methods

These experiments were performed at one location (Blackville, SC) in 2005 and three

locations (Blackville, SC, Citra, FL, Quincy, FL) in 2006. The experimental design used was a

randomized complete block with four replications. Experimental plots consisted of three raised

bed rows that were spaced 2.43 m center-to-center and covered with black polyethylene mulch.

Watermelon plants were spaced 0.91 m in-row. Replications consisted of three rows 116 m long

with a 7.62 m buffer between replications. A diagram of the experimental layout is shown in

Figures 5-1 and 5-2. The two outside rows were planted with 'Tri-X Palomar' and the interior

row was planted with 'Tri-X 313' in 2005 and 'Supercrisp' in 2006. In 2005, pollenizer cultivars

used were 'Jenny', 'Mickylee', and 'SP-1' with 'Tri-X Palomar' as a control. In 2006, the










pollenizer cultivars used were 'Companion', 'Jenny', 'Mickylee', 'Patron', 'Pinnacle',

'Sidekick', and 'SP-1' with 'Tri-X Palomar' as a control. Pollenizer seed sources are listed in

table 5-5. In order to reduce pollen contamination from neighboring plots, an eight plant buffer

(7.3 m) of 'Tri-X Palomar' was planted in the center row between each plot (Figure 5-2). It has

been demonstrated that distance from a diploid pollenizer of 6.0 m or greater will greatly reduce

the triploid fruit set (NeSmith and Duval, 2001). 'Tri-X Palomar' was chosen as the buffer

cultivar and control plot "pollenizer" because it does not produce viable pollen and its rind

coloration is distinctly different than the harvested cultivars, Tri-X 313 and Supercrisp. Eight

triploid watermelon plants were transplanted into each plot including the control or check plot.

Three plants of a pollenizer cultivar were planted in each plot except the control plot where 'Tri-

X Palomar' was planted in place of a pollenizer. Control plots were in place in order to observe

if pollen was moving from plot to plot. 'Jenny', 'Mickylee', 'Patron', 'Pinnacle', 'Sidekick', and

'SP-1' were planted at a 1:3 pollenizer to triploid ratio while 'Companion' was planted at a 1:2

pollenizer to triploid ratio. These ratios are recommended by producers of the various

pollenizers. Three plants of the 1:3 ratio pollenizers, and four plants of the 1:2 ratio pollenizer

were included in each plot in the same row as the harvested watermelon.

Soil type at the Edisto Research and Education Center (EREC) in Blackville, SC was

Dothan loamy sand (fine-loamy, kaolinitic, thermic Plinthic Kandiudults). Soil type at the North

Florida Research and Education Center (NFREC) in Quincy, FL was Norfolk loamy sand (fine-

loamy, kaolinitic, thermic Typic Kandiudults). Soil type at the Plant Science Research and

Education Unit (PSREU) in Citra, FL was Hague sand (loamy, siliceous, semiactive,

hyperthermic Arenic Hapludalfs). Drip tapes (1.89 1-min. 1/30.48 m at 68 kPa; 30.48 cm emitter

spacing) were laid under and concurrently with the polyethylene mulch. Beds were fumigated









with methyl bromide/chloropicrin 67:33 at a rate of 448 kg-ha-l broadcast at EREC in 2005, and

PSREU and NFREC in 2006. Fertilizer recommendations for EREC were 156N-0P-130.2K

kg-ha-l in 2005 and 2006 (Franklin, 1998). Fertilizer recommendations for PSREU and NFREC

were 168N-48P-140.2K kg-ha-l and 183.6N-24P-152.3K kg-ha- respectively (Olson et al.,

2006). All fertility recommendations were based on soil test results. Four-week-old watermelon

plants were transplanted at EREC on 27 Apr., 2005 and 17 Apr., 2006. Four-week-old seedlings

were transplanted at PSREU and NFREC on 21 Mar. and 3 Apr., 2006, respectively.

Plots were sprayed with fungicides and insecticides as recommended (Olson et al., 2006,

Sanders et al., 2006). Pesticide applications were timed so that there was minimal effect on

pollinators. One honeybee (Apis mellifera L.) hive was located near the center of each

replication at Citra and Quincy, FL in 2006 while at Blackville, SC in both years a grouping of

twenty honeybee hives was maintained 300 ft. north of test plots. At all locations in 2005 and

2006, watermelons were harvested once per week for three weeks. At the last harvest, all

marketable melons were harvested. The center of each fruit was sampled for total soluble solids

using a hand-held refractometer. Hollow heart measurements were taken by measuring the

length and width of hollow cavities in watermelons that had been cut longitudinally from stem

end to blossom end. Soluble solids and hollow heart data were taken from three melons per plot

during the first harvest at all locations in 2006. Soluble solids data were taken from three

watermelons per plot during the first harvest at Blackville, SC in 2005 but no hollow heart data

were taken.

Yield and soluble solids data from 2005, and hollow-heart data from 2006 were analyzed

using the GLM procedures and means separation was accomplished using Duncan's multiple

range test in the SAS system (SAS Institute, Inc., Cary, NC). In 2006, there were multiple









locations and as location was not of primary interest in this study, location was set as a random

effect. The MIXED procedure was used to analyze cultivar effect on fruit yield (kg-ha- fruit/ha,

and kg/fruit) and soluble solids. This allows for greater inference of the results and how they

may relate to many locations as compared with setting location as a Eixed effect (Cushman et al.,

2003; Schabenberger and Pierce, 2002). Pollenizer cultivar was set as a Eixed effect and

location, replication, and location by cultivar interaction were set as random effects.

Results

Treatments with pollenizer cultivars had significantly greater yield of triploid watermelons

at all locations and in both years compared to the check (Tables 5-1 & 5-2). In addition there

were significant differences among pollenizer cultivars in 2006 (Table 5-2). There were no

significant differences in triploid watermelon yields among pollenizer cultivars in 2005 (Table 5-

1). In 2006, plants pollenized by 'Sidekick' yielded 65,242 kg-ha-l but were not significantly

different than plants pollenized by 'Patron', 'SP-1', 'Jenny', or 'Mickylee' which yielded

63,677, 61,766, 61,751, and 59,599 kg-ha- respectively (Table 5-2). Plants pollenized by

'Companion' had the lowest yields at 49,976 kg-ha- which were significantly lower than those

pollenized by 'Jenny', 'SP-1', 'Patron' or 'Sidekick' but not significantly different than plants

pollenized by 'Pinnacle' or 'Mickylee' which yielded 53,333 and 59,599 kg-ha- respectively.

Plots containing 'Pinnacle' had significantly lower yields than those containing 'Sidekick' but

were not significantly different than plots containing 'Mickylee', 'SP-1', 'Jenny', or 'Patron'

(Table 5-2). Pollenizers had a significant effect on number of triploid watermelons compared to

the check. All plots with pollenizer cultivars had significantly greater numbers of melons per

hectare than the control plots at all locations in both years (Tables 5-1 & 5-2). There were no

significant differences in fruit production between the pollenizer cultivars in 2005 and 2006. In

2006, plants pollenized by 'Patron' produced 9,616 fruit/ha which was not significantly greater









than 'Companion' which produced 7,565 fruit/ha. Pollenizer cultivars had a significant effect on

average triploid watermelon fruit weight in 2006, but not in 2005 (Tables 5-1 & 5-2). Pollenizer

cultivars did not have a significant effect on soluble solids in both years (Table 5-3). In 2006,

pollenizer cultivars did not have a significant effect on hollowheart at the Citra, FL and

Blackville, SC locations (Table 5-4). Pollenizer cultivars did have a significant effect on hollow

heart at Quincy, FL with all plots with pollenizers having significantly less hollow heart in the

triploid watermelons when compared with the control plots (Table 5-4). There were no

significant differences in hollow heart incidence between pollenizer cultivars.

Discussion

This research shows that some pollenizer cultivars tested can be expected to perform better

than other cultivars, and do so at diverse locations. Similar results were reported by Fiacchino

and Walters (2003) in which triploid watermelon yields were significantly different due to

pollenizer cultivar used.

The only cultivar that showed questionable performance was 'Companion'. Due to its

growth and flowering habit it may not produce enough staminate flowers and pollen at the end of

fruit setting in the triploid crop. 'Companion' is a short internode plant that becomes overgrown

by triploid plants near the end of the season which may lead to staminate flowers that are not

readily detectable by pollinators. Differences in staminate flower production by pollenizer

cultivars have been reported however, it does not appear that flower production is the

determining factor of a pollenizer' s performance (Dittmar et al., 2005; Freeman and Olson,

2007). In both of these studies, SP-1' produced greater numbers of staminate flowers when

compared to 'Jenny' or 'Mickylee', however, data presented here indicates no difference in

triploid watermelon yields between these pollenizer cultivars. Pollenizers must be able to

continue growing and producing flowers throughout the production cycle.









There were significant differences in severity of hollow heart at Quincy between plots

containing pollenizer cultivars and the control but not between the pollenizers. Unfortunately,

this does not help to elucidate the cause of hollow heart as it may have been caused by reduced

pollination in control plots or excessive growth of the few existing watermelons. The incidence

of hollow heart at Blackville, SC and Citra, FL was low overall and this may be why there was

no effect by the pollenizers. The experimental design was successful in reducing pollen flow out

of experimental plots as indicated by minimal fruit set in control plots. This experimental design

spaced the triploid watermelon from a pollenizer cultivar by 7.3 m. NeSmith and Duval (2001)

illustrated that when distance of a triploid from a pollenizer was six meters or greater, triploid

fruit numbers diminished substantially. Triploid pistillate flowers ('Tri-X Palomar') in plot

buffers served to filter viable diploid pollen before pollinators entered another plot.

Of the cultivars tested, it appears that the pollenizers 'Jenny', 'Mickylee', 'Patron',

'Pinnacle', Sidekick', and SP-1' would be good choices. Some of the tested pollenizers

('Mickylee', 'Jenny', 'Pinnacle') can be harvested and sold if the grower has a market for seeded

watermelons. If growers have a strong market for seeded melons then there may be no reason to

plant pollenizers in-row. The pollenizers' costs vary greatly, so this must also be taken into

consideration. Of the pollenizer cultivars that were shown to perform adequately ('Jenny',

'Mickylee', 'Patron', 'Pinnacle', 'Sidekick, 'SP-1'), selection should be based on seed/plant cost

and distinctness between pollenizer and market melon.











I I


Replication 1


Replication 2


Plot 1 Plot 1

B Plot 2 Plot 2
B B B
U Plot 3 Plot 3
U U U
F Plot 4 F 7.6 mn Drive Row F Plot 4 F
EPlot 5 F F Plot 5 F
E E E
R Plot 6 Plot 6
R R R
Plot 7 Plot 7
Plot 8 Plot 8


Figure 5-1. Field diagram for pollenizer experiments at Blackville, SC, Citra, FL, and Quincy,
FL in 2005 and 2006. Columns represent individual rows. The same design was
used for replications three and four.













'Tri-X Palomar'
'Tri-X Palomar'
'Tri-X Palomar'
'Tri-X Palomar'
Data melon
Pollenizer
Data melon
B Data melon B
U U
Data melon
F F
F ~PollenizerF
E Daameo
R Data melon R
R ~Data melon

Pollenizer
Data melon
'Tri-X Palomar'
'Tri-X Palomar'
'Tri-X Palomar'
'Tri-X Palomar'


Figure 5-2. Individual three-row plot design for pollenizer experiments at Blackville, SC, Citra,
FL, and Quincy, FL in 2005 and 2006. Plot shown is using a pollenizer
recommended to be planted at a 1:3 pollenizer to seedless ratio.












Table 5-1. Pollenizer cultivar effect on 'Tri-X 313' yield at Blackville, SC during 2005
Pollenizer Yield Fruit Avg wt
cultivar (kg-ha-l) (o/a knfit


67,565 a'
63,944 a
61,759 a
10,494 b


7.6 Ns


9,386 a'
9,666 a
8,966 a
1,400 b


Jenny
SP-1
Mickylee
Tri-X Palomar x


z Yield estimates are based on plant populations of 4483 plants per hectare. Means with the same letter are
not significantly different at (P 5 0.05) by Duncan's multiple range test. x Triploid cultivar serving as check
against pollen contamination from neighboring plots.


Table 5-2. Pollenizer cultivar effect on Supercrisp' watermelon yield and average fruit weight
at Blackville, SC, Citra, FL, and Quincy, FL during 2006.
Pollenizer cultivar Y ie zri zv w
(kg-ha- )" (no./ha)" (kg/fruit)
Sidekick 65,242 a 9,386 a 7.3 a b
Patron 63,677 ab 9,616 a 7.0 b
SP-1 61,766 ab 9, 106 a 7.0 b
Jenny 61,751 ab 9, 195 a 6.9 b
Mickylee 59,599 a bc 9, 106 a 6.7 b
Pinnacle 53,333 b c 7,845 a 7.2 ab
Companion 49,976 c 7,565 a 6.9 b
Tri-X Palomar 8,545 d 1,074 b 7.8 a
LSD x 10,494 2, 116 0.7
z Yield estimates are based on plant populations of 4483 plants per hectare. Triploid cultivar serving as
check against pollen contamination from neighboring plots. x P = 0.05












Table 5-3. Pollenizer cultivar effect on soluble solids concentration of seedless watermelons at
Blackville, SC during 2005 and Citra, FL, Quincy, FL, and Blackville, SC during
2006.


Soluble solids concentration (%)
Blackville, SC 2005 Combined locations 2006
12.2 Ns


Pollenizer cultivar
Sidekick
Patron
SP-1
Jenny
Mickylee
Pinnacle
Companion
Tri-X Palomar Y
LSD x


12.1
12.3
12.3
12.3
12.1
12.4
12.2


11.0 sz
11.6
11.2


11.6


z Means with the same letter are not significantly different at (P I 0.05) by Duncan's multiple range test.
Triploid cultivar serving as check against pollen contamination from neighboring plots. x P = 0.05












Table 5-4. Pollenizer cultivar effect on hollowheart disorder in Supercrisp' watermelon at
Quincy, FL, and Blackville, SC combined with Citra, FL during 2006. Means are to
be compared within the same column.
Hollowheart area (cm2)
Blackville, SC &
Pollenizer cultivar Quincy, FL
Citra, FL
Tri-X Palomar z187.0 aY 4.7 Ns
Patron 73.3 b 12.2
Jenny 70.2 b 5.8
Sidekick 68.2 b 9.7
Companion 58.1 b 3.3
Mickylee 54.7 b 2.6
SP-1 53.5 b 15.7
Pinnacle 37.5 b 10.7
z Triploid cultivar serving as check against pollen contamination from neighboring plots Means with the
same letter are not significantly different at (PI 0.05) by Duncan's multiple range test.


Table 5-5. Seed sources for various pollenizer cultivars used during 2005 and 2006.
Pollenizer cultivar Company
Patron Zeraim Gedera Seed Co., Ltd. (Palm Desert, CA)
Jenny Nunhems USA, Inc. (Acampo, CA)
Sidekick Harris Moran Seed Co. (Modesto, CA)
Companion Seminis Vegetable Seed, Inc. (Oxnard, CA)
MickyLee Many sources
SP-1 Syngenta Seeds, Inc.(Boise, ID)
Pinnacle Southwestern Vegetable Seed, LLC. (Casa Grande, AZ.)









CHAPTER 6
COMPETITIVE EFFECT OF IN-ROW DIPLOID WATERMELON POLLENIZERS ON
TRIPLOID WATERMELON YIELD

Introduction

Due to the high cost of in-row diploid pollenizer seed, there is interest in using standard

watermelon cultivars in-row. One cultivar that is being evaluated for in-row use is 'Mickylee'

which produces an easily distinguishable fruit, a crucial characteristic for diploid pollenizers.

Most in-row pollenizer cultivars have reduced foliage in order to compete less with triploid

plants. 'Mickylee' is an attractive option as a pollenizer because of the low seed costs but it is

unclear whether the more vigorous growth habit will negatively impact seedless watermelon

yields. The obj ective of this study was to determine if pollenizer growth habit and pollenizer to

triploid spacing would have an effect on triploid watermelon yield.

Materials and Methods

Experiments were conducted at the North Florida Research and Education Center

(NFREC) in Quincy, FL. and the Plant Science Research and Education Unit (PSREU) in Citra,

FL. in the Spring of 2006 and also at NFREC in the Fall of 2006. Soil type at NFREC was

Norfolk loamy sand (fine-loamy, kaolinitic, thermic Typic Kandiudults) and at PSREU was

Hague sand (loamy, siliceous, semiactive, hyperthermic Arenic Hapludalfs). At NFREC (spring

and fall) all fertilizer was incorporated pre-plant at a rate of 183.6N-24P-152.3K kg-ha- At

PSREU two thirds of the fertilizer was applied pre-plant and the remainder of the

recommendation was fulfilled through weekly fertigation. Total fertilizer applied at PSREU was

168N-48P-140.2K kg-ha- Fertilization was based on soil test results and University of Florida

recommendations (Olson et al., 2006). At both locations, irrigation was provided through drip

tape (1.89 1-min. 1/30.48 m at 68 kPa; 30.48 cm emitter spacing) which was laid concurrently

with black polyethylene mulch in the spring and with white on black polyethylene mulch in the









fall. Soil was fumigated at plastic laying with methyl bromide/chloropicrin 67:33 at a rate of 448

kg-ha l. Beds were spaced 2.43 m center-to-center.

Experimental design was a factorial with four replications and two factors, pollenizer

cultivar and in-row spacing. In-row spacing's between one pollenizer plant and one triploid

plant were 0.2, 0.4, 0.6, 0.8, and 1.0 m. Plots consisted of six pairs (one pollenizer, one triploid)

of plants with equal pollenizer to triploid spacings. Each pair of plants was spaced 1.0 m in-row

from the next pair. On 21 Mar., 3 Apr., and 1 Aug., 4-week old watermelon seedlings were

transplanted. 'Sugarheart' triploid was used along with 'Mickylee' (standard vining habit) and

'SP-1' (reduced foliage, thin-vines) as pollenizers. Harvests of spring trials were made on 8 and

19 June at PSREU and on 21 and 28 June, and 7 July at NFREC. Fall harvests were on 11 and

25 Oct. Insecticides and fungicides were applied as needed to maintain plant health (Olson et al.,

2006). Groupings of honey bee (Apis mellifera L.) hives were placed in close proximity to all

experiments. The GLM procedures of SAS (SAS Institute, Inc., Cary, NC) were used to analyze

the effects of pollenizer cultivar on Sugarheart' watermelon yield and interactions between

pollenizer cultivar and spacing. The GLM procedures were also used to analyze the polynomial

effects of pollenizer to triploid spacing.

Results

Pollenizer cultivar and plant spacing had significant effects on seedless watermelon yield

at Citra and Quincy (P < 0.05) in the spring but not at Quincy in the fall (P > 0.05). Cultivar and

plant spacing had significant effects on fruits per plant (fpp) at both locations in the spring,

however, the significance at Citra for cultivar and plant spacing were P = 0.0983 and P =

0.0633, respectively. Plant spacing had significant linear effects on seedless watermelon yield

and fpp at both locations in the spring (Table 6-1). No significant effects on average watermelon

weight were observed in any of the experiments. Cultivar and plant spacing had no effect on









seedless watermelon yield or yield components at Quincy in the fall. No significant interaction

effects were observed between cultivar and plant spacing. A significant interaction between

location and pollenizer cultivar was detected in the spring therefore locations will be presented

separately .

Seedless watermelon yields from plants paired with 'Mickylee' at Citra and Quincy were

24.6 and 33.5 kg/plant, respectively. Yields from plants paired with SP-1' at Citra and Quincy

were 27.7 and 43.3 kg/plant, respectively, which were significantly greater than yields from

plants paired with 'Mickylee'. At Quincy, plants paired with 'Mickylee' produced 3.74 fpp

which was significantly lower than 4.85 fpp produced by plants paired with 'SP-1'. At Citra,

plants paired with 'Mickylee' produced 3.68 fpp which was lower than 4.04 fpp produced by

plants paired with SP-1'; however this was only statistically significant at P = 0.1~0.

Seedless watermelon yields and fpp increased linearly with increased spacing at both

locations in the spring. Yields from plots with 0.2 m in-row spacing's were 22. 1 and 32.0

kg/plant at Citra and Quincy, respectively. Yields from plots with 1.0 m in-row spacing were

30.8 kg/plant at Citra and 47.8 kg/plant at Quincy.

Discussion

These results appear to indicate that the vigorous growth habit of pollenizer 'Mickylee'

negatively impacted yield of the triploid cultivar Sugarheart compared to the reduced foliage of

pollenizer SP-1'. Seedless watermelon yields (kg/plant) from plants paired with 'Mickylee'

yielded 11.4 and 22.4% less than plants paired with SP-1' at Citra and Quincy, respectively. At

current pollenizer ratios recommended by seed producers, pollenizer competition could affect

two thirds of the triploid plants per hectare. These yield reductions can be expected at all in-row

spacings as there was no interaction between cultivar and spacing. Extrapolations of yield to a

per hectare basis were not performed because it is unclear how many pollenizer plants would be









necessary at these plant populations which ranged from 10,089 plants-hal at the closest

spacing's to 2,017 plants-hal at the widest. There was also no yield data from plants that were

considered to be unaffected by pollenizer competition. During the fall experiment at Quincy,

there was a severe outbreak of gummy stem blight (Didymella bryoniae (Auersw.) Rehm) which

was not controlled by the weekly fungicide applications. This no doubt reduced seedless

watermelon yields which affected the statistical outcome.

The trends in fruit yield and fruit number observed in this study are similar to other reports

in watermelon where increased plant population, and thus increased competition, changes yield

through fruit number and not average fruit mass (Brinen et al., 1979; Duthie et al., 1999a, 1999b;

NeSmith, 1993). Competition studies investigating weed species effect on watermelon yield

have also shown increasing competition lowers watermelon yield as a function of fruit number

and not fruit size (Buker et al., 2003; Monks and Schultheis, 1998).

The results from this proj ect are not in agreement with Freeman (2007) who evaluated the

performance of in-row pollenizers and found no difference in seedless watermelon yield between

plots containing 'Mickylee' or 'SP-1'. The experimental design used was intended to compare

pollenizer cultivars as a function of pollen provided by each cultivar and not its competitive

effect. This study collected yield data by plot which does not provide insight into pollenizer to

triploid competition as some plants were located directly beside pollenizers and some were not.

It is unclear why a significant reduction in yield caused by 'Mickylee' in this study is not in

agreement with the results reported by Freeman (2007).










'Mickylee' is an attractive option as a pollenizer because of the low seed costs. However,

the results of this study indicate that seedless watermelon yields and fruits per plant will

significantly decrease when 'Mickylee' is used as a pollenizer as compared with 'SP-1'

regardless of in-row spacing.










Table 6-1. Influence of pollenizer cultivar and spacing on triploid watermelon yield during 2006.
Location
Citra, FL Spring 2006 Quincy, FL Spring 2006 Quincy, FL Fall 2006
Treatment Fruit Yield Avg. wt. Fruit Yield Avg. wt. Fruit Yield Avg. wt.
(no./plant) (kg/plant) (kg/fruit) (no./plant) (kg/plant) (kg/fruit) (no./plant) (kg/plant) (kg/fruit)
Cultivar
SP-1 4.04 27.7 6.8 4.85 43.4 8.8 3.04 19.0 6.2
Mickylee 3.68 24.5 6.7 3.74 33.5 8.8 2.85 17.4 6.0
Sinfiace*** Ns *** *** Ns Ns Ns Ns
Spacing (m)
0.2 3.33 22.1 6.5 3.57 32.0 8.9 2.98 18.2 6.0
0.4 3.68 24.9 6.7 3.46 29.7 8.4 2.85 17.5 6.0
0.6 3.92 26.3 6.7 4.52 40.4 8.8 2.86 18.4 6.4
0.8 4.02 26.6 6.7 4.85 43.9 9.0 3.18 19.3 6.0
1.0 4.35 30.8 7.1 5.28 47.8 9.0 2.86 17.6 6.1
Significance Lil L*** Ns L~i L1** Ns Ns Ns Ns
' Non-significant or significant at P I 0.10, 0.05 or 0.01, respectively.









CHAPTER 7
VARIABILITY INT WATERMELON FLOWER ATTRACTIVENESS TO INSECT
POLLINTATORS

Introduction

In a field that is producing seedless watermelons, there must be both diploid and triploid

plants (Kihara, 1951; Maynard and Elmstrom, 1992). For fruit set to occur in triploid plants,

pollen must be moved from the staminate diploid flower to the pistillate triploid flower. Triploid

and diploid plants produce staminate flowers which bear pollen, however, triploid pollen is non-

viable. It is unlikely that insect pollinators can visually distinguish between the two and foraging

of staminate triploid flowers dilutes the flow of viable pollen within a field. If staminate flowers

produced by the diploid pollenizer are more attractive than triploid staminate flowers, a greater

proportion of viable pollen could be moved by pollinators which may lead to greater

reproductive success in triploid fruits. The floral attractiveness of a pollenizer could also impact

its performance. The objective of this study was to determine the floral attractiveness of

staminate flowers of three pollenizer cultivars and one triploid cultivar.

Materials and Methods

Field experiments were conducted at the North Florida Research and Education Center

(NFREC) in Quincy, FL. during the Spring and Fall of 2006. Soil type at NFREC is Norfolk

loamy sand (fine-loamy, kaolinitic, thermic, Typic Kandiudults). The experimental design was a

randomized complete block with eight replications. Experimental plots were 4.57 m long with

in-row spacing of 0.46 m and between row spacing of 4.9 m. The experiment consisted of two

rows 73.2 m long. On 3 Apr. and 1 Aug. 2006, 4-week old watermelon seedlings were

transplanted into raised beds covered with black polyethylene mulch in the spring and white on

black polyethylene mulch in the fall. Three watermelon plants were transplanted into each plot.

Number of pollinator visitations was recorded for four watermelon cultivars, 'Companion',










'Intruder', 'Mickylee' and 'SP-1'. Three cultivars are diploid pollenizers and one ('Intruder') is

a triploid. Fertilization, irrigation, and pesticide application practices recommended by the

University of Florida Institute of Food and Agricultural Sciences were followed (Olson et al.,

2006). A grouping of two honeybee (Apis mellifera L.) hives was placed near the center of the

experiment.

Sampling was performed on five occasions in the spring and three in the fall. Sampling

started when plants began to produce staminate and pistillate flowers. On sampling dates,

sampling was initiated at anthesis. Five staminate flowers were chosen in each plot and

visitations from honeybees and bumblebees (Bombus spp. Cresson) were counted for two

minutes. Three to four sampling repetitions were performed on each sampling date and are

referred to as sampling time. Previous research has illustrated an interaction between cultivar

attractiveness and sampling time, for this reason sampling times were kept succinct and sampling

time was considered a main effect. Two individuals recorded visitations in order to keep

repetition time under 45 minutes. Analysis of variance was performed using the GLM

procedures of SAS (SAS Institute, Inc., Cary, NC) to determine significance of main and

interaction effects and Duncan's multiple range test was used for means separation.

Results

Watermelon cultivar and sampling time had a significant effect (P < 0.05) on floral

visitation by insect pollinators on six of eight sampling dates. Cultivar or sampling time did not

influence pollinator visitation on 11 May or 29 Sept. Significant interactions (P < 0.05) between

time and cultivar were detected on 23 May and 22 Sept. Visitation of a diploid cultivar was

significantly greater than the triploid cultivar on six of eight sampling dates.

On 16 May, 'SP-1' had 2.4 visits per plot (vpp) which was significantly greater than

'Mickylee', 'Companion', or 'Intruder' which had 1.1, 1.0, and 0.8 vpp, respectively (Fig. 7-1).










Pollinator visitation of 'Mickylee', 'Companion', or 'Intruder' was not significantly different.

Pollinator visitations to 'Mickylee' and 'SP-1' were 2.9 vpp which was significantly greater than

'Companion' or 'Intruder' which had 1.5 and 1.0 vpp, respectively, on 19 May. An interaction

between sampling time and cultivar occurred on 23 May. During the first sampling time, 'SP-1'

had 4.2 vpp which was not significantly greater than 'Companion' or 'Mickylee' which had 3.0

and 2.75 vpp, respectively (Fig. 7-2). However, all three cultivars had significantly greater

visitation than 'Intruder' at 0.3 vpp. During the second sampling time, 'Mickylee' had 5.5 vpp

which was not significantly different than SP-1' at 2.8 vpp but was significantly greater than

'Intruder' and 'Companion' at 1.5 and 1.3 vpp, respectively. Visitation of 'SP-1', 'Intruder', and

'Companion' were not significantly different. There were no significant differences between

cultivars during the third and fourth sampling times. On 25 May, 'Mickylee' had 2.8 vpp which

was significantly greater than 'SP-1', 'Companion', or 'Intruder' at 1.8, 1.4 and 0.4 vpp,

respectively (Fig. 7-1). SP-1' and Companion' were not significantly different but both had

greater visitation than 'Intruder'.

On 15 Sept, 'SP-1' had 7.7 vpp which was greater than 'Mickylee', 'Intruder' or

'Companion' at 6.1, 5.8, and 3.7 vpp, respectively (Fig. 7-3). 'Mickylee' and 'Intruder' were not

significantly different but both had greater visitation than 'Companion'. An interaction between

sampling time and cultivar occurred on 22 Sept. During the first sampling time, SP-1' had 2.7

vpp which was not greater than 'Mickylee' at 1.8 vpp but was greater than 'Companion' and

'Intruder' at 0.7 and 0.5 vpp, respectively (Fig. 7-4). 'Mickylee', 'Companion', and 'Intruder'

were not significantly different. During the second sampling time, 'SP-1' had 6.8 vpp which was

similar to 'Mickylee' at 5.2 vpp and both had greater visitation than 'Companion' or 'Intruder'

which had 2.3 and 2. 1 vpp, respectively. 'Companion' and 'Intruder' were not significantly










different. There was no significant difference between cultivars during the third sampling time.

On 29 Sept. main effects did not influence pollinator visitation (Fig. 7-3). No data were taken

from 'Companion' on 29 Sept. because it had ceased producing staminate flowers. Complete

floral visitation data are shown in figures 7-1 7-4.

Discussion

Either 'Mickylee', 'SP-1', or both received greater floral visitation than 'Companion' or

'Intruder'. Previous research as shown that staminate flower production by 'SP-1' is greater than

that of 'Mickylee' or 'Companion' which were similar (Freeman and Olson, 2007). The number

of flowers that were used in sampling was held constant in order to determine the relative

attractiveness of each cultivars staminate flower. This research illustrates differential

attractiveness between cultivars and ploidy levels. Visitation at the whole plant level for SP-1'

could be higher than the other cultivars due to greater numbers of staminate flowers but a

staminate flower produced by SP-1' is not necessarily more attractive than a staminate flower

produced by 'Mickylee'. Other researchers have reported differences in pollinator visitation

between watermelon cultivars and between Citrullus lan2atus and Citrullus colocynthis which

was attributed to nectar sugar concentration (Wolf et al., 1999). It has been shown that floral

volatiles emitted from pollen are the most important close-range cue during foraging by

honeybees, however; visual stimuli are important long-range cues (Pernal and Currie, 2002).

'Companion' has a nearly entire leaf with reduced lobes and produces staminate flowers with

short peduncles. These factors tend to obstruct the view of 'Companion' s staminate flowers

which may be why 'Companion' was generally visited less than 'SP-1' and 'Mickylee'.

A diploid watermelon cultivar was preferred over the triploid on sampling dates where

cultivar affected pollinator visitation. Triploid watermelon plants produce mostly non-viable,

aborted pollen which may be covered with less pollenkitt than viable pollen. Pollenkitt produces










volatiles that are important in foraging decisions of pollinators. These volatiles are an indicator

of pollen reward that is available in a flower and reduced volatile emissions may indicate

reduced reward (Dobson et al., 1996). A reduction in pollenkitt produced in triploid staminate

flowers could represent reduced reward and result in flowers that are less attractive to

pollinators. Previous research has shown that Bombus spp. preferentially foraged potato flowers

that produced viable pollen over ones producing non-viable pollen which may be due to

differences in volatile emissions (Batra, 1993).

When the performance of multiple diploid watermelon pollenizer cultivars were compared,

triploid watermelon yields from plots pollenized by 'Companion' were significantly less than

plots pollenized by 'SP-1' or 'Mickylee'. The lower preference of 'Companion' may lead to less

viable pollen transported by pollinators and thus less fruit on triploid plants. A diploid pollenizer

cultivar with staminate flowers which are more attractive than triploid staminate flowers could

increase the movement of viable pollen within a field and possibly increase seedless watermelon

yield.





3
-


L. 2.5




S2




o\~ c

S 1.5






0.5


OSP-1
OCompanion
H Mickylee
5 Intruder


b


c


0


5/11/06


5/16/06


5/19/06


5/25/06


Sampling Date



Figure 7-1. Influence of cultivar on pollinator visitation to staminate watermelon flowers at Quincy, FL., Spring 2006. Visitation
means are to be compared within sampling date. Means followed by the same letter are not significantly different at P I
0.05.



























OSP-1
ina ab O Companion
3-
a M Mickylee
ns I Intruder





Sb ns








Time 1 Time 2 Time 3 Time 4

Sample Time


Figure 7-2. Interaction of cultivar and time on pollinator visitation to staminate watermelon flowers at Quincy, FL., on 23 May, 2006.
Visitation means are to be compared within sampling time. Means followed by the same letter are not significantly
different at P < 0.05.



















E7

(1 ,




O5


4



., 3

.0 2


b


5 Mickylee
OSP-1
5 Intruder
OCompanion


f


ns


I


0


9/15/06


9/29/06


Sampling Date


Figure 7-3. Influence of cultivar on pollinator visitation to staminate watermelon flowers at Quincy, FL., Fall 2006. Visitation means
are to be compared within sampling date. Means followed by the same letter are not significantly different at P I 0.05.
























I I IIO Mickylee
LO I SP-1
4 Intruder
OCompanion

On b
tl1 b
abb

g, ab






Time 1 Time 2 Time 3

Sampling Time



Figure 7-4. Interaction of cultivar and time on pollinator visitation to staminate watermelon flowers at Quincy, FL., on 23 Sept., 2006.
Visitation means are to be compared within sampling time. Means followed by the same letter are not significantly
different at P < 0.05.









CHAPTER 8
VARIABILITY IN POLLEN PRODUCTION BY DIPLOID WATERMELON POLLENIZERS

Introduction

Pollen produced by diploid watermelon pollenizers is necessary for fruit set and flesh fill

in associated triploid watermelon crops (Kihara, 1951; Maynard and Elmstrom, 1992). Viable

pollen produced by pollenizers is diluted with non-viable triploid pollen which increases

pollinator visitation rates required by pistillate triploid flowers. It is important that there be

adequate viable diploid pollen moved throughout a field and pollenizers that produce the greatest

amounts of pollen may perform better with respect to triploid watermelon yield. Significant

differences in pollen production have been reported between cultivars of diploid watermelon as

well as in other plant species. The obj ective of this proj ect was to determine the amount of

pollen produced by four pollenizer cultivars to investigate possible effects on pollenizer

performance .

Materials and Methods

Experiments were conducted at the North Florida Research and Education Center

(NFREC) in Quincy, FL during the fall of 2006. Soil type at NFREC is Norfolk loamy sand

(fine-loamy, kaolinitic, thermic, Typic Kandiudults). The experimental design was a randomized

complete block with four replications. Experimental plots were 4.57 m long with in-row spacing

of 0.91 m and between row spacing of 2.43 m. On 1 Aug. 2006, 4-week old watermelon

seedlings were transplanted into raised beds covered with white on black polyethylene mulch.

Beds were fumigated with methyl bromide/chloropicrin 67:33 at a rate of 448 kg-hal broadcast.

Three seedlings were planted in each plot. Fertilization, irrigation, and pesticide application

practices recommended by the University of Florida Institute of Food and Agricultural Sciences

were followed (Olson et al., 2006).










Sampling was initiated on 31 Aug. with additional samples taken on 8 Sept. and 14 Sept.

On sampling dates, watermelon flowers were removed before anthesis, placed into plastic

containers and covered to exclude pollinators. Two flowers per cultivar were analyzed from

each replication. Flowers were allowed to open and anther dehiscence was verified before

flowers were processed. Flower petals were excised with a razor blade and peduncles were

removed before flowers were placed into separate vials containing 5 mL of a solution of 70:30

ethanol/ethyl acetate mixture. This solution served to preserve the pollen and also to remove

pollenkitt from the exterior of the pollen grains. The removal of pollenkitt was necessary to

obtain uniform pollen distribution in the liquid media. Sample vials were sonicated in a water-

bath sonicator to remove all pollen from anthers. After the anthers and any other remaining

floral structures were removed, vials were sonicated again to ensure the removal of all pollenkitt.

Three 50 CIL sub-samples were taken from each vial and pollen grains were counted on a grided

microscope slide. Sub-sample values were then extrapolated to obtain total number of pollen

grains per flower.

Pollen sub-sample counts were averaged for each flower. Analysis of variance was

performed using the GLM procedures of SAS (SAS Institute Inc., Cary, N.C.) and means

separation was performed using Duncan's multiple range test.

Results

Pollenizer cultivar and sampling date had significant effects (P < 0.05) on pollen

production per flower. There was no significant (P > 0.05) interaction between cultivar and

sampling date. On 31 Aug., 'Mickylee' produced 49,975 pollen grains per flower (gpf) which

was not significantly greater than 'Companion' at 44,800 gpf but both were greater than 'SP-1'

and 'Jamboree' at 37,813 and 36,700 gpf, respectively (Table 1). Pollen production by

'Companion' was not significantly greater than 'SP-1' or 'Jamboree'. On 8 Sept., 'Companion'










produced 62,275 gpf which was not significantly greater than 'Mickylee' at 60,250 gpf or 'SP-1'

at 53.138 gpf but was greater than 'Jamboree' at 44,975 gpf. Pollen production by 'SP-1' and

'Jamboree' were not significantly different on 8 Sept. On 14 Sept., 'Mickylee' produced 58,900

gpf which was significantly greater than 'Companion', 'Jamboree', and 'SP-1' at 50,825, 48,475,

and 42,250, respectively. Seasonal averages for pollen production are shown inTable 1.

Discussion

The results of this study illustrate that the amount of pollen produced by diploid

watermelon plants differs by cultivar and also changes throughout the season. Pooled data for

pollen production illustrates that 'Mickylee' and 'Companion' produce significantly greater

amounts of pollen per flower than 'SP-1' or 'Jamboree'. However, the pollen output per flower

may not accurately represent the pollen output per plant. Previous research on flower production

by pollenizers illustrated that SP-1' produced significantly greater numbers of staminate flowers

when compared to 'Mickylee' or 'Companion' (Freeman and Olson, 2007). The increased

production of staminate flowers by SP-1' may result in greater pollen output per plant when

compared with the other cultivars.

The trend observed was that pollen production starts low, increases and then decreases as

the season progresses. These results are in contrast the Stanghellini and Schultheis (2005) who

reported that sampling day did not affect pollen production per flower. However, the duration of

sampling used by Stanghellini and Schultheis (2005) was not stated and flowers sampled over a

shorter time frame may not exhibit the variation observed here. As watermelon plants begin to

branch and produce flowers on secondary terminals, it has been observed that flower size

decreases. The decrease in flower size apparently correlates with the decrease in pollen

production per flower. Although pollen production per flower may decrease as the season










progresses, it is likely that pollen production per plant will increase to a point as the number of

staminate flowers produced increases.

In theory, pollenizers that produce the greatest amount of pollen could outperform other

pollenizers with lower pollen output. Greater pollen output by a pollenizer may also facilitate

the reduction in pollenizer plant numbers used per unit area. However, other experimental

results suggest that pollen production alone is not a reliable indicator of pollenizer performance

as the use of 'SP-1' resulted in significantly greater triploid watermelon yield when compared to

the use of 'Companion'. There are many factors that influence the performance of diploid

watermelon pollenizers and pollen production is likely a strong contributor. However, it is not a

reliable factor on which to judge a pollenizers potential.









Table 8-1. Pollen production by four diploid watermelon pollenizer cultivars at Quincy, FL
during the Fall of 2006.
Pollen grains per flower
Cultivar 31 Aug. 8 Sept. 14 Sept. Combined
Mickylee 49,775 az 60,250 az 58,900 az 56,308 az
Companion 44,800 a b 62,275 a 50,825 b 52,633 a
SP-1 37,813 b 53,138 ab 42,550 c 44,500 b
Jamboree 36,700 b 44,975 b 48,475 bc 43,383 b
z Means followed by the same letter are not significantly different at P I 0.05 by
Duncan's multiple range test.










LIST OF REFERENCES


Adlerz, W.C. 1966. Honey bee visit numbers and watermelon pollination. J. Econ. Entomol.
59:28-30.

Ambrose, J.T. 1997. The importance of honey bees in North Carolina. N.C. Coop. Ext. Serv.
Beekeeping Note #1A.

Arndt, G.C., J.L. Rueda, H.M. Kidane-Mariam, and S.J. Peloquin. 1990. Pollen fertility in
relation to open pollinated true seed production in potatoes. Amer. Potato J. 67:499-505.

Arney, M., S.R. Fore, and R. Brancucci. 2006. Watermelon reference book. National
Watermelon Promotion Board. Orlando, Fla.

Ban, D., S. Goreta, and J. Borosic. 2006. Plant spacing and cultivar affect melon growth and
yield components. Scientia Hort. 109:238-243.

Batra, S.W.T. 1993. Male-fertile potato flowers are selectively buzz-pollinated only by Bombus
terricola Kirby in upstate New York. J. Kansas Ent. Soc. 66:252-254.

Brevis, P.A., D.S. NeSmith, H.Y. Wetzstein, D.B. Hausman. 2006. Production and viability of
pollen and pollen-ovule ratios in four rabbiteve blueberry cultivars. J. Amer. Soc. Hort.
Sci. 131:181-184

Brinen, G.H., S.J. Locascio, and G.W. Elmstrom. 1979. Plant and row spacing, mulch, and
fertilizer rate effects on watermelon production. J. Amer. Soc. Hort. Sci. 104:725-726.

Bryan, H.H. 1966. Effect of plastic mulch on the yield of several vegetable crops in North
Florida. Proc. Fla. State Hort. Soc. 79:139-146.

Buker, R.S., W.M. Stall, S.M. Olson, D.G. Schilling. 2003. Season-long interference of yellow
nutsedge (Cyperus esculentus) with direct-seeded and transplanted watermelon (Citrullus
lan2atus). Weed Tech. 17:751-754.

Butler, C.G. 1951. The importance of perfume in the discovery of food by the worker honeybee
(Apis mellifera L.). Proceedings of the Royal Society of London, Series B, 138:403-413.

Clark, G.A., D.Z. Haman, and F.S. Zazueta. 2005. Injection of chemicals into irrigation systems:
rates, volumes, and injection periods. Univ. Fl. Coop. Ext. Serv. BUL250. 9 Dec. 2006.
(http:.//edi s.ifas.ufl. edu/AE 11 6)

Cockerham, L.E. and G.J. Galleta. 1976. A survey of pollen characteristics in certain Vaccinium
species. J. Amer. Soc. Hort. Sci. 101:671-676.

Connell, J. H. 1990. Apparent versus "real" competition in plants, p. 9-23. In: J.B. Grace and D.
Tilman (eds.) Perspectives on Plant Competition. Academic Press. New York.










Cushman, K.E., D.H. Nagel, T.E. Morgan, P.D. Gerard. 2004. Plant populationaffects pumpkin
yield components. HortTechnology 14:326-331.

Dafni, A., M. Neppi, and E. Pacini. 2005. Pollen and stigma biology, p. 83-147. In A. Dafni.,
P.G. Kevan and B. Husband (eds.) Practical Pollination Biology. Enviroquest, Cambridge,
Canada.

Daniello, F.J. 2003. Watermelon. Tex. Coop. Ext. Horticulture Crop Guide Series. 10 Dec. 2006.
(http:.//aggiehorticulture.tamu. edu/extension/vegetable/cropguides/watermeo~tl

Delaplane, K.S., and D.F. Mayer. 2000. Crop pollination by bees. CAB Intl., Wallingford, U.K.

Dittmar, P.J., J.R. Schultheis, and D.W. Monks. 2005. Characterization of the growth and
development of commercially available watermelon pollenizers. HortScience 40:872
(ab str.)

Dobson, H.E.M. 1988. Survey of pollen and pollenkitt lipids Chemical cues to flower visitors?
American Journal of Botany 75:170-182.

Dobson, H.E.M. 1991. Pollen and flower fragrances in pollination. Acta. Hort. 288:313-320.

Dobson, H.E.M., J. Bergstrom, G. Bergstrom, and I. Groth. 1987. Pollen and flower volatiles in
two Rosa species. Phytochemistry 26:3171-3173

Dobson, H.E.M., I. Groth, and G. Bergstrom. 1996. Pollen advertisement: Chemical contrasts
between whole-flower and pollen odors. American Journal of Botany 83:877-885.

Duthie, J.A., B.W. Roberts, J.V. Edelson, and J.W. Shrefler. 1999a. Plant density-dependent
variation in density, frequency, and size of watermelon fruits. Crop Sci. 39:412-417

Duthie, J.A., J.W. Shrefler, B.W. Roberts, and J.V. Edelson. 1999b. Plant density-dependent
variation in marketable yield, fruit biomass, and marketable fraction in watermelon. Crop
Sci. 39:406-412.

Edelstein, M. and H. Nerson. 2002. Genotype and plant density affect watermelon grown for
seed consumption. HortScience 37:981-983.

Erdem, Y. and A.N. Yuksel. 2003. Yield response of watermelon to irrigation shortage. Sci.
Hort. 98:365-383.

Fiacchino, D.C. and S.A. Walters. 2003. Influence of diploid pollenizer frequencies ontriploid
watermelon quality and yields. HortTechnology 13:58-61.

Firbank, L.G. and A.R. Watkinson. 1990. On the effects of competition: from monocultures to
mixtures, p. 165-192. In: J.B. Grace and D. Tilman (eds.) Perspectives on Plant
Competition. Academic Press. New York.










Fortescue, J.A. and D.W. Turner. 2004. Pollen fertility in M~usa: viability in cultivars grown in
southern Australia. Australian J. of Agr. Res. 55:1085-1091

Franklin, R. 1998. Nutrient management for South Carolina. Clemson Univ. Coop. Ext. Serv.
Extension Circular 476.

Free, J.B. 1993. Insect pollination of crops, 2nd ed. Academic, London.

Freeman, J.H. 2007. Use and effects of diploid pollenizers for triploid watermelon [Citrullus
lanatus (Thunberg) Matsumura & Nakai] production. Univ. FL., Gainesville, PhD Diss.
46-56.

Freeman, J.H. and S.M. Olson. 2007. Characteristics of watermelon pollenizer cultivars for use
in triploid production. Int. J. Veg. Sci. In Press

von Frisch, K. 1967. The Dance Language and Orientation of Bees. Belknap Press. Cambridge,
Ma.

Gillaspy, G., H. Bendavid, W. Gruissem. 1993. Fruits a developmental perspective. Plant Cell
5:1439-1451.

Goreta, S., S. Perica, G. Dumicic, L. Bucan, and K. Zanic. 2005. Growth and yield of
watermelon on polyethylene mulch with different spacings and nitrogen rates. HortScience
40:366-369.

Hara, H. 1969. The correct author's name for Citrullus lan2atus (Cucurbitaceae). Taxon 18:346-
347.

Harbo, J.R. and R.A. Hoopinger. 1997. Honey bees (Hymenoptera: Apidae) in the United States
that express resistance to Varroa jacobsoni (Mesostigmata: Varroidae). J. Econ. Entomol.
90:893-898.

Hidalgo, P.J., C. Galan, and E. Dominguez. 1999. Pollen production in the genus Cupressus.
Grana 38:296-300.

Hochmuth, G.J, E. Kee, T.K. Hartz, F.J. Dainello, and J.E. Motes. 2001. Cultural management,
p. 78-97. In: D.N. Maynard (ed.) Watermelons characteristics, production and marketing.
ASHS Press. Alexandria, VA.

Hochmuth, G.J., R.C. Hochmuth, and S.M. Olson. 2001. Polyethylene mulching for early
vegetable production in north Florida. Univ. Fla. Coop. Ext. Serv. Circular 805. 9 Dec.
2006. (http://edi s.ifas.ufl. edu/CV213)

Holiday, R. 1960. Plant population and crop yield. Nature 186:22-24

Karst, T. 1990. Seedless watermelon sure to grow. The Grower 23:61.










Kartesz, J.K. 2006. PLANTS profile for Citrullus lan2atus. U.S. Dept. Agric. NRCS. 3 Dec. 2006.
(http:.//plants.usda.gov/j ava/profile?symbol=CILA3).

Kihara, H. 1951. Triploid watermelons. Proc. Amer. Soc. Hort. Sci. 58:217-230.

Kultur, F., H.C. Harrison, and J.E. Staub. 2001. Spacing and genotype affect fruit sugar
concentration, yield, and fruit size of muskmelon. HortScience 36:274-278.

Lamont, W.J., Jr. 1993. Plastic mulches for the production of vegetable crops. HortTechnology
3:35-39.

Lang, G.A. and E.J. Parrie. 1992. Pollen viability and vigor in hybrid southern highbush
blueberries (Vaccinium corymbosum L. x spp.). HortScience 27:425-427.

Lavi, U., S. Nachman, I. Barucis, D. Gaash, A. Kadman. 1996. The effect of pollen donors and
pollen viability on fruitlet drop in Macadamia integrifolia (Maiden & Betche). Tropic.
Agric. 73:.249-251.

Lu, W., J.V. Edelson, J.A. Duthie, and B.W. Roberts. 2003. A comparison ofyield between high
and low intensity management for three watermelon cultivars.HortScience 38:351-356.

Marr, C.W. and K.L.B. Gast. 1991. Reactions by consumers in a farmers' market to prices for
seedless watermelon and ratings of eating quality. HortTechnology 1:105-106.

Maynard, D.N. 2001 An introduction to the watermelon, p. 9-20. In: D.N. Maynard (ed.)
Watermelons characteristics, production and marketing. ASHS Press. Alexandria, VA.

Maynard, D.N. 1989. Triploid watermelon seed orientation affects seedcoat adherence on
emerged cotyledons. HortScience 24:603-604.

Maynard, D.N. 1992. Growing seedless watermelon. Univ. Fla. Coop. Ext. Serv. Fact sheet
HS687. 12 Oct. 2006. (http://edis.ifas.ufl.edu/CV006)

Maynard, D.N. and G.W. Elmstrom. 1989. Evaluation of triploid watermelon cultivars in central
and southwest Florida. Proc. Fla. State Hort. Soc. 102:313-319.

Maynard, D.N. and G.W. Elmstrom. 1992. Triploid watermelon production practices and
varieties. Acta Hort. 318:169-173.

Maynard, E.T. and W.D. Scott. 1998. Plant spacing affects yield of 'Superstar' muskmelon.
HortScience 33:52-54.

McCreight, J.D. 1998. Botany and culture, p. 2-6. In: T.A. Zitter, D.L. Hopkins, and C.E.
Thomas (eds.) Compendium of cucurbit diseases. APS Press. St. Paul, MN.

Monks, D.W. and J.R. Schultheis. 1998. Critical weed free period for large crabgrass (Digitaria
sanguinalis) in transplanted watermelon. Weed Sci. 46:530-532.










Motsenbocker, C.E. and R.A. Arancibia. 2002. In-row spacing influences triploidwatermelon
yield and crop value. HortTechnology 12:437-440.

Nepi, M. and E. Pacini. 1993. Pollination, pollen viability and pistil receptivity in Cucurbita
pepo. Annals of Botany. 72:527-536.

NeSmith, D.S. 1993. Plant spacing influences watermelon yield and yield components.
HortScience 28:885-887.

NeSmith, S. and J. Duval. 2001. Fruit set of triploid watermelon as a function of distance from a
diploid pollenizer. HortScience 36:60-61.

Nettles, V.F. 1963. Planting and mulching studies with cucurbits. Proc. Fla. State Hort. Soc.
76:178-182.

Nikkanen, T., T. Aronen, H. Haggman, and M. Venalainen. 2000. Variation in pollen viability
among Picea abies genotypes potential for unequal paternal success. Theor. Appl. Genet.
101:511-518.

Olsen, L., R. Hoopinger, and E.C. Martin. 1979. Pollen preferences of honeybees sited on four
cultivated crops. J. Apicultural Res. 18:196-200.

Olson, S.M., E.H. Simonne, W.M. Stall, P.D. Roberts, S.E. Webb, T.G. Taylor, and S.A. Smith.
2006. Cucurbit production in Florida, p. 191-237. In: S. M. Olson and E. H. Simonne
(eds.) Vegetable production handbook for Florida. Univ. Fla. Coop. Ext. Serv. and Vance
Publishing. Lenexa, KS.

Parties, H.K., F. Schnaithmann, and H.H. Geiger. 2005. Pollen viability of Hordeum spp
genotypes with different flowering characteristics. Euphytica 145:229-235.

Pernal, S.F and R.W. Currie. 2002. Discrimination and preferences for pollen-based cues by
foraging honeybees, Apis mellifera L. Animal Behaviour 63:369-390.

Prieto-Baena, J.C., P.J. Hidalgo, E. Dominguez, and C. Galan. 2003. Pollen production in the
Poaceae family. Grana 42: 153-160.

Radosevich, S.R. and M.L. Roush. 1990. The role of competition in agriculture, p. 341-363. In:
J.B. Grace and D. Tilman (eds.) Perspectives on Plant Competition. Academic Press. New
York.

Reiners, S. and D.I.M. Riggs. 1997. Plant spacing and variety affect pumpkin yield and fruit size
but supplemental nitrogen does not. HortScience 32:1037-1039.

Reiners, S. and D.I.M. Riggs. 1999. Plant population affects yield and fruit size of pumpkin.
HortScience 34: 1076-1078.

Rhodes, B., K.B. Gruene, and W.M. Hood. 1997. Honey bees waste time on triploid male
flowers. Cucurbit Genet. Coop. Rpt. 20:45.










Robinson, R.W. and D.S. Decker-Walters. 1997. Cucurbits. CAB Intl., Wallingford, U.K.

Rodriguez-Riano, T. and A. Dafni. 2000. A new procedure to asses pollen viability. Sex. Plant
Reprod. 12:241-244.

Rubatzky, V.E. and M. Yamaguchi. 1997. World vegetables, 2nd ed. Chapman & Hall Publ.,
New York.

Sanders, D.C. (ed.), J.M. Kemble, E.J. Sikora, R.L. Hassell, G. Miller, T. Keinath, J.K.
Norsworthy, P. Smith, G.E. Boyhan, W.T. Kelley, D.B. Langston, A.S. Culpepper, A.S.
Sparks, J.E. Boudreaux, J.M. Cannon, D.H. Nagel, R.G. Snyder, D. Ingram, M.R.
Williams, B.O. Layton, J.D. Byrd, M.W. Shankle, A. Rankins, R.B. Batts, M.E. Clough,
N.G. Creamer, J.M. Davis, W.R. Jester, D.W. Monks, L.M. Reyes, J.R. Schultheis, A.
Thornton, G.T. Roberson, K.A. Sorensen, J.F. Walgenbach, D.B. Orr, D.R. Tarpy, C.W.
Averre, M.A. Cubeta, K. Ivors, G.J. Holmes, K.M. Jennings, F.J. Louws, D.F. Ritchie,
C.R. Crozier, G.D. Hoyt, D.N. Maynard, R.S. Mylavarape, and H.J. Savoy. 2006.
Vegetable crop guidelines for the southeastern U.S. Vance Publ. Corp., Lincolnshire, Ill.,
in cooperation with the N.C. Veg. Growers Assn., Raleigh, N.C.

Sanders, D.C., J.D. Cure, and J.R. Schultheis. 1999. Yield response of watermelon to planting
density, planting pattern, and polyethylene mulch. HortScience 34: 1221-1223.

Schabenberger, O. and F.J. Pierce. 2002. Contemporary statistical models for the plant and soil
sciences. CRC Press. Boca Raton, Fla.

Smaj strla, A.J., B.J. Bowman, G.A. Clark, D.Z. Haman, D.S. Harrison, F.T. Izuno, D.J. Pitts, and
F.S. Zazueta. 2002. Efficiencies of florida agricultural irrigation systems. Univ. Fl. Coop.
Ext. Serv. Fact Sheet BUL247. 10 Dec. 2006. (http://edis.ifas .ufl.edu/AE 110)

Stanghellini, M. S., J.T. Ambrose, and J.R. Schultheis. 1997. The effects of honey bee and
bumble bee pollination on fruit set and abortion of cucumber and watermelon. Amer. Bee
J. 137:386-391.

Stanghellini, M. S., J.T. Ambrose, and J.R. Schultheis. 1998. Seed production in watermelon: a
comparison between two commercially available pollinators. HortScience 33:28-30.

Stanghellini, M.S. and J.R. Schultheis. 2005. Genotypic variability in staminate flower and
pollen grain production of diploid watermelons. HortScience 40:752-755.

Taylor, M.D. and S.J. Locascio. 2004. Blossom-end rot: a calcium deficiency. J. Plant. Nutr.
27:123-139.

U. S. Department of Agriculture. 2006. National watermelon report. U. S. Dept. Agr. Agricultural
Marketing Service. Thomasville, Ga. 15 Dec. 2006 (http://www.ams.usda.gov)

U. S. Department of Agriculture. 2005. Quick stats. U. S. Dept. Agr. Natl. Agr. Statistics Serv.
Washington, D.C. 12 Dec. 2006. (http ://www.nass.usda.gov/QuickStats/
CreateFederal All.j sp)










U. S. Department of Agriculture. 2002. Census of agriculture. U. S. Dept. Agr. Fla. Ag. Statistics
Serv. Tallahassee, Fla. 8 Dec. 2006. (http://www. nass.usda.gov/Stati stics by_State/
Florida/index.asp)

Vithanage, V. 1991. Effect of different pollen parents on seediness and quality of 'Ellendale'
tangor. Scientia Hort. 48:253-260.

Wallace, H.M. and L.S. Lee. 1999. Pollen source, fruit set and xenia in mandarins. J. Hort. Sci.
Biotechnology 74:82-86

Walters, S.A. 2005. Honey bee pollination requirements for triploid watermelon. HortScience
40:1268-1270.

Wehner, T.C. 2006. Watermelon crop information taxonomy, morphology, physiology. Hort.
Sci. Dept. NCSU. 16 Dec. 2006
(http:.//cuke.hort.ncsu. edu/cucurbit/wmelon/wmelonmain. html)

Wiemann, S. (ed.) 1992. The Packer Fresh Trends. Vance Publishing Corp., Lincolnshire, IL

Wolf, S., Y. Lensky, and N. Paldi. 1999. Genetic variability in flower attractiveness to
honeybees (Apis mellifera L.) within the genus Citrullus. HortScience 34:860-86









BIOGRAPHICAL SKETCH

Joshua Herbert Freeman was born on October 24, 1980 to Linda and Herbert Freeman of

Columbia, S.C. He first became interested in agriculture while working on cattle farm near his

home. After graduating from Ridge View High School he attended Clemson University where

earned a bachelor' s degree in entomology. In the fall of 2002, he enrolled in the University of

Florida and pursued a doctor of plant medicine degree. His career aspirations changed and in the

fall of 2004, he began working on doctorate of philosophy in horticultural science at the

University of Florida.