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1 ORGANIC PRODUCTION OF GRAFTED HEIRLOOM TOMATOES: NEMATODE MANAGEMENT, FRUIT QUALITY, AND ECONOMICS By CHARLES EDWARD BARRETT A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2011
2 2011 Charles Edward Barrett
3 To my grandfather, one of my biggest inspirations
4 ACKNOWLEDGMENTS I thank Dr. Xin Zhao for all of her help and guidance throughout this two year journey. I thank my committee of experts Dr. Robert McSorley, Dr. Charles Sims, and Dr. Alan Hodges. I am very grateful for all of their excellent advice that made this project possible. I am lucky to have a great family that was interested in my research even if at times it was just to humor me. I thank my girlfriend Paola Ferst for sticking by me through good or bad and for keeping me honest. My friend Joshua Adkins really pushed me to achieve my goals and gave me tips, editorial help and someone to enjoy a cold beverage with. Thanks to Jorge for being someone to drink coffee with and not think about all the things I had to do. Thank you to: Dr. Cantliffe for allowing me this opportunity Dr. Brecht for advice and postharvest help Dr. Hube r for answering my random questions and being one of and Dr. Stall for answering the gray wall mystery. I also thank Desire, Wenjing, for being excellent lab mates and for all their help My field trials could not have bee n better thanks to the expertise of Buck Nelson Timmy, and th e rest of the crew at the PSREU. Steffen and Chris were my efficiency experts and made my field work happen even though the biodiversity of organic farming was a little unnerving at times.
5 TA BLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ ............ 6 LIST OF FIGURES ................................ ................................ ................................ .......... 7 ABSTRACT ................................ ................................ ................................ ..................... 8 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ .... 10 2 GRAFTING FOR ROOT KNOT NEMATODE CONTROL AND YIELD IMPROVEMENT IN ORGANIC HEIRLOOM TOMATO PRODUCTION .................. 15 Background ................................ ................................ ................................ ............. 15 Materials and Methods ................................ ................................ ............................ 17 Results and Discussion ................................ ................................ ........................... 21 3 FRUIT QUALITY AND SENSORY ATTRIBUTES OF ORGANIC HEIRLOOM TOMATOES ARE NOT INFLUENCED BY GRAFTING ................................ .......... 33 Background ................................ ................................ ................................ ............. 33 Materials and Methods ................................ ................................ ............................ 34 Results and Discussion ................................ ................................ ........................... 39 4 COST BENEFIT ANALYSIS OF USING GRAFTED TRANSPLANTS FOR ROOT KNOT NEMATODE MANAGEMENT IN ORGANIC HEIRLOOM TOMATO PRODUCTION ................................ ................................ ....................... 45 Background ................................ ................................ ................................ ............. 45 Materials and Methods ................................ ................................ ............................ 47 Results and Discussion ................................ ................................ ........................... 51 5 CONCLUSION ................................ ................................ ................................ ........ 63 LIST OF REFERENCES ................................ ................................ ............................... 65 BIOGRAPHICAL SKETCH ................................ ................................ ............................ 69
6 LIST OF TABLES Table page 2 1 Effect of grafting treatments on root knot nematode galling ratings z of heirloom tomato cultivars Brandywine and Flamme y ................................ ......... 28 2 2 Effect of grafting t reatments on leaf area and above ground biomass of heirloom tomato cultivars Brandywine and Flamme z ................................ ......... 29 3 1 Consumer demographic information. ................................ ................................ .. 42 3 2 Effect of grafting treatments on heirloom tomato fruit sensory attributes z for scion cultivars Brandywine and Flamme. ................................ ........................... 43 3 3 Effect of grafting treatments on heirloom toma to fruit quality attributes z for scion cultivars Brandywine and Flamme. ................................ ........................... 44 4 1 Sources and prices for materials used to produce grafted and nongrafted heirloom tomato transplants. ................................ ................................ .............. 57 4 2 Costs of grafted and nongrafted organic heirloom tomato transplants. z ............. 58 4 3 Estimated partial z net return per plant ($/plant) for no y plants grown organically with low root knot nematode pressure x ...................... 59 4 4 Estimated partial z y grafted onto the roo x grown organically with low nematode pressure w ................................ ................................ ................................ ........... 60 4 5 Estimated partial z y plants grown in a transitional organic field with high nematode pressure x ......... 61 4 6 Estimated partial z y x grown in a transitional organi c field with high nematode pressure w ................................ ................................ .................. 62
7 LIST OF FIGURES Figure page 2 1 Cumulative marketable yield for nongrafted and grafted heirloom tomato cul tivars Flamme (A) and Brandywine (B) from the organic field trial conducted in 2010.. ................................ ................................ ............................ 30 2 2 Cumulative marketable yield for nongrafted and grafted heirloom tomato cultivars Flamme (A) and Bra ndywine (B) from the organic field trial conducted in 2011.. ................................ ................................ ............................ 31 2 3 Cumulative marketable yield for nongrafted and grafted heirloom tomato cultivars Flamme (A) and Brandywine (B) from the 2011 field trial designed to reflect a transition period from conventional to organic.. ................................ .... 32
8 Abstract o f Thesis Presented t o t he Graduate School o f t he University o f Florida i n Partial Fulfillment o f t he Requirements f or t h e Degree o f Master o f Science ORGANIC PRODUCTION OF GRAFTED HEIRLOOM TOMATOES: NEMATODE MANAGEMENT, FRUIT QUALITY, AND ECONOMICS By Charles Edward Barrett December 2011 Chair: Xin Zhao Major: Horticultural Science Growers are looking for s ustainable alternatives to methyl bromide as a soil fumigant that are effective and economical. Increased demand for organically produced fruits and vegetables has also contributed to the need for ecologically friendly soilborne disease control methods. Gr afting may be a valuable tool for vegetable growers but concerns regarding the disadvantages and challenges associated with grafting must be addressed before grafting will be widely used in the United States. There were four objectives carried out with th is two year study. The first objective was to determine if grafting heirloom tomatoes onto interspecific or intraspecific rootstocks could be effective for root knot nematode control under organic production in Florida. The second objective was to assess t he influence of grafting treatments on yield and crop vigor. The third objective was to determine if grafting treatments affect fruit quality attributes. The final objective was to determine if grafting to overcome root knot nematodes could be cost effecti ve on an organic farm. Three spring field trials were conducted, one in 2010 (organic) and two in 2011
9 (intraspecific), and nongrafted and self grafted scion controls. In 2010, no root knot nematode galls were observed and total marketable yields were not significantly different within scion treatments. In 2011, galls were observed on roo ts in every treatment in both field trials. The rootstocks reduced galling by 89% on average in the organic field trial. Under severe nematode pressure in the transitional field trial, the higher marketable yields than nongrafted and self aste tests. There were no differences in fruit nutritional contents. Grafted and nongrafted transplants were estimated to cost $0.78 and $0.17, respectively. Sensitivity analyses conducted using these estimated transplant production costs revealed that und er severe root knot nematode pressure, grafting may be an economically feasible soilborne disease control option. This study demonstrated that grafting could be successfully implemented for root knot nematode control in organic heirloom tomato production. The yield of grafted tomatoes was influenced by the rootstock scion interaction and the root knot nematode population. The use of nematode resistant rootstocks did not have a significant impact on tomato quality attributes. Grafted transplants do cost more to produce, but can reduce the risk of economic crop losses due to root knot nematodes.
10 CHAPTER 1 INTRODUCTION Grafting is a horticultural technique that fuses two or more different plants together to grow as one plant. The plant (s) that provides the sho ot, leaves and fruit is (are) referred to as the scion. The roots are provided by a plant called the rootstock. Commercial grafting has been used in the production of fruit trees (e.g. peach, apple, citrus) and vegetables (e.g. tomato, eggplant, melon). R ecords of tree grafting date back hundreds of years whereas early vegetable grafting records date back to only the ( Fusarium oxyysporum ) in watermelon (Lee, 1994). In addit ion to improved resistance to soilborne pathogens and diseases such as root knot nematode s verticillium wilt, southern blight, and bacteria wilt; grafted vegetables often demonstrate greater vigor, enhanced nutrient and water uptake, and improved toleranc e to environmental stresses like soil salinity, low temperature, and flooding ( King et al., 2010; Lee et al. 2010 ; Louws et al., 2010; Schwarz et al., 2010). Vegetable grafting is currently widely used in greenhouses, high tunnels, and some open field pro ducing areas in many Asian and Mediterranean countries ( Lee et al. 2010) Japan and Korea are among the leaders in growing grafted vegetables using an estimated 721.3 million and 766.3 million grafted transplants a year, respectively (Lee et al., 2010). An estimated 40 million grafted transplants are used each year in the United States (Kubota et al., 2008). However, grafted transplants in the United States are almost completely isolated to use in the greenhouse tomato industry (Kubota et al., 2008). Grow ers in the United States are concerned with the disadvantages associated with grafting (Lee et al., 2010). The cost of grafted transplants is a major barrier
11 preventing growers from adopting this technique (King et al. 2008; Kubota et al., 2008; Kubota, 2 008; Lee et al., 2010; Rivard et al. 2010b). In a recent study, estimated prices for nongrafted tomato transplants in the United States ranged from $0.13 to $0.51 while price estimates for grafted tomato transplants ranged from $0.59 to $1.25 ($1.88 afte r markup) (Rivard et al. 2010b). According to Lee et al. (2010), grafted vegetable transplants were estimated to cost $0.40 to $1.20. If grafted transplants are to be used, a grower will need to know how these higher initial costs will be recovered. Produ ctivity of grafted vegetables may be directly related to the economic feasibility of the adoption of grafting technology. If yields are maintained or reduced as a result of grafting, and all other costs are held constant, the grower never makes up the extr a cost incurred for the grafted transplants and therefore profits are reduced. However, if a grower experiences higher yields, some or all of that cost could be recovered. In Florida, growers fumigating with expensive pesticides for root knot nematodes (RK N) and other soilborne pathogens, could also reduce some production expenses by using grafted transplants instead of fumigating (King et al., 2008). Nematodes are a major problem in the southern United States and worldwide (Rivard et al., 2010a; Roberts et al., 2005; Sasser, 1980). Warm temperatures, sandy soils, and excess moisture create an ideal habitat for nematodes (Roberts et al., 2005). Conditions in Florida in the spring and fall growing seasons are usually highly favorable for nematode populations to cause economic crop losses on susceptible crops. While many commercial cultivars have resistance to root knot nematodes among other soilborne pathogens, there is a lack of such resistance in heirloom tomatoes (Rivard and Louws, 2008).
12 In contrast to th e conventional production systems, organic farmers have fewer options for soilborne disease control ( Rivard and Louws, 2008 ). Some disease management practices such as crop rotation may be space prohibitive due to the smaller size of many organic farms. Cr op rotation can also take many years to be effective which o ften requires more land in rotation to keep productive land available. Crop rotation may be less effective if the pathogen has a wide range of host s Grafting with resistant rootstocks can be rap idly incorporated into integrated pest management practices for controlling soilborne diseases. Resistant rootstocks can effectively act as a non host plant in crop rotations with susceptible cultivars. Organic markets in the United States have grown stea dily for over a decade and one emerging problem in the organic sector is a lack of supply (Greene et al., 2009). Grafting could offer stability to these markets by promoting more competitive plants and a reduced risk of crop failure (Taylor et al., 2008). Some growers in Florida and North Carolina have begun experimenting with grafting on their farms in an attempt to overcome soilborne pathogens for heirloom tomato production (grower pers. comm. ; Kubota, 2008; Rivard et al., 2010a ). However, systematic stud ies on grafted heirloom tomatoes are scarce particularly under Florida conditions. Heirloom tomatoes with distinct flavor and quality attributes represent a popular niche market for local organic and small growers (Jordan, 2007). It has been suggested t hat many commercial varieties of fruits and vegetables have lost much of their flavor because modern breeding has targeted developing commodities with longer shelf lives and better shipping capabilities (Klee, 2010). Breeders are now looking into heirloom cultivars as sources for flavor genes ( Klee, 2010 ). Grafting can allow for immediate use
13 of disease resistant genes from rootstocks while maintaining the outstanding flavor afforded by heirloom scions. Although Rivard et al. (2010a) showed that grafted tra nsplants can be used to effectively control southern blight and root knot nematodes sensory attributes and nutritional content of the fruit was not mentioned. A previous greenhouse study by Di Gioia et al ( 2010 ) showed that soluble solid content, titrata ble acidity, and sensory profiles of h eirloom tomato fruit were not affected by grafting onto interspecific rootstocks whereas vitamin C content was reduced as a result of grafting. Grafted vegetable research has yielded mixed results regarding the affect s of grafting on fruit quality attributes, possibly due to the use of varying scion rootstock combinations, growing environments, seasons, and grafting methods (Edelstein, 2004; Martnez Ballesta et al., 2008; Rouphael et al., 2010). The influence of graft ing on fruit taste and fruit quality of different scion rootstock combinations deserves more attention as it may impact the adoption of this technique. Conventional growers are paid based on fruit weight and may be less concerned about taste and nutritiona l content than the organic or smaller market farmer. Small farmers often have a close connection with the purchasers of their produce and therefore have more to lose if grafting affects fruit taste or fruit quality Organic farmers are in a unique position to gain from grafting because consumers are willing to pay more for organic produce, and produc e with better taste (Greene et al., 2009; Klee, 2010 ). F our main research objectives were explored in this two year study. One objective was to determine if gr afting heirloom tomatoes onto different rootstocks, i.e., interspecific and intraspecific, can be used for root knot nematode control in organic production in Florida sand y soils Another objective was to assess the influence of
14 grafting on crop vigor and yield of heirloom tomato scions. A third objective was to determine the effect of grafted treatments on fruit quality and sensory attributes. Finally, sensitivity analyses were performed to estimate the economic feasibility of integrating heirloom tomato g rafting on an organic farm.
15 CHAPTER 2 GRAFTING FOR ROOT KNOT NEMATODE CONTRO L AND YIELD IMPROVEM ENT IN ORGANIC HEIRLOOM TOMATO PRODUCTION Background Mo dern tomato breeding has le d to improvements in postharvest attributes but this has come with a noticea ble decrease in fruit flavor (Klee, 2010). Educated consumers have be gun demanding heirloom tomatoes for their superior flavor and unique appeal (Bland, 2005; Jordan, 2007; Klee, 2010). This increased interest has helped expand a niche market for local org anic growers (Jordan, 2007). However, heirloom tomatoes can be difficult to grow in Florida due to imminent pest and disease pressure. One of the major pest management challenges are root knot nematodes ( Meloidogyne spp.) which thrive in warm weather and m oist, sandy soils (Roberts et a l ., 2005; Sasser, 1980). Root knot nematodes (RKN) cause root galls that damage the root system and result in stunted plant growth and significant yield loss RKN persist in the soil for many years and have a broad host range These characteristics make RKN difficult to control on organic farms. The small size of many organic farms may prevent utilization of the long rotation times needed to ameliorate soil conditions between susceptible crops. Organic growers often face pest and disease challenges with few effective control methods, making organic heirloom tomato production even more difficult and potentially less profitable than conventional production (Rivard and Louws, 2008; Rivard et al., 2010a). With the use of appropria te rootstocks, grafting may be a useful technique for vegetable producers to overcome soilborne pathogens including RKN. Vegetable grafting began Fusarium oxysporum Smith ) in watermelons and is curr ently widely used in cucurbitaceous and
16 solanaceous crop production in Asian and Mediterranean countries (Lee, 1994; Lee et al., 2010). Recently, investigators have begun examining vegetable grafting as a tool for United States producers. This research ha s focused on: grafted seedling production, use, and economics (Kubota et al., 2008; Rivard et al. 2010b); grafting as an alternative to methyl bromide in field production (Freeman et al., 2009); and the use of resistant rootstocks for controlling soilborn e diseases and RKN (Bausher, 2009; Lopez Perez et al., 2006; Rivard and Louws, 2008; Rivard et al., 2010a). With the phase out of methyl bromide for soil fumigation and the continued rise in demand for organic produce in the United States, the need for alt ernative disease control methods that do not rely on synthetic biocides has increased (Greene et al. 2009; King et al. 2008; Louws et al. 2010). Intraspecific tomato hybrids ( S olanum lycopersic um L. ) and interspecific tomato hybrids ( S. lycopersi cum x S habrochaites S.Knapp & D.M. Spooner) have been employed worldwide as disease resistant rootstocks in grafted tomato production (King et al., 2010). It is unclear how the differences between intraspecific and interspecific hybrid tomato rootstocks will af fect field grown indeterminate heirloom tomatoes. Hence, rootstock evaluations for heirloom tomato production in open field conditions should involve both types of rootstocks. Grafting has been used to successfully produce heirloom tomatoes in a North Caro lina organic system by effectively managing bacterial wilt ( Ralstonia solanacearum (Smith) Yabuuchi et al. ) and fusarium wilt (Rivard and Louws, 2008). Additionally, it was shown that southern blight ( Sclerotium rolfsii Sacc. ) and southern RKN [ M. incognit a (Kofoid & White ) Chitwood] could be managed by
17 grafting heirloom tomatoes onto interspecific hybrid rootstocks (Rivard et al., 2010a) Interest in tomato grafting is emerging among small and organic growers in Florida. The results from these North Caroli na studies are promising and suggest that grafting may be applicable in Florida heirloom tomato production. However, appropriate rootstocks for Florida conditions need to be determined. The purpose of this study was to assess heirloom tomato grafting for RKN control under organic production in naturally infested Florida sandy soils. It is hypothesized that grafting onto resistant rootstocks can reduce nematode galling incidence. Intraspecific and interspecific hybrid rootstocks were compared with respect to their influence on nematode resistance, crop vigor, and fruit yield. Materials and Methods Scion and rootstock cultivars Grafted tomato seedlings were produced using certified organic heirloom tomato seed and commercially available non treated rootstoc k seed s The heirloom tomato cultivars Brandywine and Flamme were used as nongrafted red, open pollinated, indeterminate variety valued for its excellent flavor and large size. ball sized, orange, open pollinated, indeterminate variety. Seeds, Salinas, CA) were used as interspecific ( S. habrochaites x S. lycopersicum S. lycopersicum ) hybrid. Both rootstocks were chosen for their high resistance to soilborne pathogens, root knot nematodes ( Meloidogyne sp p .) and vigorous growth habit. Tr ansplant production Rootstock seeds were sown two days before scion seeds on 16 Feb 2010 and 11 Feb 2011. Seedlings were grown in Fafard Organic Formula
18 Custom potting mix (Apopka, FL) using 128 cell count Speedling Flats (Sun City, FL). At the 4 5 true leaf stage, seedlings were tube grafted. Grafting procedures were adapted from Rivard and Louws (2006) in which young seedlings are grafted and held together using 2.0 mm or 1.5 mm silicon clips (Hydro Gardens, Colorado Springs, CO). Grafting took place 3 4 d and 28 d after scions were sown for 2010 and 2011, respectively. The grafted seedlings were then placed in a temperature and humidity controlled walk in cooler at 25 C and ~95% RH with no light for 24 hr. Thereafter, the grafted seedlings were gradual ly exposed to light and humidity was reduced for 6 d until the seedlings were healed. The grafted seedlings were then transported to the greenhouse to harden off before transplanting into the field. Field trials Three field trials were conducted at the U niversity of Florida Plant Science Research and Education Unit in Citra, FL. One trial was conducted in the spring of 2010 while two were conducted in the spring of 2011. In both years, one trial was grown on certified organic land following the rules outl ined by the National Organic Program (U.S. Dept. Agr., 2002). The organic research land was certified by Quality Certification Services (Gainesville, FL). Organic yellow squash ( Cucurbita pepo L.) was grown during the 2010 fall growing season to encourage a natural RKN infestation for the 2011 organic field trial. Additionally, in the spring of 2011, a trial was conducted on a site with a history of continuous nematode infestation that had been managed conventionally in previous years. The plants used in th is trial were produced and grown following organic practices. This trial was designed to reflect growing conditions during a typical three year transition period from conventional to organic production. The soil
19 type found in all three field trials is Cand ler sand, 0 to 5 percent slopes, hyperthermic, uncoated Typic Quartzipsam m ents, with a pH of 6.0. In all tri als there were eight treatments consisting of nongrafted and self grafted scion controls for (NGBW, BW/BW ) and ( NGFL FL/FL) and the scion rootstock combinations (BW/MU, FL/MU) The seed lings were transplanted on 10 Apr. 2010 and 2 Apr 2011. A randomized complete block de sign was used with five blocks (replications). In the 2010 trial there were 12 plants per treatment in each block. In 2011, there were 15 plants per treatment in the organic field and 8 plants per treatment in the transitional field. In all three trials th e in row plant spacing was 0.46 m (18 inches) with 1.83 m (6 feet) between row centers The plants were grown in raised beds with black plastic mulch and drip irrigation. A preplant application of Nature Safe organic fertilizer 10N 0.9P 6.6K (Cold Spring, KY) was applied at the rate of 17 9 kg N / ha (200 lb N /acre ). Supplemental liquid fertilizer applications were injected into the drip system weekly at a rate of 0.45 kg N /ha 1.3P 0.8K (Gloucester, MA). Supplem ental calcium was also supplied through injection at a rate of 0.10 kg /ha Ca with Calplex (Botanicare, Chandler, AZ). All the nutrient inputs were approved by the Organic Materials Review Institute (OMRI Eugene, O R ) for use in certified organic production The plants were staked and trellised as needed throughout the season following the stake and weave system common to Florida tomato production (Olson et al., 2011).
20 Nematode galling Assessments of nematode infestation on plant roots were conducted after the final harvest. On 13 July 2010 and 30 June 2011, the roots of five plants per treatment in each block in the organic fields and three plants per treatment in each block in the transitional field were assessed for nematode galls. The rating scheme prop osed by Zeck (1971) that estimates nematode infestation levels on a plant was used. This scheme is a scale from 0 10 (0 = no galling, 10 = plant and roots are dead). Three researchers assessed each plant individually and then the ratings were averaged to f orm a consensus rating for that plant. The consensus ratings were then averaged for each treatment in each block (five plants/plot in organic field; three plants/plot in transitional field). In addition, two nematode samples from each field w ere submitted the University of Florida Nematode Assay Lab for identification of species Fruit yield Tomato harvests began 58 days after transplanting (DAT) in 2010 and 63 DAT in 2011. In 2010, there were four harvests occurring on 7, 13, 17, and 25 June. In 2011, th ere were 6 harvests in the organic field and 5 harvests in the transitional field occurring on 4, 8, 13, 16, 22 (organic only), 23 (transitional only) and 28 (organic only) June. Fruit were harvested at the breaker stage of maturity when the mature color begins to show at the blossom end. Each harvest was graded and weighed for marketability based on organic grower standards. Non characteristic fruit and those exhibiting blossom end rot, cat facing, splitting, and insect/disease damage were counted and wei ghed to calculate marketable yield. Crop vigor One representative plant per treatment was destructively harvested in each block following the final harvest on 25 June 2010 and 30 June 2011 in the organic fields. Leaf area was measured using a LI COR area meter ( LI 3100; Lincoln, NE). After
21 recording leaf area each plant was dried in a forced air drying room at 75C for 5 days and weighed for above ground biomass. Statistical analyse s Data analyses were performed for both scion varieties separately usin g the GLIMMIX procedure of SAS version 9.2 (SAS Institute, Cary, NC) All yield, crop vigor, and nematode galling data were analyzed using a one way analysis at = 0.05 Results and Discussion Nematode galling Although the 2010 organic research field was selected because of the record of RKN infestation in previous years no RKN galls were observed on the tomato plants in the field trial regardless of the treatm ent. Grasses were known to be the dominant crop in the field for at least two years prior to the 2010 trial. In addition to the history of grasses, the hard freezes and record low temperatures during Jan Mar 2010 may have contributed to the low RKN popul ation in the field. Yellow squash was grown during the fall of 2010 in the organic field to build a natural RKN population for the spr ing 2011 season. RKN trials had been conducted in the transitional field for >10 years and there was a well established RK N population in that site. In the 2011 trials, all the treatments showed RKN galling despite the use of rootstocks. However, RKN galling index ratings were significantly lower in both fields for r the non and self grafted 2 1). The nematode species found in both fields was identified by the Nematode Assay lab as M. javanica (Treub) Chitwood, using species specific PCR primers (Dong et al 2001). In the o rganic field, the hybrid
22 rootstocks performed similarly and significantly reduced root galling compared to the nongrafted and self grafted treatments for both scions by 89% on average. In the transitional field, both rootstocks significantly reduced root g alling for both scions in comparison with the non and self grafted scion treatments. However, the rootstock led to the lowest galling ratings for both scion cultivars (P=0.01). The self ling index ratings than the defense response which resulted in reduced galling rating s but further investigation will be required to elucidate a cause Intermediate levels of disease resistance and yield in self grafted tomatoes have been reported in previous research (Rivard 2006) The RKN galling ratings were generally higher in the t ransitional field than the organic field, suggesting a more severe infestation (Table 2 1). This trend was observed Under different field infestation levels, the high resistance to RKN was c onsistent when the two heirloom tomato cultivars were grafted onto In when the soil RKN infestation increased In this study, which were assessed by Rivard et al. (2010a). These three interspecific tomato rootstocks are from similar breeding line s and tend to exhibit tolerance to RKN rather than resi stance when soil RKN population levels are high. RKN resistance is conferred by the Mi 1 gene that was introduced into commercial tomato rootstocks and cultivars from the wild tomato relative Solanum peruvianum L. (Lpez Prez et al
23 2006; Medi na Filho and Stevens, 1980). Lpez Prez et al. ( 2006) showed that Mi gene and exhibited tolerance to RKN ( M. incognita ) since RKN Mi gene res istance, retained yields Prez et al 2006). Our relatively were con sistent with the study by Lpez Prez et al. (2006). In the transitional field a significant reduction in root galling was also observed with the BW/BW treatment. The effect of self grafting on RKN resistance deserves further research. Nevertheless, there were generally lower root galling ratings with self grafted than nongrafted treatments for both scion cultivars in the organic and transitional fields. Fruit yield For the cultivar Flamme in 2010, the grafted plants produced significantly lower marketabl e yields than the nongrafted control for the first two harvests. However, there were no significant differences in total marketable yield for the Figures 2 1 A 2 2 A, and 2 3 A ). Reduced early yields may be an effect of the grafting process. Khah et al. (2006) reported greater early yields for nongrafted plants and hypothesized that the stress associated with grafting and healing delayed flowering in grafted plants. There were no significant differences in marketable yiel Figure 2 1 B ). In the organic and transitional fields. In the organic field the NGBW and BW/SU treatments produce d significantly higher total marketable yields than the BW/BW and
24 BW/MU treatments ( Figure 2 2 B). However in the transitional field BW/MU demonstrated significantly higher total marketable yields than the BW/BW and NGBW treatments (Fig ure 2 3 B ). The BW/ SU treatment resulted in statistically similar yields to Overall, t otal fruit yields showed trends similar to marketable fruit yields (data not shown). Some of these yield differences in 2011 ma y be attributed to the presenc e of RKN. With no RKN pressure in the 2010 trial, there were no differences in total marketable yield with either scion cultivar. However, with high RKN pressure in the 2011 transitional field, the highest marketable yield for were consistent with the study by Lpez Prez et al. (2006), in which significantly higher tomato fruit yield was observed with resistant rootstocks at high RKN ( M. incognita ) densities. According to Rivard et al. (2010a), t otal and marketable tomato fruit yield s were higher on interspecific hybrid rootstocks under severe RKN and s outhern blight disease pressure In contrast, grafting did not exhibit any significant effect on he irloom tomato yield under low disease pressure and it was unclear if grafting onto interspecific hybrid rootstocks would be beneficial in such circumstance s (Rivard et al., 2008) Lpez Prez et al. (2006) did not detect a yield response with plants graf ted onto resistant rootstocks at intermediate populations of RKN. In our study, NG BW and BW/SU preformed similarly at intermediate levels of RKN infestation in the 2011 organic field trial while BW/BW and BW/MU yielded significantly less marketable fruit. It is unclear why tomato yield was reduced for BW/MU since it showed significantly lower root galling ratings compared to NGBW and BW/BW, and did not differ significantly from
25 BW/SU in terms of RKN resistance. This response could be related to the genetic greenhouse rootstocks aimed at enhanced crop vigor and extended growing seasons in addition to disease resistance It could be that the increased vigor and vegetative growth t hat is useful in greenhouse conditions f ruit yield in the shorter field grown season. More studies are warranted to examine the influence of vigorous interspecific hybrid rootstocks on the yield of indeterminate cul tivars grown in field production systems. N ew rootstocks developed for open field production would help establish more integrated pest management techniques for growers not using greenhouses or high tunnels (Kubota et al., 2008). Scion rootstock in fluences were observed in this study. was susceptible to RKN, marketable fruit yields were not significantly affected by grafting with resistant rootstocks. This indicates that other factors, in addition to RKN infestation, may be involved in det ermining tomato yield It was noted that l One effect that occurred in 2011 but not in fruit diagnosed with the abiotic disorder graywall (W.M. St Graywall incidence was greater in the transitional field than in the organic field, which may have contributed to the overall reduction in marketable yield per plant observed in the transiti onal field trial in contrast to the organic field trial ( Figures 2 2 and 2 3 ). Graywall is a physiological disorder and its cause is unclear, but it can be reduced by adequate K (Olson, 2004). It was most severe in the field with the highest nematode
26 press ure, and it is unclear whether its increased incidence there could be attributed to adverse effects of RKN on nutrient and water uptake. Crop Vigor Rootstock effects were also observed in leaf area and above ground biomass evaluations. When grafted to th produced significantly more above ground biomass than NGBW, BW/BW, and BW/SU in both years (Table 2 2). Furthermore, BW/MU produced significantly greater leaf area 10. In the 2011 trial, the leaf area of BW/MU was greater than that of BW/BW and BW/SU but there was no significant performed For both years, FL/MU produced significantly greater leaf area than NGFL, FL/FL, and FL/SU. In 2011, above (Table 2 2). greenhouse (Di Gioia et al., 2010). The effect of the rootstock should be carefully examined when grafting is used for a specific growing condi tion. The interspecific hybrid growth. This is advantageous for greenhouse tomato production where season extension is strongly emphasized. However when used in the open field this increase in vegetative growth may not be beneficial. This is due to the shorter field production cycle in Florida where early yields are important to achieve the greatest profit. On the other
27 exhibited by this rootstock to high populations of RKN. Despite the presence of RKN in 2011, both yield and crop vigor for all treatments were greater in 2011 than those from 2010 ( Figures 2 1 2 2, and 2 3, Tables 2 1 and 2 2). The 2010 and 2011 growing seasons were different with regard to average temperature and rainfall. The 2010 growing season was 8. 74 C cooler and there was 27.6 cm more rain on average. The dr i er, more mild 2011 season may have been more favorabl e for growing irrigated tomatoes. Interest in vegetable grafting is growing in the United States therefore more research is n eeded to determine the rootstock effects on crop performance under site specific conditions and different production systems. With respect to controlling RKN, our studies indicated the interspecific hybrid rootstock tended to exhibit tolerance under severe RKN pressure to help improve the heirloom tomato yield. In fields with intermediate levels of RKN infestation, the intraspecific hybrid rootstock was more effective in reducing root gall s and maintaining fruit yield. Interestingly, there was a lack of a clear relationship between root galling and tomato yields. Scion rootstock interactions were revealed as reflected by the different ial response of the two heirloom tomato scions to the two rootstocks used. When assess ing whether or not to use grafted tomato plants for RKN management, g rowers need to consider the severity of the RKN infestation the growing system and the scion and ro otstock cultivars to be used.
28 Table 2 1. Effect of grafting treatments on root knot nematode galling ratings z of heirloom tomato cultivars Brandywine and Flamme y Treatment x Organic field Transitional field Brandywine NGBW 7.18 a 9.30 a BW/BW 5.86 a 7.30 b BW/MU 1.72 b 3.88 c BW/SU 0.28 b 0.54 d Flamme NGFL 6.02 a 8.06 a FL/FL 5.28 a 6.12 a FL/MU 0.52 b 3.48 b FL/SU 0.16 b 0.00 c z Root knot nematode galling index proposed by Zeck (1971), ratings for spring 2011. y Means separated with Fisher at same letter in each column indicates no significant difference; scion cultivars were analyzed separately. x
29 Table 2 2 Effect of grafting treatments on leaf area and above ground biomass of heirlo om tomato cultivars Brandywine and Flamme z 2010 2011 Leaf area y Biomass x Leaf area y Biomass x Treatment w (cm) (g/plant) (cm) (g/plant) Brandywine NGBW 314 5 b 17 7 b 13137 ab 349 ab BW/BW 292 6 b 171 b 11343 b 316 b BW/M U 554 9 a 23 9 a 18300 a 47 8 a BW/SU 264 9 b 15 9 b 9618 b 28 1 b Flamme NGFL 2420 b 172 a 687 5 b 248 b FL/FL 2358 b 168 a 8000 b 27 8 b FL/MU 3833 a 20 4 a 10460 a 38 3 a FL/SU 1729 b 16 5 a 692 8 b 271 b z same letter in each column indicates no significant difference; scion cultivars were analyzed separately. y Mean total leaf area per plant. x Mean total above ground dry weight per plant w
30 Figure 2 1. Cumulative marketab le yield for nongrafted and grafted heirloom tomato cultivar s Flamme (A) and Brandywine (B) from t he o rganic field trial conducted in 2010 Each harvest was analyzed using a one way analysis of rs represent the least significant difference grafted A B
31 Figure 2 2. Cumulative marketable yield for nongrafted and grafted heirloom tomato cultivar s Flamme (A) and Brandywine (B) from t he o rganic field trial conducted in 2011 Each harvest was a nalyzed using a one way analysis of represent the least significant difference grafted A B
32 Figure 2 3. Cumulative marketable yield for nongrafted and grafted heirloom tomato cultivar s Flamme (A) and Brandywine (B) from t he 2011 field trial designed to reflect growing conditions during a typical three year transition period from conventional to organic. Each harvest was analyzed using a one way analysis represent the least significant difference grafted A B
33 CHAPTER 3 FRUIT QUALITY AND SENSORY ATTRIBUT ES OF ORGANIC HEIRLO OM TOMATOES ARE NOT INF LUENCED BY GRAFTING Background Grafting is a horticultural technique primarily used to control soilborne pa thogens, provide relief from abiotic stressors, and improve crop productivity in Cucurbitaceous and Solanaceous vegetables. This technique may be especially intriguing for organic producers because it can be used to overcome soilborne pathogens for which t hey may have limited control options. Many recent studies have demonstrated the effectiveness of grafting for control ling root knot nematodes, bacterial wilt, fusarium wilt, and southern blight in the United States (Bausher, 2009; Kubota et al., 2008; Lope z Perez et al., 2006; Rivard and Louws, 2008; Rivard et al., 2010a). Grafting research and breeding efforts for both tomatoes and tomato rootstocks have traditionally focused on improving disease resistances and increasing yield rather than fruit quality (Lee, 1994; King et al., 2010; Klee, 2010; Rouphael et al., 2010). According to Klee (2010), consumers have noticed a decrease in fruit and vegetable flavors as breeding efforts have resulted in enhanced postharvest attributes and they are willing to pay m ore for produce with improved taste. With this increase in consumer interest for fruits and vegetables with superior flavor, more recent studies ha ve examined grafting effects on fruit quality (Di Gioia et al., 2010; Fernandez 2005). Many studies concerning grafting effects on fruit quality have reported varying results (Edelstein, 2004; Mar tnez Ballesta et al., 2008; Rouphael et al., 2010). carotene, glucose, fructose, and soluble solids in tomato fruit as a result of grafting have been demonstrated (Fernandez Garcia et al.,
34 2004; Oda et al., 1996). M eanwhile, some previous reports show ed no differences in soluble solids, pH, lycopene, and titratable acidity in fruit from grafted and nongrafted plants (Di Gioia et al., 2010; Khah et al., 2006; Romano and Paratore, 2001). Furthermore, reduced fruit conc entrations of vitamin C, soluble solids, total sugars, and lycopene due to grafting or rootstock influence were demonstrated (Di Gioia et al., 2010; To date, few studies have examined the effect of rootstocks on fruit quality and sensory attributes of heirloom tomatoes (Di Gioia et al. 2010). Without a clear unde rstanding of how grafting influences fruit nutritional content and sensory attributes, growers may be less likely to invest the extra cost associated with grafted transplants. This cost, as reported by Rivard et al. (2010b) could be 64% to 354% higher for grafted plants produced in the United States. U ncertainties regarding the effect of grafting on fruit quality and sensory attributes may be especially discouraging for heirloom tomato growers who market their fruit as having exceptional flavor and eating q uality Grafting may provide an effective management tool for growers to control soilborne pathogens and cope with environmental stressors However, if fruit quality is adversely affected as a result of grafting, growers may be less likely to adopt this t echnique. The purpose of this study was to examine fruit quality and sensory attributes of two distinctly different heirloom tomato cultivars grafted onto intra and inter specific hybrid rootstocks. These plants were grown on certified organic land in ord er to evaluate grafting as a viable tool for organic producers in Florida. Materials and Methods Grafted transplants Certified organic heirloom tomato seeds and non treated
35 heirlo style, open pollinated, indeterminate heirloom cultivar known for outstanding flavor. interspecific ( S. lycopersicum x S. habrochaites ) hybrid rootstock wh S. lycopersicum ) hybrid rootstock. Both rootstocks have vigorous growth habit and resistance to root knot nematodes ( Meloidogyne spp.). T he rootstock seeds were sown on 16 February 2010 and 11 February 2011, two days before scion seeds, as recommended by both rootstock seed companies. Sp eedling (Sun City, FL) 128 cell count flats and Fafard Organic Formula Custom potting mix (Apopka, FL) were used to grow the seedlings. Seedlings were tube grafted at the 4 5 true leaf stage. Grafting took place 34 d (2010) and 28 d (2011) after scions were sown. The grafting and healing protocol was adapted from Rivard and Louws (2006). The newly grafted seedlings were held together with 1.5 mm or 2.0 mm silicon clips (Hydro Garde ns, Colorado Springs, CO). After grafting, the seedlings were placed in a climate controlled walk in cooler at 25 C and ~95% RH without light for 24 hr. The seedlings were progressively exposed to increased light durations and reduced humidity for 6 d, un til the graft unions had healed. Healed grafted seedlings were relocated to a greenhouse to harden off for 5 d before transplanting. Field experiments Tomato seedlings were transplanted on 10 April 2010 and 2 April 2011. Both field experiments were arrang ed in a randomized complete block
36 design with five blocks. There were 12 plants per treatment in each block in 2010 and 15 plants per treatment in 2011. Both trials consisted of eight treatments: non grafted (NGBW, NGFL) and self grafted (BW/BW, FL/FL) con trols, and the grafted combinations (BW/MU, BW/SU, FL/MU, FL/SU). The plants were grown on raised beds with black plastic mulch and drip irrigation. Nature Safe 10N 0.9P 6.6K (Cold Spring, KY) Organic Materials Review Institute (OMRI) approved granular fer tilizer was applied prepl ant at a rate of 179 kg N/ h a (200 lb N / acre) 1.3P 0.8K (Gloucester, MA) OMRI approved fish and seaweed based, liquid fertilizer was injected into the drip system throughout the season to provide supplemental f ertilization. The stake and weave system common to Florida fresh market tomato production was utilized and plants were trellised to provide vertical support (Olson et al., 2011). Both field trials took place at the University of Florida Plant Science Rese arch and Education Unit in Citra, FL., in the spring of 2010 and 2011. The tomato plants were grown on certified organic land in compliance with the National Organic Program (U.S. Dept. Agr., 2002). The soil type in both fields was Candler sand, 0 to 5 per cent slopes, hyperthermic, uncoated Typic Quartzipsam m ents, with a pH of 6.0. There were four harvests in 2010 and six harvests in 2011. Consumer sensory analyses Consumer taste tests were conducted in 2010 and 2011 at the University of Florida s ensory l a b in Gainesville, FL Fruit were harvested at the breaker stage and allowed to ripen to maturity before analysis. In the 2010 study, tomato fruit from NGBW, BW/BW, BW/MU, and BW/SU were harvested on June 13 and stored at ambient temperature for 3 days prio r to the sensory evaluation. Fruit from both
37 FL/FL, FL/MU, and FL/SU were harvested on 8 June and analyzed on 14 June, while tomatoes from NGBW, BW/BW, BW/MU, and BW/FL were harv ested on 13 June and assessed on 17 June. Fruit from the five field blocks were pooled for each treatment to provide enough ripe fruit for >100 sensory analysis samples. Tomatoes were cut into cubes about 2.5 cm thick. Each serving sample consisted of 2 cu bes of tomato fruit. private booths, each containing a computer monitor, keyboard, and sliding window for presenting the sample to be tested. Sensory test ballot presentation and data collection is completed on the computers which are equipped with Compusense Five (Compusense, Guelph, Canad a). All procedures used were approved by the University of Florida Institutional Review Board. Passersby were recruited to serve as consumer panelists with signs placed near the sensory lab. Each panelist first checked in at the front desk, signed a volunt ary consent form, and was directed to a booth. The panelist then received instruction from the computer monitor to begin the sensory test. The sensory tests began with three demographic questions; gender, age, frequency of tomato consumption (Table 3 1). T overall acceptability, firmness, tomato flavor, and sweetness. The hedonic scale ranged from 1 9 (1 = dislike extremely, 2 = dislike very much, 3 = dislike moderately, 4 = dislike slightly, 5 = neither like nor dislike, 6 = like slightly, 7 = like moderately, 8 = like very much, 9 = like extremely). Between each of the four tomato samples, t he panelists were
38 the taste test, each panelist was compensated with their choice of a free soda or a coupon for food on campus. The order the tomato samples were p resented to each panelist was randomized. To reduce bias caused by the order in which the samples were presented, all possible orders were presented approximately an equal number of times. Following each sensory panel the data were collected from all compu ters and compiled. Fruit quality attributes Vitamin C, soluble solids content (SSC), pH, and total titratable acidity (TTA) were determined for tomato fruit from all 8 treatments harvested 13 June 2010 and 8 June 2011. Five ripe and representative fruit were blended for 30 s to form a homogenate for each treatment. This was replicated three times in both years. The homogenate was centrifuged for 20 min at 15,000 rpm and 5 C. Then the supernatant was filtered through 8 layer cheese cloth to obtain a clari fied extract. Vitamin C was measured using a PowerWave XS2 microplate spectrophotometer (BioTek, Winooski, VT) with absorbance at 540 nm (Terada et al., 1978). SSC was measured with an Abbe Mark II, digital refractometer (Reichert Technologies, Depew, NY). Initial pH was recorded and TTA was determined by potentiometric titration of 6 m L of tomato extract to an end point of pH = 8.2 with 0.1 N NaOH using a 719 S Titrino automatic titrator (Metrohm, Herisau, Switzerland). Statistical analyses Al l data were analyzed using a one way analysis of variance sensory test data were collected and analyzed using the Compusense Five software used for data collection and analysis by the Univ ersity of Florida Sensory lab. The fruit
39 quality data were analyzed using the GLM procedure of SAS version 9.2 (SAS Institute, Cary, NC). Results and Discussion Consumer sensory analyses In 2010 the consumers perceived taste differences significant differences regarding overall appearance, overall acceptability, and tomato flavor. For the overall appearance and tomato flavor attributes, NGBW was rated significantly high er than BW/SU (Table 3 2). NGBW was rated significantly higher than BW/MU and BW/SU for the overall acceptability attribute. BW/BW was rated similarly to all other treatments for all taste attributes. In 2010 it appeared that the rootstock might have had a consistent negative effect on taste however, this trend did significant differences were observed for the measured sensory analysis attributes. These results are consistent with those of Di Gioia et a l (2010) where it was demonstrated that grafting did not influence the sensory attributes sweetness, sourness, and tomato fted onto interspecific hybrid rootstock cultivars Beaufort and Maxifort which were produced from a similar breeding line as the rootstock Mulifort used in this study. Tomato flavor is a complex balance of sugar and acid contents with aroma volatiles (K rumbein and Auerswald, 1998). Cultural practices and environmental conditions during fruit development can affect the ratios of flavor compounds in the fruit. Harvest maturity also has a major influence on flavor in climacteric fruits like tomatoes (Matthe is and Fellman, 1999). Environmental conditions were more amicable and yields
40 were much greater in 2011 compared to 2010 (data not shown). As a result, more fruit were available at similar stages of maturity in the 2011 study and no differences in sensory attributes were observed One possible explanation for the differences detected in 2010 may be that with fewer fruit to choose from, there was more variability in fruit maturity. When a tomato is picked before reaching maturity and ripened off the vine, th flavor than tomatoes ripened on the vine (Kader et al., 1977). Grafting may also affect the maturity of fruit at harvest. Grafted plants can delay early harvests compared to no ngrafted plants because they may be less developmentally mature due to the grafting and healing processes (Khah et al., 2006; Lee et al., 2010). Khah et al. (2006) show ed that there were no significant differences in the number of flowers per plant later i n the growing season. In our studies fruits from the second and third harvests were used in order to reduce the variability of fruit maturity between grafted and nongrafted treatments. Fruit quality Vitamin C, SSC, pH, and TTA were measured in 2010 and 20 11. No significant differences between treatments were found in 3 3). This was expected as previous studies reported few consistent effects of grafting or rootstock on nutritional quality attributes of tomato es. Khah et al. (2006) demonstrated that pH, Brix, lycopene content and firmness were unaffected tomato rootstocks. Similarly, Di Gioia et al. (2010) showed that total so luble solids and total titratable acidity were not significantly influenced by grafting heirloom tomatoes onto interspecific hybrid rootstocks. Rouphael et al. (2010) pointed out that grafted fruit
41 quality attributes may be dependent on the selection of sc ion, rootstock, and growing environment. It has been suggested that grafting can have a positive impact on tomato fruit quality (Martnez Ballesta et al., 2008). Meanwhile, it has also been indicated that grafting could affect tomato fruit quality negativ ely (Edelstein, 2004). Scion and rootstock combinations can even perform al., 2009). There are many possible scion rootstock combinations and growing environments. Clearly, more of these scenarios will need to be examined before researchers fully understand the impact of grafting with different rootstocks on fruit quality attributes. These studies will need to assess specific rootstocks for specific growing conditions in a variety of regions Heirloom tomato fr uit are desired for their exceptional flavor s colors, and unique shapes. Overall, neither grafting nor rootstock demonstrated a prominent effect on sensory attributes and other fruit qualit y measurements tomato fruit in the pr esent study. Nevertheless, growers interested in using grafted plants need to be aware that scion rootstock interactions are still not fully understood. It is suggested that different grafting combinations be evaluated under site specific conditions before selecting appropriate rootstocks and incorporating this technique on a large scale.
42 Table 3 1. Consumer demographic information. Percent of Percent of Percent of Characteristic Category 75 consumers z 75 consumers y 69 consumers x Gender Male 51 52 54 Female 49 48 46 Age Under 18 0 1 3 18 29 80 79 74 30 44 15 13 14 45 65 4 7 9 Over 65 1 0 0 Tomato consumption frequenc y More than once a week 52 32 49 Once a week 26 25 20 More than once a month 17 27 16 Once a month 5 13 10 Never 0 3 5 z y 75 consumers participated in the taste test x 69
43 Table 3 2. Effect of grafting treatments on heirloom tomato fruit sensory attributes z for scion cultivars Brandywine and Flamme. Treatment Appearance Acceptability Firmness Tomato flavor Sweetness y NGBW 6.39 a 6.76 a 6.45 6.61 a 6.19 BW/BW 6.31 ab 6.23 ab 6.05 6.23 ab 5.91 BW/MU 6.05 ab 6.20 b 6.49 5.97 ab 5.77 BW/SU 5.76 b 6.11 b 6.21 5.96 b 5.80 P value w 0.02 0.01 0.21 0.03 0.25 x NGBW 6.30 6.16 6.26 6.12 5.59 BW/BW 6.12 6.35 6.41 6.29 6.07 BW/MU 6.39 6.01 6.10 5.88 5.71 BW/SU 6.48 6.29 6.17 6.36 6. 10 P value w 0.50 0.42 0.57 0.20 0.09 y NGFL 6.11 6.19 5.93 6.27 a 5.80 FL/FL 6.01 5.69 5.99 5.67 a b 5.29 FL/MU 5.79 5.72 5.61 5.73 a b 5.52 FL/SU 5.91 5.83 5.87 5.63 b 5.49 P value w 0.54 0 .09 0.38 0.03 0.20 z Sensory attribute ratings from hedonic scale with values 1 9 (1 = dislike extremely, 9 = = 0.05 same letter in each column indicates no significant difference; scion cultivars were analyzed separately and by year. y 75 participants x 69 participants w P
44 Table 3 3 Effect of grafting treatmen ts on heirloom tomato fruit quality attributes z for scion cultivars Brandywine and Flamme. Treatment Vitamin C y (mg AA/100 g fw) Soluble solids content (Brix) pH Total t itratable a cidity (% Citric acid) 2010 NGBW 26.78 3.47 4.33 0.32 B W/BW 25.27 3.20 4.29 0.38 BW/MU 24.85 2.40 4.31 0.34 BW/SU 25.75 3.37 4.26 0.43 P value x 0.19 0.10 0.22 0.60 NGFL 28.20 3.87 4.33 0.46 FL/FL 27.59 3.67 4.34 0.52 FL/MU 25.96 3.73 4.31 0.51 FL/SU 29.07 3.97 4.35 0.47 P value x 0.26 0.84 0.09 0.06 2011 NGBW 32.33 4.93 4.45 0.32 BW/BW 31.47 4.93 4.47 0.33 BW/MU 30.79 4.97 4.44 0.31 BW/SU 30.06 4.80 4.47 0.29 P value x 0.33 0.45 0.74 0.13 NGFL 35.90 4.97 4.32 0.35 FL/FL 35.15 4.90 4.30 0.37 FL/MU 35 .29 4.83 4.34 0.34 FL/SU 34.83 4.93 4.33 0.36 P value x 0.11 0.61 0.50 0.10 z Quality attributes measured from five randomly selected fruit per treatment with three replications, scion cultivars were analyzed separately and by year. y Vitamin C content r eported as m g of ascorbic acid per 100 g fresh weight. x P
45 CHAPTER 4 COST BE NEFIT ANALYSIS OF US ING GRAFTED TRANSPLANTS FOR ROOT KNOT NEMATODE MANAGEMENT IN ORGANIC HEIRLOOM TOMATO PRODUCTION Background Veg etable grafting is popular in Asian and European countries where continuous cropping and intensive production is practiced. This technique offers resistance/tolerance to biotic and abiotic stressors in a variety of cucurbit aceous and solanaceous crops (Kub ota et al., 2008; Lee et al., 2010; Lpez Prez et al., 2006; Louws et al., 2010; Rivard et al., 2010a; Venema et al., 2008). In the United States, vegetable grafting is gain ing in importance because of the phase out of soil fumigation with methyl bromide (King et al., 2008; Rivard et al. 2010b). King et al. (2008) pointed out that because the price of methyl bromide is increasing and the price of grafted plants is decreasing, grafting may be an economically viable method of disease control in the United S tates. The continued increase in demand for foods produced organically may also have helped fuel the interest in vegetable grafting in the United States (Greene et al. 2009; Kubota et al., 2008; Lee et al., 2010; Rivard et al., 2010b). For instance, o rga nic growers have tried grafting to control root knot nematodes (RKN) (Kubota et al., 2008) which are a major problem in the sandy soils common to Florida (Roberts et al., 2005) RKN resistant tomato rootstocks have been shown to reduce RKN galling and main tain yields both in the United States (Bausher, 2009; Rivard et al., 2010b) and elsewhere (Louws et al., 2010; Verdejo Lucas and Sorribas, 2008). However, grafting in the United States has not yet reached its full potential as a control for soilborne patho gens. It has been estimated that 40 million grafted vegetable transplants are currently used in the U.S. every year. Most of these plants are produced in Canada and are used
46 by major greenhouse tomato producers for season extension and increased crop vigo r (Kubota et al., 2008). In contrast, it has been estimated that over 2 00 million grafted tomato transplants are used annually in Japan and Korea combined for improved crop production and relief from soilborne pathogens, temperature extremes, and excess sa lts (Lee et al., 2010). Grafting in the United States is expected to expand greatly in the coming years as more uses are realized, high quality transplants become more available, and prices for grafted transplants are reduced ( King et al., 200 8 ; Kubota, 20 08; Lee et al., 2010 ). High labor costs and low return per plant have been suggested as barriers to adoption of grafted vegetable production in the United States (Rivard et al., 2010b). Lee et al. (2010) reported prices of grafted transplants between $0.4 0 and $1.20 for various crops. Grafted tomato transplants can cost between $0.60 and $0.90 per transplant without factoring in seed costs (Kubota et al., 2008). Although interest in this technique is on the rise, there has been little reported on the price of grafted transplants for vegetable production in the United States (Rivard et al. 2010b). The price of domestic grafted tomato plants has been estimated by Rivard et al. (2010b) as between $0.59 (on farm, organic) and $1.88 (retail, twin leader) in two different transplant production facilities. However to our knowledge, there have been few studies examining both the cost of grafted tomato transplants and their expected return. This information could help growers in the United States decide if the extra cost of grafted transplants could be justified by increased output or by the reduction of production inputs when using grafting to overcome soilborne diseases
47 Florida growers and transplant producers interested in vegetable grafting need information base d on local production systems. The purpose of this study was to determine the cost of producing grafted heirloom tomato transplants on farm and estimate the economic return with expected yields for organic growers interested in implementing this technique. Sensitivity analyses were performed to assess the economic feasibility of growing grafted heirloom tomatoes. These analyses were created using fruit yield information from field trials of heirloom tomatoes grown under different levels of RKN infestation. Materials and M ethods Transplant production Certified organic scion seeds and untreated rootstock seed s were used to produce transplants in accordance to the rules outlined by the National Organic Program (U.S. Dept. Agr., 2002). The heirloom tomato cult ivar Brandywine (Tomato Fest, Little River, CA) was used for the scion and nongrafted interspecific hybrid rootstock cultivar Multifort (De Ruiter Seeds, Bergschenhoek, The Net chosen for its vigor and resistance to soilborne pathogens including RKN. To provide seedlings with similar stem diameter for grafting, rootstock seeds were sowed 2 d pr ior to sowing the scion seeds. Grafting occurred 34 d (2010) and 28 d (2011) after the scion seeds were sowed. Seedlings were splice grafted at the 3 5 leaf stage. A 1.5 mm or 2.0 mm silicon grafting clip (Hydro Gardens, Colorado Springs, CO) was used to h old the grafted scion and rootstock together. Grafted seedlings were healed in a climate controlled walk in cooler at 95% relative humidity, 25 C, and without light for 24 hr. Relative humidity was reduced and li ght exposure was increased for 6 d
48 followin g grafting until the grafted transplants were healed. The transplants were then hardened off in the greenhouse for 3 d before transplanting into the field. Grafting and healing procedures were adapted from Rivard and Louws (2006). Nongrafted transplants we re grown in the greenhouse until transplanting into the field. Transplanting took place on 10 April 2010 and 2 April 201 1 Field trials An organic field trial was conducted in 2010 and repeated in 2011. A transitional organic field trial was also conducte d in 2011 at a site with a history of nematode infestation. This trial was designed to resemble a field in the 3 year transition to organic. A randomized completed block design with 5 replications (blocks) was used for all three field trials. Each trial co nsisted of three treatments: nongrafted BW (NGBW), self grafted BW (BW/BW) and BW grafted onto MU (BW/MU). All field trials were conducted at the University of Florida Plant Science Research and Education Unit (PSREU) in Citra, FL. The soil type was Candl er sand, 0 to 5 percent slopes, hyperthermic, uncoated Typic Quartzipsamments and had a pH of 6.0. Tomato harvests for the organic fields took place on 7, 13, 17, and 25 June 2010, and 4, 8, 13, 16, 22, and 28 June 2011. The transitional field was harvest ed on 4, 8, 13, 16, and 23 June 2011. All tomatoes were graded using grower standards for marketability. Fruit that were not marketable were culled according to their defect (e g. blossom end rot, cat facing, splitting, etc.) After grading, all fruit wer e counted and weighed. At the completion of each trial, the roots of five plants per treatment in each block in the organic fields and three plants per treatment in each block in the transitional field were assessed for nematode galls. Both years, the root gall rating scheme proposed by Zeck (1971) was used to estimate nematode infestation levels on plant root systems. This
49 scale is organized from 0 10 (0 = no galling, 10 = plant and roots are dead). Three researchers assessed each plant individually and th en the ratings were averaged for each plant. The plant ratings were then averaged for each treatment in each block (five plants per plot in the organic field s ; three plants per plot in the transitional field). Economic a nalyses Sources and prices for mate rials and labor used to perform the partial budget analysis were identified for estimating the cost of producing grafted heirloom tomato transplants (Table 4 1). A detailed partial budget analysis was conducted using data acquired during this grafted heirl oom tomato study. All phases of grafted and nongrafted transplant production were recorded to provide accurate estimates for labor, materials, and total transplant production costs. Production costs were based on a target of 1,000 grafted and nongrafted tr ansplants. The 2011 average wage for an entry level agricultural worker in the state of Florida was $8.45/h (State of Florida, Agency for workforce innovation, 2011). This wage was used for all labor calculations. The cost of BW seed for the nongrafted tra nsplants reflected the over seeded rate of 10% (1,100 seeds) to account for 90 % germination. Scion and rootstock seed costs for the grafted transplants reflected the over seeded rate of 25% (1,250 seeds each) to account for 90 % germination and 90% grafting success. The cost of one grafted vs. nongrafted transplant was then calculated from the total cost of production for 1,000 transplants. Healing chamber labor and material estimates were based on experience gained at the University of Florida, and reflecte d the most practical option for local growers and grafters. Because t he walk in cooler used in t his study for healing the grafted transplants may be conveniently substituted by a simpler structure, the healing chamber
50 cost was estimated based on a modified system that could be easily constructed. Hence, this economic analysis did not include the price of grafted transplants produced using a commercial walk in cooler as healing chamber Sensitivity analyses were conducted to compare partial net returns for g rafted and nongrafted plants grown under organic and transitioning to organic growing conditions. These partial net returns per plant were calculated by subtracting the cost of the transplant from the estimated return and do not account for other productio n costs (e.g. transplanting labor, field preparation, mulch, fertilizer, etc.). Sensitivity analyses were carried out using the mean yield per plant 3 standard errors and a range of average price per pound received for organic heirloom tomato fruit. The mean yield per plant and standard error for nongrafted and grafted plants were estimated from the analyses of yield data from the 2010 and 2011 field trials using the GLIMMIX procedure in SAS 9.2 (SAS institute, Cary, NC). According to the data provided by the UF/IFAS Florida Automated Weather Network (F. A.W .N.) for Citra, FL, the spring 2010 growing season ( February July) was 15.7 F (8.74 C) colder and had 10. 9 inches (27.6 cm) more rainf a ll compared to the spring of 2011. Overall, the 2011 spring se ason was a much more mild and dry growing season and was more favorable for growing tomatoes. The tomato yield data used to construct the grafted and nongrafted analyses for the organic field were pooled from 2010 and 2011 to form a more representative dat a set. The range of prices per pound used for the sensitivity analyses were derived from the monthly average price of a 10 lb carton of organic heirloom tomatoes as published by the United States Department of Agriculture from 2008 (U.S. Dept. Agr., 2009)
51 Results and D iscussion Transplant cost analyses Sources and prices for materials used in production of grafted and nongrafted heirloom tomato transplants are shown in Table 4 1. Grafted transplants required more materials, seeds, and labor and were more expensive to produce than nongrafted plants. In this study, grafted transplants cost $0.78 per plant while nongrafted transplants cost $0.17 per plant (Table 4 2). Our results are consistent with the report by Rivard et al. (2010b) that estimated $0.59 pe r grafted plant and $0.13 per nongrafted plant for organically produced tomato transplants The reason grafted transplant prices were higher than nongrafted in the present study was similar to that stated by Rivard et al. (2010b). The bulk of this price di fference is associated with the price of the rootstock seeds. In the present study, t he rootstock seed cost accounted for 36% of the total cost of the grafted transplants and 46% of the cost difference between grafted and nongrafted trans plants I t has bee n suggested that high labor costs could be a major barrier to adoption of grafted vegetable production (Kubota et al., 2008; Rivard et al., 2010b). However, labor costs were not considered a major contributor to grafted transplant cost and accounted for 15 % of the cost difference between grafted and nongrafted transplants Over all, grafting added $0.61 per transplant to the cost of production. This is similar to the $0.60 to $0.90 (excluding seed cost) per grafted transplant price reported by Kubota et al. (2008). Our results were also consistent with the per transplant price increase of $0.46 in North Carolina and $0.74 in Pennsylvania for grafted tomato production as reported by Rivard et al. (2010b). The cost of building an inexpensive but effective heal ing chamber was considered in the cost estimation of grafted transplants instead of the walk in cooler that was actually used since a walk in cooler may not be
52 available to some growers. However, it should be noted that using a walk in cooler as a healing chamber may help reduce the cost of producing grafted transplants on farm when one is available. The reduction in cost would be accomplished by avoiding the cost of building a healing chamber. Many growers have walk in coolers and grafted vegetable product ion typically takes place prior to the start of the season during what may be considered a down time for walk in cooler use. Lowering the cost of grafted transplants and rootstock seeds could increase adoption by growers in the United States. The price re duction of grafted transplants may be more important for commercial producers who rely on propagators to supply large quantities of high quality trans plants. Meanwhile, a decrease in rootstock seed cost may be more important for small scale growers who may be more interested in producing grafted seedlings on site. Sensitivity analyses Sensitivity analyses are useful for systematically estimating changes in variables in an economic model. In the present study, we use d sensitivity analyses to estimate the re turn per plant of grafted and nongrafted plants with varying yields and prices per pound of tomatoes. Sensitivity analyses were developed to compare grafted transplant cost and economic returns associated with expected yields. Excluding the extra cost of g rafted transplants, overall production costs would be similar whether grafted or nongrafted transplants were used. Comparisons were made between plants grown in a field with relatively low RKN infestations and plants grown in a field with high RKN infestat ions to assess the economic feasibility of using grafted transplants for RKN control.
53 This study focus ed on organic heirloom tomato production because of the unique opportunity for vegetable grafting to be adopted by these typically smaller growers. Heirlo om tomatoes often command a higher market price than regular fresh market tomato es Organic produce also c ommand s a higher price at market therefore; organic heirloom tomatoes offer a niche market with price premiums that afford more opportunity for grower s to experiment with grafted transplants. This is especially true when using grafted transplants with high resistance/tolerance to soilborne diseases for yield improvement in fields with a history of soilborne disease. Root knot nematode galling was not o bserved during the organic field trial conducted in 2010. There was root galling in the 2011 organic field trial but the lower galling ratings for grafted plants did not result in increased yield as compared to nongrafted plants. The 2010 and 2011 growing seasons were also very d ifferent with respect to climatic conditions The 2010 growing season was 8.74 C cooler and had 27.6 cm more rain on average. Yield data from the organic fields were pooled from the two seasons to provide a representative estimate for an average year. The results of the sensitivity analyses presented in Table s 4 3 and 4 4 were representative of expected yields for grafted and nongrafted heirloom tomato plants grown in an organic field with relatively low RKN pressure. NGBW plants p roduced a mean marketable yield of 1.8 lbs per plant and at that yield for the lowest tomato price per pound ( $1.80 ) the estimated partial net return was $3.07 per plant. This was $1.49 more than the estimated partial net return for the mean marketable yie ld of BW/MU at 1.31 lbs per plant at the same price of $1.80 per pound. This comparison demonstrates that grafting may not be economically feasible when applied to fields with low RKN
54 pressure and insignificant yield improvement as a result of grafting Ta ylor et al. (2008) came to a similar conclusion that farmers growing seedless watermelons should not consider using grafted plants if fusarium wilt ( Fusarium oxysporum ) is not an issue. On the other hand, grafting may be a cost effective practice under hig h disease pressure. on a farm in North Carolina as a result of soilborne diseases (as cited in Rivard et al. 2010 b ). In this case, implementation of grafted plants allowed the grower to maintain or ganic tomato fruit yields and remain profitable where it was previously not possible. Table s 4 5 and 4 6 show ed the sensitivity analysis results based on expected yields for nongrafted and grafted plants grown in a research plot representing a field under transition to organic with high RKN pressure. The NGBW plants in this transitional field trial had a mean marketable yield of 0.35 lbs per plant with an expected partial net return of $0.46 per plant when paid $1.80 per pound of heirloom tomato fruit. The mean marketable yield of BW/MU plants was 1.44 lbs per plant which was 76% higher than that of NGBW. The expected partial net return per plant for BW/MU was $1.82 when paid $1.80 per pound. This represents a $1.36 per plant difference between the grafted a nd nongrafted estimated partial net return in the transitional field. The $1.82 expected partial return per plant for BW/MU was lower than the $3.07 for nongrafted plants under low disease pressure. However, when high levels of RKN infestation occurred, th e grafted plants demonstrated great potential for ma intaining fruit yield and reducing economic crop loss es These findings suggest that grafting could be an economically feasible approach to controlling RKN in heirloom tomato production in organic and tr ansitional organic
55 systems with severe RKN pressure. Grafting could be critical for growers in the transition process from conventional to organic farming systems with high populations of soilborne pathogens such as nematodes Many of the pest control stra tegies employed in organic or alternative cropping systems can take multiple seasons to have a beneficial effect (McSorley, 2002) whereas, grafting effects are immediate. Resistant rootstocks can also reduce field infestation levels for following crops and provide a non host root system in a crop rotation. Grafting may also reduce the need for expensive fumigants in conventional farming systems thereby reducing input costs. This study focused on the use of grafting to contro l RKN in addition, grafting has been used successfully in the United States for managing bacterial wilt, fusarium wilt (Rivard and Louws, 2008), as well as southern blight (Rivard et al., 2010a). As the demand for organically produced fruits and vegetables continues to rise, more organic farmers will need effective soilborne disease control methods. Grafting is an effective tool for soilborne disease management that carries economic considerations with it. A grower must understand the benefits and limitations associated with grafting and only use this technique when appropriate. Our findings suggest the use of grafted plants in fields with a history of high soilborne disease pressure. This research focused on organic heirloom tomato production to demonstrate a scenario in which grafting co uld provide the most benefit. Actual production costs for individual farmers will vary and for that reason only transplant costs were included in our cost benefit analyses T h is study w as designed to provide a base line reference for growers interested in producing and using grafted transplants on farm. Yields and production costs can be estimated from grower experience and used in conjunction with the
56 analyses presented in this study to make a decision of whether or not to implement grafting on their farms Further work should examine local production methods and costs to provide accurate information for growers in diverse environments. Grafting shows many promising applications and a better understanding of the economic risks involved might help promote ad option of this useful technique. More rootstocks should be developed for open field production which in Florida is typically associated with short, wet, and hot seasons The season extension capability of many greenhouse rootstock varieties may be restrict ive for field production. Early harvests may be more important to open field tomato growers to capture highest market prices. It is expected that more growers in the United States will consider using grafted transplants for soilborne disease control in th e near future (King et al. 200 8 ; Kubota, 2008; Lee et al. 2010). Researchers, extension agents, and growers will need to work together to ensure that rootstocks suited for open field conditions and the appropriate scion rootstock combinations are used to optimize the benefits of this technique. The economic viability of grafted vegetable production will ultimately depend on farmers to know their soilborne disease incidence on site and choose the right rootstock and scion to meet their needs. Heirloom vege tables do not yield as much as hybrid vegetables (Bland 2005 ) O rganic farmers may get a higher return per plant through the use of hybrids rather than heirlooms and this must be weighed against the loss of the heirloom premium market price.
57 Table 4 1 Sources and prices for materials used to produce grafted and nongrafted heirloom tomato transplants. Price z Lifespan y Item Description Unit ($/unit) (years) Source Seedling materials Nongrafted /scion 30 seeds 1.18 TomatoFest, Little River, CA Rootstock 250 seeds 57.00 Paramount Seeds, Palm City, Florida Fafard custom organic mix Potting soil 40 quart bag 9.50 BWI, Apopka, FL Speedling 128 cell planter flats Styrofoam seedling tray 5 flats 34.70 5 Speedling, I nc., Sun City, FL Liquid organic fertilizer 1 gallon 45.50 Gloucester, MA Grafting Supplies 2.0 mm clip s Silicone grafting clip s 1000 clips 42.00 Hydro Gardens, Colorado Springs, CO Razor blades, hand sanitiz er, paper towels, etc Tools for grafting Per 1250 grafted plants 8.00 Local/regional department store Healing Chamber Supplies Cool mist humidifier Maintains humidity Per chamber 25.00 5 Local/regional department store Air conditioner Window un it Per chamber 159.00 5 Local/regional hardware store Wood, PVC pipe, plastic sheeting, etc Frame and covering for chamber Per chamber 26.86 5 Local/regional hardware store z Based on fall 2011 prices y Expected years of use, a straight line depreci ation was applied for the number of years indicated
58 Table 4 2. Costs of grafted and nongrafted organic heirloom tomato transplants. z Grafted y Nongrafted x Labor w Material Labor Materi al Item $/1000 plants $/1000 plants Seeds v 49.56 43.66 u 285.00 Seedling Potting soil 19.00 9.50 production Flats t 27.76 12.49 Seed sowing and care 92.95 59.15 Liquid fertilizer 91.00 45.50 Grafted transplant Grafting s 52.81 production Silicon clips 56.70 Miscellaneous supplies 8.00 Post graft care 21.13 Healing chamber r Humidifier 5.49 Air conditioner 31.80 Building supplies 26.86 Assembly 16.90 Subtotal 183.79 601.17 59. 15 111.15 Total 784.96 170.30 Cost/plant 0.78 0.17 z Estimate of costs based on fall 2011 prices for a target 1,000 grafted transplants y Seeds over sowed by 25% to account for 90 % graft success and 90% germination x Seeds over sowed by 10% to a ccount for 90 % germination w $8.45/hr pay wage for all labor v Indeterminate heirloom tomato cultivar, certified organic seed u Interspecific hybrid rootstock t 128 cell count transplant flats, straight line depreciated for 5 years estimated use s 200 plants/grafter/h graft rate r Straight line depreciated for 5 years estimated use
59 Table 4 3. Estimated partial z net return per plant ($/plant) for nongrafted y plants grown organically with low root knot nematode pressure x z Matrix values represent [ (yield*$/lb) transplant cost]. Other production, harve st, and packing costs (e.g. land preparation, drip tape, mulch, fertilizer, pest control, labor, etc.) must be factored in to achieve a full net return per plant y susce ptible to root knot nematodes x Root knot nematode pressure was assessed by root galling ratings (Zeck, 1971) w Yields presented were the estimated mean yield 3 standard errors, the estimated mean yield was based on pooled data from the 2010 and 2011 o rganic field trials v Prices per pound were calculated from published 2008 monthly averages for 10 lb cartons of organic heirloom tomato fruit (USDA, 2009) 1 lb = 0.454 kg Standard error Yield w (lbs/plant) Tomato price v ($/lb) 1.80 2.00 2.20 2.40 2.60 2.80 3.00 3.20 3 1.39 2.33 2.61 2.89 3.17 3.45 3.72 4.00 4.28 2 1.53 2.58 2.88 3.19 3.49 3.80 4.10 4.41 4.72 1 1.66 2.82 3.16 3.49 3.82 4.15 4.49 4.82 5.15 Mean 1.80 3.07 3.43 3.79 4.15 4.51 4.87 5.23 5.59 +1 1.93 3.31 3.70 4.09 4.47 4.86 5.25 5.63 6.02 +2 2.07 3.56 3.97 4.39 4.80 5.21 5.63 6.04 6.46 +3 2.21 3.80 4.24 4.68 5.13 5.57 6.01 6.45 6.89
60 Table 4 4. Estimated partial z net return per plant ($/plant) for y x grown organically with low nematode pressure w Standard error Yield v (lbs/plant) Tomato price u ($/lb) 1.80 2.00 2.20 2.40 2.60 2.80 3.00 3.20 3 0.90 0.85 1.03 1.21 1.39 1.57 1.75 1.93 2.11 2 1.04 1 .09 1.30 1.51 1.71 1.92 2.13 2.34 2.54 1 1.17 1.33 1.57 1.80 2.04 2.27 2.51 2.74 2.98 Mean 1.31 1.58 1.84 2.10 2.37 2.63 2.89 3.15 3.41 +1 1.45 1.82 2.11 2.40 2.69 2.98 3.27 3.56 3.85 +2 1.58 2.07 2.39 2.70 3.02 3.34 3.65 3.97 4.29 +3 1.72 2.31 2.66 3.00 3.35 3.69 4.03 4.38 4.72 z Matrix values represent [(yield*$/lb) transplant cost] Other production, harvest, and packing costs (e.g. land preparation, drip tape, mulch, fertilizer, pest control, labor, etc.) must be factored in to achieve a full n et return per plant y oom, beefsteak tomato cultivar. x knot nematodes and vigorous habit w Root knot nematode pressure was ass essed by root galling ratings (Zeck, 1971) v Yields presented were the estimated mean yield 3 standard errors, the estimated mean yield was based on pooled data from the 2010 and 2011 organic field trials u Prices per pound were calculated from publish ed 2008 monthly averages for 10 lb cartons of organic heirloom tomato fruit (USDA, 2009) 1 lb = 0.454 kg
61 Table 4 5. Estimated partial z net return per plant ($/plant) for y plants grown in a transitional organic field with high nematode pressure x Standard error Yield w (lbs/plant) Tomato price v ($/lb) 1.80 2.00 2.20 2.40 2.60 2.80 3.00 3.20 3 0.25 0.63 0.68 0.73 0.78 0.83 0.88 0.93 0.98 2 0.05 0.27 0.28 0.29 0.30 0.31 0.32 0.33 0.34 1 0.15 0.10 0. 13 0.15 0.18 0.21 0.24 0.27 0.30 Mean 0.35 0.46 0.53 0.60 0.67 0.74 0.81 0.87 0.94 +1 0.55 0.82 0.93 1.04 1.15 1.26 1.37 1.48 1.59 +2 0.75 1.18 1.33 1.48 1.63 1.78 1.93 2.08 2.23 +3 0.95 1.54 1.73 1.92 2.11 2.30 2.49 2.68 2.87 z Matrix values represen t [(yield*$/lb) transplant cost] Other production, harvest, and packing costs (e.g. land preparation, drip tape, mulch, fertilizer, pest control, labor, etc.) must be factored in to achieve a full net return per plant y erminate, heirloom, beefsteak tomato cultivar that is susceptible to root knot nematodes x Root knot nematode pressure was assessed by root galling ratings (Zeck, 1971), high root galling ratings in the transitional organic field indicated a severe nemato de infestation w Y ields presented were the estimated mean yield 3 standard errors, the estimated mean yield was based on data from the 2011 transitional organic field trial v Prices per pound were calculated from published 2008 monthly averages for 10 lb cartons of organic heirloom tomato fruit (USDA, 2009) 1 lb = 0.454 kg
62 Table 4 6. Estimated partial z net return per plant ($/plant) for y x grown in a transitional organic field with hi gh nematode pressure w Standard error Yield v (lbs/plant) Tomato price u ($/lb) 1.80 2.00 2.20 2.40 2.60 2.80 3.00 3.20 3 0.84 0.73 0.90 1.07 1.24 1.41 1.58 1.74 1.91 2 1.04 1.10 1.30 1.51 1.72 1.93 2.14 2.35 2.56 1 1.24 1.46 1.71 1.96 2.20 2.45 2.7 0 2.95 3.20 Mean 1.44 1.82 2.11 2.40 2.69 2.97 3.26 3.55 3.84 +1 1.64 2.18 2.51 2.84 3.17 3.50 3.83 4.15 4.48 +2 1.85 2.54 2.91 3.28 3.65 4.02 4.39 4.76 5.13 +3 2.05 2.90 3.31 3.72 4.13 4.54 4.95 5.36 5.77 z Matrix values represent [(yield*$/lb) tra nsplant cost] Other production, harvest, and packing costs (e.g. land preparation, drip tape, mulch, fertilizer, pest control, labor, etc.) must be factored in to achieve a full net return per plant y eefsteak tomato cultivar x knot nematodes and vigorous habit w Root knot nematode pressure was assessed by root galling ratings (Zeck, 1971), high root galling ratings in the transitional organic field indicated a severe nematode infestation v Y ields presented were the estimated mean yield 3 standard errors, the estimated mean yield was based on data from the 2011 transitional organic field trial. u Prices per pound were ca lculated from published 2008 monthly averages for 10 lb cartons of organic heirloom tomato fruit (USDA, 2009) 1 lb = 0.454 kg
63 CHAPTER 5 CONCLUSION Vegetable grafting is used successfully in intensive agricultural production systems throughout the wo rld. With the phase out of methyl bromide for soil fumigation, growers in the United States are searching for sustainable alternatives for pest management The steadily increasing demand for organic fruits and vegetables has also helped drive the need for new methods of controlling soilborne diseases that do not rely on synthetic chemicals. Interest in grafting is emerg ing in the United States but adoption has remained low. Growers are concerned that grafting will have a nega tive impact on crop performance and fruit quality. More importantly the higher cost of grafted transplants has presented a major barrier that has prevented a more wide spread adoption of this technique. Growers need to know how the extra costs associated with using grafted plants will b e recovered and what effects grafting will have on fruit attributes before they consider it economically feasible This research demonstrated that through the use of appropriate rootstocks, grafting can be used to successfully overcome the root knot nemat ode species Meloidogyne javanica in organic production of heirloom tomatoes in the open field. Yield was generally unaffected by grafting treatments under low nematode pressure. However, tomato yields were maintained by using a nematode resistant interspec ific hybrid rootstock under severe nematode pressure as compared to nongrafted plant s Given that nematode infestations can be particularly severe during the transition to organic production, grafting may play an effective role in pest management in the tr ansition process. To address concerns with regard to a possible rootstock effect on fruit quality and sensory attributes, fruit asses s ments and consumer taste tests were
64 conducted. The rootstocks used in this study showed no consistent e ffect on fruit qual ity attributes including fruit taste. A partial budget analysis was performed to determine the cost of producing grafted toma to transplants on farm. The major contributor to the cost of grafted transplants in this study was the price of rootstock seeds. In time, the price of rootstock seeds should drop as more rootstocks are developed for United States producers, making grafting more affordable. Finally, sensitivity analyses were performed to estimate expected partial returns for grafted and nongrafted plan ts grown under high and low root knot nematode pressure conditions. The use of g rafted plants was demonstrated to be economical ly feasible when specific scion rootstock combination was used in a field with a severe root knot nematode infestation. Growers using grafted transplants will need to choose approp riate rootstocks for their site specific growing conditions. Future research should be conducted in major production regions with multiple rootstocks including both intraspecific and interspecific hybrid s, in order to fully elucidate the scion rootstock interactions This will help growers select the most suitable rootstock for their production system s and reduce the risk of economic losses.
65 LIST OF REFERENCES Bausher, M.G. 2009. Commercial tomato rootstock performance when exposed to natural populations of root knot nematodes in Florida. HortScience 44:1021 1021 (abstr.). Bland, S.E. 2005. Consumer acceptability of heirloom tomatoes. M S thesis. University of Georgia, Athens, GA. Davis, A.R., P. P erkins Veazie, R. Hassel, A. Levi, S.R. King, and X. Zhang. 2008. Grafting effects on vegetable quality. HortScience 43:1670 1672. Di Gioia, F., F. Serio, D. Buttaro, O. Ayala, and P. Santamaria. 2010. Influence of rootstock on vegetative growth, fruit yie heirloom tomato. J. Hort. Sci. Biotechnol. 85:477 482. Dong, K., R.A. Dean, B.A. Fortnum, and S.A. Lewis. 2001. Development of PCR primers to identify species of root knot nematodes: Meloidogyne arenaria M. hapla M. incognita and M. javanica Nematropica 31:273 282. Edelstein, M. 2004. Grafting vegetable crop plants: pros and cons. Acta Hort. 659:235 238. Fernandez Garcia, N., V. Martinez, and M. Carvajal. 2004. Fruit quality of grafted tomato plants grown under salin e conditions. J. Hort. Sci. Biotechnol. 79:995 1001. Freeman, J., S. Rideout, and A. Wimer. 2009. Performance of grafted tomato seedlings in open field production. p. 045 1 to 045 2. In: G.L. Obenaf (ed.). 2009 Annual international research conference on m ethyl bromide alternatives and emissions reductions. Methyl Bromide Alternatives Outreach, Fresno, CA. 20 September 2011.
66 King, S.R., A.R. Davis, X. Zhang, and K. Crosby. 2010. Genetics, breeding and selection of rootstocks for Solanacea e and Cucurbitaceae. Scientia Hort. 127:106 111. Klee, H.J. 2010. Improving the flavor of fresh fruits: genomics, biochemistry, and biotechnology. New Phytologist 187:44 56. Krumbein, A. and H. Auerswald. 1998. Characterization of aroma volatiles in tomato es by sensory analyses. Nahrung 42:395 399. Kubota, C. 2008. Use of grafted seedlings for vegetable production in North America. Acta Hort. 770:21 28. Kubota, C., M.A. McClure, N. Kokalis Burelle, M.G. Bausher, and E.N. Rosskopf. 2008. Vegetable grafting: History, use, and current technology status in North America. HortScience 43:1664 1669. Lee, J.M.1994. Cultivation of grafted vegetables I. current status, grafting methods, and benefits. HortScience 29:235 239. Lee, J.M., H.J. Bang, and H.S. Ham. 1999. Q uality of cucumber fruit as affected by rootstock. Acta Hort. 483:117 123. Lee, J. M., C. Kubota, S.J. Tsao, Z. Bie, P. Hoyos Echevarria, L. Morra, and M. Oda. 2010. Current status of vegetable grafting: Diffusion, grafting techniques, automation. Scientia Hort. 127:93 105. Lpez Prez, J. A., M. Le Strange, I. Kaloshian, and A.T. Ploeg. 2006. Differential response of Mi gene resistant tomato rootstocks to root knot nematodes ( Meloidogyne incognita ). Crop Protection 25:382 288. Louws, F.J., C. Rivard, and C. Kubota. 2010. Grafting fruiting vegetables to manage soilborne pathogens, foliar pathogens, arthropods and weeds. Scientia Hort. 127:127 146. Martnez Ballesta, M., L. Lpez Prez, M. Hernndez, C. Lpez Berenguer, N. Fernndez Garca, and M. Carvajal. 200 8. Agricultural practices for enhanced human health. Phytochem. Rev. 7:251 260. Mattheis, J.P. and J.K. Fellman. 1999. Preharvest factors influencing flavor of fresh fruit and vegetables. Postharvest Bio. and Technol. 15:227 232. McSorley, R. 2002. Nematod e and insect management in transitional agricultural systems. HortTechnology 12:597 600. Medina Filho, H.P. and M.A. Stevens. 1980. Tomato breeding for nematode resistance: survey of resistant varieties for horticultural characteristics and genotype of aci d phosphates. Acta Hort. 100:383 393.
67 and yield of tomato fruits. Acta Hort. 807:619 624. tomatoes on disease resistant rootstocks for small scale organic production. 20 September 2011.
68 Rouphael, Y., D. Schwarz, A. Krumbein, and G. Colla. 2010. Impact of grafting on prod uct quality of fruits and vegetables. Scientia Hort. 127:172 179. Sasser, J.N. 1980. Root knot nematodes: A global menace to agriculture. Plant Dis. 64:36 41. Schwarz, D., Y. Rouphael, G. Colla, and J.H. Venema. 2010. Grafting as a tool to improve toleranc e of vegetables to abiotic stresses: thermal stress, water stress, and organic pollutants. Scientia Hort. 127: 162 171. State of Florida, Agency for workforce innovation. 2011. Occupational employment statistics and wages, 2011 wage estimates. Department of Economic Opportunity, Tallahassee, FL. 20 September 2011. < http://www.labormarketinfo.com/library/oes.htm > Taylor M., B. Burton, W. Fish, and W. Roberts. 2008. Cost benefit analysis of usin g grafted watermelon transplants for fusarium wilt disease control. Acta Hort. 782:343 350. Terada M., Y. Watanabe, M. Kunitomo, and E. Hayashi.1978. Differential rapid analysis of ascorbic acid 2 sulfate by dinitrophenylhydrazine method. Ann. Biochem. 84 :604 608. U.S. Department of Agriculture, Agricultural Marketing Service. 2002. Code of Federal Regulations, Title 7, Part 205. National Organic Program. 08 August 2011.
69 BIOGRAPHICAL SKETCH Charles Edward Barrett was born in Amsterdam, NY. When he was 5 years old his family moved to Edgewater, FL. Ch arle s grew up loving the ocean, the springs and all of H igh S chool in May of 2002 and decided to work before going to college. Charles earned his A.A. from Daytona Beach Community College in December of 2007 and began at the University of Florida in January 2008. Charles felt inspired in Gainesville and after receiving his B.S. in b otany, he was accepted in to the UF graduate school for an opportunity to earn a M.S. in h orticultur al s cience Upon compl etion of his M.S. program Charles will decide to either continue his education or seek employment.