Identification of Phosphorus Efficient Potato Cultivars

MISSING IMAGE

Material Information

Title:
Identification of Phosphorus Efficient Potato Cultivars
Physical Description:
1 online resource (103 p.)
Language:
english
Creator:
Lee, Wei Chieh
Publisher:
University of Florida
Place of Publication:
Gainesville, Fla.
Publication Date:

Thesis/Dissertation Information

Degree:
Master's ( M.S.)
Degree Grantor:
University of Florida
Degree Disciplines:
Horticultural Sciences
Committee Chair:
LIU,GUODONG
Committee Co-Chair:
ZOTARELLI,LINCOLN
Committee Members:
ALVA,ASHOK K
ROWLAND,DIANE L

Subjects

Subjects / Keywords:
phosphorus -- potato
Horticultural Sciences -- Dissertations, Academic -- UF
Genre:
Horticultural Sciences thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract:
As a nonrenewable mineral resource,mineable phosphate rock will be depleted in a few decades across the world.Efficient use of Phosphorus (P) becomes imperative for sustainable cropproduction. Use of P-efficient cultivars can lead to reduced P fertilizerconsumption and is an important priority to adapt to the dwindling P resourceworldwide and to sustain food security. This research included a two-year potexperiment, one-year field experiment, and hydroponics trial. Sevenpotato (Solanum tuberosum L.)cultivars (‘Atlantic’, ‘Harley Blackwell’, ‘La Chipper’, ‘Marcy’, ‘Satina’,‘Red LaSoda’, and ‘Yukon Gold’) widely grown in Florida were tested in thisstudy. In pot and field experiments, potatoes were grown on a low P sandy soilwithout or with 59 kg/ha P to compare the cultivars’ ability for P utilizationand mobilization. Plant photosynthetic rate, SPAD reading, specific leafweight, P concentration, P utilization efficiency, rhizosphere P concentrationwere measured in this study. The hydroponics trial was conducted in green houseto understand the relationship between root: shoot ratio and P supply. The pot and field experimentsdemonstrated that ‘Harley Blackwell’ and ‘Satina’ were P efficient cultivars withgreater P mobilization ability as compared to the other tested cultivars,because of their great relative biomass and P accumulation. ‘Harley Blackwell’and ‘Satina’ performed as well in the soil without supplemental P as the soil withP application. ‘Red LaSoda’ showed as a P responsive cultivar, which shoot andtuber yield increased as P rate increased but the growth was significantlyreduced without P application as compared to the other cultivars. The result inthe hydroponics trial was agreed with those of the pot and field experiments. The biodiversity of potato germplasm in mobilizing insolublephosphate and utilizing limited bioavailable P was demonstrated in this study;however, further studies are needed to evaluate this trial using a large poolof germplasm. This genetic diversity for P-use efficiency provides greatopportunities for us to mitigate the potential P crisis in potato production.
General Note:
In the series University of Florida Digital Collections.
General Note:
Includes vita.
Bibliography:
Includes bibliographical references.
Source of Description:
Description based on online resource; title from PDF title page.
Source of Description:
This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility:
by Wei Chieh Lee.
Thesis:
Thesis (M.S.)--University of Florida, 2013.
Local:
Adviser: LIU,GUODONG.
Local:
Co-adviser: ZOTARELLI,LINCOLN.
Electronic Access:
RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2014-06-30

Record Information

Source Institution:
UFRGP
Rights Management:
Applicable rights reserved.
Classification:
lcc - LD1780 2013
System ID:
UFE0046333:00001


This item is only available as the following downloads:


Full Text

PAGE 1

1 IDENTIFICATION OF PHOSPHORUS EFFICIENT POTATO CULTIVARS By WEI CHIEH LEE A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIEN CE UNIVERSITY OF FLORIDA 2013

PAGE 2

2 2013 WEI CHIEH LEE

PAGE 3

3 To my family

PAGE 4

4 ACKNOWLEDGMENTS I would like to thank Dr. Liu and Dr. Alva for their continuous support and guidance and encouragement throughout my master years. I would also like to thank my committee members, Dr. Rowland and Dr. Zotarelli f or their comments and guidance. My sincere gratitude goes to the Hastings, Citra, and Parrish team s Douglas Gergela, Dan Beach William "Buck" Nelson Alan Jones and David Fleming for their kindly support on my research project. I would also like to express my deep appreciation to our biological s cientist s and lab mates Scott Prospect, Ben Hogue, Moshe Doron, Yiping Cui, Teresa Paola Salame and all the OPS helpin g me on my research project. Special gratitude goes to Mihai Giurcanu and Xi Liang for their guidance on my statistical analysis. Finally, I would like to thank my family and friends for their patience, support, and unconditional love.

PAGE 5

5 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ ............ 7 LIST OF FIGURES ................................ ................................ ................................ ........ 10 LIST OF ABBREVIATIONS ................................ ................................ ........................... 11 ABSTRACT ................................ ................................ ................................ ................... 13 CHAPTER 1 LITERATURE REVIEW ................................ ................................ .......................... 15 The Importance and Limitation Of Phosphorus ................................ ....................... 15 Phosphorus Deficiency Symptoms ................................ ................................ ......... 18 Mechanism of Phosphorus Efficiency in Plants ................................ ...................... 21 Root morphology ................................ ................................ .............................. 22 Root exudates ................................ ................................ ................................ .. 25 P Utilization Efficiency ................................ ................................ ...................... 27 Identification of P Efficient Genotypes ................................ ................................ .... 27 Summary ................................ ................................ ................................ ................ 30 2 POT EXPERIMENT ................................ ................................ ................................ 31 Introduction ................................ ................................ ................................ ............. 31 Materials and Methods ................................ ................................ ............................ 33 Tuber Growing Condition and Nutrients Management ................................ ..... 33 Photosynthetic Rate Measurement ................................ ................................ .. 34 Leaf greenness Measurement ................................ ................................ .......... 35 Soil P Extraction and A nalysis ................................ ................................ .......... 35 Relative Biomass Calculation ................................ ................................ ........... 35 Statistical Analyses ................................ ................................ .......................... 35 Results ................................ ................................ ................................ .................... 35 Discussion ................................ ................................ ................................ .............. 38 Summary ................................ ................................ ................................ ................ 40 3 FIELD EXPERIMENT ................................ ................................ ............................. 52 Introduction ................................ ................................ ................................ ............. 52 Materials and Methods ................................ ................................ ............................ 53 Tuber Planting and Nutrient Management ................................ ........................ 53 Specific Leaf Weight Measurement ................................ ................................ .. 5 3 Shoot and Tuber Biomass Measurement ................................ ......................... 54

PAGE 6

6 Plant Tissue P Content Analysis ................................ ................................ ...... 54 Soil extraction and P analysis ................................ ................................ ........... 54 Statistical Analysis ................................ ................................ ............................ 55 Result s ................................ ................................ ................................ .................... 55 The Emergence Rate ................................ ................................ ....................... 55 Specific Leaf Weight ................................ ................................ ......................... 55 The Shoot Growth ................................ ................................ ............................ 56 Tuber Yield and Size ................................ ................................ ........................ 56 Phosphorus Concentration, Accumulation, and Use Efficiency ........................ 57 Discussion ................................ ................................ ................................ .............. 58 Summary ................................ ................................ ................................ ................ 61 4 HYDROPONICS ................................ ................................ ................................ ..... 75 Introduction ................................ ................................ ................................ ............. 75 Materials and methods ................................ ................................ ............................ 75 Plant Materials and Growth C onditions ................................ ............................ 76 Plant Tissue P Content Analysis ................................ ................................ ...... 76 Statistical Analysis ................................ ................................ ............................ 77 Result s ................................ ................................ ................................ .................... 77 Discussion ................................ ................................ ................................ .............. 78 Conclusion ................................ ................................ ................................ .............. 81 5 CONCLUSION ................................ ................................ ................................ ........ 85 LIST OF REFERENCES ................................ ................................ ............................... 87 BIOGRAPHICAL SKETCH ................................ ................................ .......................... 103

PAGE 7

7 LIST OF TABLES Table page 2 1 ANOVA table for Shoot biomass of the pot experiment in Hastings, FL, 2012 ... 47 2 2 ANOVA table for t uber fresh weight in a pot experiment in Gainesville, FL, 2013 ................................ ................................ ................................ ................... 47 2 3 ANOVA table for shoot P concentration (%) in a pot experiment in Hastings, FL, 2012 ................................ ................................ ................................ ............. 48 2 4 ANOVA table for shoot Phosphorus use efficiency (PUE) in a pot experiment in Hastings, FL, 2012. ................................ ................................ ......................... 48 2 5 ANOVA table for Tuber P concentration (%) in a pot experiment at Gainesville, FL, 2013. ................................ ................................ ......................... 48 2 6 ANOVA table for Tuber Phosphorus use efficiency (PUE) of the pot experiment at Gainesville ................................ ................................ ................... 48 2 7 ANOVA table for photosynthe t ic rates in a pot experiment at Hastings, FL, 2012. ................................ ................................ ................................ .................. 49 2 8 Photosynthe tic rates in a pot experiment in Hastings, FL, 2012. ........................ 49 2 9 ANOVA table for photosynthe tic rates in a pot experiment at Gainesville, FL, 2013. ................................ ................................ ................................ .................. 50 2 10 Photosynthe tic rates in a pot experiment in Gainesville, FL, 2013. .................... 50 2 11 ANOVA table for SPAD reading ................................ ................................ ......... 50 2 12 ANOVA table for P concentration in root zone soil in a pot experiment in Hastings, FL, 2012. ................................ ................................ ............................ 51 2 13 ANOVA table for P concentration in root zone soil in a pot experiment in Gainesville, FL, 2013. ................................ ................................ ......................... 51 3 1 ANOVA table for rhizosphere soil P conc entration ................................ ............. 66 3 2 ANOVA table for emergence rate ................................ ................................ ....... 66 3 3 Specific leaf weight ................................ ................................ ............................. 66 3 4 ANOVA table for relative s pecific leaf weight ................................ ..................... 66 3 5 Relative specific leaf weight ................................ ................................ ............... 67

PAGE 8

8 3 6 ANOVA table for cul tivar shoot biomass ................................ ............................. 67 3 7 Shoot biomass ................................ ................................ ................................ .... 67 3 8 ANOVA table for relative shoot biomass ................................ ............................ 68 3 9 Relative shoot biomass ................................ ................................ ...................... 68 3 10 ANOVA table for cultivar tuber biomass ................................ ............................. 68 3 12 AN OVA table for rela tive tuber biomass ................................ ............................. 69 3 13 Relative tuber biomass at 8, 12 and 15 weeks after planting ............................. 69 3 14 ANOVA table for tuber size by cul tivar and treatment ................................ ........ 70 3 15 ANOVA table for shoot P concentration ................................ ............................. 70 3 16 Shoot P concentration ................................ ................................ ........................ 70 3 17 ANOVA table for relative shoot P concentration ................................ ................. 71 3 18 Relative shoot P concentration ................................ ................................ ........... 71 3 19 ANOVA table for cultivar P concentration in tube r ................................ .............. 71 3 20 Tuber P concentration ................................ ................................ ........................ 71 3 21 ANOVA table for relative tuber P c oncentration ................................ .................. 72 3 22 Relative tuber P concentration ................................ ................................ ............ 72 3 23 Phosphorus accumulation (mg/plant) ................................ ................................ 72 3 24 ANOVA table for relative P accumulation ................................ ........................... 72 3 25 Relative P accumulation ................................ ................................ ..................... 73 3 26 ANOVA t ab le for tuber PUE ................................ ................................ ............... 73 3 27 Tuber PUE ................................ ................................ ................................ .......... 73 3 28 ANOVA table for relative tuber PUE ................................ ................................ ... 74 3 29 Relative tuber PUE ................................ ................................ ............................. 74 4 1 Concentration of P in 50 ml Hoagland solution with 0.3 g of tricalcium phosphate and addition of different amounts of CaCl2 or CaSO4 to attain different Ca concentrations 0 to 50 mM ................................ .............................. 84

PAGE 9

9 4 2 A NOVA table for total biomass ................................ ................................ ........... 84 4 3 A NOVA table for relative biomass ................................ ................................ ...... 84 4 4 A NOVA table for root: shoot ratio ................................ ................................ ....... 84 4 5 A NOVA table for P accumulation ................................ ................................ ........ 84

PAGE 10

10 L IST OF FIGURES Figure p age 2 1 Shoot biomass ................................ ................................ ................................ .... 41 2 2 Tuber biomass ................................ ................................ ................................ .... 42 2 3 P conce ntrations in shoot ................................ ................................ ................... 43 2 4 Shoot Phosphorus use efficiency ................................ ................................ ....... 43 2 5 Tuber P concentration ................................ ................................ ........................ 44 2 6 Tuber Phosphorus use efficiency ................................ ................................ ....... 44 2 7 SPAD readings ................................ ................................ ................................ ... 45 2 8 P concentration in root zone soil in Hastin gs, FL ................................ ............... 46 2 9 P concentration in root zone soil in Gainesville, FL ................................ .......... 47 3 1 Emergence rate ................................ ................................ ................................ .. 62 3 2 Linear regression of specific leaf weight ................................ ............................. 62 3 3 Shoot biomass ................................ ................................ ................................ .... 63 3 4 Tuber biomass ................................ ................................ ................................ .... 64 3 5 Shoot P concentration least square means ................................ ........................ 65 3 6 Tuber P concentration least square means ................................ ....................... 65 4 1 Total biomass ................................ ................................ ................................ ..... 82 4 2 Relative biomass ................................ ................................ ................................ 82 4 3 Root to shoot ratio ................................ ................................ .............................. 83 4 4 Phosphorus accumulation ................................ ................................ .................. 83

PAGE 11

11 LIST OF ABBREVIATIONS C A Al cm 2 DAP g GWS HB IFAS k g kg/ha L C M MAS mg mL P Pn ppm PSB PUE RB RL Rubisco Degrees C elsius Atlantic Aluminum Square c entimeters Days after planting Gram G enome w ide s election Harley Blackwell Institute of Food and Agricultural Sciences K ilograms K ilograms per hectares La Chipper Marcy M arker assisted selection Milligrams Milliliters Phosphorus Photosynthetic rate P art pe r million Phosphorus solubilizing bacteria Phosphorus use efficiency Relative biomass Red LaSoda R ibulose bisphosphate carboxylase

PAGE 12

12 S SLW TCP WAP YG Satina Specific leaf weight Tri Calcium Phosphate Weeks after planting Yukon Gold

PAGE 13

13 Abstract of Thesis Presented to the Gra duate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science IDENTIFICATION OF PHOSPHORUS EFFICIENT POTATO CULTIVARS By Wei Chieh Lee December 2013 Chair: M ajor: Horticultural Science s As a nonrenewable mineral resource, mineable phosphate rock will be depleted in a few decades across the world. Efficient use of Phosphorus (P) becomes imperative for sustainable crop production. Use of P efficient cultivars c an lead to reduced P fertilizer consumption and is an important priority to adapt to the dwindling P resource worldwide and to sustain food security Th is research included a two year pot experiment one year field experiment, and hydroponics trial. S even potato ( Solanum tuberosum L. widely grown in Florida were tested in this study. In pot and field experiment s potatoes were grown on a low P sandy soil without or with 59 kg /ha P Plant photosynthetic rate, SPAD reading, specific leaf weight, P concentration, P utilization efficiency, rhizosphere P concentration were measured in thi s study. The hydroponics trial was conducted in green house to understand the relationship between root: shoot ratio and P supply The pot and field experiment s demonstrated that Harley Blackwell and Satina were P efficient cultivar s with greater P mob ilization ability as compared to the other

PAGE 14

14 tested cultivar s because of their great relative biomass and P accumulation Harley Blackwell and Satina formed as well in the soil without supplemental P as the soil with P application Red LaSo da d as a P responsive cultivar, which shoot and tuber yield increased as P rate increased but the growth was significantly reduced without P application as compared to the other cultivars The result in the hydroponics trial was agreed with those of the pot and field experiment s The biodiversity of potato germplasm in mobiliz ing insoluble phosphate and utiliz ing limited bioavailable P was demonstrated in this study; however, further studies are needed to evaluate this trial using a large pool of germplasm. T his genetic diversity for P use efficiency provides great opportunities for us to mitigate the potential P crisis in potato production.

PAGE 15

15 CHAPTER 1 LITERATURE REVIEW Potato ( Solanum tuberosum L.) is an important food crop worldwide, with an annual producti on of 295 million Mg (National Potato Council, 2011). In 2010, total potato production in the USA was 18 million Mg, ranked fifth in the world (V anderzaag and H orton 1983) Potato is also one of the major winter/s pring crops grown in Florida St. Johns, Putnam and Flagler counties are the main production area in the state (USD A National Agricultural Statistics Service 2011 ). The warm and long day length winter in Florida has allowed the potato season start earlie r than other area s which in favor of the better price for Florida potatoes. There is about 33,000 to 37,000 acres of potato grow n in Florida annually (National Potato Council, 20 13) Potato is a high nutri ent demand crop, which respon ds to Phosphorus (P) fertili z ation vigorously and is not tolerant to low P soil (Alvarez Sanchez et al., 1999; Dechassa et al., 2003) Institute of Food and Agricultural Sci ences ( IFAS ) P recommendation rate is 120 lbs/acre, i.e. the annual P use for Florida potato pro duction is approximately 2,100 t ons. However, for potato production area is usually rich in P The h igh P application rate is necessary because the P in soil is fixed and unavailable to potato plants P otato production is distributed throughout a wide geographic area ( 47S 65N) (Hijmans, 2001) With adaption to such a range of growing conditions, there is a considerable biodiversity in potato ger m plasm, which provides a useful source for s electing P efficient genotypes. The Importance and Limitation Of Phosphorus Along with nitrogen (N) and potassium (K), P is one of the major nutrients essential for plant g rowth and development. Phosphorus plays an irreplaceable role in

PAGE 16

16 several key functions, including photosynthesis, respiration, energy transfer, sugar and starch transformation and nutrient translocation. 82 % of world P production is used on crop productio n (Al Abbas and Barber, 1964) s ince modern agricultu re mainly uses P fertilizers to meet the plant P demand. To ensure food security of the grow ing world population crop production has significant increase in P c onsumption The major resources of profitable phosphate mine s can categorize into three groups: Sedimentary P deposits Igneous P deposits, and Biogenic P deposits. Among the three groups, s edimentary P deposits are the most common on the earth, it can be found on every continent and with varied range s of age. Around 80% of commercial phosphate mines are obtained from marine sedimentary deposits (Follmi, 1996) About 80 % of world P production comes from nonre newable se dimentary reserves. Due to the global population growth and the food demand and P fertilizer requirement both increase However the economically exploitable P reserves will be de p leted within 50 years (Cisse and Mrabet, 2004) Because no P substitute exists, the increased the cost for mining P and the depletion of P reserves may s eriously threaten the global food security. According to the World Bank, rock phosphate price got a major leap during 2 007, and hit the highes t price to US $ 430 per metric ton, in Aug, 200 8 (The World Bank, 2013) In 2013, the price of rock phosphate was around US $ 170 per metric ton, which was 4.5 times more than ten years ago. In US, phosphate rock ore was mainly mined in Florida and North Carolina. US import s rock phosphate main ly from Morocco, which provides more than 80% of the import. I n a ddition to the limitation of the reserve, the efficiency of applied P fertilizer is usually lower than 20% (Shenoy and Kalagudi, 2005) Soil usually contain sufficient

PAGE 17

17 amount of P compounds, which ranging from 200 to 3000 mg/kg, averaged at 1200 mg/kg (Harrison, 1987) For those cultivate d soil, the soil P concentration was even greater because of the routine P fertilizer application, but the rapid transformation from the applied P fertilizer to unavailable form s to plant s is the ma in obstacle for keeping plant s from uptake. The form of P present in the soil is depended on soil pH. There are many different forms of P occur in soil, and that can be categorize into three pools, which are water solu ble P, active P, and fixed P. The solu ble P pool is the smallest, only few pounds of P per acre (Mardamootoo et al., 2013) The solu ble P is most common in orthophosphate form, but some organic P may exist as well. Orthophosphate form is the only P form that count as plant available. Orthophosphate includ e H 3 PO 4 H 2 PO 4 HPO 4 2 and PO 4 3 In the pH range from 4 to 10, H 2 PO 4 and HPO 4 2 would be dominant. Plant s would deplete the orthophosphate within the rhizosphere rather rapidly if no replenishment for solu ble P pool occurs in time. The active P pool is composted by the solid phase of P which is relatively easy to be released into soil solution. The active P pool serves as the source for solu ble P pool. Since the size of solu ble P form is so small, the active P form is the actual main source of plant ava ilable P. The fixed P pool is where most of P in the soil locates, it contain s very insoluble inorganic P compounds and hardly mineraliz able organic P compounds. The formation of insoluble inorganic P compounds is determined by the soil pH. In w eathered ac idic soils ( mainly ultisols and oxisols ) P tends to bind with aluminum ( Al ) and Iron ( Fe ) and form Aluminum phosphate (AlPO 4 ) (K sp =9.8410 21 ) and Iron (III) phosphate (FePO 4 2H 2 O) (K sp =1.0 10 22 ). In c alcareous and alkaline calcareous soils (m ainl y ari disols) P tends to bind with calcium (Ca) and magnesium (Mg) and the form calcium phosphate ( Ca 3 (PO 4 ) 2 )

PAGE 18

18 ( K sp = 2.0710 33 ) and magnesium phosphate (Mg 3 (PO 4 ) 2 ) (K sp = 1.04 10 2 4 ) Because the K sp is so small, those fixed P compounds have minimum contributi on to crop growth in the soil O ne of the challenges of modern agriculture is to figure out how we c an increase the solubility of these compounds and mobilize the fixed P to plant available form. So far, we rely on grea t amount of P fertilizer application to sus tain crop production. However, not only the limitation of P reserve, the runoff from excess P applied agricultural soil may also pollute surface water resulting in contamination of water quality, which is also called eutrophication (Carpenter, 2008) To alleviate the situation of potential P crisis and environmental risk scientists have been working on the strategy to enhance plant Phosphorus use efficiency. Phosphorus Deficiency Symptoms Phosphorus def iciency has great impact on crop production, and that including potato (Hegney and McPharlin, 1999; Hegney et al., 2000) Phosphorus is an essential component in many structures and enzyme activities for plant; including nucleic acids, phospholipids, phosphoproteins, sugar phosphates, enzymes, energy rich phosphate compounds, any phosphorylation required enzyme activity, and carbon metabolism (Sinclair and Vadez, 2002) The sufficient concentration of inorganic P (Pi) in plant cytoplasm is usually falling in the range of 5 10 mM (Bieleski, 1973) Stable cytoplasmic Pi concentration is vital for several enzyme activ i ties and synthesis, which including concentration were positively related (Brooks et al., 1988; Warren and Adams, 2002) I norganic P in plant s may present as different forms, which is depended on the physical compartments (cytoplasm, vacuole, apoplast and nucleus) Pi locates, and the pH of these compartments (Schachtman et al., 1998) I n cytoplasm where pH is 7.2 Pi is

PAGE 19

19 approximately equally partitioned between the ionic forms H 2 PO 4 and HPO 4 2 In the more acidic compartments, vacuole and apoplast, H 2 PO 4 will be the dominant species. Phosphorus is relative mobile within the plant, th ere were many studies focus ing on P acquisition endogenous P pool size, and P exchange between different compartments (B ieleski 1973; Jain et al., 2012; Lei et al., 2011; Pratt, j.,Boisson,A.M.,Gout,E., Bligny,R.,Douce,R.,Aubert,S., 2009; Schachtman et al., 1998) Cytoplasm P i concentration and homeostasis are considered most import ant to enzyme regulation and signal transduction (Mimura, 1999; Rausch,C., Bucher,M., 2002; Shin et al., 2004) Despite the short term fluctuation of external P avai lability, cytoplasm P i concentration tends to remain relatively constant at the expense of the P i in vacuole (Lee et al., 1990; Lee and Ratcliffe, 1993) Long term P deprivation will significantly reduce cytoplasm P concentration (Gout et al., 2011) In that case, plant photosynthesis and carbon fixation will decrease significantly (Cakmak, 200 2; Qiu and Israel, 1994; Rao and Terry, 1995) Phosphorus is a key substrate and modulator for multiple photosynthetic and carbohydrate metabolism enzymes, including Rubisco, phosphoribulokinase, fructose 1,6 bisphosphatase, sucrose phosphate synthase an d ADPglucose pyropho sphorylase (Hurry et al., 2000; Nielsen et al., 1998; Paul and Stitt, 1993; Paul and Pellny, 2003) The deficiency of P leads to the inhibition of pho tosynthesis at several levels The exchang e of Pi and triose phosphate between the chloroplast and cytoplasm is crucial on regulation of photosynthetic and carbohydrate metabolism (Winter and Huber, 2000) Both Rubisco activity and the capacity for ribulose bisphosphate regeneration are affected by P deficiency for several plant species (Jacob and Lawlor, 1991; Lewis et al., 1994; Reich and Oleksyn, 2009; Warren and Adams, 2002) RuBP regeneration

PAGE 20

20 capacity can be reduced if the availability of fixed carbon, the initial activity of the Calvin cycle enzymes, and the supply of ATP and NADPH are limited (Rodriguez et al., 1998) Generally speaking, plant growth is more affected by P limitation than the rate of photosynthesis per unit of leaf area (Jacob and Lawlor, 1991; Terry and Rao, 1991) Increasing specific leaf weight ( SLW ) is usually accompanied with P deficiency (Field and Mooney, 1986; Schlesinger and Chabot, 1977; Witowski and La mont, 1991) It is common to find smaller and thicker leaf on P deficient plant. I n previously study, photosynthesis per unit of leaf area has been positively correlated to specific leaf weight for several species (Nel son and Schweitzer, 1988) and the high SLW can be explained by the greater concentration of the photosynthate accumulation. However it is also been reported that phosphate and potassium, which are essential for photosynthesis, were negatively related to SLW (Luquet et al., 2005; Pettigrew, 1999; Zia ul Hassan and Arshad, 2010) The availability of carbon assimilates in leaf might not be the major responsible factor for t he inhibition of leaf area expansion and plant growth (Schlesinger and Chabot, 1977; Sobrado, 2012) Cell expansion is driven by turgor pressure (Lockhart, 1965) which is extremely sensitive to water deficit (Tardieu et al., 2011; Thomas et al., 1989) Pl ant P status can positively affected by plant water status (Gutirrez Boem and Thomas, 1998) ; P deficiency could reduce leaf turgor and stomatal conductance o n many plant species include cotton, cassava, wheat, rice, soybean, strawberry and corn (Chen and Lenz, 1997; Gutirrez boem and Thomas, 1999; Radin and Eidenbock, 1984; Sato et al., 1996) Therefore, increasing SLW under P limited condition can be better explained by the wa ter deficit rather than greater photosynthesis per unit of leaf area.

PAGE 21

21 In a low P condition, increase root shoot ratio is common on many crop s (Ca kmak et al., 1994; Ciereszko and Barbachowska, 2000; Fernandes and Soratto, 2011; Muller et al., 2007) The P uptake efficiency could be enhanced by a greater root shoot ratio (Machado and Furl ani, 2004; Schenk, 2006) Another common plant P deficient symptom is purple leaf/stem, which is the result of anthocyanin accumulation. Low p hosphate status in plant induced the expression of the genes that regulate the secondary metabolism of anthocyani n biosynthesis (Hammond et al., 2003) Anthocyanins are red o r purple flavonoid which can protect nucleic acids from UV damage and chloroplasts from photoinhibitory damage caused by P limited photosynthesis (Hoch et al., 2001; Nilsson et al., 2012; Zeng et al., 2010) Mechanism o f Phosphorus Efficiency i n Plants Phosphorus efficiency is the ability of plant species or cultivars to maint ain high yield under P limiting condition (Gourley et al., 1993) In P limited environment, plant s have developed several mechanisms to overcome P deficiency, such as improving the ability of a plant to take up more P in a low P condition, and the ability of a plant to produce greater biomass per unit P taken up. The mechanisms that enhancing plant P uptake efficiency including modification of root architecture (Balemi and Sche nk, 2009) development of large and shallow root system (Rubio et al., 2001) more secondary root (Zhu and Lynch, 2004) more root hairs and thinner roots (Bates and Lynch, 2000; Fohse et al., 1991) increasing root exudates (low molecular weight organic acids, protons, chelators and enzymes) (Bhattacharyya et al., 2013) association wit h mycorrhiza (Miyasaka and Habte, 2001) production of cluster roots and expression of high affinity P transporters A ll of which contribute to increased P uptake efficiency of the plant. There are several mechanisms have been reported related to enhancing P

PAGE 22

22 utilization efficiency: alternative P independent enzymes glycolytic pathways, efficient cytoplasmic P homeostasis and better ability to translocate P from other plant parts (Czarnecki et al., 2013) Enhancing the above morphological, physiological, biochemical and molecular adaptation mechanisms expression in P deficiency condition through plant breeding can greatly increase P use efficiency in crop production. Root mor phology To overcome the low P stress and increase P uptake, plant species may develop various adaptation mechanisms to access any available P or mo bilize every insoluble P in soil; one of the most common morphological adaptations is enhancing root surface area to increase root soil interface. Since P is highly immobile in soil unlike nitrogen and potassium which readily taken up by root via both mass flow and diffusion, only small amount (1 5%) of P is driven by mass flow, and the amount growing roots inte rcepted is even lower. Most of the plant P demand is delivered via diffusion by physically contact with root surface, but phosphate diffusion coefficients in soil is generally low, which range from 0.3 to 3.310 13 m 2 s 1 (Clarksib and Scattergood, 1982) Increasing root length, root hair density, and decreasing root radius resulting in a higher ratio of surface area to volume soil are commonly observed on P deficient plant, and those changes are consider P efficient t raits (Foehse and Jungk, 1983; Gahoonia and Nielsen, 1998; Jungk, 2001; Schenk and Barber, 1979) Because of the immobility of P in soil, cultivated topsoil us ually hold most of P compare to other layers. Plant would alter the gravitropism of basal root, and increase the proportion of carbon allocation to adventitious root growth and respiration to explore extended area in topsoil (Bai et al., 2013; Bonser et al., 1996; Nielsen et al., 1998) The

PAGE 23

23 response of root gravitropism to Phosphorus availability varies among genotypes, and genotypic adaptation to low Phosphorus availability is cor related with the ability to allocate roots to topsoil under P stress (Bonser et al., 1996; Liao et al., 2001 ) Root hair is differentiated from root epidermis cells, which is responsible for most of th e ion absorption. Also, the fine root hair has allowed it to penetrate into void, cracks, and pores of the ambient soil (Misra and Gibbons, 1996) Hence, root hairs get more effectively contact with soil. The presence of root hair could greatly increase ions uptake by many fold, especially for those sparingly soluble nutrients, such as P (Datta et al., 2011; Gahoonia and Nielsen, 1997; Key es et al., 2013) A wide variation exist in root hairs within plant varieties (Krasilnikoff et al., 2003) and advances in genetics provide the capability to breed plants with improved root hairs trait, by manipu lation of length and density to provide potential enhance P uptake efficiency (Gahoonia and Nielsen, 2004; Jungk, 2001; Lambers et al., 2013; Zhu et al., 2005) T he advance of sampling device on root study, the root system is no longer considered the hidden half of a plant (Bohm and Kopke, 1977; Nakano et al., 2012; Vogt et al., 1998) and the scientist s are able to observe and evaluate the interaction between fertilizer rate and root parameter. More studies have been focus on the root development and nitrogen rates interaction rather than P rates (Munoz Arboleda et al., 2006) Prev i ous study had reported potato root system and its interaction with fertilizer placement (De Roo and Waggoner, 1961; Weaver, 1926) but no information abo ut the root development with different P rates for potato. In a greenhouse experiment, Dechassa et al have found that though potato had long and dense root hair as cabbage, and potato s P efficiency was much lower than cabbage (Dechassa et al., 2003) This

PAGE 24

24 study revealed that there were other major factors to influence P efficiency besides morphological root characteristics such as long root hairs D espise the advance of root sampling device; there are still many obsta cle s to observe root development Also, root development may vary with soil type, irrigation and microorganisms in the soil. All the above challenges need to be overcome to further understand potato root development and P rates relationship Proteoid root is an other lateral root structure that has been reported relevant to plant P uptake efficiency. The term p is because proteoid roots were first discovered in the Proteaceae (Purnell, 1960) Watt and Evans (199 9) define proteoid root as an entire root from any species that forms one or more clusters along its length. Plant species with proteoid roots usually do not form mycorrhizal symbioses, and can grow in soils with sparse ly soluble nutrients (Skene, 1998) Phosphate compounds which bonded with Fe, Al, and Ca bonded P, in soil are relative readily to be mobilized by proteoid roots, because proteoid roots exude large quantities of organic acid, such as malate and citrate under P stress (Shane et al., 2013; Zeng et al., 2013; Zhu et al., 2005) of the plant only form proteo i d root in P deficient condition (Campbell and Sage, 2002; de Campos et al., 2013; Keerthisinghe et al., 1998) Not all the plant sp ecies equipped with proteo i d root. So far, 28 species from the Betula ceae, Casuarinaceae, Eleagnaceae, Leguminosae, Moraceae, and Myricaceae families have been reported with proteoid root (Watt and Evans, 1999) Researche rs are studying on genetic regulati on for proteoid root formation and we may manipulate proteoid root to form in the other plant family by the adva nced bioengineering technology

PAGE 25

25 Root e xudates Plant roots have the remarkable ability to secrete both low a nd high molecular weight molecules into the rhizosphere in response to biotic and abiotic stresses (Bertin et al., 2003) T o study root exudates require the s uitable and accurate sampling procedures which allow non des tructive and repetitive sampling from soil grown roots to enhanc e our understanding of the dynamics of related rhizosphere processes ; scientists found that amino acid exudation rates were more affected by growth conditions and sampling procedures than orga nic acid exudation (Oburger et al., 2013) Plant root exudates including a complex mixture of organic acid anions (citric, oxalic malic, fumaric, succinic, acetic, butyric, valeric, glycolic, piscidic, formic, acon itic, lactic, pyruvic, glutaric, malonic, aldonic, erythronic, and tetronic acid ) (Fox and Comerford, 1990; Lipton et al., 1987) amino acid, inorganic acid (HCO 3 OH H + ), gaseous molecules (CO 2 ,H 2 ), enzymes (phosphatase), sugars, vitamins, purines /nucleosides (Fries and Forsman, 1951) root border cells and mucilage (Dakora and Phillips, 2002; Eltrop and Marschner, 1996; Rovira, 1969) which direct or indirect facilitate the acquisition of mineral nutrients in rhizosphere required for plant growth especially for P acquisition (Gard ner et al., 1983; Ohwaki and Hirata, 1992) Plant availab le form of i norganic P in the soil is related to the soil pH which can be adjusted by the acid root exudates. Also, the organic P in the soil needs to be digested by microorganisms or phosphatase to become plant available form. The indirect effects are the influence on rhizosphere microflora. The so il microorganisms present in the rhizosphere that capable of solubilizing inorganic P were benefit from the root exudates (Kucey et al., 1989; Lambers et al., 2013; Wang et al., 2005) Therefore, root exudates indirectly effects the P mobilization by effects those microorganisms in the rh i zosphere.

PAGE 26

26 Root exudates not only enhance the availability of sparingly soluble P in the soil, it sometime also involve in heavy metal tolerance such as aluminum and cadmium (Ward et al., 2011; Xu et al., 2012; Zoghlami et al., 2011) In acid soil, aluminum (Al) toxicity and P deficiency often coexist Though the underlying mechanism for crop to adapt this condition is still poorly understood, recent research on cereals and legumes have found that P addit ion to acid soils could enhance Al tolerance, especially for the P efficient genotype which rel ease more malate citrate, and oxalate in different level under acid soils condition (Arunakumara et al., 2013; Kikui et al., 2007; Klug and Horst, 2010; Liang et al., 2013; Liu et al., 2009) Among all the root exudates, organic acid is the major one involve in P mobilization (Kania et al., 2003) Study on P solubilizing bacteria (PSB) also found that most of the PSB solubilize mineral phosphates by secreting a variety of organic acids And am ong these o rganic acid s citrate and malate are the most effective one on P mobilization (Chen et al., 2006; Gietl, 1992; Gyaneshwar et al., 1998; Kochuan, 1995; Martinoia and Rentsch, 1994; Schulze et al., 2002) Under P stress, the synthesis of malate and citrate in proteoid roots requires the aid of enzymes phosphoenolpyruvate carboxylase malate dehydrogenase and citrate synthase (Yu et al., 2012) Manipulation of the expression of these enzymes could result in plants with greater P accumulation and improved tolerance to Al (Chen et al., 2011; Johnson et al., 1994; Johnson et al., 1996; Johnson et al., 1996; Liang et al., 2013) Studies on barley, wheat and lupin have shown that P efficient cultivars have greater root citrat e or malate secretion induced by P deficiency and excess of Al (Kania et al., 2003; Li et al., 2000) It showed that lupin root exudates contained high

PAGE 27

27 concentration of citrate c ompared with wheat, and l upin has better Phosphorus acquisition efficiency while rock phosphate as the only P source (Akhtar et al., 2008; Sepehr et al., 2012) All the above findings confirmed that root organic acid secre tion is playing an important role on enhancing crop P a cquisition efficiency. Current studies have focused on using molecular genetic technique to improve crop root exudation of organic acid (Gao et al., 2010; Nilsson et al., 2007; Wang et al., 2013; Zhou et al., 2008) How we apply the technique to increase potato root exudates will require more genetic research. P U tilization Efficiency Besides improving P acqu isition Plants also increase the efficiency of P use during P starvation via up regulation of a wide array of P starvation inducible hydrolases that scavenge and recycle P from intra and extracellular organic P compounds (Plaxton and Tran, 2011) Phosphorus utilization efficiency is the ability of a plant to produce higher dry matter per unit of P absorbed (Richardson et al., 2011) The details regarding the mechan ism of greater P utilization efficiency is not clearly understood but it could be related to the a bility of a plant in releasing Pi from the vacuole to the cytoplasm (c ytoplasmic P homeostasis) or to selective allocation of P between cytoplasm and vacuole in favor of cytoplasm that ensure sufficient Pi concentration in metabolically active compartments for normal functioning of plant metabolism (Balemi and Negisho, 2012) Also, using alternative P independent enzymes me tabolic pathways and energy sources could also increase plant internal P utilization Identifica tion o f P Efficient Genotypes Using P efficient cultivars in agricultural industry could greatly reduce the consumption of P resource and upgrade crop producti on (Byerlee, 1996) How to select

PAGE 28

28 the P efficient cultivars become critical to ensure our food security. Hydronponics system is often used in plant nutrition research; because it allows us to manipulate the growing co nditions as designed, such pH, temperature, electr ic al conductivity, nutrient composition, and aeration. It also allow s scientist to analyze and monitor the growth solution relatively easy and without disrupting plant growth (Kim et al., 2013) However, hydroponics condition may have impact on plant root morphology or general plant growth, field experiment is still needed to conform the finding. Several studies have used hydroponics system with different supply of P t o select P efficient cultivars or examine the morphological and physiological responses (Beebe et al., 2006; da Silva et al., 2008; da Silva and Maluf, 2012; Sain et al., 1994; Wang et al., 2008; Wang et al., 2013) Rock phosphate or tri calcium phosphate are often used as sparingly soluble P source in nutrient solution to mimic the low P availabilit y in the soil, and to exam cultivars P mobilization ability. In phosphate plant study, plant biomass, P concentration, root shoot ratio, specific leaf weight, root exudates, root mycorrhiza association, root morphology (root length diameter, angle, densit y, root hair and proteoid root) were often used as an index to evaluate P efficiency. Generally, P efficient cultivars show greater root shoot ratio, total biomass, root exudates, root hair density, shallow er and thinner root system under P limited environ ment Phosphorus concentration in plant is measured to calculate P uptake P utilization efficiency (PUE) and P efficiency ratio (PER) s pecific P uptake (SPU) were as follow: P uptake (mg plant 1 ) = (1) (Akhtar et al., 2008)

PAGE 29

29 PUE = (2) (Elloitt and White, 1994) PER = (3) (Blair and Godwin, 1991) SPU = (4) (Zhu et al., 2001) Among those P efficiency evaluation index, which index or trait may best predict potato cultivars P efficiency to tuber production is not clearly understood. Greenhouse experiment alon e with field trial is necessary to help us better understand potato P use efficiency. After identify P efficient potato cultivars and the elite traits associate to it, one can apply molecular technique to further accelerate the breeding process. M arker ass isted selection (MAS) is an important technique for P efficient cultivars g enome w ide s election (GWS) MAS could have two times more genetic gain over phenotypic selection, maintain recessive alleles, speed up the backcrossing process and be more accurate for those traits that are difficult to manage through phenotypic selection, such as root traits (Xu and Crouch, 2008) Marker development require previous knowledge of the given crop genome. Identification and fine map ping regarding P efficient QTL on different plant species is still developing. The study on P efficient gene expression are focusing on those major crop, such as maize, wheat, lupin, soy bean (Beebe et al., 2006; Chen et al., 2009; Liao et al., 20064; Yan et al., 2004; Zhu et al., 2005; Zhu et al., 2005) Several P efficiency proteoid root formation related markers been identified, but how to apply it on potato will required our effort on further genetic study. So far, only little information regarding potato P efficien t traits gene expression ha s been reported (Hammond et al., 2003)

PAGE 30

30 Summary Devel oping P efficient cultivars is very important to world food security. Several traits contribute to plant P efficiency Identifying the P efficient tra it that is o bjective and consistent for potato crop production is need ed Combining the knowledge of physi ological and morphological response s to P deficiency may lead us to select elite cultivars that better adapt to P limited condition s A s soils are rich in mineral P in Florida, the cultivar equipped with outstanding P mobilization ability is desirable for Florida sustainable potato production. R esearches in green house and in field are required to understand the most effective trait to potato P efficiency.

PAGE 31

31 CHAPTER 2 POT EXPERIMENT I ntroduction Since the Green Revolution and environmental movement of the 1960s and 1970s, new constraints, such as rapid raise in fertilizer price, environmental regulations and mineral depletion, have had serious impacts on the crop production. Repeated application of excess P fertilizers has increased the demand for P fertil izers (Sharpley and Withers, 1994) hence the need for additional mining. The above practice also contributes to P loading to adjacent water bodies and related environmental quality impacts (Ticconi and Abel, 2004) One estimate of worldwide annual usage of P fertilizers is 39 million tons (Heffer, 2009) Current projections indicate that the annual P fertilizer need for worldwide agricu ltural production by 2050 will be 83.7 million tons (Tilman et al., 2001) Depletion of available P reserves is estimated to occur in 69 100 years, assuming that P fertilizer usage would increase at a rate of 0.7 to 2. 0% per year till 2050, and no increase beyond 2050 (Smit et al., 2009) The high grade P reserve in the USA is expected to be depleted in 2033 (USGS, 2009) Phosphorus is a nutrient element essential for plant growth a nd development. The deficiency of P leads to retardation of terminal growth, poor root and vine growth delayed maturity, poor yield and quality (Alvarez Sanchez et al., 1999; Fleisher et al., 2013; Grewal and Singh, 1976; Locascio and Rhue, 1990; Mccollum, 1978; Pursglove and Sanders, 1981; Singh, 1987) De pending on the applicat ion methods, crops, irrigation and soil types, current P use efficiency ranges from 15 to 30% (Syers, J.K., Johnston A.E., Curtin, D., 2008) Phosphorus application rates for different crops hav e increased globally during the last few decades, particularly since 1990 (Buckingham

PAGE 32

32 and Jasinski, 2010) The increasing demand of P, in turn, accelerates the depletion of P reserve. The expected increase of P f ertilizer cost in future years may impact global food security because of the continued high demand for P fertilizers and depletion of P reserves. Therefore, there is an urgent need to explore options to enhance P use efficiency. T here are two farming syst ems that can enhance P use efficiency: high input and high output farming system and low input and high output farming system (Murphy et al., 2005; Van Alphen and Stoorvogel, 2000) To achieve l ow input and high output, an e lite genotype with enhanced P use efficiency is needed. Conventional farming systems are basically high input and high output. As nonrenewable mineral resources continue to be depleted, low input systems become increasingly im portant. Several strategies have been evaluated to improve phosphate mineral solubility to increase P availability. Use of rhizosphere bacteria to improve P solubility has not been successful because of poor ecological fitness, low metabolite production, v ariability in inoculant delivery systems, and inconsistent performance in field applications (Shenoy and Kalagudi, 2005) Phosphate in soils is present in insoluble forms and only sparingly available to plants in highl y weathered soils of the tropics and subtropics, as well as in calcareous/alkaline soils. The morphological characteristics are different among plant genotypes and play a key role in P acquisit ion when grown on low P soils. Potato is an important food crop worldwide, with an annual production of 295 million ton (National Potato Council, 2011). In 2010, total potato production in the USA was 18 million ton ranked as the fifth in the world. I nspecting the germplasm for P use efficiency could potentially incr ease the future potato yield without excess P application

PAGE 33

33 The evaluation of wheat cultivars has shown that in low P stress growing conditions, the grain yields of the P efficient wheat genotypes were 72 to 88% greater than those of the P inefficient genot ypes (Li et al., 1995; Wang et al., 2005) Poor management of P fertilization in agricultural production contributes to degradation of surface water quality in addition to low P use efficiency. One approa ch to minimize the above problems is to explore the current germplasm resources to identify P efficient genotypes that can be used in the potato variety improvement program. The objectives of this study were to: (i) identify P efficient potato cultivars an d (ii) explore the physiological traits (photosynthetic rate, shoot biomass, leaf greenness ) that contribute to enhanced P mobilization from the soil P reserve and increase P uptake. Materials and Methods Tuber Growing Condition and Nutrients Management Ce rtified potato seeds of m ost commonly grown cultivars in Florida ( LaSoda ) were obtained from USDA, Beltsvillle, Maryland One seed piece (a pproximately 85 g) was plant ed in a plastic pot ( 21.6 cm diameter and 20.3 cm deep ) filled with 12 kg air dried sandy loam soil collected from top 30 cm from an area located in Hastings, FL in 2012 and Gainesville, FL in 2013 The soil used in this experiment was Ellzey fine sand (sa ndy, siliceous, hyperthermic, Arenic Endoaqualf) ( Soil Survey Staff, 1999 ; Acharya and Mylavarapu, 2011) fo rm Hastings for both experiments The bulk soil was amended with N and K at rat es equivalent to 224 and 168 kg/ ha (Zotarelli et al., 2013) using ammonium nitrate, and potassium sulfate, respectively. The treatments included: (i) no P applied, and (ii) I FAS recommended P application rate 59 kg /ha for low soil P concentration u sing triple superphosphate.

PAGE 34

34 The experiment was conducted using a randomized complete block design with three replicates. Each pot was irrigated by drip system with one emitter per pot to deliver 400 to 500 mL water every other day to reach field capacity Plants were harvested 84 days after planting. Shoot and tuber were washed and chopped into slices th e n oven dr ied at 70 C till constant weight was achieved. Plant Tissue P Content Analysis The oven dried plant shoots w ere ground to pass a 40 mesh stainless steel sieve and dry ashed (Kalra, 1998) Ground tissue sample was weighed (0.30.05g) into porcelain c rucibles and placed in a Thermolyne Muffle Furnace ( Cole Parmer North America Vernon Hills, IL ). The temperature was increased at 10 C/ min till 2 50 C, which was maintained for 30 min and then increase d to 550 C for 6 hours. The ash was cooled and 2.25 mL 6N HCl was added 15 min later filtered through No.41 filter paper, and diluted to 50 mL with de ionized water. P concentration was analyzed by Automated Discrete Analyzer (AQ2, SEAL Analytical, Hanau, Germany) based on US EPA Method 365.1 ( U.S. environmen tal Protection Agency, 1993 ). Phot osynthetic Rate Measurement Apparent photosynth etic rate (APR) was measured using Li COR 6400 XT (LI COR Inc, Lincoln, NE) u nder saturated photosynthetic photon flux density from a n LED light source during 9 to 11 a.m. Fl 1 CO 2 relative humidity of the air in the leaf chamber was maintained at 70% and leaf temperature at 25 C. The constant values of apparent photosynthetic rate and intercellular CO 2 concentration of each sample leaf were re corded afte r the monitor value stabilized.

PAGE 35

35 Leaf greenness Measurement SPAD meter (Konika Minolta, made in Japen, SPAD 502PLUS ) was used to measure leaf chlorophyll content and measurements were made on 30, 36, 41, 44, 52, 58, 63, 70 days after planting. Sh oots were harvested and dried in oven at 70 C for 72 h and dry weights were recorded. Soil P Extraction a nd Analysis Root zone soil w as collected by shaking off the soil from the roots. Soil samples were air dr ied and 20.2 g soil sa mple extracted with 20 mL Mehlich 3 extratant ( Mehlich, 1984 ) The suspension was shaken for 5 min, filtered and P concentration was analyzed by AQ2 (SEAL Analytical, Hanau, Germany). Relative Biomass C a lculation Relative biomass (RB) was calculated as follows Where DM t is the dry weight of tissue in a given treatment and is the mean of dry weight at zero P applied Statistical Analyses All data were su bjected to analysis of variance using Statistical Analysis software JMP version 10 (SAS Institute Inc.). Student t test was used for evaluation of significance between the two means. Result s The first pot experiment conducted in Hastings showed that cultivars and P application had significant impact on shoot biomass (Table 2 1). Yukon Gold showed the least shoot biomass in both P and P treatments ( Figure 2 1 A ) Relative shoot

PAGE 36

36 biomass was greater in Harley Blackwell and Satina as compared to the other cultiv ars while that of Marcy and Red LaSoda were the least ( Figure 2 1 B ). Since the heavy rain at the end of the season, we were not able to collect the tuber yield data in this experiment. The following year experiment was repeated in Gainesvi l le, FL The tuber yield was significantly influenced by P treatments, the cultivar differences were non significan t ( Table 2 2). Most of the cultivars showed greater tuber yield with P application, except for Yukon Gold and Atlantic (Figure 2 2A) Yukon Gold an d Atlantic showed greater relative tuber biomass while Red LaSoda and La Chipper were lower than the other cultivars (Figure 2 2B) For the experiment conducted in Hastings, a significant difference in shoot P concentration of plants between P vs. P amended soil and between cultivars was found ( Table 2 3 ). In the no n P amended soil, there were no significant differences among the cultivars with res pect to shoot P concentration (Figure 2 3) In P amended LaSoda significantly greater than influenced by cultivar (Table 2 4) UE than the other cultivars, while The experiment in Gainesville showed that only P rate significantly influenced the tuber P concentration and no cultivar effect was found ( Table 2 5). Also, tuber PUE was only influenced by P rate (Table 2 6). In non P treatment, t greater or equal tuber P concentration as compared to the other cultivars in non P

PAGE 37

37 treatment, its tuber PUE was the least (Figure 2 5, 2 showed greate r or equal tuber PUE as compared to the other cultivars. Photosynthetic rate (Pn) of potato canopy in Has tings and Gainesville experiments were significantly affected by cultivar, time of measurement, and the interaction between cultivar and P application ( Table 2 7, 2 8). In Hastings, Atlantic and La Chipper Pn were signi ficant ly g reat er or equal in P amended soil as compared with that in the no n P amended soil th r oughout the entire growth period ( Table 2 7 ). In the early growing season (36 DAP) LaSoda was significantly greater in the plants grown in P amended soil as compared to that of the plants in P unamended soil. This difference was non existent in the subsequent measurements i.e. 48 and 64 DAP. At 48 DAP, no difference was found between P and no P amended treatment for all cultivars Pn, but most of the cultivars showed greater or equal Pn without P application. At 64 DAP, only Atlantic showed greater Pn with P application than without P application, and no difference was found for othe r cultivars between treatments. The Pn response in the Gainesville experiment was not significantly affected by P application but by the cultivar, interaction between cultivar*P and P*time ( Table 2 8). At 37 DAP, most of the cultivars, except Mar cy and Satina showed no difference between P and P treatment. No P treated Marcy Pn was greater or equal to other cultivars regardless the P treatment at both 37 and 46 DAP. Harley Blackwell also showed greater Pn without P than with P application at 46 DAP. The SPAD reading s for a given cultivar was similar regardless of the P treatments ( Table 2 9) In both P and P treatment, was the greatest in SPAD, and was the l east

PAGE 38

38 I n the first and second pot experiment P ra te and the interaction between P and cultivars showed significant influence on root zone P concentration (Table 2 10 2 11 ). I n the first and second pot experiment of root zone P conc entration as compared to the other cultivars (Figure 2 showed greater or equal root zone P concentration, while compared to the other cultivars. Discussion P otato response to P deficiency in the soil was cultivar dependent and the differences could be an index for us to identify the P efficient cultivars. The low relative tuber yield and tuber P concentration with P application. This phenomenon suggested responded to P fertilization. P responsive cultivar, as e vident from t his cultivar high response to P amendment and poor performance under P stress. D iffusion is the main mechanism for plant P uptake and mass flow only account for only 1 5% of the actual P uptake (M cLaughlin et al., 1992) Thus, the deple tion of P in rhizosphere is common for various plant species (Bhat and Nye, 1973; Jungk, 1996; Kraus et al., 198 7; Owusubennoah and Wild, 1979) However, stud ies also showed that increase rhizosphere P concentration while sparingly soluble phosphate as the P source because of P stress triggered root exudates secretion dissolve the P from sparingly soluble phosphate (Bhattacharyya et al., 2013; Hoffland et al., 1989; Neumann and Romheld, 1999; Sepehr et al., 2012) Phosphorus deficiency can induce the release of

PAGE 39

39 root exudates (Kucey et al., 1989; Lambers et al., 2013; Wang et al., 2005) which can enhance the solubility of the fixed P in the rhizosphere, and increase extractable P conc entration within the root zone. Dechassa et al (2003) found that potato P efficiency was more likely due to other major factors (ex. root exudates, P transporter) be sides morphological root characteristics such as long root hairs In this study, the soil we used was from Hastings potato field, which was constantly fertilized with P, the total P concentration in soil wa s 85 and 97 ppm for Hastings and Gainesville experiment, respectively But those P in the soil was mostly in plant un available form, in other word sparingly soluble P. We supposed that the cultivars with better P mobilization ability should show great er P concentration in rhizosphere, but th ose with greater P uptake efficiency should have lower P conc entration showed high root zone P concentration in non P amended treatment And the tissue P not considered as a P efficient cultivar. SPAD reading is correlated to leaf chlorophyll content, and it is been reported to be highly related to nitrogen rate (Giletto and Echeverria, 2013) Among the tested seven genotypes, the leaf chlorophyll conte nt showed a similar trend for both P and P treatments. The genetic variations could be the main factor while nitrogen application was the same. had the lowest on SPAD reading Th e S PAD result positively correlated to the result of shoot and tuber biomass in first and second experiment. Since SPAD is very easy to measure, it could be used as an index to evaluate potato cultivars productivity, but it s not able to distinguish cultivar s P efficiency.

PAGE 40

40 Cultivar, and Cultivar*P interaction effects on Pn were significant in both experiments. W e were not able to find the significant correlation for Pn to P rate, and the result from two experiments was not consistence Unlike the reports of s howing there is a positive relation between P and Pn (Cakmak, 2002; Qiu and Israel, 1994; Rao and Terry, 1995) our study did not support the above relationship. Summary By comparing t he physiological and morphological responses of the seven potato cultivars we considered Red LaSoda as a P responsive cultivar while Satina was considered as a P efficient cultivar based on its responses in non P amended soil, high productivity and P UE for both shoot and tuber B ecause of ability to utilize fixed P in non P control, it could be an elite cultivar for the soil that rich in plant P but in plant unavailable form. Potato leaf greenness (SPAD) could be used as an index for general cultivar evaluation, but cannot be used to evaluate differences in cultivar s P efficiency. is worth for further study on the root exudates production.

PAGE 41

41 Figure 2 1 Shoot biomass A ) and relative biomass B ) o f seven cultivars ( 84 days after planting ) grown in a sandy soil with no P or with 59 kg/ha P application of the pot experiment conducted in Hastings, FL. A HB LC M RL S ,,, and YG Means followed by similar letters are not significantly different at P 0.05 cde bc def def ef ab f bc b cd b cd a def 0 20 40 60 80 100 A HB LC M RL S YG Shoot biomass (g/plant) Cultivars No P 59 kg/ha P A 0 0.2 0.4 0.6 0.8 1 A HB LC M RL S Y Relative biomass (no P/P) Cultivars B G

PAGE 42

42 Figure 2 2 Tuber biomass A) and relative biomass (DW no P /DW P ) B) of seven cultivars ( 84 days after planting ) gr own in a sandy soil with no P or with 59 kg/ha P application in a pot experiment conducted in Gainesville, FL. A LC M RL and YG Means followed by similar lett ers are not significantly different at P 0.05.

PAGE 43

43 Fig ure 2 3 P concentrations in s hoot of different cultivars grown in a sandy soil with no P and 59 kg/ha P in a pot experiment conducted in Hastings, FL A HB LC M RL S and YG Means followed by similar letters are not significantly different at P 0.05 Figure 2 4 Shoot Phosphorus use efficiency with no P or 59 kg/ha P application in a pot experiment in Hastings, FL A HB LC M RL S and YG Means followed by similar letters are not significantly different at P 0.05 c c a bc ab c c 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 A HB LC M RL S YG Shoot P (%) Cultivars No P 59 kg/ha P abc a cd bc de ab e BC AB D AB CD A CD 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 A HB LC M RL S YG PUE ( g shoot DW / mg P) Cultivars No P 59 kg/ha P

PAGE 44

44 Fig ure 2 5 Tuber P concentration with no P or 59 kg/ha P application in a pot experiment in Gainesville, FL A HB LC M RL S and YG Means followed by similar letters are not significantly different at P 0.05 Figure 2 6 Tuber Phosphorus use efficienc y with no P or 59 kg/ha P application in a pot experiment in Gainesville, FL. A LC M RL LaSoda Means followed by similar letters are not significantly differe nt at P 0.05. ab ab ab b ab b a AB AB A B A AB AB 0 0.05 0.1 0.15 0.2 0.25 0.3 A HB LC M RL S YG Tuber P % Cultivars No P 59 kg/ha P abc abc bc ab abc a c AB AB B A AB AB AB 0 0.1 0.2 0.3 0.4 0.5 0.6 A HB LC M RL S YG PUE (Tuber DW g/ mg P) Cultivars No P 59 kg/ha P

PAGE 45

45 Figure 2 7 SPAD readings of cultivars with (a ) 5 9 kg/ha P and (b) without P fertilization in a pot experiment conducted at Hastings, FL.

PAGE 46

46 Figure 2 8 P c oncentration in root zone soil at the end of 84 days of potato plant growth with no P or 59 kg/ha P application in a pot experiment in Hastings, FL A HB LC M RL S and YG Means followed by similar letters are not significantly different at P 0.05 b ab a b ab ab a BC C A BC AB BC AB 0 50 100 150 200 250 300 350 400 450 A HB LC M RL S YG Root zone P (mg/kg) Cultivars No P 59 kg/ha P

PAGE 47

47 Fig ure 2 9 P c oncentration in root zone soil at the end of 84 days of potato plant growth with no P or 59 kg/ha P application on a pot experiment in Gainesville, FL A HB LC M RL S and YG Means followed by similar letters are not significantly different at P 0.05 Table 2 1 ANOVA table for Shoot biomass of the pot experiment in Hastings, FL, 2012 Source DF F ratio P value Cultivars 6 4.7058 0.0023** P 1 9.7026 0.0044** Cultivars*P 6 1.0495 0.4171 Replicates 2 0.1981 0.8215 *, **, *** Significant at 0. 10 0.0 5 and 0.001 probability level, respectively. Table 2 2 ANOVA table for t uber fresh weight in a pot experiment in Gainesville, FL, 2013 Source DF F ratio P value Cultivars 6 1.0828 0.3827 P 1 4.3195 0.0422** Cultivars*P 6 1.0755 0.3879 Replic ates 6 0.2514 0.9568 *, **, *** Significant at 0. 10 0.0 5 and 0.001 probability level, respectively. c ab ab bc bc bc a A B AB AB AB AB AB 0 50 100 150 200 250 300 350 400 A HB LC M RL S YG Root zone soil P (mg/kg) Cultivars No P 59 kg/ha P

PAGE 48

48 Table 2 3 ANOVA table for shoot P concentration (%) in a pot experiment in Hastings, FL, 2012 Source DF F ratio P value Cultivars 6 2.0592 0. 0934* P 1 13.9796 0.0 009** Cultivars*P 6 1. 7667 0. 1454 Replicates 2 1.0970 0. 3388 *, **, *** Significant at 0. 10 0.0 5 and 0.001 probability level, respectively. Table 2 4 ANOVA table for shoot Phosphorus use efficiency (PUE) in a pot experiment in Hasting s, FL, 2012. Source DF F ratio P value Cultivars 6 11.442 <.0001*** P 1 1.5350 0. 2264 Cultivars*P 6 0.7138 0. 6418 Replicates 2 0.3935 0. 6787 *, **, *** Significant at 0. 10 0.0 5 and 0.001 probability level, respectively. Table 2 5 ANOVA table for Tuber P concentration (%) in a pot experiment at Gainesville, FL, 2013. Source DF F ratio P value Cultivars 6 1. 3853 0. 2363 P 1 16.5846 0.0 001*** Cultivars*P 6 1. 1195 0.3 626 Replicates 6 1.2267 0. 3063 *, **, *** Significant at 0. 10 0.0 5 and 0.001 pr obability level, respectively. Table 2 6 ANOVA table for Tuber Phosphorus use efficiency (PUE) of the pot experiment at Gainesville Source DF F ratio P value Cultivars 6 1. 2446 0. 2976 P 1 0.0930 0. 7616 Cultivars*P 6 0.5979 0. 7307 Replicates 6 0.9334 0. 4783

PAGE 49

49 Table 2 7 ANOVA table for photosynt h e tic rates in a pot experiment at Hastings, FL, 2012. Source DF F ratio P value Cultivars 6 14.7710 < .0 001* ** P 1 0. 3035 0. 5840 Replicates 7 0.0464 0.9999 Cultivars*P 6 6.9601 < .0 001* ** Time 2 72.1449 < .0 001* ** Cultivars*Time 12 2.5284 0. 0054** P*Time 2 11.4318 0.3898 Cultivars*P*Time 12 2.8780 0. 0017** *, **, *** Significant at 0.10, 0.05, and 0.001 probability level, respectively. Table 2 8 Photosynth e tic rates (CO 2 mol m 2 s 1 ) for seven potat o cultivars grown in a sandy soil without P addition ( P) or with 59 kg/ha P addition in a pot experiment in Hastings, FL, 2012. Cultivars 36 DAP 48 DAP 64 DAP P P P P P P A 6.62 abcde 7.54 abc 9.13 abc 10.27 abc 7.87 bc 10.63 a HB 4.2 def 5.00 bcdef 12 .10 ab 4.96 bc 8.80 abc 7.24 bc LC 7.14 abcd 7.88 ab 10.15 abc 14.96 a 8.43 abc 8.87 ab M 3.41 f 3.78 ef 12.10 ab 9.86 abc 6.34 abc 6.56 bc RL 4.53 cdef 9.12 a 10.42 abc 10.34 abc 8.01 abc 8.80 abc S 4.08 def 10.18 a 9.41 abc 3.84 c 6.87 bc 6.03 c YG 5.62 bcdef 7.93 ab 15.16 a 9.83 abc 9.04 ab 8.23 abc Comparison was made within time of measurement. Means followed by similar letters are not significantly different at P 0.05.

PAGE 50

50 Table 2 9 ANOVA table for p hotosynth e tic rates in a pot experiment at Gainesville, FL, 2013. Source DF F ratio P value Cultivars 6 3.1745 0.0138** P 1 0.8273 0.3694 Replicates 3 0.9885 0.4094 Cultivars*P 6 1.9819 0.0954* P Time 1 6.6993 0.0137** Cultivars*Time 6 1.3562 0.2576 P*Time 1 0.7572 0.3898 Cultivars*P*Time 6 1.5699 0.1832 *, **, *** Significant at 0.10, 0.05, and 0.001 probability level, respectively. Table 2 10 Photosynth e tic rates (CO 2 mol m 2 s 1 ) for seven potato cultivars grown in a sandy soil without P addition ( P) or with 59 kg/ha P addition in a pot experiment in Gainesville, FL, 2013. Cultivars 36 DAP 48 DAP P P P P Atlantic 18.16 ab 17.73 ab 15.82 abcde 17.39 abc Harley Blackwell 15.21 ab 16.80 ab 17.50 abc 8.41 def La Chipper 13.96 ab 16.84 ab 8.14 ef 11.47 cdef Marcy 18.99 a 16.56 ab 21.76 a 16.74 abc Red LaSoda 15.25 ab 17.38 ab 13.58 cdef 7.53 f Satina 17.09 ab 12.59 b 16.37 abcd 12.96 bcdef Yukon Gold 17.22 ab 17.23 ab 12.48 bcdef 19.90 ab Comparison was made within time of measurement. Means followed by similar letters are not significantly different at P 0.05. Table 2 11 ANOVA table for SPAD reading Source DF F ratio P value Cultivars 6 5.7711 <.0001*** P 1 0.0118 0.9136 Cultivars*P 6 0.2921 0.9394 *, **, *** Significant at 0.10, 0.05, and 0.001 probability level, respectively.

PAGE 51

51 T able 2 1 2 A N OVA table for P c oncentration in root zone soil in a pot experiment in Hastings, FL, 2012. Source DF F ratio P value Cultivars 6 3.4880 0.3490 P 1 2 39.0724 <.0001*** Cultivars*P 6 2.9238 0.0 258 ** Replicates 2 0.5110 0. 6058 *, **, *** Significant at 0. 10, 0.05, and 0.001 probability level, respectively. Table 2 1 3 A NOVA table for P c oncentration in root zone soil in a pot experiment in Gainesville, FL, 2013. Source DF F ratio P value Cultivars 6 1.1512 0.3490 P 1 20.4049 <.0001*** Cultivars*P 6 4 .1072 0.0023** Replicates 6 1.0251 0.4219 *, **, *** Significant at 0.10, 0.05, and 0.001 probability level, respectively.

PAGE 52

52 CHAPTER 3 FIELD EXPERIMENT Introduction Potato ( Solanum tuberosum L. ) is one of the major winter/spring crops in Florida, mostl y grown in St. Johns, Putnam and Flagler counties A typical yield range for Florida chip potato production is from 275 to 400 cwt/acre (Zotarelli et al., 2013) Yield increase s as the production moves into northern counties. Parrish is the main potato production area in southwest Florida and located in Manatee County, which annual impact of agriculture to economy is about $500 million. T he field we carried our experiment was regularly applied with P fertilizer; the accumulation of P in the soil is quite high (110 120ppm) Even with this high soil P concentration, grower still regularly apply P fertilizer, and potato do response to the P application. Most of the P in soil were fixed as plant unavailable forms. The cul tivars with outstanding P mobilizing ability to dissolve the fixed P in the soil into plant available form could greatly reduce the P fertilizer requirement Several plant mechanisms were reported to increase soil P solubility, the most common one is to ch ange the rhizosphere pH to optimum range for insoluble P change into soluble P forms (Bertin et al., 2003) O rganic acids citrate and malate, may be the most effective root exudates on P mobilization (Chen et al., 2006; Duffner et al., 2012; Gietl, 1992; Gyaneshwar et al., 1998; Kochuan, 1995; Martino ia and Rentsch, 1994; Schulze et al., 2002) Phosphorus is one of the macronutrient s for plant The deficiency of P could cause yield reduction, anthocyanins accumulation root shoot ratio and specific leaf weight (SLW) enhancement (Hammond et al., 2003; Hegney and McPharlin, 1999; Hegney et al., 2000; Uhde Stone et al., 2003) In this study, a field experiment was

PAGE 53

53 conducted to understand seven potato cultivars responses to P limitation on SLW, bulking, shoot biomass accumulation, tissue P concentration, and tuber size. T he objective of this study was to evaluate the cultivar P efficien cy by comparing the physiologi cal and morphological response between P and non P treated plot s Materials and Methods Tuber Planting and Nutrient Management This experiment was conducted at Jones P otato F arm a private farm for commercial production of potatoes at Parrish, Florida in M anatee County S even potato cultivars most common ly grown in Florida were used: LaSoda Certified seed s were obtained from Seed Pro Inc, Crystal, ME Seed pieces (a ppr oximately 85g) w ere planted at 8 inch spacing in seepage irrigated sandy soil field in Jones potato farm at Parrish, FL. Treatments included: no P which received N P K fertilizer s at 80 0 150 and P which received 80 120 150 lbs/ac, respectively as pre pla nt applications using a m m onium nitrate, ammonium sulfate, triple super phosphate and muriate of potash respectively. Both treatments were applied with 100 0 100 and 50 0 30 fertilizers at emergence and layby, respectively A randomized complete block des ign was adapted with five replications and each plot size was 80 ft long for both P and no P amended plots At 3 weeks after plan ting (WAP), emergence rate was determined by visual estimation. S pecific Leaf Weight Measurement Leaf area (cm 2 ) was measured w ith an electronic planimeter LiCor 3000 (Li Cor, Inc., Lincoln, NE) than oven dried at 70 till constant weight. Leaf specific mass was

PAGE 54

54 calculated from leaf dry mass (mg) divided by leaf area (cm 2 ). Measurements were taken at 5, 8, and 12 weeks after planting (WAP) Shoot and Tuber Biomass Measurement Shoot biomass was measured at 5, 8, and 12 WAP. Tuber biomass was measured at 8, 12, and 15 WAP. At harvest (15 WAP), potatoes were graded into four sizes, and following are the correlation to USDA standard grade ; XL (A3 A4 ) >3.5 inch, L ( A2 ) =2.8 3.5 inch, M ( A1 A2 ) =1.8 2.8 inch, S (B C ) <1.8 in ch. Plant Tissue P Content Analysis The oven dried plant shoots w ere ground to pass a 40 mesh stainless steel sieve and dry ashed (Kalra, 1998) Ground tissue sample was weighed (3 00 5 0 m g) into porcelain crucibles and placed in a Thermolyne Muffle Furnace 53600 ( Cole Parmer North America Vernon Hills, IL ). The temperature was increased at 10 C/ min till 2 50 C, which was maintained for 30 min and then increase d to 550 C for 6 hours. The ash was cooled and dissolved with 2.25 mL 6N HCl 15 min later filtered through No.41 filter paper, and diluted to 50 mL with de ionized w ater. P concentration was analyzed by Automated Discrete Analyzer (AQ2, SEAL Analytical, Hanau, Germany) based on US EPA Method 365.1 ( U.S. environ mental Protection Agency, 1993 ). Phosphorus use efficiency was calculated as following: PUE = Soil extraction and P analysis Root zone soil w as collected by shaking off the soil from the roots at 5 and 8 WAP Soil samples we re air dr ied and 20.2 g soil sa mple extracted with 20 mL of

PAGE 55

55 Mehlich 3 extractant ( Mehlich, 1984 ) The suspension was shaken for 5 min, filtered and P concentration was analyzed by AQ2 (SEAL Analytical, Hanau, Germany). Stat istical Analysis All data were transformed to follow a normal distribution values and subjected to analysis of variance using Statistical Analysis software SAS (Institute Inc., Cary, N.C.). s t was used fo r evaluation of significance between the two means. Result s This field experiment was conducted in two plot s with o r without P application Because these two plots were identical with the history of planting, and the soil test showed that P concentration w as the same between two plots before planting. The soil P concentration background of the 2 plot s were the same with F test and P value as 0.2540 and 0.6490, respectively 59 kg/ha phosphate application in P plot should increase soil P concentration by 60 ppm. Only the interaction of P*time and cultivar*P*time significantly influenced rhizosphere P concentration during the growth period n o significantly differen ce was found in rhizosphere soil P concentration s for all treatments at all time ( Table 3 1). Th e Emergence R ate The emergence rate at 3 WAP was influenced by cultivar and P application ( Table 3 2 ) O nly Atlantic and Marcy showed greater emergence rate in P treatment as compared to no n P treatment ( Figure 3 1) I n both P and non P treatment s Sa tina showed the greater or equal emergence rate than other cultivars. S pecific Leaf W eight Specific leaf weight was affected by measuring time for all of the cultivars, and the interaction between time*P was significant for most of the cultivars ( Table 3 3).

PAGE 56

56 For relative SLW, no difference was found at 8 WAP, while rs at 12 WAP ( Table 3 3).Cultivar, time, and the interaction between cultivar and time showed significant impact on relative SLW ( Table 3 lower or equal relative SLW than the other cultivars at 12 WAP ( Table 3 5). We were able to find a negative linear correlation between shoot P concentration and SLW at 8 and 12 WAP ( Figure 3 2). The Shoot Growth The shoot growth rate was greater with P application than that without P application especially be tween 8 to 12 WAP ( Figure 3 3 ). Most of the cultivars except Satina and Yukon Gold shoot growth leveled off after 8 WAP without P application Either P or P*time have significant impact on shoot biomass for all the cultivars, except Table 3 6) Most of the cultivars showed greater shoot biomass between P and no P treatment at 12 WAP ( Table 3 7). Relative shoot biomass was influenced by cultivar, time, and interaction between cultivar and time ( Table 3 8). Satina showed greate r or equal relative shoot biomass at both 5 and 12 WAP as compared to the other cultivars ( Table 3 9) Tub er Yield and Size Potato started bulking between 6 to 8 WAP, and the samples were taken at 8, 12 and 15 WAP The bulking rate was slower at non P trea tment between 12 to 15 WAP (Fig ure 3 4) T affected by the interaction between P application and time of measuring ( Table 3 10) Phosphorus

PAGE 57

57 tuber yield as compared to non P treated at 15 WAP ( Table 3 11). Relative tuber biomass was significantly influenced by time of measuring ( Table 3 12 greater or equal tuber biomass than other cultivars at all t he time of measuring ( Table 3 13 ). Tuber size was compared between P and no P treatments for a given cultivar. No more S size tubers with P than w ithout P application (Table 3 14 ). Phosphorus Concentration, A ccumulation, and Use Efficiency Shoot P concentration was increasing between 5 to 8 WAP, and decreasing between 8 to 12 WAP ( Figure 3 5 ). Only time of measurement had the influence on shoot P concentration ( Table 3 15). No difference was found between P treatments for all of the tested cultivars regarding s hoot P concentration ( Table 3 16 ). Relative shoot P concentration was not affected by cultivar effect (Table 3 17), that n o difference in relative shoot P concentration w as found for all of the cultivars at all time ( Table 3 18) T uber P concentration was decreasing from 8 to 12 WAP and was increasing from 12 to 15 WAP ( Figure 3 6 ). Most of the cultivars tuber P concentration was greater with P application as compared to non P treatment, except for ( Table 3 19) application than without at 15 WAP ( Table 3 20). Cultivar, time of measurement, and the interaction b etween cultivar and time of measurement were significantly affecting relative t uber P concentration ( Table 3 21 equal relative tuber P concentration at 12 and 15 WAP as compared to the other cultivars ( Table 3 22 ).

PAGE 58

58 Phosphorus accumulation in plant was only affected by time of measurement ( Table 3 23). No significant difference was found between P treatments for all cultivars ( Table 3 24). However, cultivar did show significant influence on relative P accumulation ( Ta ble 3 25). as compared to other cultivars at 8 and 15 WAP. nd d greater tuber PUE without P application than with P application at 15 WAP (Table 3 26, 3 27 ). Relative tuber PUE was influenced by cultivar, time, and the interaction betwe en cultivar and time (Table 3 28 ). showed significantly greater PUE and equal relative PUE than the other cultivars at all time ( Table 3 29). Dis cussion This field experiment was conducted in two plot s wi th o r without P application Because these two plots were identical with the history of planting, and the soil test showed that P concentration was the same between two plots before planting. Phosphorus treated plot was considered as standard, and the diff erence between P and non P treated plot is what we are focusing in this study. In literature reduced wheat tiller emergence rate was reported under Phosphorus deficiency (Rodriguez et al., 1998) Because p otato was planted from seed piece s which contain nutrient s to support the emergence that e xternal P status had less influence than cultivar itself on emergence rate. Increasing SLW could be triggered by P deficiency, and it many plant species ( Gutirrez boem and Thomas, 1998 ; Radin and Eidenbock, 1984;

PAGE 59

59 Hanada, 1995; Gutirrez boem and Thomas, 1999) Usually SLW is considered to reflect carbon accumulation in the leaf but it is not the major factor to inhibit leaf expansion Leaf expansion is also sensitive to P and water stress ( Schlesinger and Chabot, 1977; Sobrado and Medina, 1980; Fie l d and Monney, 1986; Witowski and Lamont, 1999) P lant P status could regulate the water status by alter ing sto matal conductance and density, and it is negative related to SLW in many plant species (Gutirrez Boem and Thomas, 1998; Gutirrez boem and Thomas, 1999; Radin and Eidenbock, 1984) In t h e early season of our study, plant may not sense the P stress yet or the seedling is so small that water was sufficient to maintain leaf cell turgor pressure at all time the diseases and pests (Huber, 1980) which caused the damage of leaf and reduced the dry mass. Therefore, o nly at the mid season may all seven cultivars showed the either affected by P supply nor by the interaction between P and time relative SLW was less or equal to the other cultivars at 12 WAP suggesting that t his cultivar may have the ability to maintain turgor under wider range of water deficit or have better P acquisition ability in no P application plot to maintain the stomatal conductance. Potato started bulking in between 5 to 8 WAP. In this period, tuber was the main sink for the plant (Moorby, 1968) and shoot growth rate increased to support the demand of the sin k. But in P deficiency condition, root shoot ratio usually increased that shoot growth rate been reduced to support root growth (Cakmak, 2002; Fernandes and Soratto, 2011) Also, shoot P concent ration decreased between 8 to 12 WAP, which

PAGE 60

60 was overlap to the period bulking started. And the trend of shoot P concentration was opposite to tuber P concentration. Indicated that translocation of P from shoot to tuber occurred during 8 to 12 WAP. This res ult was agreed with Moorby (1968) that tuber is a stronger P sink for potato. Among seven cultivars, Satina and Yukon Gold showed similar shoot and tuber production with or without P application. Either these two cultivars have better P acquisition abi lity or have better P utilization ability to keep as high production as with P application treatment. Though Yukon Gold showed similar productivity between P and non P, its low yield has it become undesirable great pro ductivity, this cultivar showed significant enhancement in PUE on non P treatment compare to P treatment is interested to us. Previous research found that PUE could be manipulated by genes expression under P deficiency condition (Hammond et al., 2003; Lopez Bucio et al., 2000; Vance et al., 2003) p otato PUE. We did not find greater tuber PUE Satina than the other cultivars without P application at the end of the season but the relative P accumulation was high suggested that the greater tuber yield may due to better P acquisition ability instea d of P utilization ability The cultivars with outstanding P mobilizing ability to dissolve the fixed P in the soil into plant available form is desired for Florida region. Potato t uber size is an important component to determine market price. Generally, s ize M ( 1.8 to 2.8 inches ) tuber has the better price. For yellow and red potato, M grade price is more than double as compared to L and XL grade. We were not

PAGE 61

61 able to find any size portion change between P and no P treatment for the seven tested cultivars. Suggesting that tuber size is not affected by P availability. Summary Among seven cultivars, Satina always showed greater or equal relative value in biomass, tissue P concentration and P accumulation than other cultivars Therefore, Satina was conside red P efficient cultivars in this experiment. better in maintaining its growth and P content without P application than the other cultivars. With all the measurements we make on these seven potato cultivars SLW seems to reveal the cultivar P efficiency. Specific leaf weight is relatively easy to measure, and it is less destructive than other measurements. It could be an index for evaluating potato P efficiency in the future study.

PAGE 62

62 Figure 3 1 Emergence rate at 3 weeks after pl anting A LC M RL LaSoda Comparison was made within the cultivar Means followed by similar letters are not significantly different at P 0. 1 Figure 3 2. Linear regression of specific leaf weight (SLW) to shoot P concentration at 8 and 12 WAP. b b a a 0 10 20 30 40 50 60 70 80 90 A HB LC M RL S YG Emergence rate (%) Cultivars No P 59 kg/ha P y = 0.11x + 0.8947 R = 0.4743 0 0.2 0.4 0.6 0.8 1 1.2 0 1 2 3 4 5 6 7 8 9 shoot P concentration (%) SLW

PAGE 63

63 Figure 3 3 Shoot biomass for A ) all cultivars without P and B ) with 59 kg/ha P application at 5, 8 and 12 weeks after planting A

PAGE 64

64 Figure 3 4 Tuber biomass at 8, 12 and 15 weeks after planting A ) without P and B ) with 59 kg/ha P application A

PAGE 65

65 Figure 3 5 S hoot P concentration least square means at 8, 12, and 15 weeks after planting. Figure 3 6. Tuber P concentration least squ are means at 8, 12 and 15 weeks after planting

PAGE 66

66 Table 3 1 A NOVA table for rhizosphere s oil P concentration Source DF F ratio P value Cultivar 6 0.77 0.5986 P 1 0.97 0.3285 Cultivar*P 6 0.07 0.9987 Time 2 1.57 0.2149 Cultivar*Time 12 0.21 0.9720 P*Time 2 6.26 0.0153* Cultivar*P*Time 12 4.78 0.0005** Time= Time of measurement P= P application *, **, *** Significant at 0. 10 0.0 5 and 0.001 probability level, respectively. Table 3 2 ANOVA t able for e mergence r ate Source DF F ratio P value Cultivar 6 12.4097 <.0001* P 1 5.9330 0.0183** Cultivar*P 6 1.4551 0.2120 *, **, *** Significant at 0.10, 0.05, and 0.001 probability level, respectively. Table 3 3 Specific leaf weight Cultivars 5 WAP 8 WAP 12 WAP P P P P P P A 4.555 ab 4.372 ab 3.928 a 3.445 ab 4.915 a 5.796 a HB 4.371 ab 5.144 ab 4.371 a 3.385 ab 4.688 a 4.258 a LC 4.52 ab 4.334 ab 4.52 a 3.417 ab 5.46 a 5.002 a M 5.554 a 4.056 b 5.554 a 3.584 ab 5.344 a 5.209 a RL 4.286 ab 4.29 ab 4.286 ab 2.7 b 4.821 a 5.236 a S 3.886 b 3.87 b 3.886 ab 3.203 ab 4. 907 a 5.807 a YG 4.421 ab 5.021 ab 4.421 ab 3.36 ab 5.038 a 5.21 a Comparison was made within time of measurement. Means followed by similar letters are not significantly different at P 0.05. A Table 3 4. ANOVA table for relative s pecific leaf weight Source DF F ratio P value Cultivar 6 4.12 0.0012** Time 2 18.4 <0.0001*** Cultivar*Time 12 3.37 0.0005** *, **, *** Significant at 0.10, 0.05, an d 0.001 probability level, respectively.

PAGE 67

67 Table 3 5. Relative specific l eaf weight Cultivars 5 WAP 8 WAP 12 WAP Atlantic 1.041 b 1.139 0.847 c Harley Blackwell 0.849 b 1.131 0.878 bc La Chipper 1.040 b 1.139 1.090 a Marcy 1.360 a 1.068 1.024 ab Red LaS oda 0.991 b 1.172 0.918 bc Satina 1.001 b 1.115 0.844 c Yukon Gold 0.880 b 1.099 0.966 abc Comparison was made within time of measurement Means followed by similar letters are not significantly different at P 0. 1 Table 3 6 ANOVA t able for cultivar shoot biomass Cultivars P Time P*Time F ratio P value F ratio P value F ratio P value A 9.11 0.0174** 253.46 <0.0001*** 17.79 0.0001** HB 18.89 0.0004** 736.02 <0.0001*** 47.57 <0.0001*** LC 2.08 0.1868 277.06 <0.0001*** 2.31 0.1328 M 5.55 0.0274** 364.44 <0.0001*** 0.41 0.6681 RL 1.04 0.3179 335.06 <0.0001*** 4.74 0.0189** S 1.64 0.2389 626.77 <0.0001*** 2.8 0.0926* YG 2.54 0.1238 368.67 <0.0001*** 0.22 0.806 A probability level, respectively. Table 3 7. Shoot biomass Cultivars 5 WAP 8 WAP 12 WAP P P P P P P A 2.80 3.67 26.13 24.43 36.4 6 b 61.24 a HB 3.33 a 2.03 b 23.70 21.97 31.59 b 57.43 a LC 1.87 2.30 22.23 22.47 37.87 b 47.91 a M 1.52 b 2.44 a 21.03 22.43 40.77 44.41 RL 3.05 2.94 25.57 22.40 40.94 b 52.97 a S 4.73 4.04 23.43 24.73 43.94 b 52.28 a YG 4.79 3.78 19.13 16.93 40.53 40.07 Comparison was made within cultivar at the time of measurement. Means followed by similar letters are not significantly different at P 0.05. A

PAGE 68

68 Table 3 8 ANOVA table for relative shoot biomass Source DF F ratio P value Cultivar 6 3.88 0.0061* Time 2 16.55 < 0 .0001*** Cultivar*Time 12 4.63 < 0 .0001*** Time= Time of measurement P= P application *, **, *** Significant at 0. 10 0.0 5 and 0.001 probability level, respectively. Table 3 9 Relative shoot biomass Cultivars 5 WAP 8 WAP 12 WAP Atlantic 0.745 b 1.067 0.481 d Harley Blackwell 1.629 a 1.076 0.551 cd La Chipper 0.737 b 0.959 0.735 bc Marcy 0.603 b 0.918 0.841 ab Red LaSoda 1.021 ab 1.136 0.771 bc Satina 1.142 ab 0.943 0.859 ab Yukon Gold 1.237 ab 1.127 1.027 a Comparison was made within time of measurement. Means followed by similar letters are not significantly different at P 0.1. T able 3 10. ANOVA t able for cultivar tuber bi omass P Time P*Time Cultivars F ratio P value F ratio P value F ratio P value A 0.08 0.7853 133.32 <0.0001*** 2.28 0.1347 HB 0.34 0.5626 303.09 <0.0001*** 3.83 0.0359** LC 0.27 0.6205 225.03 <0.0001*** 2.21 0.1419 M 0.07 0.8035 205.87 <0.0001*** 2.9 6 0.082* RL 0.04 0.8416 259.24 <0.0001*** 12.07 0.0006** S 0.09 0.7703 75.5 <0.0001*** 2.42 0.1206 YG 0.66 0.4392 70.13 <0.0001*** 0.78 0.4744 A probability level, respectively.

PAGE 69

6 9 Table 3 11. Tuber biomass (kg/ha) Cultivars 8 WAP 12 WAP 15 WAP P P P P P P A 4837.0 4226.5 19027.9 16892 .6 26306.1 b 32165.0 a HB 5275.8 a 3585.3 b 17628.6 16697.5 26061.9 b 29479.6 a LC 4553.8 4029.1 16739.2 16678.7 24109.0 29296.5 M 4907.9 3568.6 15374.9 14267.2 22918.9 26550.2 RL 7095.7 a 4125.0 b 19691.2 19400.6 21484.7 b 26855.3 a S 9702.3 6619.5 18898.7 189 10.8 25939.9 28625.2 YG 6771.0 5504.9 16410.9 14050.9 21240.6 22033.9 Comparison was made within the cultivar at the time of measurement. Means followed by similar letters are not significantly different at P 0.1. A Table 3 1 2 AN OVA table for relative tuber biomass Source DF F ratio P value Cultivar 6 0.57 0.7470 Time 2 28.04 <.0001*** Cultivar*Time 12 1.23 0.2859 Time= Time of measurem ent. P= P application.*, **, *** Significant at 0.10, 0.05, and 0.001 probability level, respectively. Table 3 1 3 Relative tuber biomass at 8, 12 and 15 weeks after planting Cultivars 5 WAP 8 WAP 12 WAP Atlantic 1.109 b 1.111 0.669 bc Harley Blackwell 1.454 ab 1.049 0.782 b La Chipper 1.066 b 0.984 0.604 bc Marcy 1.354 ab 1.074 0.745 bc Red LaSoda 1.691 a 1.012 0.547 c Satina 1.446 ab 0.987 1.044 a Yukon Gold 1.217 b 1.154 0.788 ab Comparison was made within time of measurement. Means followed by s imilar letters are not significantly different at P 0.1.

PAGE 70

70 Table 3 14 ANOVA table for tuber size by cultivar and treatment Cultivars XL L M S F ratio P F ratio P F ratio P F ratio P A 1.175 0.3393 0.0019 0.9672 0.5901 0.4852 0.2342 0.6538 HB 1.0292 0.3677 0.6799 0.456 0.008 0.9332 0.0013 0.9725 LC 0.0367 0.8574 0.4154 0.5544 0.1614 0.7084 0.0073 0.936 M 3.2054 0.1479 0.001 0.9765 1.9607 0.2395 0.083 0.7876 RL 0.5208 0.5104 0.4409 0.543 0.663 0.4612 0.4746 0.5287 S 0.0001 0.9943 0.3324 0.5951 0.8069 0.4198 0.0059 0.9424 YG 1.2415 0.3276 4.1716 0.1106 0.1225 0.744 6.6892 0.0609* XL: >3.5 inches, L: 2.8 to 3.5 inches, M: 1.8 to 2.8 inches, S: <1.8 inches. P is P value. A Significant at 0.10. Table 3 1 5. ANOVA t able for shoot P concentration Cultivars P Time P*Time F ratio P value F ratio P value F ratio P value A 0.2 0.6686 233.77 <0.0001*** 1.01 0.3856 HB 0.71 0.4251 560.74 <0.0001*** 8.38 0.0035** LC 0.19 0.666 96.77 <0.00 01*** 0.01 0.9858 M 0.1 0.7554 161.04 <0.0001*** 0.16 0.8531 RL 1.23 0.2987 152.31 <0.0001*** 1.99 0.1698 S 0.04 0.8503 106.16 <0.0001*** 1.92 0.17 YG 2.55 0.1487 112.07 <0.0001*** 0.54 0.5927 A probability level, respectively. Table 3 16. Shoot P concentration Cultivars 8 WAP 12 WAP 15 WAP P P P P P P A 0.093 0.088 0.479 0.466 0.261 0.311 HB 0.097 b 0.114 a 0.475 0.574 0.252 0.221 LC 0.118 0.122 0.568 0.593 0.299 0.295 M 0.112 0.116 0.597 0.633 0.335 0.327 RL 0.123 0.103 0.485 0.538 0.274 0.333 S 0.095 0.102 0.622 0.504 0.225 0.256 YG 0.1 09 0.125 0.535 0.661 0.237 0.254 Comparison was made within the cultivar at the time of measurement. Means followed by similar letters are not significantly different at P 0.1. A

PAGE 71

71 Table 3 1 7 ANOVA table for relative shoot P concentration Source DF F ratio P value Cultivar 6 1.06 0.4067 Time 2 1.25 0.2955 Cultivar*Time 12 2.92 0.0033** Time= Time of measurement. P= P application.*, **, *** Significant at 0.10, 0.05, and 0.001 probability level, respectively. Table 3 1 8 Relative shoot P concentration Cultivars 5 WAP 8 WAP 12 WAP Atlantic 0.953 0.979 1.138 Harley Blackwell 1.168 1.194 0.861 La Chipper 1.030 1.033 0.986 Marcy 1.008 1.049 0.938 Red LaSoda 0.869 1.115 1.133 Satina 1.075 0.857 1.210 Yukon Gold 1.125 1.199 1.063 Table 3 1 9 ANOVA table for cultivar P concentration in tube r Cultivars P Time P*Time F ratio P value F ratio P value F ratio P value A 7.33 0.0136** 17.09 <0 .0001*** 2.79 0.0857* HB 3.55 0.0735* 10.72 0.0006** 1.06 0.3654 LC 0.46 0.5183 21.02 <0.0001*** 0.91 0.4283 M 4.05 0.0577* 11.08 0.0006** 1.44 0.2608 RL 2.25 0.1491 11.15 0.0006** 2.47 0.11 S 0.62 0.4563 2.39 0.1311 1.79 0.2067 YG 4.23 0.0786* 3.24 0.0765* 3.56 0.0623* A probability level, respect ively. Table 3 20. Tuber P concentration Cultivars 8 WAP 12 WAP 15 WAP P P P P P P A 0.109 0.106 0.074 0.088 0.102 b 0.138 a HB 0.101 b 0.121 a 0.082 0.082 0.093 0.111 LC 0.146 0.128 0.099 0.096 0.122 0.125 M 0.106 0.107 0.094 0.082 0.094 0.083 RL 0.123 b 0.143 a 0.111 0.105 0.105 0.114 S 0.092 0.096 0.105 a 0.089 b 0.112 0.106 YG 0.085 b 0.117 a 0.085 0.085 0.082 b 0.126 a Comparison was made within the cultivar at the time of measurement. Means followed by similar letters are not significantly differen t at P 0.1. A

PAGE 72

72 Table 3 21. ANOVA table for relative t uber P concentration Source DF F ratio P value Cultivar 6 6.77 0.0002** Time 2 10.26 0.0002** Cultivar*Time 12 3.55 0.0009** Time= Time of measurement P= P application *, **, *** Significant at 0. 10 0.0 5 and 0.001 probability level, respectively. Table 3 22 Relative tuber P concentration Cultivars 5 WAP 8 WAP 12 WAP Atlantic 1.014 ab 0.837 d 0.740 de Harley Blackwell 0.828 cd 0.986 c 0.871 cd La Chipper 1.132 a 1.031 bc 0.949 bc Marcy 0.986 abc 1.134 ab 1.140 a Red LaSoda 0.855 bcd 1.055 abc 0.915 bc Satina 0.951 bc 1.174 a 1.056 ab Yukon Gold 0.721 d 1.005 bc 0.646 e Comparison was similar letters are not significantly different at P 0.1. T able 3 2 3 Phosphorus accumulation (mg/plant) Cultivars 8 WAP 12 WAP P P P P Atlantic 14.958 ab 13.395 b 14.906 b 21.551 ab Har ley Blackwell 13.849 b 14.639 b 14.994 b 16.204 ab La Chipper 15.436 ab 15.760 ab 17.558 ab 18.509 ab Marcy 14.891 ab 15.996 ab 19.501 ab 15.623 b Red LaSoda 16.622 ab 15.030 ab 21.542 ab 22.946 a Satina 18.721 a 15.563 ab 19.063 ab 18.482 ab Yukon Gold 12.975 b 13.926 b 15.974 ab 15.777 b not significantly different at P 0.1. Table 3 24. ANOVA table for relative P accumulation Source DF F ratio P value Cultivar 6 3.0568 0.0094* Time 1 0.9533 0.3896 Cultivar*Time 6 3.1443 0.001** Time= Time of measurement P= P application *, **, Significant at 0. 10 and 0.0 5 probab ility level, respectively.

PAGE 73

73 Table 3 25. Relative P accumulation Cultivars 8 WAP 12 WAP Atlantic 1.230 0.414 c Harley Blackwell 0.889 0.784 b La Chipper 0.944 0.781 b Marcy 0.854 1.470 a Red LaSoda 1.213 0.818 b Satina 1.426 1.022 ab Yukon Gold 0.8 27 0.959 ab similar letters are not significantly different at P 0.1. T able 3 26 ANOVA t able for tuber PUE P Time P*Time Cultivars F ratio P value F ratio P value F ratio P value A 0.62 0.4417 8.61 0.002** 1.07 0.3633 HB 0.1 0.7589 6.27 0.0073** 0.96 0.3996 LC 3.57 0.0946* 5.37 0.0178** 1.42 0.2727 M 2.03 0 .1691 2.42 0.1144 0.64 0.537 RL 3.39 0.0803* 8.25 0.0024** 2.35 0.1213 S 0.9 0.3711 2.23 0.1465 1.61 0.2374 YG 5.63 0.0499** 5.96 0.0165** 6.03 0.016** A *, **, *** Significant at 0.10, 0.05, and 0.001 probability level, respectively. Table 3 2 7 Tuber P UE Cultivars 8 WAP 12 WAP 15 WAP P P P P P P Atlantic 0.0238 0.0201 0.1281 a 0.0939 b 0.1333 0.1198 Harley Blackwell 0.0262 0.0149 0.1 088 0.1084 0.1328 0.1416 La Chipper 0.0157 0.0158 0.0864 0.0870 0.1043 a 0.1269 b Marcy 0.0235 0.0172 0.0818 0.0859 0.1311 0.1500 Red LaSoda 0.0284 0.0142 0.0883 0.0920 0.1035 a 0.1158 b Satina 0.0549 0.0343 0.0912 0.1087 0.1133 0.1231 Yukon Gold 0.0423 a 0.0278 b 0.0971 a 0.0843 b 0.1433 a 0.0893 b Comparison was made within the cultivar at the time of measurement. Means followed by similar letters are not significantly different at P 0.1.

PAGE 74

74 Table 3 2 8 ANOVA table for relative tuber PUE Source DF F ratio P value Cultivar 6 10.03 <.0001*** Time 2 3.58 0.0351** Cultivar*Time 12 4.31 0.0001*** Time= Time of measurement. P= P application. *, **, *** Significant at 0.10, 0.05, an d 0.001 probability level, respectively. Table 3 29 Relative tuber PUE Cultivars 8 WAP 12 WAP 1 5 WAP Atlantic 0.996 cd 1.383 a 0.917 bc Harley Blackwell 1.442 ab 0.964 b 0.817 bc La Chipper 0.776 d 0.920 b 0.406 c Marcy 1.001 cd 0.780 bc 0.647 c Re d LaSoda 1.314 abc 0.898 bc 1.557 b Satina 1.129 bc 0.701 c 0.744 bc Yukon Gold 1.645 a 0.942 b 3.182 a not significantly different at P 0.1.

PAGE 75

75 CHAPTER 4 HYDROPONICS Introduction s primary potato production region, soil is usually rich in total P. However, P availability to plants continue to be restricted due to P fixation with Fe Al in low pH and Ca in high pH soils. In this study, hydroponics with different form s of P was used to evaluate P uptake efficiency of three popular potato cultivars in Florida. T ricalcium phosphate (TCP) as i nsoluble P source with addition of calcium sulfate. The addition Ca to TCP solution decrease d the P solubility and hence bioavailability. In the solution containing TCP and CaSO 4 Ca released from CaSO 4 precipitated most of P released from TCP, resulting in available P concentration of only 0.04 ppm as a result of dynamic equilibrium between TCP and CaSO 4 in water. In addition, when TCP is the only P source, depletion of solution Ca concentration prompts increased release of Ca from TCP, which in turn also release P. Therefore, a cultivar with greater Ca uptake can be a P efficient cultivar since Ca uptake promotes increased P release and its uptake. We hypothesized that P efficient potato cultivar would have greater root : : shoot ratio under low P or insoluble P condition. A cultivar that performs better in TCP solution is expected to depict P m obilization ability, therefore, is well adapted to Florida production conditions. P LaSoda responsive) were used to further evaluat e P mobiliz ation in hydroponics. Materials and methods Precipitation of soluble P by Ca was evaluated by adding 0.3 g of TCP to 50 mL solutions each containing 5, 10, 30, or 40 mM Ca as CaCl 2 or 7 mM Ca as CaSO 4

PAGE 76

76 These solutions were shaken for 12 hr and P concentration was analyzed by Automated Discrete Analyzer (AQ2 )( SEAL Analytical, Hanau, Germany). Plant Materials and Growth Conditions LaSoda from USDA, Beltsvillle, Maryland were use d in this experiment. Tubers were grown in Correa modified Hoagland solution with the following composition (mg L 1 ): NO 3 N, 160; NH 4 + N, 12; K, 239; Ca, 152; Mg, 38.2; S, 40; Fe, 1.68; Cu, 0.24; Mo, 0.128 ; Mn, 1.25; Zn, 0.6; B, 0.8; Si, 10, pH adjusted to 6.5 (Correa et al., 2008) The seed pieces were removed after the seedling had 4 6 unfolded leaves. Two seedlings were grown in 1750 mL plastic containers filled with the above Hoagland solution. Oxygen was supplied by adding 100L 3 % H 2 O 2 twice a w eek The treatments included: (i) 10 mg L 1 P as control (ii) 1 mg L 1 P (iii) 0.5 g Tricalcium Phosphate (TCP) + 4 g CaSO 4 i.e. with an initial P concentration of 0.035 mg L 1 TCP was used as the P source to mimic low P availability condition in the soil, and to evaluate the potential effects of P efficient cultivars to mobilize P. The experiment was conducted using the above three cultivars with 6 replications in a completely randomized design. After 28 da ys, the seedlings were harvested and oven dried at 70C for 72 hr. Shoot and roots were weighted separately, and shoot P concentration was determined by AQ2 as described below Plant Tissue P Content Analysi s The oven dried plant biomass was ground to pas s a 40 mesh stainless steel sieve, weighed (0.30.05g) into porcelain crucibles and placed in a Thermolyne Muffle Furnace (Barndtead, Dubuque, USA) The temperature was increased at 10C/min till 250C, which was maintained for 30 min, and then increased to 550C for 6 hours. The ash was cooled to room temperature and 2.25 mL 6N HCl was added, 15 min later

PAGE 77

77 filtered through No.41 filter paper, and diluted to 50 mL with de ionized water. P concentration was analyzed by AQ2 based on US EPA Method 365.1 (O'Del, 1993) Stat istical Analysis All data were subjected to analysis of variance using Statistical Analysis software JMP version 10 (SAS Institute Inc.). Student s t test was used for evaluation of sign ificance between t he two means. Result s The concentration of P decreased while that of Ca increased ( Table 4 1 ) The P concentration i n TCP solution without the addition of Ca was 1.286 ppm. Both CaSO 4 and TCP are sparlingly soluble in water, i.e. K sp v alues are 2.07 10 3 3 and 2.4 10 5 mol 2 L 2 respectively. The solubility of CaSO 4 in water at room temperature is 0.21g/100 mL. Therefore, addition of 4 g C aSO 4 to 1750 mL nutrient solution is expected to maintain the solution super saturated with respect to CaSO 4 throughou t 28 days of seedling growth experiment. The P concentration in this solution was 0.035ppm After 28 days in hydroponics, seedlings biomass decreased significantly in the low P and TCP solution compared to high P solution ( Table 4 2). With high P supply, Red LaSoda LaSoda TCP was LaSoda greater biomass ( Figure 4 1) Relative biomass was calculated as the ratio of biomass of the plants grown with low P or with TCP in relation to that of the pla nts grown with high P solution. This response parameter was only influenced by the interaction between cultivar and

PAGE 78

78 treatment ( Table 4 3). Harley Blackwell and Red LaSoda showed similar RB under both low P and TCP treatments, while showed greater RB in low P as compared that in TCP treatment ( Figure 4 2 ). Both TCP and low P treated plants showed significantly greater root : shoot ratio than that of the high P treatment for all three cultivars ( Table 4 4 ). There was no significant difference between cultivars in low P and TCP treatments regarding root : shoot ratio ( Figure 4 3). Seedling P accumulation was significantly influenced by cultivar, treatment, and the interaction between cultivar and treatment ( Table 4 5 ). High P treated seedling s howed significantly greater P accumulation as compared to low P and TCP, and Red LaSoda showed greater P accumulation than La Chipper and Harley Blackwell in high P treatment ( Figure 4 4). In low P condition, Red LaSoda had less P accumulated as co mpar ed to other cultivars, while in TCP treatment it also had the least P accumulation than the other cultivars. Discussion N utrient solution containing 10 ppm P provided sufficient P to support potato seedling growth for 28 days. Phosphate ions are negati vely charged. Therefore, uptake of phosphate results in the roots to shed negatively charged hydroxyl or bicarbonate ions to maintain electrical balance, which will in turn, increase the solution pH. Increasing pH will reduce TCP solubility; hence decrease the concentration of the most plant available P forms, i.e. H 2 PO 4 and HPO 4 2 (Hinsinger, 2001; John, 1967) Since CaSO 4 was added to decrease P bioavailability t o obtain P from growth media, P efficient genotypes/cultivars can develop an adaptive mechanism including producing more root to intercept with P or to uptake more Ca ions (Bais et al., 2006; Dakora and Phillips, 2002; Gerke et al., 2000; Hoffland, 1992) Increased root growth is usually

PAGE 79

79 accompany with P stress to acquire more P from soil for different crop species including rape, wheat, barley, and rice (Raghothama, 1999) Increasing r oot shoot ratio is considered an adaption to low P condition and the ratio may become an index for P uptake efficiency (Mariotto Cezar et al., 2013 ; Schenk, 2004) In this study, b oth TCP and low P treated plants showed significantly greater root : shoot ratio than that of the high P treatment for all of the three tested cultivars. These re sults are in agreement with previous study that enhanced roo t growth or reduced shoot biomass are positively related to low P condition (Aziz et al., 2006; Lynch and Brown, 2001; Yaseen and Malhi, 2009) Decreasing plant biom ass is common in response to P deficiency (Wissuwa, 2005) The proportion of biomass reduction in low P or relative insoluble P (TCP) solutions as compared to the biomass in high P so lution (Relative biomass; RB) can be important for identification of P responsive and P mobilizing cultivars. P responsive cultivars could increase biosynthesis with increasing P supply; therefore, P responsive cultivars will have greater difference between high P and low P or TCP treatmen t, i.e. smaller RB at low P or TCP treatment than other cultivars. Red LaSoda showed the greatest biomass in high P but the least in low P. Though Red LaSoda root : shoot ratio increased significantly in low P treatment, that did not enhance the total biomass. Since in the low P condition, no matter how much root mass has been produced, 1 ppm P was all the cultivar can get. Therefore, the energy Red LaSoda deposited into root growth at the low P condition did not pay back by the greater P uptake. Also Red LaSoda P accumulation in both of the l ow P and TCP treatment s was significantly lower than the high P treatment. This result suggested Red LaSoda should have greater P

PAGE 80

80 demand than the other cultivars, and the P uptake ability was low i n P limiting conditions. However, Red LaSoda did perform well with sufficient P supply, indicated that it is a P responsive cultivar, and it s low RB in both low P and TCP s uggest ed that was not able to adapt in P deficient condition. La Chi pper showed great RB in the low P treatment, but low RB in TCP treatment. Indicates this cultivar has better ability to adapt to low P condition but not equipped with P mobilizing ability. Compared to other cultivars, Harley Blackwell had greater or equ al total biomass, root : shoot ratio, RB and P accumulation in the TCP treatment, which indicated Harley Blackwell has better P mobilization ability. This cultivar was able to continuously mobilize the P from TCP in solution to support the growth. Plant response to P availability may differ at different growth stages T he result showed in this study could only represent 28 days old seedling stage of these three potato cultivars. Potato is a high nutrition demanding crop compared to other major crops (Hopkins et al., 2010; Stark and Love, 2003) Florida soils are typically sandy soils with high concentration of Ca due to the continuous Ca fertilization, and/o r irrigation with high Ca water (Sartain, 2008) P hosphorus fixation with Ca can greatly reduce the plant available P concentration in soil; hence most of Florida soils with high pH need P fertilization despite containing high concentration s of total P. In soils with high amount of fixed P, a cultivar with the outstanding P mobilization ability is preferred to utilize this P reserve with out excess P application which will probably increase the amount of precipitated P in the soil. Since was able to maintain its growth and P accumulation in sparingly P solution indicating that was able to

PAGE 81

81 acquire P from fixed P form in Florida soil. can be classified as a P efficient cultivar which may have a gre at potential to be used for P efficient breeding in the future Conclusion Increasing root : shoot ratio was observed on potato grown in low P and sparingly soluble P solution, but no significant difference was found between cultivars howed similar biomass in high and sparingly soluble P solution that indicating this cultivar has a potential of acquiring P in Ca rich soil such as Florida soil. and TCP solution, but high biomass in high P solution.

PAGE 82

82 Fig ure 4 1 Total biomass of 28 days old three potato cultivars seedlings grown in modified Hoagland solution with different P concentrations Means followed by similar letters, within a P concentration, s ign ificantly different at 1 Low P 1ppm P, High P 10ppm P TCP Tricalcium phosphate. RL LaSoda LC Fig ure 4 2 Relative biomass of 28 days old three potato cultivars seedlings grown in modified Hoagland solution with different P concentrations Means followed Low P 1ppm P, High P 10ppm P TCP Tricalcium phosphate. RL ab c b a b a b a a 0 2 4 6 8 10 12 Low P High P TCP Total biomass (g/plant) Treatments LC HB RL a ab b b ab b 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 LC HB RL Relative viomass Cultivars Low P TCP

PAGE 83

83 Fig ure 4 3 Root to shoot ratio of 28 days old three potato cultivars seedlings grown in modified Hoagland solution with different P concentrations Means followed 1 Low P 1p pm P, High P 10ppm P TCP Tricalcium phosphate. RL LaSoda Fig ure 4 4 Phosphorus accumulation in 28 days old three potato cultivars seedlings grown in modified Hoagland solution with different P concentrat ions Means followed by similar letters, within a P concentration, significantly different at P ab bc abc ab bc ab a c ab 0 0.1 0.2 0.3 0.4 0.5 0.6 Low P High P TCP Root : Shoot Treatments LC HB RL a b b a b a b a c 0 0.5 1 1.5 2 2.5 3 Low P High P TCP P accumulation (g/plant) Treatments LC HB RL

PAGE 84

84 1 Low P 1ppm P, High P 10ppm P TCP Tricalcium phosphate. RL LaSoda Table 4 1 Concentration of P in 50 ml Hoagl and solution with 0.3 g of tricalcium phosphate and addition of different amounts of CaCl2 or CaSO4 to attain different Ca concentrations 0 to 50 mM Ca source [Ca] (mM) [P] (ppm) SE CaCl 2 0 1.286 0.027 CaCl 2 5 0.140 0.081 CaCl 2 10 0.149 0.026 CaCl 2 30 0.059 0.025 CaCl 2 40 0.049 0.019 CaSO 4 7 0.035 0.023 N=5 Table 4 2 A NOVA table for total biomass Source DF F ratio P value Cultivar 2 7.5963 0.0016** Treatment 2 20.6973 <0.0001*** Cultivar*T reatment 4 4.1030 0.0072** *, **, *** Significant at 0.10, 0.05, and 0.001 probability level, respectively. Table 4 3 A NOVA table for relative biomass Source DF F ratio P value Cultivar 2 0.9049 0.4169 Treatment 1 1.5348 0.2265 Cultivar*T reatment 2 3.3121 0.0523* *, **, *** Significant at 0.10, 0.0 5, and 0.001 probability level, respectively. Table 4 4. A NOVA table for root: shoot ratio Source DF F ratio P value Cultivar 2 0.0324 0.9682 Treatment 2 3.9451 0.0275** Cultivar*T reatment 4 1.1954 0.3281 *, **, *** Significant at 0.10, 0.05, and 0.0 01 probability level, respectively. Table 4 5. A NOVA table for P accumulation Source DF F ratio P value Cultivar 2 3.1781 0.0542* Treatment 2 124.0921 <0.0001*** Cultivar*T reatment 4 12.3948 <0.0001*** *, **, *** Significant at 0.10, 0.05, and 0.001 probability level, respectively.

PAGE 85

85 CHAPTER 5 CONCLUSION Phosphate is a limiting resource and it is also one of the essential nutrients to plant. Developing P efficient cultivars is an urgent task t o protect world food security. Observation on the physiol ogical and morphological responses of potato cultivars grown in Florida soil could help us identifying the P efficient cultivar that can maintain high yield without regularly P fertilizer application to reduce the production cost and the chance of eutrophi cation Generally, Florida soil is rich in P, but the fixation effect is so strong that only the cultivar equipped with outstanding P mobilization ability could keep up the growth and yield as grown in P fertilized plot. In the pot experiment conducted in Hastings and Gainesville, no evident showed that photosynthesis was reduced in the non P treated pot, but the differences between P and non Red LaSoda relatively poor production without P applicati on, and great production with P application, it is considered a P responsive cultivar W hile Satina was considered as a P efficient cultivar based on high productivity and PUE for both shoot and tuber in non P amended soil Potato leaf greenness (SPAD) i s not a representative index for potato P efficiency, but it could be used as an index for general cultivar evaluation T h e Satina had greater or equal relative value in biomass, tissue P concen tration and P accumulation than the other cultivars Satina was further confirmed as a P efficient cultivars in this experiment. We also confirmed that tuber is the stronger P sink as compared to shoot, plant translocate most of the P into tuber when du ring tuber development. Specific leaf weight seems to reveal the cultivar P efficiency, and could be use d as a less destructive

PAGE 86

86 way to evaluate P efficiency Potato emergence rate and tuber size was not affected by external P status in this experiment. In the hydroponics trial, i ncreasing root : shoot ratio was observed on potato grown in low P and sparingly soluble P biomass in high and sparingly soluble P solution that indicating this cultivar has a potential of a P responsive cultivar, as its low biomass in both low P and TCP solution, but high biomass in high P solution. This finding further is agreed with the previous field and pot e condition. The cause of its low productivity in P limited environment could be the lack of exudat es production under P deficiency condition.

PAGE 87

87 LIST OF REFERENCES Akhtar, M.S., Y. Oki, and T. Adachi. 2008. Genetic variability in phosphorus acquisition and utilization efficiency from sparingly soluble P sources by Brassica cultivars unde r P stress environment. J. Agron. Crop Sci. 194(5):380 392. Al Abbas, A.H. and S.A. Barber. 1964. A soil test for phosphorus based upon fractlonatlon of soil phosphorus: I. Correlation of soil phosphorus fractions with plant available phosphorus. Soil Sci Soc Amer Proc 28(2):218 221. Alvarez Sanchez, E., J. Etchevers, J. Ortiz, R. Nunez, V. Volke, L. Tijerina, and A. Martinez. 1999. Biomass production and phosphorus accumulation of potato as affected by phosphorus nutrition. J. Plant Nutr. 22(1):205 217. A runakumara, K.K.I.U., B.C. Walpola, and M. Yoon. 2013. Aluminum Toxicity and Tolerance Mechanism in Cereals and Legumes A Review. J. Korean Soc. Appl. Biol. Chem. 56(1):1 9. Aziz, T., M.A. Rahmatullah, M.A. Maqsood, I.A. Tahir, and C. MA. 2006. Phosphoru s utilization by six Brassica cultivars (Brassica juncea L.) from tri calcium phosphate; a relatively insoluble P compound. Pak. J. Bot. 38(5):1529 1538. Bai, H., B. Murali, K. Barber, and C. Wolverton. 2013. Low Phosphate Alters Lateral Root Setpoint Angl e and Gravitropism. Am. J. Bot. 100(1):175 182. Bais, H.P., T.L. Weir, L.G. Perry, S. Gilroy, and J.M. Vivanco. 2006. The role of root exudates in rhizosphere interactions with plants and other organisms. Annu.Rev.Plant Biol. 57:233 266. Balemi, T. and K. Negisho. 2012. Management of soil phosphorus and plant adaptation mechanisms to phosphorus stress for sustainable crop production: a review. J. Plant Nutr. Soil Sci. 12(3):547 562. Balemi, T. and M.K. Schenk. 2009. Genotypic variation of potato for phospho rus efficiency and quantification of phosphorus uptake with respect to root character istics. J. Plant Nutr. Soil Sci 172(5):669 677. Bates, T. and J. Lynch. 2000. The efficiency of Arabidopsis thaliana (Brassicaceae) root hairs in phosphorus acquisition. Am. J. Bot. 87(7):964 970. Beebe, S., M. Rojas Pierce, X. Yan, M. Blair, F. Pedraza, F. Munoz, J. Tohme, and J. Lynch. 2006. Quantitative trait loci for root architecture traits correlated with phosphorus acquisition in common bean. Crop Sci. 46(1):413 423 Bertin, C., X. Yang, and L. Weston. 2003. The role of root exudates and allelochemicals in the rhizosphere. Plant Soil 256(1):67 83.

PAGE 88

88 Bhat, K.K.S. and P.H. Nye. 1973. Diffusion of phosphate to plant roots in soil. I. Quantitative autoradiogr aphy of the d epletion zone Plant Soil 38:161 175. Bhattacharyya, P., S. Das, and T.K. Adhya. 2013. Root Exudates of Rice Cultivars Affect Rhizospheric Phosphorus Dynamics in Soils with Different Phosphorus Statuses. Commun. Soil Sci. Plant Anal. 44(10):1643 1658. Bie leski, R.L. 1973. Phosphate Pools, Phosphate Transport, and Phosphate Availability. Annu. Rev. Plant Physiol. Plant Mol. Biol. 24:225 252. Blair, G. and D. Godwin. 1991. Phosphorus efficiency in pasture species. VII. Relationships between yield and P uptak e in two accessions of white clover. Crop and Pasture Sci. 42(7):1271 1283. Bohm, W. and U. Kopke. 1977. Comparative root investigations with 2 profile wall methods. J. Agron. Crop Sci. 144(4):297 303. Bonser, A., J. Lynch, and S. Snapp. 1996. Effect of ph osphorus deficiency on growth angle of basal roots in Phaseolus vulgaris. New Phytol. 132(2):281 288. Brooks, A., K.C. Woo, and S.C. Wong. 1988. Effects of phosphorus nutrition on the response of photosynthesis to CO 2 and O 2 activation of ribulose bispho sphate carboxylase and amounts of ribulose bisphosphate and 3 phospho glycerate in spinach leaves Photosynth. Res. 15(2):133 141. Buckingham, D.A. and S.M. Jasinski. 2010. Phosphate rock sstatistics. Historical Statistics for Mineral and Material Commodit ies in the United States, Washington, DC: U.S 140. Byerlee, D. 1996. Modern varieties, productivity, and sustainability: Recent experience and emerging challenges. World Dev. 24(4):697 718. Cakmak, I., C. Hengeler, and H. Marschner. 1994. Partitioning of s hoot and root dry matter and carbohydrates in bean plants suffering from phosphorus, potassium and magnesium deficiency. J. Exp. Bot. 45(9):1245 1250. Cakmak, I. 2002. Plant nutrition research: Priorities to meet human needs for food in sustainable ways. P lant Soil 247(1):3 24. Campbell, C. and R. Sage. 2002. Interactions between atmospheric CO2 concentration and phosphorus nutrition on the formation of proteoid roots in white lupin (Lupinus albus L.). Plant Cell Environ. 25(8):1051 1059. Carpenter, S.R. 2 008. Phosphorus control is critical to mitigating eutrophication. Proc. Natl. Acad. Sci. U. S. A. 105(32):11039 11040. Chen, J., L. Xu, Y. Cai, and J. Xu. 2009. Identification of QTLs for phosphorus utilization efficiency in maize (Zea mays L.) across P le vels. Euphytica 167(2):245 252.

PAGE 89

89 Chen, K. and F. Lenz. 1997. Responses of strawberry to doubled CO2 concentration and phosphorus deficiency .2. Gas exchange and water consumption. Gartenbauwissenschaft 62(2):90 96. Chen, Y.P., P.D. Rekha, A.B. Arun, F.T. S hen, W. Lai, and C.C. Young. 2006. Phosphate solubilizing bacteria from subtropical soil and their tricalcium phosphate solubilizing abilities. Appl. Soil Ecol. 34(1):33 41. Chen, Z., Q. Cui, C. Liang, L. Sun, J. Tian, and H. Liao. 2011. Identification o f differentially expressed proteins in soybean nodules under phosphorus deficiency through proteomic analysis. Proteomics 11(24):4648 4659. Ciereszko, I. and A. Barbachowska. 2000. Sucrose metabolism in leaves and roots of bean (Phaseolus vulgaris L.) dur ing phosphate deficiency. J. Plant Physiol. 156(5 6):640 644. Cisse, L. and T. Mrabet. 2004. World Phosphate Produc tion: Overview and Prospects Phosphorus Research Bulletin 15:21 25. Clarksib, D.T. and C.B. Scattergood. 1982. Growth and phosphate transpo rt in barley and tomato plants during the development of, and recovery from, phosphate stress. J. Exp. Bot. 33(136):865 875. Correa, R.M., J.E. Brasil Pereira Pinto, C.A. Brasil Pereira Pinto, V. Faquin, E.S. Reis, A.B. Monteiro, and W.E. Dyer. 2008. A com parison of potato seed tuber yields in beds, pots and hydroponic systems. Sci. Hortic. 116(1):17 20. Czarnecki, O., J. Yang, D.J. Weston, G.A. Tuskan, and J. Chen. 2013. A dual role of strigolactones in phosphate acquisition and tilization in plants. Int. J. Mol. Sci. 14(4):7681 7701. da Silva, A.A., I. Arn, C.V. Simoes de Lima, A.d.B. Schneider, and C.A. Delatorre. 2008. Differentiation in hydroponic solution of wheat genotypes in relation to tolerance to phosphorus starvation. Rev. Bras. Cienc. Solo 32(5 ):1949 1958. da Silva, E.C. and W.R. Maluf. 2012. Hydroponic technique for screening of tomato genotypes for phosphorus uptake efficiency. Hortic. Bras. 30(2):317 321. Dakora, F. and D. Phillips. 2002. Root exudates as mediators of mineral acquisition in l ow nutrient environments. Plant Soil 245(1):35 47. Dakora, F. and D. Phillips. 2002. Root exudates as mediators of mineral acquisition in low nutrient environments. Plant Soil 245(1):35 47. Datta, S., C.M. Kim, M. Pernas, N.D. Pires, H. Proust, T. Tam, P Vijayakumar, and L. Dolan. 2011. Root hairs: development, growth and evolution at the plant soil interface. Plant Soil 346(1 2):1 14.

PAGE 90

90 de Campos, M.C.R., S.J. Pearse, R.S. Oliveira, and H. Lambers. 2013. Viminaria juncea does not vary its shoot phosphoru s concentration and only marginally decreases its mycorrhizal colonization and cluster root dry weight under a wide range of phosphorus supplies. Ann. Bot. 111(5):801 809. De Roo, H.C. and P.E. Waggoner. 1961. Root development of potatoes J. Agron. 53:15 17. Dechassa, N., M. Schenk, N. Claassen, and B. Steingrobe. 2003. Phosphorus efficiency of cabbage (Brassica oleraceae L. var. capitata), carrot (Daucus carota L.), and potato (Solanum tuberosum L.). Plant Soil 250(2):215 224. Duffner, A., E. Hoffland, a nd E.J.M. Temminghoff. 2012. Bioavailability of zinc and phosphorus in calcareous soils as affected by citrate exudation. Plant Soil 361(1 2):165 175. Elloitt, K. and A. White. 1994. Effects of light, nitrogen, and phosphorus on red pine seedling growth a nd nutrient use efficiency. For. Sci. 40(1):47 58. Eltrop, L. and H. Marschner. 1996. Growth and mineral nutrition of non mycorrhizal and mycorrhizal Norway spruce (Picea abies) seedlings grown in semi hydroponic sand culture .2. Carbon partitioning in pla nts supplied with ammonium or nitrate. New Phytol. 133(3):479 486. Fernandes, A.M. and R.P. Soratto. 2011. Nutrition, dry matter accumulation and partitioning and phosphorus use efficiency of potato grown at different phosphorus levels in Nutrient solution Revista Brasileira de Cincia do Solo 36(5):1528 1537. Field, C. and H. Mooney. 1986. The photosynthesis nitrogen relationship in wild plants. Cambridge University Press, Cambridge. Fleisher, D.H., Q. Wang, D.J. Timlin, J. Chun, and V.R. Reddy. 2013. Effects of carbon dioxide and phosphorus supply on potato dry matter allocation and canopy morphology. J. Plant Nutr. 36(4):566 586. Foehse, D. and A. Jungk. 1983. Influence of phosphate and nitrate supply on root hair formation of rape, spinach and tomato plants. Plant and Soil 74:359 368. Fohse, D., N. Claassen, and A. Jubgk. 1991. Phosphorus efficiency of plants .2. significance of root radius, root hairs and aation anion balance for phosphorus influx in 7 plant species. Plant Soil 132(2):261 272. Follm i, K. 1996. The phosphorus cycle, phosphogenesis and marine phosphate rich deposits. Earth Sci. Rev. 40(1 2):55 124. Fox, T.R. and N.B. Comerford. 1990. Low Molecular Weight Organic Acids in Selected Forest Soils of the Southeastern Usa. Soil Sci. Soc. Am. J. 54(4):1139 1144.

PAGE 91

91 Fries, N. and B. Forsman. 1951. Quantitative determination of certain nucleic acid derivatives in pea root exudate. Physiol. Plantarum 4(2):410 420. Gahoonia, T. and N. Nielsen. 1997. Variation in root hairs of barley cultivars doubled soil phosphorus uptake. Euphytica 98(3):177 182. Gahoonia, T. and N. Nielsen. 1998. Direct evidence on participation of root hairs in phosphorus (P 32) uptake from soil. Plant Soil 198(2):147 152. Gahoonia, T. and N. Nielsen. 2004. Root traits as tools for creating phosphorus efficient crop varieties. Plant Soil 260(1 2):47 57. Gao, N., Y. Su, J. Min, W. Shen, and W. Shi. 2010. Transgenic tomato overexpressing ath miR399d has enhanced phosphorus accumulation through increased acid phosphatase and proton secretion as well as phosphate transporters. Plant Soil 334(1 2):123 136. Gardner, W.K., D.G. Parbery, D.A. Barber, and L. Swinden. 1983. The acquisition of phosphorus by lupinus albus L .5. the diffusion of exudates away from roots a computer simulati on. Plant Soil 72(1):13 29. Gerke, J., L. Beissner, and W. Romer. 2000. The quantitative effect of chemical phosphate mobilization by carboxylate anions on P uptake by a single root. I. The basic concept and determination of soil parameters. J. Plant Nutr Soil Sci. Z. Pflanzenernahr. Bodenkd. 163(2):207 212. Gietl, C. 1992. Malate dehydrogenase isoenzymes cellular locations and role in the flow of metabolites between the cytoplasm and cell organelles. Biochim. Biophys. Acta 1100(3):217 234. Giletto, C. M. and H.E. Echeverria. 2013. Chlorophyll meter for the evaluation of potato N status. American Journal of Potato Research 90(4):313 323. Gourley, C.J.P., D.L. Allan, and M.P. Russelle. 1993. Defining phosphorus efficiency in plants. Plant Soil 155:289 29 2. Gout, E., R. Bligny, R. Douce, A. Boisson, and C. Rivasseau. 2011. Early response of plant cell to carbon deprivation: in vivo P 31 NMR spectroscopy shows a quasi instantaneous disruption on cytosolic sugars, phosphorylated intermediates of energy metab olism, phosphate partitioning, and intracellular pHs. New Phytol. 189(1):135 147. Grewal, J.S. and S.N. Singh. 1976. Critical levels of available phosphorus for potato in alluvial soils. Indian J. Agric. Sci. 46(12):580 584. Gutirrez Boem, F.H. and G.W. T homas. 1998. Phosphorus nutrition affects wheat res ponse to water deficit. Agron J 90(2):166 171.

PAGE 92

92 Gutirrez boem, F.H. and G.W. Thomas. 1999. Phosphorus nutrition and water deficits in field grown soybeans. Plant and Soil 207(1):87 96. Gyaneshwar, P., G. Kumar, and L. Parekh. 1998. Effect of buffering on the phosphate solubilizing ability of microorganisms. World J. Microbiol. Biotechnol. 14(5):669 673. Hammond, J.P., M.J. Bennett, H.C. Bowen, M.R.E. Broadley D.C., and May ST, Rahn C, Swarup R, Woolaway KE White PJ. 2003. Changes in gene expression in arabidopsis shoots during phosphate starvation and the potential for developing smart plants. J. Plant Physiol 132(578 596). Harrison, A.F. 1987. Soil organic phosphorus: A review of world literature. CAB In ternational, Wallingford, UK. Heffer, P. 2009. Assessment of fertilizer use by crop at the global level. International Fertilizer Industry Association, Paris. Hegney, M. and I. McPharlin. 1999. Broadcasting phosphate fertilisers produces higher yields of p otatoes (Solanum tuberosum L.) than band placement on coastal sands. Aust. J. Exp. Agric. 39(4):495 503. Hegney, M., I. McPharlin, and R. Jeffery. 2000. Using soil testing and petiole analysis to determine phosphorus fertiliser requirements of potatoes (So lanum tuberosum L. cv. Delaware) in the Manjimup Pemberton region of Western Australia. Aust. J. Exp. Agric. 40(1):107 117. Hijmans, R. 2001. Global distribution of the potato crop. Am. J. Potato Res. 78(6):403 412. Hinsinger, p. 2001. Bioavailability of s oil inorganic P in the rhizosphere as affected by root induced chemical changes: a review. Plant Soil 237(2):173 195. Hoch, W., E. Zeldin, and B. McCown. 2001. Physiological significance of anthocyanins during autumnal leaf senescence. Tree Physiol. 21(1) :1 8. Hoffland, E. 1992. Quantitative evaluation of the role of organic acid exudation in the mobilization of rock phosphate by rape. Plant Soil 140(2):279 289. Hoffland, E., G. Findenegg, and J. Nelemans. 1989. Solubilization of Rock Phosphate by Rape .2 Local Root Exudation of Organic Acids as a Response to P Starvation. Plant Soil 113(2):161 165. Hopkins, B.G., J.W. Ellsworth, T.R. Bowen, A.G. Cook, S.C. Stephens, V.D. Jolley, A.K. Shiffler, and D. Eggett. 2010. Phosphorus fertilizer timing for Russet Burbank potato grown in calcareous soil. J. Plant Nutr. 33(4):529 540. Huber, D. M. 1980. The role of mineral nutrition in defense. Plant disease, an advanced treatise 5 : 381 406

PAGE 93

93 Hurry, V., A. Strand, R. Furbank, and M. Stitt. 2000. The role of inorganic phosphate in the development of freezing tolerance and the acclimatization of photosynthesis to low temperature is revealed by the pho mutants of Arabidopsis thaliana. Plant J. 24(3):383 396. Jacob, J. and D.W. Lawlor. 1991. Stomatal and mesophyll limitat ions of photosynthesis in phosphate deficient sunflower, maize and wheat plants. Journal of Experiment Botany 42:1003 1011. Jain, A., V.K. Nagarajan, and K.G. Raghothama. 2012. Transcriptional regulation of phosphate acquisition by higher plants. Cell Mol. Life Sci. 69(19):3207 3224. John, E.H. 1967. The Effect of pH on the uptake and accumulation of phosphate and sulfate ions by bean plants. Am. J. Bot. 54(5):560 564. Johnson, J., D. Allan, and C. Vance. 1994. Phosphorus stress induced proteoid roots show altered metabolism in Lupinus Albus. Plant Physiol. 104(2):657 665. Johnson, J., D. Allan, C. Vance, and G. Weiblen. 1996. Root carbon dioxide fixation by phosphorus deficient Lupinus albus Contribution to organic acid exudation by proteoid roots. Plant Physiol. 112(1):19 30. Johnson, J., C. Vance, and D. Allan. 1996. Phosphorus deficiency in Lupinus albus Altered lateral root development and enhanced expression of phosphoenolpyruvate carboxylase. Plant Physiol. 112(1):31 41. Jungk, A. 1996. Dynamics of nutrient movement at the soil root interface in Plant roots. The hidden half. Marcel Dekker, New York, USA. Jungk, A. 2001. Root hairs and the acquisition of plant nutrients from soil. J. Plant Nutr. Soil Sci. Z. Pflanzenernahr. Bodenkd. 164(2):121 129. Kalra, Y.P. 1998. Handbook of reference methods for plant analysis CRC Press, Florida. Kania, A., N. Langlade, E. Martinoia, and G. Neumann. 2003. Phosphorus deficiency induced modifications in citrate catabolism and in cytosolic pH as related to citrate exudation in cluster roots of white lupin. Plant Soil 248(1 2):117 127. Keerthisinghe, G., P. Hocking, P. Ryan, and E. Delhaize. 1998. Effect of phosphorus supply on the formation and function of proteoid roots of white lupin (Lupinus albus L.). Plant Ce ll Environ. 21(5):467 478. Keyes, S.D., K.R. Daly, N.J. Gostling, D.L. Jones, P. Talboys, B.R. Pinzer, R. Boardman, I. Sinclair, A. Marchant, and T. Roose. 2013. High resolution synchrotron imaging of wheat root hairs growing in soil and image based modell ing of phosphate uptake. New Phytol. 198(4):1023 1029.

PAGE 94

94 Kikui, S., T. Sasaki, H. Osawa, H. Matsumoto, and Y. Yamamoto. 2007. Malate enhances recovery from aluminum caused inhibition of root elongation in wheat. Plant Soil 290(1 2):1 15. Kim, H., W. Kim, M. Roh, C. Kang, J. Park, and K.A. Sudduth. 2013. Automated sensing of hydroponic macronutrients using a computer controlled system with an array of ion selective electrodes. Comput. Electron. Agric. 93:46 54. Klug, B. and W.J. Horst. 2010. Oxalate exudation into the root tip water free space confers protection from aluminum toxicity and allows aluminum accumulation in the symplast in buckwheat (Fagopyrum esculentum). New Phytol. 187(2):380 391. Kochuan, L.V. 1995. Cellular mechanisms of aluminum toxicity and resistance in plants. Annu. Rev. Plant Physiol. Plant Mol. Biol. 46:237 260. Krasilnikoff, G., T. Gahoonia, and N. Nielsen. 2003. Variation in phosphorus uptake efficiency by genotypes of cowpea (Vigna unguiculata) due to differences in root and root hair length and induced rhizosphere processes. Plant Soil 251(1):83 91. Kraus, M., A. Fusseder, and E. Beck. 1987. In situ determination of the phosphate gradient around a root by radioautography o f frozen soil sections. Plant S oil 97:407 418. Kucey, R., H. Janzen, and M. Leggett. 1989. Microbially mediated increases in plant available phosphorus. Adv. Agron. 42:199 228. Lambers, H., J.C. Clements, and M.N. Nelson. 2013. How a phosphorus acquisition strategy based on carboxylate exudation powers the success and agronomic potential of Lupines (Lupinus, Fabaceae). Am. J. Bot. 100(2):263 288. Lee, R.B., R.G. Ratcliffe, and T.E. Southon. 1990. 31P NMR Measurements of the cytoplasmic and vacuolar Pi content of mature maize roots: relationships with phosphorus stat us and phosphate fluxes. J. Exp. Bot. 41(9):1063 1078. Lee, R. and R. Ratcliffe. 1993. Nuclear magnetic resonance studies of the location and function of plant nutrients in vivo. Plant Soil 155:45 55. Lei, M., Y. Liu, B. Zhang, Y. Zhao, X. Wang, Y. Zhou, K.G. Raghothama, and D. Liu. 2011. Genetic and genomic evidence that sucrose Is a global regulator of plant responses to phosphate starvation in Arabidopsis. Plant Physiol. 156(3):1116 1130. Lewis, J.D., K.L. Griffin, R.B. Thomas, and B.R. Strain. 1994. Ph osphorus supply affects the photosynthetic capacity of loblolly pine grown in elevated carbon dioxide. Tree Physiology 14(11):1229 1244. Li, J., X. Liu, W. Zhou, J. Sun, Y. Tong, W. Liu, Z. Li, P. Wang, and S. Yao. 1995. Technique of wheat breeding for eff iciently utilizing. Science in China Series B Chemistry Life Sciences & Earth Sciences 38(11):1313 1320.

PAGE 95

95 Li, X., J. Ma, and H. Matsumoto. 2000. Pattern of aluminum induced secretion of organic acids differs between rye and wheat. Plant Physiol. 123(4):1537 1543. Liang, C., M.A. Pineros, J. Tian, Z. Yao, L. Sun, J. Liu, J. Shaff, A. Coluccio, L.V. Kochian, and H. Liao. 2013. Low pH, aluminum, and phosphorus coordinately regulate malate exudation through GmALMT1 to improve soybean adaptation to acid soils. Pl ant Physiol. 161(3):1347 1361. Liao, H., G. Rubio, X. Yan, A. Cao, K.M. Brown, and J.P. Lynch. 200 1 Effect of phosphorus availability on basal root shallowness in common bean Plant Soil 232 (1 2): 69 79 Liao, H., X. Yan, G. Rubio, S. Beebe, M. Blair, and J. Lynch. 20064. Genetic mapping of basal root gravitropism and phosphorus acquisition efficiency in common bean. Funct. Plant Biol. 31:959 970. Lipton, D., R. Blanchar, and D. Blevins. 1987. Citrate, malate, and succinate concentration in exudates from P sufficient and P stressed Medicago Sativa L seedlings. Plant Physiol. 85(2):315 317. Liu, J., J.V. Magalhaes, J. Shaff, and L.V. Kochian. 2009. Aluminum activated citrate and malate transporters from the MATE and ALMT families function independently to confer Arabidopsis aluminum tolerance. Plant J. 57(3):389 399. Locascio, S. and R. Rhue. 1990. Phosphorus and micronutrient sources for potato. Am. Potato J. 67(4):217 226. Lockhart, J.A. 1965. An analys is of irreversible plant cell elongation. J. Theor. Biol. 8(2):264 275. Lopez Bucio, J., M.F. Nieto Estrella. 2000. Organic acid metabolism in plants: from adaptive physiology to transgenic varieties for cultiva tion in extreme soils. Plant Science 160(1):1 13. Luquet, D., B. Zhang, M. Dingkuhn, A. Dexet, and A. Clement Vidal. 2005. Phenotypic plasticity of rice seedlings: Case of phosphorus deficiency. Plant. Prod. Sci. 8(2):145 151. Lynch, J.P. and K.M. Brown. 2001. Topsoil foraging an architectural adaptation of plants to low phosphorus availability. Plant Soil 237(2):225 237. Machado, C.T. and A.M.C. Furlani. 2004. Kinetics of phosphorus uptake and root morphology of local and improved varieties of maize. Sci entia Agricola 61:69 76. Mardamootoo, T., K.F.N.K. Kwong, and C.C. Du Preez. 2013. Assessing environmental phosphorus status of soils in Mauritius following long term phosphorus fertilization of sugarcane. Agric. Water Manage. 117:26 32.

PAGE 96

96 Mariotto Cezar, T .C., S.R. Machado Coelho, D. Christ, V. Schoeninger, and A.J. Bispo de Almeida. 2013. Nutritional and antinutritional factors during the storage process of common bean. J Food Agr Environ 11(1):268 272. Martinoia, E. and D. Rentsch. 1994. Malate compartme ntation responses to a complex metabolism. Annu. Rev. Plant Physiol. Plant Mol. Biol. 45:447 467. Mccollum, R. 1978. Analysis of potato growth under differing P regimes .2. time by P status interactions for growth and leaf efficiency. Agron. J. 70(1):58 67. McLaughlin, M.J., I.R. Fillery, and A.R. Till. 1992. Operation of the phosphorus, sulphur and nitrogen cycles. p. 67 renewable sources: sustainability and global change. Mimura, T. 1999. Regulation of phosphate transport and homeostasis in plant cells. p. 149 200. In: Anonymous International Review of Cytology. Academic Press. Misra, R. and A. Gibbons. 1996. Growth and morphology of eucalypt seedling roots, in relation to soil strength arising from compaction. Plant Soil 182(1):1 11. Miyasaka, S. and M. Habte. 2001. Plant mechanisms and mycorrhizal symbioses to increase phosphorus uptake efficiency. Commun. Soil Sci. Plant Anal. 32(7 8):1101 1147. Moorby, J. 1968. The influence of carbohydrate and m ineral nutrient supply on the growth of potato tubers. Ann. Bot. 32(1):57 68. Muller, R., M. Morant, H. Jarmer, L. Nilsson, and T.H. Nielsen. 2007. Genome wide analysis of the Arabidopsis leaf transcriptome reveals interaction of phosphate and sugar metabo lism. Plant Physiol. 143(1):156 171. Munoz Arboleda, F., R.S. Mylavarapu, C.M. Hutchinson, and K.M. Portier. 2006. Root distribution under seepage irrigated potatoes in northeast Florida. Am. J. Potato Res. 83(6):463 472. Murphy, K., D. Lammer, S. Lyon, B. Carter, and S. Jones. 2005. Breeding for organic and low input farming systems: An evolutionary participatory breeding method for inbred cereal grains. Renew. Agr. Food Syst. 20(1):48 55. Nakano, A., H. Ikeno, T. Kimura, H. Sakamoto, M. Dannoura, Y. Hir ano, N. Makita, L. Finer, and M. Ohashi. 2012. Automated analysis of fine root dynamics using a series of digital images. J. Plant Nutr. Soil Sci. 175(5):775 783. Nelson, R. and L. Schweitzer. 1988. Evaluating soybean germplasm for specific leaf weight. Cr op Sci. 28(4):647 649. Neumann, G. and V. Romheld. 1999. Root excretion of carboxylic acids and protons in phosphorus deficient plants. Plant Soil 211(1):121 130.

PAGE 97

97 Nielsen, K., T. Bouma, J. Lynch, and D. Eissenstat. 1998. Effects of phosphorus availability and vesicular arbuscular mycorrhizas on the carbon budget of common bean (Phaseolus vulgaris). New Phytol. 139(4):647 656. Nilsson, L., M. Lundmark, P.E. Jensen, and T.H. Nielsen. 2012. The Arabidopsis transcription factor PHR1 is essential for adaptation to high light and retaining functional photosynthesis during phosphate starvation. Physiol. Plantarum 144(1):35 47. Nilsson, L., R. Mueller, and T.H. Nielsen. 2007. Increased expression of the MYB related transcription factor, PHR1, leads to enhanced pho sphate uptake in Arabidopsis thaliana. Plant Cell Environ. 30(12):1499 1512. Oburger, E., M. Dell'mour, S. Hann, G. Wieshammer, M. Puschenreiter, and W.W. Wenzel. 2013. Evaluation of a novel tool for sampling root exudates from soil grown plants compared t o conventional techniques. Environ. Exp. Bot. 87:235 247. O'Del, J.W. 1993. Method 365.1 determination of phosphorus by semi automated colorimetry. U.S. Environmental Protection Agency, Ohio. Ohwaki, Y. and H. Hirata. 1992. Differences in carboxylic acid e xudation among p starved leguminous crops in relation to carboxylic acid contents in plant tissues and phospholipid level in roots. Soil Sci. Plant Nutr. 38(2):235 243. Owusubennoah, E. and A. Wild. 1979. Autoradiography of the depletion zone of phosphate around onion roots in the presence of vesicular arbuscular Mycorrhiza. New Phytol. 82(1):133 140. Paul, M. and T. Pellny. 2003. Carbon metabolite feedback regulation of leaf photosynthesis and development. J. Exp. Bot. 54(382):539 547. Paul, M. and M. Stit t. 1993. Effects of nitrogen and phosphorus deficiencies an levels of carbohydrates, respiratory enzymes and metabolites in seedlings of tobacco and their response to exogenous sucrose. Plant Cell Environ. 16(9):1047 1057. Pettigrew, W. 1999. Potassium def iciency increases specific leaf weights and leaf glucose levels in field grown cotton. Agron. J. 91(6):962 968. Plaxton, W.C. and H.T. Tran. 2011. Metabolic Adaptations of Phosphate Starved Plants. Plant Physiol. 156(3):1006 1015. Pratt, j.,Boisson,A.M.,Go ut,E., Bligny,R.,Douce,R.,Aubert,S. 2009. Phosphate (Pi) starvation effect on the cytosolic Pi concentration and Pi exchanges across the tonoplast in plant cells: an in vivo 31P nuclear magnetic resonance study using methylphosphonate as a Pi analog. Plant Physiol. 151(3):1646 1657. Purnell, H. 1960. Studies of the family Proteaceae. I. Anatomy and morphology of the roots of some Victorian species. Aust. J. Bot. 8:38 50.

PAGE 98

98 Pursglove, J.D. and F.E. Sanders. 1981. The growth and phosphorus economy of the earl y potato (Solanum tuberosum). Commun. Soil Sci. Plant Anal. 12(11):1105 1121. < http://www.tandfonline.com/doi/abs/10.1080/00103628109367222 >. Qiu, J. and D.W. Israel. 1994. Carbohydrate accumulation and utilization in soybean plants in response to altered phosphorus nutrition. Physiologia Plantarum 90:722 728. Radin, J.W. and M.P. Eidenbock. 1984. Hydraulic conductance as a factor limiting leaf expansion of phosphorus deficient cotton plants. Plant Physiol. 75(2):372 377. Raghothama, K. 1999. Phosphate acquisition. Annual review of plant biology 50(1):665 693. Rao, I.M. and N. Terry. 1995. Leaf phosphate status, photosynthesis, and carbon partitioning in sugar beet (IV Changes with time following increased supply of phosphate to low phosphate plants). Plant Physiol. 107(4):1313 1321. Rausch,C., Bucher,M. 2002. Molecular mechanisms of phosphate transport in plants. Planta 216(1):23 37. Reich, P.B. and J. Oleksyn. 2009. Leaf phosphorus influences the photosynthesis nitrogen relation: a cross biome analysis of 314 species. Oecologia 160(2):207 212. Richardson, A.E., J.P. Lynch, P.R. Ryan, E. Delhaize, F.A. Smith, S.E. Smith, P.R. Harvey, M.H. Ryan, E.J. Veneklaas, H. Lam bers, A. Oberson, R.A. Culvenor, and R.J. Simpson. 2011. Plant and microbial strategies to improve the phosphorus efficiency of agriculture. Plant Soil 349(1 2):121 156. Rodriguez, D., M.C. Pomar, and J. Goudriaan. 1998. Leaf primordia initiation, leaf em ergence and tillering in wheat (Triticum aestivum L.) grown under low phosphorus conditions. P lant S oil 202:149 157. Rovira, A. 1969. Plant Root Exudates. Bot. Rev. 35(1):35 37. Rubio, G., T. Walk, Z. Ge, X. Yan, H. Liao, and J. Lynch. 2001. Root gravitro pism and below ground competition among neighbouring plants: A modelling approach. Annals of Botany 88(5):929 940. Sain, S., D. Barnes, and D. Biesboer. 1994. Hydroponic and tissue culture evaluation of Alfalfa (Medicago Sativa L) subpopulations selected for phosphorus efficiency. Plant Sci. 99(1):17 26. Sartain, J.B. 2008. Soil and tissue testing and interpretation for Florida turf grasses. The Institute of Food and Agricultural Sciences, Florida SL 181. Sato, A., A. Oyanagi, and M. Wada. 1996. Effect of phosphorus content of the emergence of tillers in wheat cultivars. J. A. R. Q. 30:27 30.

PAGE 99

99 Schachtman, D.P., R.J. Reid, and S.M. Ayling. 1998. Phosphorus uptake by plants: From soil to cell. Plant Physiol. 116(2):447 453. Schenk, M.K. and S.A. Barber. 1979. Phosphate uptake by corn as affected by soil characteristics and root morphology. Soil Sci. Soc. Am. J. 43(5):880 883. Schenk, M.K. 2006. Nutrient efficiency of vegetable crops. Acta Horticulturae 700:21 34. Schenk, M. 2004. Nutrient efficiency of vegetable crops. Schlesinger, W.H. and B.F. Chabot. 1977. The use of water and minerals by evergreen and deciduous shrubs in Okefenokee swamp. Bot. Gaz. 138(4):490 497. < http://www.jstor.org/stable/2473885 >. Schulze, J., M. Tesfaye, R. Litjens, B. Bucciarelli, G. Trepp, S. Miller, D. Samac, D. Allan, and C. Vance. 2002. Malate plays a central role in plant nutrition. Plant Soil. 247(1):133 139. Sepehr, E ., Z. Rengel, E. Fateh, and M.R. Sadaghiani. 2012. Differential capacity of wheat cultivars and white lupin to acquire phosphorus from rock phosphate, phytate and soluble phosphorus sources. J. Plant Nutr. 35(8):1180 1191. Shane, M.W., E.T. Fedosejevs, and W.C. Plaxton. 2013. Reciprocal control of anaplerotic phosphoenolpyruvate carboxylase by in vivo monoubiquitination and phosphorylation in developing proteoid roots of phosphate deficient Harsh Hakea. Plant Physiol. 161(4):1634 1644. Sharpley, A.N. and P. J. Withers. 1994. The environmentally sound management of agricultural phosphorus. Fert. Res. 39(2):133 146. Shenoy, V. and G. Kalagudi. 2005. Enhancing plant phosphorus use efficiency for sustainable cropping. Biotechnol. Adv. 23(7 8):501 513. Shin, H., H. Shin, G.R. Dewbre, and M.J. Harrison. 2004. Phosphate transport in Arabidopsis: Pht1;1 and Pht1;4 play a major role in phosphate acquisition from both low and high phosphate environments. The Plant Journal 39(4):629 642. Sinclair, T. and V. Vadez. 200 2. Physiological traits for crop yield improvement in low N and P environments. Plant Soil 245(1):1 15. Singh, J.P. 1987. Role of phosphorous and potassium content of leaf in maximizing potato yield. J. Agric. Sci. 57:565 566. Skene, K. 1998. Cluster root s: some ecological considerations. J. Ecol. 86(6):1060 1064.

PAGE 100

100 Smit, A.L., P.S. Bindraban, J.J. Schrder, J.G. Conijn., and H.G. van der Meer. 2009. Phosphorus on agriculture: global resources, trends and developments. Nutrient Flow Task Group, Netherlands 2 82. Sobrado, M.A. 2012. Leaf tissue water relations in tree species from contrasting habitats within the upper Rio Negro forests of the Amazon region. J. Trop. Ecol. 28:519 522. Stark, J.C. and S.L. Love. 2003. Potato production systems. University of Idah o, Idaho. Syers, J.K., Johnston A.E., Curtin, D. 2008. Efficiency of soil and fertilizer phosphorus: reconciling changing concepts of soil phosphorus behaviour with agronomic information. FAO, Rome 18. Tardieu, F., C. Granier, and B. Muller. 2011. Water de ficit and growth. Co ordinating processes without an orchestrator? Curr. Opin. Plant Biol. 14(3):283 289. Terry, N. and I.M. Rao. 1991. Nutrients and photosynthesis: iron and phosphorus as case studies. Cambridge, Cambridge, UK. The World Bank. 2013. Phosp hate rock. Index Mundi, 2013. < http://www.indexmundi.com/commodities/?commodity=rock phosphate&months=120 >. Thomas, A., A.D. Tomos, J.L. Stoddard, H. Tho mas, and C.J. Pollock. 1989. Cell expansion rate, temperature and turgor pressure in growing leaves of Lolium temulentum L. New Phytol. 112(1):1 5. Ticconi, C. and S. Abel. 2004. Short on phosphate: plant surveillance and countermeasures. Trends Plant Sci. 9(11):548 555. Tilman, D., J. Fargione, B. Wolff, C. D'Antonio, A. Dobson, R. Howarth, D. Schindler, W. Schlesinger, D. Simberloff, and D. Swackhamer. 2001. Forecasting agriculturally driven global environmental change. Science 292(5515):281 284. Uhde St one, C., K.E. Zinn, M. Ramirez Yanez, A. Li, C.P. Vance, and D.L. Allan. 2003. Nylon filter arrays reveal differential gene expression in proteoid roots of white lupin in response to phosphorous deficiency. Plant Physiol. 131:1064 1079. Van Alphen, B.J. an d J.J. Stoorvogel. 2000. A methodology for precision nitrogen fertilization in highinput farming systems. Precision Agric 2(4):319 332. Vance, C.P., C. Uhde Stone, and D.L. Allan. 2003. Phosphorus acquisition and use: critical adaptations by plants for se curing a nonrenewable resource. New Phytol. 157(3):423 447. Vanderzaag, D. and D. Horton. 1983. Potato production and utilization in world perspective with special reference to the tropics and sub tropics. Potato Res. 26(4):323 362.

PAGE 101

101 Vogt, K., D. Vogt, and J. Bloomfield. 1998. Analysis of some direct and indirect methods for estimating root biomass and production of forests at an ecosystem level. Plant Soil 200(1):71 89. Wang, B., J. Shen, C. Tang, and Z. Rengel. 2008. Root morphology, proton release, and c arboxylate exudation in lupin in response to phosphorus deficiency. J. Plant Nutr. 31(3):557 570. Wang, G., D. Zhou, Q. Yang, J. Jin, and X. Liu. 2005. Solubilization of rock phosphate in liquid culture by fungal isolates from rhizosphere soil. Pedosphere 15(4):532 538. Wang, J., J. Sun, J. Miao, J. Guo, Z. Shi, M. He, Y. Chen, X. Zhao, B. Li, F. Han, Y. Tong, and Z. Li. 2013. A phosphate starvation response regulator Ta PHR1 is involved in phosphate signalling and increases grain yield in wheat. Ann. Bot. 111(6):1139 1153. Wang, Y., H. Xu, J. Kou, L. Shi, C. Zhang, and F. Xu. 2013. Dual effects of transgenic Brassica napus overexpressing CS gene on tolerances to aluminum toxicity and phosphorus deficiency. Plant Soil 362(1 2):231 246. Ward, C.L., A. Klein ert, K.C. Scortecci, V.A. Benedito, and A.J. Valentine. 2011. Phosphorus deficiency reduces aluminium toxicity by altering uptake and metabolism of root zone carbon dioxide. J. Plant Physiol. 168(5):459 465. Warren, C.R. and M.A. Adams. 2002. Phosphorus af fects growth and partitioning of nitrogen to Rubisco in Pinus pinaster. Tree Physiol. 22(1):11 19. Watt, M. and J. Evans. 1999. Proteoid roots. Physiology and development. Plant Physiol. 121(2):317 323. Weaver, J.E. 1926. Root development of field crops. M cGraw Hill Book Co, New York. Winter, H. and S. Huber. 2000. Regulation of sucrose metabolism in higher plants: Localization and regulation of activity of key enzymes. Crit. Rev. Biochem. Mol. Biol. 35(4):253 289. Wissuwa, M. 2005. Combining a modelling wi th a genetic approach in establishing associations between genetic and physiological effects in relation to phosphorus uptake. Plant Soil 269(1 2):57 68. Witowski, E.T.F. and B.B. Lamont. 1991. Leaf specif mass confounds leaf density and thickness. Oecolo gia 88:486 493. Xu, J., Y. Zhu, Q. Ge, Y. Li, J. Sun, Y. Zhang, and X. Liu. 2012. Comparative physiological responses of Solanum nigrum and Solanum torvum to cadmium stress. New Phytol. 196(1):125 138. Xu, Y. and J.H. Crouch. 2008. Marker assisted selecti on in plant breeding: From publications to practice. Crop Sci. 48(2):391 407.

PAGE 102

102 Yan, X., H. Liao, S. Beebe, M. Blair, and J. Lynch. 2004. QTL mapping of root hair and acid exudation traits and their relationship to phosphorus uptake in common bean. Plant Soi l 265(1 2):17 29. Yaseen, M. and S.S. Malhi. 2009. Differential growth response of wheat genotypes to ammonium phosphate and rock phosphate phosphorus sources. J. Plant Nutr. 32(3):410 432. Yu, L., J. Yan, S. Guo, and W. Zhu. 2012. Aluminum induced secreti on of organic acid by cowpea (Vigna unguiculata L.) roots. Sci. Hortic. 135:52 58. Zeng, H., X. Feng, B. Wang, Y. Zhu, Q. Shen, and G. Xu. 2013. Citrate exudation induced by aluminum is independent of plasma membrane H+ ATPase activity and coupled with pot assium efflux from cluster roots of phosphorus deficient white lupin. Plant Soil 366(1 2):389 400. Zeng, X., W.S. Chow, L. Su, X. Peng, and C. Peng. 2010. Protective effect of supplemental anthocyanins on Arabidopsis leaves under high light. Physiol. 138( 2):215 225. Zhou, J., F. Jiao, Z. Wu, Y. Li, X. Wang, X. He, W. Zhong, and P. Wu. 2008. OsPHR2 is involved in phosphate starvation signaling and excessive phosphate accumulation in shoots of plants. Plant Physiol. 146(4):1673 1686. Zhu, J., S. Kaeppler, an d J. Lynch. 2005. Mapping of QTL controlling root hair length in maize (Zea mays L.) under phosphorus deficiency. Plant Soil 270(1 2):299 310. Zhu, J. and J. Lynch. 2004. The contribution of lateral rooting to phosphorus acquisition efficiency in maize (Z ea mays) seedlings. Funct. Plant Biol. 31(10):949 958. Zhu, Y., S. Smith, A. Barritt, and F. Smith. 2001. Phosphorus (P) efficiencies and mycorrhizal responsiveness of old and modern wheat cultivars. Plant Soil 237(2):249 255. Zhu, Y., F. Yan, C. Zorb, and S. Schubert. 2005. A link between citrate and proton release by proteoid roots of white lupin (Lupinus albus L.) grown under phosphorus deficient conditions? Plant Cell Physiol. 46(6):892 901. Zia ul Hassan and M. Arshad. 2010. Cotton growth under potassi um deficiency stress is influenced by photosynthetic apparatus and root system. Pak. J. Bot. 42(2):917 925. Zoghlami, L.B., W. Djebali, Z. Abbes, H. Hediji, M. Maucourt, A. Moing, R. Brouquisse, and W. Chaibi. 2011. Metabolite modifications in Solanum lyco persicum roots and leaves under cadmium stress. Afr. J. Biotechnol. 10(4):567 579. Zotarelli, L., B.M. Santos, P.J. Dittmar, P.D. Roberts, and S.E. Webb. 2013. Potato production. In: S.M. Olson and E. Simonne (eds.). Vegetable production handbook for Flori da. The Institute of Food and Agricultural Sciences.

PAGE 103

103 BIOGRAPHICAL SKETCH Wei Chieh Lee was born in Taiwan in 1987. She got her b achelor degree in Plant Pathology from National Chung Hsing University in 2009. Wei Chieh then got an intern position at Ohi o State University Plant Pathology lab. She work ed on transformation, DNA extraction from both plant tissue and fungi, PCR and sequencing, using fluorescence microscope, plasm id mini prep, DNA electrophoresis and related greenhouse tasks. After a year of the lab work, W ei Chieh decided to pursue her m After her m aster s he w ants her career in agricultur e to proceed