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[III LIIIIIII‘IIII‘ “I, I] D ‘I ' I I I I I I ; I I’; If; ' > ‘ - 2—21“ III" IIIIII'III‘ THt-fszs willllilllglllrlll 3 1293 O1 4412 This is to certify that the thesis entitled ASSESSMENT OF ROOT MORPHOLOGY AS AN INDICATOR OF DROUGHT RESISTANCE IN COMMON BEAN (Phaseolus vulgaris L.) presented by Maurice D. Yabba has been accepted towards fulfillment of the requirements for ‘ Master degree in Science ‘ Major professor Date 10120/97 0-7639 MS U is an Affirmative Action/Equal Opportunity Institution LIBRARY Michigan State University PLACE iN RETURN Box to remove this checkout from your record. TO AVOID FINE return on or before date due. DATE DUE DATE DUE m1: DUE 1m mus-m4 ASSESSMENT OF RESIST ASSESSMENT OF ROOT MORPHOLOGY AS AN lNDICATOR OF DROUGHT RESISTANCE IN COMMON BEAN (Phaseolus vulgan's L.) By Maurice D. Yabba A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Crop Physiology (- Crop and Soil Science 1 997 SESSMENTl AS RESlE Drought lir ms md evider moistm‘e stress. Wipes under Wlogical re: Mailiylene giyc Wider limiting am oondlJilted in Mic “BAN PEG ex MWire stress ,1 man“ index “ Md Under limitir ABSTRACT ASSESSMENT OF ROOT MORPHOLOGY AS AN INDICATOR OF DROUGHT RESISTANCE IN COMMON BEAN (Phaseolus vulgaris L.) By Maurice D. Yabba Drought limits yield in most common bean (Phaseolus vulgaris L.) growing areas and evidence suggests that roots may regulate shoot growth during moisture stress. This study was conducted to assess yield of eight bean genotypes under moisture stress and non-stress conditions and to compare root morphological response in 10" M abscisic acid (ABA), -0.52 and -1.07 MPa polyethylene glycol (PEG), and 0.76 m x 30 mm polyvinyl chloride (PVC) tubes under limiting and non-limiting moisture conditions. The research was conducted in Michigan using a rainshelter for field trials, a growth chamber for ABA and PEG experiments, and a greenhouse for the PVC experiments. Moisture stress reduced yield up to 46%. The geometric mean and stress tolerance index were better predictors than the drought susceptibility index of yield under limiting moisture. ABA increased total root length. ABA, PEG, and moisture stress increased the percentage of smaller diameter roots. Significant correlations occurred between total root length in PVC tubes and total root length in ABA and PEG. Seed weight affected total root length. Copyright by Maurice D. Yabba 1 997 Dedicated to my children Micheal, Bonakala, and Elangeni lemme and encourageme suggestions thron. “BI patience were W patience dee Iwould als< for their suggestlo widance Committl I would like throughout my sta; 'am QralefL Fergusm I°f their The assista, W0” and ma in' 8%” Is greatly al Thanks to B: Ile Crops barn iOr t ACKNOWLEDGEMENTS i wish to express my gratitude to Dr. Eunice F. Foster for her guidance and encouragement during my stay at Michigan State University. Her helpful suggestions through the different phases of this research and my life along with her patience were instrumental for the completion of my studies. I appreciate your patience deeply. I would also like to thank Drs. Jim Kelly, Delbert Mokma, and David Dilley for their suggestions and review of this thesis in their capacity as members of my guidance committee. I would like to thank Dr. James Jay for his support and encouragement throughout my stay at Michigan State University. I am grateful to Dr. Alvin Smucker and his staff Vera Bakic and John Ferguson for their assistance with digitizing and processing of my root samples. The assistance of Greg Parker and all those who helped with the irrigation and maintaining the rainshelter at the Kellogg Biological Research Station is greatly appreciated. Thanks to Brian Graff, Tom Galecka, Norm Blakely, and Jerry Taylor at the Crops barn for their assistance with the processing of the samples and «wing that l was Iwould like i won, and Tawain Their assistance we Special thanl wove water. I deeply appr Collaborative Resea ensuring that I was able to conduct the experiments smoothly. I would like to thank Charles Heimiller, Eric Baka, Ester Nobles, Mike Carroll, and Tawainga Katsvairo for all their assistance throughout this research. Their assistance were invaluable. A Special thanks goes to wife Sundra Philletta Yabba for keeping my head above water. I deeply appreciate the financial support from the Bean-Cowpea Collaborative Research Support Program (MSU). iii UST OF TABLES UST 0F FIGURE INTRODUCTION LITERATURE RE Root Grow Drought Re Effects of I Effects of 5 ABA and D Po'Yethyler Literature c CHAPTER 1 FIELDSELEcrlo introductior Materials al Calculation ReSUItS 8m: 1995 1 996 Greater vali USl0n_ Lne‘ature C TABLES OF CONTENTS LIST OF TABLES ........................................................................................ vii 4 LIST OF FIGURES .................................................................................... xvii lNTRODUCTION .......................................................................................... 1 LITERATURE REVIEW ................................................................................. 5 Root Growth ....................................................................................... 7 Drought Resistance ............................................................................ 10 Effects of Drought on Growth, Development, and yield ...................... 12 Effects of Drought on Photosynthesis and Stomatal Conductance... 14 ABA and Drought ................................................................................ 16 Polyethylene (PEG) and Drought ....................................................... 18 Literature cited .................................................................................... 20 CHAPTER 1 FIELD SELECTION FOR DROUGHT RESISTANCE Introduction ......................................................................................... 30 Materials and Methods ....................................................................... 32 Calculations ....................................................................................... 34 Results and Discussion ...................................................................... 35 1995 Field Experiment ............................................................. 35 1996 Field Experiment ............................................................. 46 Greater validity of 1995 data ............................................................... 58 Conclusion .......................................................................................... 60 Literature Cited ................................................................................... 61 CHAPTER 2 BEAN SEEDLING ROOT GROWTH AS AN INDICATOR OF FIELD PERFORMANCE UNDER MOISTURE STRESS Introduction ........................................................................................ 63 Materials and Methods ....................................................................... 66 Genotypes ............................................................................... 66 Growth Chamber Study ........................................................... 66 iv Results an Root Lang -1 .0] Polyviny|.cl Expe PVC Polyvinyl-cl Expe Correlation: PVC PVC Conclusion, Literamre C CHAPTER 3 GROWTH. Root Statistics ........................................................................ .69 ABA Experiment ..................................................................... 69 PEG Experiment ................................................................... 70 Greenhouse Study ................................................................. 70 Correlations ........................................................................... 72 Results and Discussion Root Length Control Experiment Root Length ........................................... 72 ABA Experiment Root Length ................................................ 76 -0.52 MPa Polyethylene Glycol Experiment Root Length ...... 83 -1.07 MPa Polyethylene Glycol Experiment Root Length ...... 85 Ratios ............................................................................................... 90 Control Ratios ........................................................................ 90 ABA Ratios ............................................................................. 90 -0.52 MPa Ratios .................................................................... 93 -1.07 MPa Ratios .................................................................... 93 Delta Values ABA Deltas ............................................................................. 101 -0.52 MPa PEG Deltas ........................................................... 101 -1.07 MPa PEG Deltas ........................................................... 104 Polyvinyl-chloride Experiment Experiment1 .......................................................................... 104 PVC Experiment 1 Ratios ....................................................... 119 Polyvinyl-chloride Experiment Experiment 2 ........................................................................... 1 19 Rooting pattern ............................................................ 119 PVC Experiment 2 Ratios ............................................. 130 Correlations ....................................................................................... 133 PVC Experiment 1 .................................................................. 133 PVC Experiment 2 ................................................................. 141 Conclusion ........................................................................................ 141 Literature Cited .................................................................................. 148 CHAPTER 3 THE EFFECT OF ABA, PEG, AND WATER STRESS ON ABOVE GROUND . GROWTH. Introduction ........................................................................................ 151 Materials and Methods153 Genotypes ............................................................................... 1 53 Growth Chamber Study ........................................................... 154 ABA Experiment ...................................................................... 156 PEG Experiment ..................................................................... 156 Greenhouse Study .................................................................. 157 Results and Discussion Control Treatment: Leaf, Stern, and Root Dry Weight ............ 158 ABA Treatinent: Leaf, Stern, and Root dry weight .................. 161 Deltas .......................................................................... 163 -0.52 MPa PEG Treatment: Leaf, stem, and root dry weight..163 Deltas .......................................................................... 166 -1.07 MPa PEG Treatment: Leaf, stem, and root dry weight. 168 Deltas .......................................................................... 168 comparison Across Experiments ........................................... 168 Effects of Nutrient Solution Versus Water .............................. 173 Polyvinyl-chloride Experiment 1: Leaf, stem, and root dry weight ..................................................................................... 1 75 Polyvinyl-chloride Experiment 2: Leaf, stem, and root dry weight ..................................................................................... 177 Effects of Water stress ........................................................... 177 Correlations ............................................................................ 177 Conclusion .............................................................................. 180 Literature Cited ....................................................................... 185 Summary and conclusion .................................................................. 187 Recommendations ............................................................................. 189 CHAPTER1 l. Characteristl apartments MI. in 1995 a 2 Yield of non-: wmbined yie suswptible ir index (STI) o own in a ra Hickory Corn 3- Correlations l Md Combinei Wide me ”Id Stress to! US V. Station in Hic 4~ Yield under 5 yield reductio mean (GM), a (”lam/Us v! .aithe KGIIOQC In 1 Droi 5' :Nhite mOId‘ t 996 QTOWing LIST OF TABLES CHAPTER 1 1. Characteristics of common bean genotypes grown in field experiments at Kellogg Biological Station, Hickory Corners, Mi. in 1995 and 1996 ............................................................................ 33 2. Yield of non-stress treatment, percent yield reduction, combined yield for stress and non-stress treatments, drought susceptible index (DSI), Geometric mean, and stress tolerance index (STI) of eight bean (Phaseolus vulgaris L.) genotypes grown in a rainshelter at the Kellogg Biological Station in Hickory Comers, MI in 1995. Drought intensity index = 0.35 ............... 44 3. Correlations of yield under stress, yield under non-stress, and combined yield for stress and non-stress treatment to geometric mean (GM), drought susceptibility index (DSI), and stress tolerance index (STI). Data from bean (Phaseolus vulgan's L.) plants grown at the Kellogg Biological Station in Hickory Comers, Ml. In 1995 ................................................ 47 4. Yield under stress and non-stress treatments, percent yield reduction, drought susceptibility index (DSI), geometric mean (GM), and stress tolerance index (STI) of bean (Phaseolus vulgaris L.) genotypes grown in a rainshelter at the Kellogg Biological Station in Hickory Corners, MI in 1996. Drought intensity index = 0.05 .............................................. 55 5. White mold, bronzing, and yellowing observed during the 1996 growing season at KBS ............................................................... 57 6. Correlations of yield under stress, yield under non-stress treatment, and combined yield for moisture treatments to geometric mean (GM), drought susceptibility index (DSI), and stress tolerance index (STI). Data from bean (Phaseolus vulgaris L.) plants grown at the Kellogg Biological Station in Hickory Corners, MI. in 1996 ................................ 59 CHAPTER 2 l. Chaacteris apartments 2 Total root le germinated aid transpla 9mm chan strength Ho: 23120°C day Roots are di 3. Percentage r oommm bea dumber for 4 environment: half strength water at 23/2 PIIOIOPGriod.. 4' R0“ growth I Solution versi 5' Total rClOt len 9e’"Iinated in and tra"Splarl for 1 @Watures d'V'ded Into 5 CHAPTER 2 1. Characteristics of been genotypes grown in field experiments at KBS. East Lansing, MI. 1995 and 1996 ................... . Total root length of eight common bean genotypes germinated in a germination chamber for 4 d at 25°C and transplanted to an environmentally controlled growth chamber for 1.4 d in a control solution of half strength Hoagland’s solution or deionized water at 23120°C day/night temperatures and a 15 h photoperiod. Roots are divided into 5 classes based on width diameter ............... Percentage of roots in individual root classes for eight common bean genotypes germinated in a germination chamber for 4 d at 25°C and transplanted to an environmentally controlled growth chamber for 14 d in half strength Hoagland’s nutrient solution or deionized water at 23120°C day/night temperatures and a 15 h photoperiod ....................................................................................... Root growth response to half strength Hoagland’s nutrient solution versus deionized water ........................................................ Total root length of eight common bean genotypes germinated in a germination chamber for 4 d at 25°C and transplanted to an environmentally controlled growth chamber for 14 d in 10‘ M ABA at 23120°C day/night temperatures and a 15 h photoperiod. Roots were divided into 5 classes based upon root diameter .............................. Comparison of root length of eight common bean genotypes germinated in a germination chamber for 4 d at 25°C and transplanted to an environmentally controlled growth chamber for 14 d at 23l20°C day/night temperatures and a 15 h photoperiod from the four treatments imposed. Roots were divided into 5 classes based upon root diameter ..................... Percentage of roots from individual root classes of eight common bean genotypes germinated in a germination chamber for 4 d at 25°C and transplanted to an environmentally controlled growth chamber for 14 d at 23l20°C day/night viii .. 67 73 75 77 78 79 temperatu a Cunparisc classes of treatments at 25°C anr g'owth chal ada15h, 9. Total root is germinated tansplanted chamber for 15 h photope at 0.52 MPa “Pm root die 10. Percentage r common bea mm TOT 4 firmmomenta day/flight tem 9W (PEG 6 11‘ TOW I’Oot lens a germination t° an environl temperatures and a 15 h photoperiod in 10“ M ABA ....................... Comparison of percentage of roots from individual root classes of eight common been genotypes from four. treatments germinated in a germination chamber for 4 d at 25°C and transplanted to an environmentally controlled growth chamber for 14 d at 23l20°C day/night temperatures and a 15 h photoperiod ..................................................................... Total root length of eight common bean genotypes germinated in a germination chamber for 4 d at 25°C and transplanted to an environmentally controlled growth chamber for 14 d at 23l20°C day/night temperatures and a 15 h photoperiod in a polyethylene glycol (PEG) solution of -0.52 MPa. Roots are divided into 5 classes based upon root diameter .............................................................................. 10. Percentage of roots from individual root classes of eight 11. 12. 13. common bean genotypes germinated in a germination chamber for'4 d at 25°C and transplanted to an environmentally controlled growth chamber for 14 d at 23120"C day/night temperatures and a 15 h photoperiod in a polyethylene glycol (PEG 600) solution of -0.52 MPa ........................................... Total root length of eight bean genotypes germinated in a germination chamber for 4 d at 25°C and transplanted to an environmentally controlled growth chamber for 14 d at 23/20°C day/night temperatures and a 15 h photoperiod in a polyethylene glycol (PEG) solution of -1.07 MPa. Roots are divided into 5 classes based upon root diameter ............. Percentage of roots from individual root classes of eight common bean genotypes germinated in a germination chamber for 4 d at 25°C and transplanted to an environmentally controlled growth chamber for 14 d in a polyethylene glycol (PEG-600) solution of -1.07 MPa at 23120°C day/night temperatures and a 15 h photoperiod ............................................... Various ratios of different root classes in plants grown in the growth chamber in control, ABA or PEG 600 (-0.52 or -1.07 MPa) solutions .......................................................... 14. Ratios of root classes that had significant genotypic ix 81 82 84 86 87 .89 .. 91 dilierence- in growth I deionized 15. Table of al significanc 16. Ratios Iron control ex; 17. Table of re experiment 18. Ratios frorr to the contr 19. Table of all apartment 20. Ratios from to the contr: 21- Mean differs “Ch TOOI cli individual ro m“ the con 2. PGIYGthylene A" ”Withers r axPeriment ir I001 Class ”or 23' Po”ethylene All ”unlbers l Bioenmem ir '°°i Class fro II 0.7 in PVC “40 d at 25 photoperiod i We EXPQFIm differences in the control experiment of seedlings grown in growth pouches in a hydroponic solution that contained deionized water or half strength Hoagland’s nutrient solution .......... 92 15. Table of all ratios from ABA experiment that had genotypic significance ....................................................................................... 94 16. Ratios from the ABA experiment that correspond to the control experiment ratios that had genotypic significance ................ 95 17. Table of ratios from polyethylene glycol (-0.52 MPa) experiment that have genotypic significance .................................... 96 18. Ratios from the -0.52- MPa PEG experiment that correspond to the control experiment ratios that had genotypic significance ....... 97 19. Table 'of all ratios from polyethylene glycol (-1.07 MPa) experiment that have genotypic significance ..................................... 98 20. Ratios from the -1.07 MPa PEG experiment that correspond to the control experiment ratios that had genotypic significance ........ 100 21. Mean difference between ABA and control (delta) for each root class. All numbers represents ABA experiment individual root classes minus the appropriate root class from the control treatment ................................................................... 102 22. Polyethylene glycol (-0.52 MPa) delta conversions. All numbersrepresents polyethylene glycol (0.52 MPa) experiment individual root classes minus the appropriate root class from the control treatment .................................................... 103 23. Polyethylene glycol (-1.07 MPa) delta conversions. All numbers represents polyethylene glycol (-1.07 MPa) experiment individual root classes minus the appropriate root Class from the control treatment ................................................... 105 24. Total root length of four common bean genotypes grown in 0.7 m PVC tubes of 30 cm diameter in a greenhouse for 40 d at 28°C :1: 2 day/night temperatures and a 15 h photoperiod in stress and non-stress conditions. PVC Experiment 1 ............................................................................. 106 .53 25. Statistical analysis of root growth under stress and non-stress 27. 28. 29. 30. 31. 32. Conditionsof the PVC 1 experiment. Data presented for actual length in each class and for percentage of total root length In each class .................................................................................... . Cumulative total root length of four common bean genotypes grown in 0.7 m PVC tubes of 30 cm diameter in a greenhouse for 40 d at 28°Ct2 day/night temperatures and a 15 h photoperiod in a stress and non—stress treatment. PVC Experiment 1 ........................................ Percentage of root length for individual sections of four common bean genotypes grown in 0.7 m PVC tubes of 30 cm diameter in a greenhouse for 40 d at 28°C :1: 2 day/night temperatures and a 15 h photoperiod in stress and non-stress conditions. Experiment 1 ........................................ Percentages of roots in individual root classes when data was combined for all' depths of a 0.7 m PVC tubes of 30 cm diameter for four common bean genotypes. Plants were grown in a greenhouse for 40 d at 28°C:l:2 day/night temperatures and a 15 h photoperiod in a stress and non-stress treatment. Experiment 1 ................................................ Ratios of total root length across all soil depths of PVC Experiment 1 and which correspond to the control experiment ratios (Pouch study) that had genotypic significance... Percentage of total root length at each soil depth in two different experiments using 0.7 m PVC tubes. Plants in PVC Experiment 1 were planted in June 1996 and grown at 28°C12°C. Plants in PVC Experiment 2 were planted in September 1996 and grown at 25°C:t—2°C ................................................................... Total root length of four common bean genotypes grown in 0.7 m PVC tubes of 30 cm diameter in a greenhouse for 40 d at 25°C :1: 2 day/night temperatures and a 15 h photoperiod in stress and non-stress conditions. PVC Experiment 2 ............................................................................ Statistical analysis of root growth under stress and non-stress Conditions of the PVC 2 experiment. Data presented for actual root length in each class and for percentage of total root length I'OOt 109 .112 ..113 . 118 .. 120 121 . 123 37. 39. in each class ..................................................................................... . Cumulative total root length of four common bean genotypes grown in 0.7 m PVC tubes of 30 cm diameter in a greenhouse for 40 d at 25 :I: 2°C day/night temperatures and a 15 h photoperiod in a stress and non-stress treatment. PVC Experiment 2............... .............................................................. . Percentage er total root length-for individual sections of four‘common bean genotypes grown in 0.7 m PVC tubes of 30 cm diameter in a greenhouse for 40 d at 25 t 2°C day/night temperatures and a 15 h photoperiod in a Stress and non-stress treatment PVC Experiment 2 ............................................................ . Percentages of roots in individual root classes when data was combined for all depths of a 0.7 m PVC tubes of 30 cm diameter for four common bean genotypes. Plants were grown in a greenhouse for 40 d at 25°C:l.-2 day/night temperatures and a 15 h photoperiod in a stress and non-stress treatment. Experiment 2 ................................................. . Comparison of all ratios with genotypic significance from the control treatment in the pouch study to the same ratios from PVC. 2 experiment .................................................................... Correlations of root classes from control, ABA, -0.52 MPa PEG, and -1.07 MPa PEG (pouch study) containing deionized water or half strength Hoagland’s nutrient solution with corresponding root classes of plants grown in a 0.76 m PVC tube at depth 1 - 15.2 cm. PVC Experiment 1 .................................. . Correlations of root classes from control, 052 MPa PEG, and -1.07 MPa PEG (pouch study) containing deionized water or half strength Hoagland’s nutrient solution with corresponding root classes of plants grown in a 0.76 m PVC tube at depth 15.3 - 30.5 cm. PVC Experiment 1 .............................. Correlations of root classes from control, ABA, -0.52 MPa PEG, and -1.07 MPa PEG (pouch study) containing deionized water or half strength Hoagland’s nutrient solution with corresponding root classes of plants grown in a 0.76 m PVC tube at depth 30.6 - 45.7 cm. PVC Experiment 1 .............................. 125 127 128 131 132 135 ..136 ..137 40. Correlationsof root classes from control, ABA, -0.52 MPa PEG, and -1.07 MPa PEG (pouch study) containing deionized water or half strength Hoagland’s nutrient solution with corresponding root classes of plants grown in a 0.76 in PVC tubeatdepth45.8-61.0cm.PVCExperiment1 ................................ 138 41. Correlations of root classes from -0.52 MPa PEG and -1.07 MPa PEG (pouch study) containing deionized water or half strength Hoagland’s nutrient solution with corresponding root classes of plants grown in a 0.76 m PVC tube at depth 45.8 - 61.0 cm. PVC Experiment 1 ................................ 139 42. Correlations of root classes from control, ABA, -0.52 MPa PEG, and -1.07 MPa PEG (pouch study) containing deionized water or half strength Hoagland’s nutrient solution with corresponding root classes of plants grown in a 0.76 m PVC tube at depth 1 - 15.2 cm. PVC Experiment 2 .................................. 142 43. Correlations of root classes from control, 052 MPa PEG, and -1.07 MPa PEG (pouch study) containing deionized water or half strength Hoagland’s nutrient solution with corresponding root classes of plants grown in a 0.76 m PVC tube at depth 15.3 - 30.5 cm. PVC Experiment 2 .............................. 143 CHAPTER 3. . 1. Characteristics of common bean genotypes grown in field experiments at Kellogg Biological Station, Hickory Corners, MI. in 1995 and 1996 .......................................................................... 155 2. Dry weight (g) of leaves, stems, shoots, and roots and root/shoot ratio and 100 seed weight of eight common bean genotypes germinated in a germination chamber for 4 d at 25°C and transplanted to an environmentally controlled growth chamber for 14 d at 23120°C day/night temperatures and a 15 h photoperiod in a control solution of half strength Hoagland's solution or deionized water .................................................................. 160 3. Dry weight (g) of leaves, stems, shoots, and roots and root/shoot ratio and 100 seed weight of eight common bean genotypes germinated in a germination chamber for 4 d at xiii 25°Candt cha ada15h I. Mean diffe. for leaf, ste man 99m at 25°C ant chanber fc 15h photol 5. Dry weight rootlshoot l 'n a germin a'l environr 23l20°C da polyethylen 6 Meal differ I control (dell f“ Bight cor Chamber for controlled 9 tel"perature WSIloot r: n a 99mins 3‘ BOVernm 25°C and transplanted to an environmentally controlled growth chamber for 14 d at 23120°C day/night temperatures and a 15 h photoperiod in a solution of 10‘ M ABA .......................... . Mean difference between ABA treatment and control (delta) for leaf, stem, shoot, root, and root/shoot ratio for eight common bean genotypes germinated in a germination chamber for 4 d at 25°C and transplanted to an environmentally controlled growth chamber for 14 d at 23120°C day/night temperatures and a 15 h photoperiod ....................................................... . Dry weight (g) of leaves, stems, shoots, and roots, and root/shoot ratio of eight common-bean genotypes germinated in a germination chamber for 4 d at 25°C and transplanted to an environmentally controlled growth chamber for 14 d at 23l20°C day/night temperatures and a 15 h photoperiod in polyethylene glycol 600 solution of -0. 52 MPa ............................... . Mean difference between -0.52 MPa PEG treatment and control (delta) for leaf, stem, shoot, root, and rootlshoot ratio for eight common bean genotypes germinated in a germination chamber for 4 d at 25°C and transplanted to an environmentally controlled growth chamber for 14 d at 23l20°C day/night temperatures and a 15 h photoperiod .............................................. . Dry weight of leaves, stems, shoots, and roots and root/shoot ratio of eight common bean genotypes germinated in a germination chamber for 4 d at 25°C and transplanted to an environmentally controlled growth chamber for 14 d at 23l20°C day/night temperatures and a 15 h photoperiod in polyethylene glycol 600_solution of -1.07 MPa ................................ . Mean difference between -1.07 MPa PEG treatment and control (delta) for leaf, stem, shoot, root, and root/shoot ratio for eight common bean genotypes germinated in a germination chamber for 4 d at 25°C and transplanted to an environmentally controlled growth chamber for 14 d at 23120°C day/night temperatures and a 15 h photoperiod ............................................... . Comparison of leaf, stem, shoot, root dry weight and root/shoot ratio of eight common bean genetypes germinated in a germination chamber for 4 d at 25°C and transplanted to an environmentally controlled growth chamber for 14 d at 23120°C day/night xiv 162 164 165 167 169 170 temperatures and a 15 h photoperiod from the four treatments imposed ............................................................................................ 171 10. Leaf, stern, shoot, and root and R18 ratio growth response 11. 12. 13. 14. 15. to half strength Hoagland’s nutrient solution versus deionized water ............................... , ................................................................ 174 Dry weight of leaves, stems, shoots, and roots and root/shoot ratio of four common bean genotypes grown in a greenhouse for 40 d at 28°ch and a 15 h photoperiod in a . polyvinyl-chloride tube measuring 76. 2 cm in length and 30. 5 cm in diameter ........... . .................................................................... 176 Dry weight of leaves, stems, shoots, and roots and root/shoot ratio of four common bean genotypes grown in a greenhouse for 40 d at 25°C12°C and a 15 h photoperiod in a polyvinyl-chloride tube measuring 76.2 cm in length and 30.5 cm in diameter. PVC Experiment 2 ........................................................................... 178 Leaf, stem, shoot, reproductive, and root and R18 ratio growth response to stress and nonstress moisture conditions of plants grown in a greenhouse for 40 d at 28 :i: 2°C (PVC Expt. 1) and 25.1 2°C (PVC Expt. 2) day/night temperatures and a 15 h photoperiod in PVC tubes ............................................................... 179 Correlation coefficient for leaf, stem, shoot, and R18 ratio among four common bean genotypes to plants grown in a greenhouse for 40 d at 28 a: 2°C day/night temperatures and a 15 h photoperiod in PVC tubes. PVC Experiment 1 ........................ 177 Correlation coefficient for leaf, stem, shoot, and R18 ratio among four common bean genotypes to plants grown in a greenhouse for 40 d at 25 :t: 2°C day/night temperatures and a 15 h photoperiod in PVC tubes. PVC Experiment 2 ........................ 182 1. PAR interc bean grown the Kellogg ZLeaftempe beatgmwr harainshr Corners,M 3. Transpirati been growl 'n a rainshl Corners, M 4' Net-mm prl bean grow it a rainsni Corners, M .bea” grow It a TalnShl corI'lers, IV 5. NeUU'On pr P93“ growl ll 8 raihShr r3, N 7. Mean mOnl recorded 8 MI. In 1995 8. PAR Interc gr "‘6 Kalle: LIST OF FIGURES . PAR intercepted by the canopy of eight genotypes of common been grown under stress and nonstress moisture conditions at the Kellogg Biological Station, Hickory Comers, MI. In 1995 .................... . Leaf temperature of eight genotypes of common been grown under stress and nonstress moisture conditions in a rainshelter at the Kellogg Biological Station, Hickory comers, Ml. In 1995 .................................................................................. . Transp'iration rate of eight genotypes of common been grown under stress and nonstress moisture conditions in a rainshelter at the Kellogg Biological Station, Hickory Comers, MI. In 1995 ............ . ....................................................................... . Neutron probe counts of eight genotypes of common been grown under stress and nonstress moisture conditions in a rainshelter at the Kellogg Biological Station, Hickory 36 37 38 Corners, Ml. In 1995 .................................................................................... 40 . Neutron probe counts of eight genotypes of common bean grown under stress and nonstress moisture conditions in a rainshelter at the Kellogg Biological Station, Hickory Comers, Ml. In 1995 ..................................................................................... . Neutron probe counts of.eight genotypes of common bean grown under stress and nonstress moisture conditions in a rainshelter at the Kellogg Biological Station, Hickory Comers, MI. In 1995 ..................................................................................... . Mean monthly maximum and minimum temperature (°F) recorded at the Kellogg Biological Station, Hickory Comers, MI. In 1995 and 1996 .................................................................................... . PAR intercepted by the canopy of eight genotypes of common been grown under stress and nonstress moisture conditions at the Kellogg Biological Station, Hickory Comers, Ml. In 1996 .................... 41 42 .43 48 9. Leattempel mmgmwn “rainshe Corners, MI 10.Transpiratic beat grown hammflw Corners, Ml 11.Neutron prc bean grown 'n a rainshe Corners, Ml 12.Neutron prc I“ grown in a rainshe Corners, Ml 13.1mm prc bean growr in a rainshe COITlefs, M; 9. Leaf temperature of eight genotypes of common been grown under stress and nonstress moisture conditions in arainshelter at the Kellogg Biological Station, Hickory Comers, Ml. In 1996 .................................................................................. 49 10.Transpiration rate of eight genotypes of common been grown under stress and nonstress moisture conditions in a rainshelter at the Kellogg Biological Station, Hickory Comers, Ml. In 1996.; ........... '. ..................................................................... 50 11.Neutron probe counts of eight genotypes of common bean grown under stress and nonstress moisture conditions in a rainshelter at the Kellogg Biological Station, Hickory Comers, Ml. In 1996 ..................................................................................... 52 12.Neutron probe counts of eight genotypes of common bean grown under stress and nonstress moisture conditions in a rainshelter at the Kellogg Biological Station, Hickory Corners, Ml. In 1996 ..................................................................................... 53 13.Neutron probe counts of eight genotypes of common been grown under stress, and nonstress moisture conditions in a rainshelter at the Kellogg Biological Station, Hickory Comers, Ml. In 1996 ..................................................................................... 54 C grown a potentia Bliss, 19 Thus, it 1 Pl. agncultur ooclrred even wee 1991). It I iIEId 0f fie POIEntial (i The Poorly Und “Metal cl {Hale and ( drought res Ming Wate methods for Introduction Common bean (Phaseolus vulgaris L.) is an important legume that is grown and consumed on all continents (Adams et al., 1985). The crop has the potential to be well adapted to subsistence agricultural systems (Graham, 1981; Bliss, 1985) but drought is a persistent problem in most bean growing areas. Thus, it is important to develop drought resistant cultivars. Plants are constantly exposed to stress under both natural and agricultural conditions. Some environmental stresses such as air temperature occurred within a few minutes, whereas others took days, (e.g. soil water) or even weeks or months (e.g. mineral nutrients) to develop (T aiz and Zeiger, 1991 ). It has been estimated that physiochemical stresses have reduced the yield of field grown crops in the United States to only 22% of the crop’s genetic potential (Boyer, 1982). The physiological mechanisms that help impart drought tolerance are still poorly understood. Carbon and nitrogen partitioning and remobilization, stomatal closure, osmotic adjustment, and root development may be involved (Hale and Orcutt, 1987; Foster et al., 1995). Plants are usually classified as drought resistant or drought susceptible based upon the level of yield reduction during water stress (Hale and Orcutt, 1987). Rapid, inexpensive, and reliable methods for screening large numbers of gerrnplasm would greatly aid efforts to develop d On dassifled (Kramer, 1 oorditicne differ for d deficit Th potential 3 In rr breeding ft 1987). Ho Potential yi Efforts to in Stability cal Environme, in unPredic: Wale tat affect y 0ticon; and docIlllleriteC U’igUlbU/at a) item in We minted mo, develop drought resistant lines. Drought is a meteorological and environmental event that can be classified as permanent or seasonal based on the duration of the water stress (Kramer, 1980), and drought resistance is not a simple response. It is conditioned by a number of component responses which interact and which differ for different crops and in response to the intensity and duration of water deficit. The degree of plant water deficit depends on the extent to which water potential and cell turgor are reduced below their optimum values (Kramer, 1980). In most crops, advances in crop yields have been obtained through breeding for increased yield potential and crop management (Hale and Orcutt, 1987). However, in developing countries, bridging the gap between actual and potential yields in adverse environmental conditions can be more valuable than efforts to increase the yield potential of the crop (Acosta-Gallegos, 1988). Yield stability can be achieved through breeding for adaptation to adverse environmental stresses, and this is a more realistic approach to increasing yields in unpredictable environments (Acosta-Gallegos, 1988). Water stress causes many changes in metabolism and development that can affect yield performance. Stomatal closure is one of the changes that occurs and the role of abscisic acid (ABA) in stomatal closure has been documented in many plants (Taiz and Zeiger, 1991), including cowpea (Wgna unguiculata) and cassava (Manihot esculenfa). ABA is also thought to affect root growth in water stressed environments (Taiz and Zeiger, 1991). Drought stress inhibited root growth (Robertson et al., 1990), however, plants often increased their root to st ”(eluded the development 1 Root si. ti maintaining Outsidean a ope’ative fact deficits has ir correlated wit Filthennore, the foot and : differer'loes ir 9900type (w “Defiant ch; Nume et al., 1990) relatively lne 9e""Dlasm ( fit at. (1985) Pclyettmem CHINCH20 Thec 3 their root to shoot ratio under water limiting conditions. Robertson et al., (1990) concluded that ABA mediates drought-induced changes in the primary development of sunflower (Helianthus annus) roots. Root size, morphology, depth, length, density, and function are important in maintaining high leaf water potential against evapotranspiration demands. Considering all root attributes, root length density is probably the major operative factor (Newman, 1974). Past research on bean adaptation to water deficits has indicated that genotypic differences in biomass and yield are correlated with differences in root growth (Sponchiado et al., 1989). Furthermore, studies using grafted plants to compare the relative contribution of the root and shoot genotype to adaptation to water deficits demonstrated that differences in yield under water stress were due primarily to variation in root genotype (White and Castillo, 1989). Thus, root development appears to be an important characteristic to consider when breeding for drought resistance. Numerous methods have been reported for investigating root growth (Brar et al., 1990). In order to be useful to plant breeders, methods must be reliable, relatively inexpensive, and must permit rapid evaluation of large numbers of germplasm (Brar et al., 1990). The growth pouch method outlined by McMichael et al. (1985) met this criteria with regard to screening for root growth. Polyethylene glycol (PEG) is an inert, nonionic, long chain polymer [(HOCHz- CH,)x(CH,OH)] that has the advantage of providing a precise level of water deficit in plants. It has been used to simulate drought in plants. The objectives of this study were (1) to investigate root morphological MIDAS rootg‘Mh oft semi“ assenlhe rele Moonditlol noudtesandF 4 response to ABA or PEG in common been (2) to assess the relationship between root growth of plants grown in 15.24 cm X 16.51 cm growth poqu and that of plants grown in 76.20 cm x 30.48 cm polyvinyl chloride (PVC) tubes, and (3) to assess the relationship of yield from field-grown plants under stress and non- stress conditions with root growth and development of plants grown in growth pouches and PVC tubes. Tv vulgaris l seeded G W domestic studies (I 1986; De Generall- (Gonzale C1 People 0 is non in defiCl'ent In most r Literature Review Two. centers of domestication for common been or dry bean (Phaseolus vulgaris L.) are recognized: Mesoamerica, the center of evolution for small- seeded genotypes, and the Andes, the center of evolution for large-seeded genotypes (Gonzalez et al., 1995). Evidence for the existence of these two domestication centers comes from archeological, anatomical, and molecular studies (Evans, 1976; Kaplan, 1981; Kaplan and Kaplan, 1988; Gepts and Bliss, 1986; Debouck et al., 1993). The two gene pools differ in their yield potential. Generally, Andean accessions yield less than Mesoamerican accessions (Gonzalez et al., 1995). Common bean supplies a large part of the daily protein requirement of the people of South America, the Caribbean, Africa, and Asia (Laing et al., 1983). It is rich in protein (20 to 25%) but, as with most legumes, the proteins are deficient in sulfur containing amino acids (Laing et al., 1984). Bean yield is low in most developing countries, averaging less than 1 t he" and increasing to less than 1.4 t ha" in most developed countries (Laing et al., 1984). When grown in tropical and subtropical environments, bean is affected by an array of diseases, pests, water stress, and soil fertility problems (Schwartz and Pastor-Corrales, 1989). Although diseases and low soil fertility are the most widespread problems, more than 60% of beans grown in the developing countries of Latin America, Africa, and Asia suffer from water stress at some 6 stage of crop growth (White and Singh, 1991). A recent study on bean distribution by environment in Latin America showed that the physiological water requirement of the plant was not fulfilled in 93% of the areas where beans are grown (Fairbaim, 1993). Because of scarce and irregular rainfall patterns, beans grown in rainfed areas in Latin America commme suffer moisture deficits during their reproductive phase (Laing et al., 1983). In semi-arid areas, the soils have a low organic matter content and water holding capacity, so yields are often reduced by drought (Fairbaim, 1993). Kadam and Salunkhe (1989) observed that 91% of the mean annual world production of dry bean in 1982 was produced in developing countries. Land area devoted to been production in developing countries has increased steadily in the last several decades (CIAT, 1992). However, production has not kept pace with population growth and must increase 42% and 72% in Latin America and Africa, respectively, by the year 2000 in order to satisfy expected demand (Janssen, 1989). Bean production in developing countries often occurs on marginal land, and few developing countries have significant reserves of arable land that can be opened to bean cultivation. Thus, increased bean production will largely have to come through increased yield per hectare rather than expansion of land under cultivation (Yan et al., 1995). Given the importance of bean as a human food source in developing countries, more research should be devoted to improving productivity of the crop (Laing et al., 1984). Root Growth The type of root system is determined genetically and is responsive to environmental factors such as soil moisture. Soil strength, aeration, temperature, salinity and toxic concentration of aluminum or other substances were additional environmental factors that affected root growth (Taylor, 1983; Gregory, 1989). The lack of moisture and available nutrients in arid and semi-arid regions (Al-Karaki et al., 1995) confined root growth to the upper soil horizons. Low mineral availability and moisture shortages in soil inhibited root growth and reduced access to subsoil moisture (Pothuluri et al., 1986; Welbank et al., 1973). Reduced root growth hastened the onset and increased the severity of plant water deficit during drought conditions (Al-Karaki et al., 1995). Deep and extensive root systems contributed to drought resistance and mineral uptake, for example phosphorus efficiency in plants (CIAT, 1990; Markhart, 1985). Roots played an important role in the growth and survival of plants during periods of drought stress. Under drought, the root was characterized by a low root density in the dry surface layer and a higher root proliferation in the deeper , wetter soil layers (Smucker et al., 1991). However, under non-stress conditions, roots proliferated in the soil zone with the lowest soil water retention (Garay and Wilhelm, 1983). Garay and Wilhelm (1983) observed in peanuts (Arachis hypogaea L.) drought stress significantly reduced root growth in the upper 40 cm of the soil profile from 20 to 50 days after planting. In contrast, Hudak and Patterson (1996) examined two varieties of soybean [Glycine max (L.) Merr.) and concluded if its ability to W roots A 37% dewfl nunber 000. short term dl may have be allocations 0 Water soil c Mar dept] Stofella et al Woe ungul 8 concluded that the ability of a plant .to survive under drought stress may reside in it’s ability to exploit the upper soil horizons (above 60 cm) with a network of fibrous roots. A 37% reduction in wheat (Trfficum aestivum L.) roots occurred in the top 20 cm ofsoil during an 18 day drought period and a 50% increase in root number occurred at the 60 to 150 cm depth (Box et al.,1989). This response to short term drought suggested that large quantities of photo—assimilated carbon may have been lost to the rhizosphere in the shallow root zone, while new allocations of plant carbon were required for the growth of new roots at the greater soil depths. Several authors have reported increased root growth at greater depths under drought stress (De Vries et al., 1989; Smucker et al., 1991; Stofella et al., 1979a), and an increase in total root growth occurred in cowpea (Wgna unguiculata) under mild drought stress (Nagarajah and Schulze 1983). Although total growth has been reported in some studies during water stress, root growth is generally favored relative to shoot growth. It is frequently assumed that root dry matter is 10% of total crop dry matter after flowering under non-stress conditions, producing root/shoot (RIS) ratios of 0.1 in temperate regions (Smucker at al., 1991). However in drier regions RIS ratios of 20% were found in barley (Hordeum vulgare) and 45% in wheat (Tn'ticum aestfvum L.) (Gregory, 1989). The RIS ratio under drought conditions have increased up to 0.3 (Passioura, 1983). Root development and capacity of plants to absorb water are closely related. As root width, depth, and branching increased, plant water stress ROOII attr lb envlr limit ‘ tesis Simil tux t axial a on foot all; 9 decreased (Hurd, 1976). When ground water was available, deep mated plants showed greater drought avoidance than shallow rooted ones but they showed Iow« avoidance, when deeper soil moisture was not present (Levitt, 1972). Rooting depth and the resistance to water flow within the root were important attributes of root systems when plants were grown in drought prone environments (Taylor, 1980). Passioura (1982) concluded that axial flow did not limit the uptake of water in legumes because their facility for secondary growth normally ensured abundant vesSels. Only a vascular disease or a large resistance at the nodes or at the junctions between roots caused a problem. Similar results have been reported by others (Hurd, 1976; Sheriff and Muchow, 1984; Blum, 1988; Gregory, 1989). According to their work, soil-to-leaf water flux and the associated water potential were affected by root length, density, root axial resistance, and root adaxial resistance when the root system was limited to a drying soil with no additional moisture reserves at deeper soil layers. Small root resistance and a large root-length density contributed to the maintenance of a higher leaf-water potential (Blum, 1988). White et al. (1990) reported that drought resistance in bean was related to rooting depth. Soil exploration by roots was associated with nutrient acquisition, especially in the case of immobile nUtrients such as phosphoms (Lynch and Van Beam, 1993). Genetic differences in bean were reported for root biomass, RIS ratio (Fawole et al., 1982; Stoffela et al., 1979a), and for root biomass distribution among distinct root types (Stofella et al., 1979b). Root architecture may also be important for soil resource acquisition (LN 3’“ structure a tithe exlri striple mo hiuence 1 Drought l Drc Plant to St sitecies st adelicate °°° 598: Water def 10 (Lynch and Van Beam, 1993). Fitter (1991) developed topological indices to quantify root architecture in two-dimensions, ranging from a herringbone structure at one extreme to a highly branched, dichotomous structure at the other extreme. Based on comparisons of ecologically distinct species and simple modeling exercises, Fitter (1991) proposed that root architecture may influence the efficiency of plant nutrient uptake. Drought Resistance Drought resistance in ecological terms is described as the ability of a plant to survive periods of low water supply (Turner, 1979). In addition, plant species selected for crop production must have the ability to produce an adequate yield (Blum, 1988). Agriculturally, drought resistance is the ability of a crop species or variety to grow and yield well in areas subjected to periodic water deficit (Turner, 1979). - Drought resistance is conferred by a number of morphological and physiological characteristics of the plant (Begg and Turner, 1976; Morgan, 1984; Turner, 1986; Acevedo,1987; Singh, 1989). Drought resistance and its related characteristics have been classified by different researchers (Levitt, 1980; Kramer, 1983; Blum, 1985, 1988; Ludlow and Muchow, 1990), but no consensus has been reached about the most useful aspects or categories of drought resistance (Levitt, 1980; Kramer, .1980; Turner and Burch, 1983; Turner, 1986). The mechanisms of drought resistance in crop plants has been divided into three categories: drought escape, dehydration avoidance and dehydration W (Kra rid W. by cornpleling drought Deh stomatal closr tidl rates of l wihstand injL evasion has 5 1980; Blum, ‘ There tells related comPlex inlet WW 1 tiara. 1985,- 1 1 tolerance (Kramer, 1980, 1983; Levitt, 1980; Turner, 1986; Blum, 1988; Ludlow and Muchow, 1990). Drought escape is the ability of a plant to escape drought by completing its life cycle during the favorable moisture conditions prior to the drought. Dehydration avoidance is the ability of a plant to prevent water loss by stomatal closure resulting in the maintenance of turgor during periods favoring high rates of transpiration. Dehydration tolerance is the ability of a plant to withstand injury when plants are under drought stress. Drought escape or evasion has sometimes been incorrectly equated to drought avoidance (Levitt, 1980; Blum, 1988). There are several individual morphological, physiological and biochemical traits related to each mechanism, however, resistance to drought depends on a complex interaction of attributes that confer both survival and a range of productivity potentials at various stages of the plant’s life cycle (Simpson, 1981; lbarra, 1985; Elizondo, 1987; Acosta-Gallegos, 1988). The different mechanisms of adaptation are not matually exclusive because plants may possess more than one type'of adaptation (Turner, 1979; Kramer, 1980). Thus, in legumes, major differences in adaptation to photo-thermal regime, to edaphic conditions and to the amount and seasonal distribution of water have been possible through the combination of physiological adaptations, anatomical variations, morphological patterns, and symbiotic associations in addition to the structure and genetics of the population (Kramer, 1980). Acosta-Gallegos and Adams (1991) concluded that the most practical method to improve performance of common bean is through the direct We“ meant so: also: toleral items to ide later treatm iterlsity of a Bellmance molype an insofar and at al. (1997) W genct} Gallegos, 15 lBillings for tile“ based Wuded it “less and r Detential an. m a QBI’IOIy 12 measurement of yield-related characteristics because seed yield is the most important economic yield of the crop. The drought susceptibility index (DSI), stress tolerance index (STI), and geometric mean (GM) have been used as a means to identify genotypes exhibiting consistent yield performance across water treatments. DSl is based on a reduction in yield adjusted for the drought intensity or a particular experiment. A value of one indicates average performance. The greater the value above one the more susceptible the genotype and the lower the value below one, the more resistant the genotype (Fischer and Maurer, 1978). However, White and Singh (1991) and Schneider et al. (1997) concluded that osr rankings resulted in the mis-classification of some genotypes. GM is believed to assess genotypic yield potential (Acosta- Gallegos, 1988). Acosta-Gallegos and Adams (1991) observed that genotypic rankings for drought resistance were ordered differently when based on GM than when based on percentage reduction in yield or DSI. Schneider et al. (1997) concluded that GM was the single strongest predictor of yield performance under stress and non-Stress conditions. STI reportedly identifies genotypic yield potential and resistance to drought (Fernandez, 1993). The larger the STI value for a genotype, the higher its drought resistance and yield potential. Effects of Drought on Growth, Development, and Yield Maintenance of a high water status throughout the life of the crop (Laing et al., 1984) is essential for maximum yield. While the ultimate effect of drought was limitation of growth and yield, specific physiological efiects of water stress 195 VET red yie. lnte liar 13 varied depending on the history of me crop and the timing and intensity of stress (White and Castillo, 1989). In bean, the most sensitive phase of development to water stress was from flowering to early pod set (Dubetz and Mahalle, 1969; Laing et al., 1983 and 1984; Halterlein, 1983; Sheriff and Muchow, 1984). Prolonged stress before flowering restricted canopy development, which in turn limited yield (Laing et al., 1984). The relative sensitivity of different stages of development to water stress varied with the degree of stress (Begg and Turner, 1976). The most common effect of water deficit during bean growth was reduction in plant size and yield (Kramer, 1983). Drought stress affected many physiological and morphological characteristics associated ultimately with seed yield. The phonological stage of the crop at the time of the stress as well as the intensity and duration of the water stress determined the amount of damage done‘to the crop and therefore yield (Acosta-Gallegos and Adams, 1991). Acosta-Gallegos and Shibata (1989) reported that the induction of drought stress at the beginning of the reproductive phase in common bean reduced seed yield twice as much as when the stress was induced at the vegetative phase. Stern length, number of branches, pods per plant, seeds per pod and yield were all reduced. The number of pods per plant was the yield component that was most affected by water stress. Pod number varied greatly while seeds per pod and particularly seed size showed comparatively small changes across environments and treatments (Acosta-Gallegos and Shibata, 1989). It was hypothesized that 14 been plants adjusted potential sink size (pod number) to the available source and then proceeded to fill that sink as rapidly'as possible (Acosta-Gallegos and Shibata, 1989). Final yield was affected by morphological traits such as biomass (Laing at al., 1983;. Scully and Wallace, 1990; Scully et al., 1991), leaf area duration, leaf area index (Laing et al., 1983, 1984), growth habit (Laing et al., 1983, 1984), basal intemode diameter, basal intemode length (Davis and Evans, 1977), hypocotyl diameter (Acquaah et al., 1991) and phenological traits such as days to flowering, days to maturity and days to pod fill (Laing et al., 1983, 1984; Scully and Wallace, 1990; Scully et al., 1991). Part of the genetic improvement in crop yield has also derived from a higher percentage of the biological yield (total plant dry weight) being partitioned into plant parts comprising economic yield (grain or seed weight). This ratio of economic yield to biological yield is termed as harvest index (HI) (Rasmusson andGengenbach, 1988). Economic yields can be increased by increasing biological yield without changing the HI or by partitioning more of the dry matter production into economic yield. Wallace et al., (1982) reported that the HI in wheat had increased from 32% in the early 1900's to 49% for current high yielding semidwarf varieties. Effect of drought on photosynthesis and stomatal conductance Dry matter accumulation in plants is largely a function of net photosynthesis and light interception by the canopy. At least 90% of the dry matter C (Zelith, have ya predide obtains certain . (Kuppel equally CO2 as: the res; Was fair reDOrtet Water dl 15 matter of higher plants is derived from CO, assimilated by photosynthesis (Zelith, 1982). Zelith suggested that the method of selection for yield may not have yet explored the potential photosynthetic capacity and that it may be predicted that only modest rate increases in photosynthesis could have been obtained during selection for higher yield. CO, assimilation and stomata responded fairly independently, in spite of a certain degree of coupling, to short term variations of environmental factors (Kuppers at al., 1988). Also, net photosynthesis and leaf conductance were not equally sensitive to soil drying. Initially, leaf conductance declined by 40% while CO2 assimilation rate remained constant. Kuppers et al. (1988) concluded that the response of CO, assimilation and stomatal conductance during soil drying was fairly independent of the water status of the leaf. Similar observations were reported by Bates and Hall (1981), indicating that stomatal closure due to soil water depletion was not associated with changes in leaf water status. In cotton (Gossypium hirsutum L), an increase in stomatal resistance was associated with a substantial reduction. in the photosynthetic rate as a result of moisture stress (Epthrath et al., 1990). In their work, stomata limited the photosynthetic process in well-watered and mildly stressed plants, while mesophyll resistance was the main factor reducing photosynthesis under more severe moisture stress. Epthrathet al., (1990) concluded that when moisture stress was initiated at 21 days after planting, plants had lower stomatal resistance and a higher photosynthetic rate than plants in which stress was initiated at 40 days after planting. 16 .Peng et al. (1991) observed that photosynthesis measured at the single leaf level prior to flowering in sorghum (Sorghum bicolor L.) was a trait which could-be used to select genotypes for higher productivity. They found that leaf photosynthesis, total biomass and grain production were significantly reduced by limitedwater supply and that leaf photosynthesis was positively correlated with total biomass and grain production. Hamdani et al. (1991) concluded that genotypic reduction in water potential, stomatal conductance and photosynthesis had the potential to be used as screening tools for drought resistance of sorghum genotypes at the vegetative stage of growth. Manthe (1994) concluded that water stress decreased photosynthesis of common bean and cowpea (Vigna unguiculata L. (Walp)) late in the growing season when the stress was severe, while stomatal conductance was affected earlier in the season. ABA and Drought ABA is sometimes referred to as the “stress hormone” because of its possible role in maintaining winter dormancy of buds and because it accumulates when plants are deprived of water (Purves et al., 1992). Apart from its widely recognized role as an agent of stomatal closure, ABA may have additional regulatory roles in the adaptation of plants to drought stress (Jones, 1978). The observation that ABA levels increase in the roots of water-stressed plants (Hubick at al., 1985; Lachno, 1984; Walton at al., 1976) and that this increase does not depend on transport from the shoot ( Walton et al., 1976) is particularly provocative. 17 Several studies (Hubick, .1983; King and Evans, 1977) reported similarities between the effects of exogenously applied ABA on plant development and the behavior of water stressed plants. Barlow and Pilet (1984) showed that exogenously applied ABA reduced cell division and DNA synthesis in the root apical meristem in corn. Similarly, Creelman et al., (1990) using soybean seedlings, observed that exogenously applied ABA had the same effect on growth and dry weight as seedlingssuffering from low water potential. Earlier studies with sunflower (Helianthus annus L.) seedlings found that drought stress inhibited root growth (Hubick, 1983) and increased ABA levels in the root tissue (Hubick, 1983; Hubick et al., 1985). Creelman et al. (1990) found'that exogenously applied ABA increased root growth of soybean seedling. Leskovar and Cantliffe (1992) working with pepper (Capsicum annuum L.) seedlings noted that exogenously applied ABA reduced root fresh and dry weights while increasing stem fresh weight and dry weight thereby, decreasing the RIS ratio. In contrast, Robertson et al., (1990), reported an increase in RIS ratio of sunflower (Helianthus annus L. Cv. Russian Grant) due to exogenously applied ABA. ABA accumulated in roots, particularly at the tips, of water-stressed plants (Saab et al., 1990; Ribaut and Pilot, 1991). It may have stimulated ion and sugar accumulation in the root (Karmoker and Van Steveninck, 1979; Van Steveninck, 1984; 1983), thereby affecting root turgor, or it may have acted as a signal for the initiation of regulatory processes involved in adaptation during growth at low water potential (Davies et al., 1986; Bradford and l-lsiao, 1982). 18 Two types of evidence support the hypothesis that messengers from the root system may affect stomatal response to water stress. - First, stomatal conductance is often much more closely related to soil water status than to leaf water status, and the root system is the only plant part that can be directly affected by soil. water status. Second, roots produce ABA and export it through the xylem sap (T aiz and Zeiger, 1991). Polyethylene (PEG) and drought Polyethylene glycol (PEG) induces a primary water stress by provoking a reduction in water availability (lzzo et al., 1989). The most serious limitation of PEG as an osmoticum has been its toxicity (lzzo et al., 1989). PEG is an inert, nonionic, long chain polymer [(HOCH,-CH,)x(Cl-I,OH)] and has the advantage of providing a precise level of water deficit in plants. Graves and Wilkins (1991) observed that PEG caused a reduction in the root and shoot dry weights among seedlings of. honey locust (Gleditsia tn'acanthos var. inermis Willd.). Perez-Molphe-Balch et al., (1996) concluded that water deficit imposed by PEG inhibited germination and shoot and root growth and also altered the pattern of protein synthesis in the roots of three rice (Oryza sativa) cultivars. ' Kaufman and Eckard (1971) concluded that PEG produced changes in plant water relations similar to those caused by drying soil at the same water potential. Studies utilizing PEG have been conducted with many species, an maize stamina P.. 1 [sweeter at al. 19 including maize (Zea mays) (lzzo at al., 1989), coleus (Krizek, OT and Semeniuk, P., 1979), white clover (Robin et al., 1989), and Capsicum annum (Schaefer et al., 1979). lit 20 Literature cited Acevedo, E. 1987. Assessing crop and plant attributes for cereal improvement in water limited Mediterranean environments. Proceedings of an international workshop, 27-31 October, 1985, Capri, ltaly. Acosta-Gallegos, JA 1988. Selection of common bean (Phaseolus vulgan’s L.) genotypes with enhanced drought tolerance and biological nitrogen fixation. Ph.D. diss. Michigan State University, East Lansing, MI. USA Acosta-Gallegos, JA, and J.K Shibata. 1989. Effect of water stress on growth and yield of indeterminate dry bean (Phaseolus vulgaris) cultivars. Field Crops Res. 20:81 -93. Acosta—Gallegos, JA, and MW. Adams. 1991. 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And other plants. Plante 147243-49. Welbank, I.J., M.J. Gibb, P.J. Taylor, and ED. Williams. 1973. Root grow th of cereal crops. Rothamstod Experiment Station, Report Part 2. Rothamstod, England. White, J.W. and J.A Castillo. 1989. Relative effect of root and shoot genotypes on yield of common been under drought stress. Crop Sci. 29:360-362. White, J.W., G. Hoogenboom, J.W. Jones, and KJ. Boote. 1990. Beangro version 1.0 a phasoolus computer simulation model. Annual report of the Bean Improvement Cooperative 33:39-40. White, J.W. and SP. Singh. 1991. Breeding for adaptation to drought. p.501- 560. In A van Schoonhoven and 0.Voysest (ed.) Common beans: Research for crop improvement. CAB lntemational, Wallingford, UK, and CIAT, Cali, Columbia. ' Yen, X, J. P. Lynch, and S. E. Beebe. 1995. Genetic variation for phosphorus efficiency of common bean in contrasting soil types: I. Vegetative Response. Crop Sci. 35:1086-1093- Zelith, I. 1982. The close relationship between not photosynthesis and crop yield. Bioscienco 32(10):796-802. Ameri. 100 m oonstr. 80% c 1993). Constra (1980) Product multifac lilleract Soil fUDg Pastor-( erUth importer); Chapter 1 Field selection for drought tolerance. Introduction Bean is the principal food legume for over 500 million people in Latin America and Africa, and it is the leading source of dietary protein for more than 100 million people (FAO, 1984). Soil fertility and drought are the primary constraints to been production in many developing countries, affecting at least 80% of the area planted to beans in Latin America (CIAT, 1988; Fairbaim, 1993). Consequently, improving the genetic adaptation of beans to edaphic constraints is important in international agriculture (Lynch and van Boom, 1993). Breeding for drought resistance has been elusive and frustrating. Amon (1980) pointed out that breeding for drought resistance was probably the least productive breeding effort in the entire field of plant breeding. Drought is multifaceted, varying greatly over different production regions and often interacting with other detrimental factors such as high temperatures, pathogenic soil fungi and the use of marginal soils (White and Singh, 1988; Schwartz and Pastor-Corrales, 1989). Similarly, the difference in timing and intensity of drought stress can influence crop yield in various ways. Acosta-Gallegos and Adams (1991) concluded that seed yield is the most important economic trait of common been, therefore, the most practical method 30 envirOr indical iridicat suscep index it ExPerin While a rESUltec Wlenlia Gallego milking: redlICiio. potential 31 to improve performance is through the direct measurement of yield-related characteristics. The Drought susceptibility index (DSI) (F ischor end Maurer, 1978), stress tolerance index (STI) (Fernandez, 1993). and geometric mean (GM) have been used in an attempt to identify genotypes exhibiting consistent performance across stress troatrnonts. The DSI is based on a reduction in yield aqusted for performance of all genotypes in a stress and nonstress environment. DSI values below one indicate tolerance and a value of zero indicates maximum tolerance (Fischer and Maurer, 1978). A DSI value of one indicates average performance and the greater the value above one, the more susceptible the genotype. The drought intensity index (Dll) is a very useful index for the characterization of the severity of drought stress among experiments used in the evaluation of genotypes (Fischer and Maurer, 1978). White and Singh (1991) and Schneider et al. (1997) found that DSI rankings resulted in the mis-classificetion of some genotypes. GM assesses the yield potential of e genotype, its porforrnanco under optimal conditions (Acosta- Gallegos, 1988). Acosta-Gallegos and Adams (1991) observed that genotypic rankings based on GM were ordered differently than when based on percentage reduction in yield or DSI. STI reportedly identifies genotypes with regard to yield potential and stress resistance. The larger the value of STI for a genotype in a stress environment, the higher its stress resistance and yield potential (Fomandez, 1 993). Drought adaptive mechanisms may be morphological, phonological, physiological and/or biochemical, but the current most reliable approach to mixed l Station during With 50 iEplica' Sites I in Mlch 4214-2 Suscep degree T3015. Univers StresS (. 32 selection for drought tolerance is the assessment of total biomass or economic yield produced under stress in the field (White and Singh, 1988). The objectives of this study were (1) to deterrnino yield response to drought stress in eight field-grown bean genotypes, and (2) to doterrnine if the geometric mean, DSI, or STI are reliable predictors of been yield under limiting andlor non-limiting soil moisture conditions. Materials and Methods A field study was conducted on a Kalamazoo sandy loam (F ine-Loamy, mixed mesic, typic Hapludolf, FAD classification) at the Kellogg Biological Station [(KBS) 42° 25' N, and 85° 30' W. 2500 masl] in Hickory Comers, Ml. during the summers of 1995 and 1996. The experimental design was a split plot with soil moisture as the main plot, genotype as the subplot, and four replications. Eight common bean genotypes varying in their response to moisture stress were included in the study. They were Sierra, a commercially grown been in Michigan; Bet 477, documented by CIAT (1984) to be drought resistance; 8- 42-M-2, developed at Michigan State University and documented as drought susceptible when grown in Michigan conditions; Lof-2-RB which exhibits some degree of drought resistance in Michigan conditions; and four “1" lines (T3008-1, T3016-1, T3110-2, and 1'3147-2) that were developed at the Michigan State University been breeding program and which vary in their yield potential under stress (Table 1). Seeds were planted on June 13 and 14, 1995 and on June 4 Table 1. Chara at Kell Genotypes Sierra l T3110-2 : T3147-2 : Lei-Z-RB , Bat477 33 Table 1. Characteristics of common bean genotypes grown in field experiments at Kellogg Biological Station, Hickory Comors, MI. in 1995 and 1996. Genotypes Pedigree Origin£ Seed¥ Seed Plant: Size Color Type Sierra Not idontified§ MSU M Pinto ll T3110-2 Sierra X Lof-2-RB MSU M Striped lII T3147-2 Sierra X Lef-2-RB MSU M Striped lll Lef-2-RB (Var 10/Chis INIFAP M Black lll 143)lpue 144 (striped) Bet 477 (51051 X ICA CIAT M Brown ll Bunsi) X (51012 X Cornell 49-242) 8-42-M-2 N81017 X Lef-2-RB MSU M Tan or Brown III T3016-1 Sierra X AC 1028 MSU M Tan or Brown Ill T3008-1 Sierra x AC 1028 MSU M Tan or Brown Ill £ MSU = Michigan State University CIAT = Centro lntemacional de Agriculture Tropical INIFAP = National Institute for Forestry, Agriculture, and Livestock Research, Mexico. ¥ M=Medium. 1: Type II = Indeterminate-bush, erect stem and branches Type III = Indeterminate-bush, prostrate main stem and branches § Derived from crosses of Durango Race Pinto with Mesoamerican Race Black (Kelly et al., 1990). 34 and 5, 1996. Unifome sized seeds were inoculated with one strain of Rhizobium phaseoli. Forty Kg of N per hectare were applied as 20-20-20 prior to planting in both years. Seeding rate was 8 seeds per 30 cm. After emergence, seedlings were thinned to 4 seeds per 30 cm. Experimental plots consisted of four rows, 3.10 m long with an inter-row spacing of 50 cm. Moisture stress was initiated 45 days after planting (DAP). Three applications of fungicide (Benlate for anthracnoso and Sevin for Japanese beetles at 1.12 Kg he") were made in 1995 at two week intervals starting on July 14. In 1996 only two applications of Benlate were made. Both years, soil moisture was recorded using a neutron probe to deterrnino moisture at three depths: 0-38 cm, 39-76 cm, and 77-114 cm. Poromoter (Ll-Cor, LI-1600 Steady State Poromoter) and ceptometer (Decagon Sunfleck Ceptometer, Pullman, WA) data were recorded weekly for 8 weeks in both years beginning at 34 DAP. The Poromoter measured loaf transpiration, diffusive resistance, and leaf temperature. The ceptometer measured the difference between the amount of photosynthetically active radiation (PAR) above and below the canopy. In 1996, leaf temperature was taken at the V2 and V5 stage of development (Singh, 1982) using an infrared thenrlomoter (Horiba, Non-contact Infrared Therrnometor IT-330, Kyoto, Japan). The MSTAT micro-computer statistical package for agricultural sciences was used for data analysis. Calculations Y. = The potential yield of a given genotype in a nonstress environment. 35 Y. = The yield of a given genotype in a stress environment. Y. = Mean yield in nonstress environment. Y. = Moan yield in stress environment. Y,‘ = Stress yield from a single genotype. Y, = Nonstress yield from a single genotype. Stress tolerance index (STI) = (Y. x Y,)IY.’ Geometric mean (GM) = m Drought intensity index (Dll) = 1 - (YJY.) Drought susceptible index (DSI) = (1 - YJY,)IDII Results and Discussion 1995 field experiment A significantly greater quantity of PAR was intercepted by the canopy of the nonstress than stress treatment in 1995 on 41, 48, and 71 DAP (P s 0.10, 0.10, and 0.05, respectively) (Figure 1), indicating a more fully developed canopy in the nonstress treatment. There was a tendency for greater PAR interception in the nonstress treatments at another sampling dates except day 1. The difference in PAR intercepted by the canopy ranged from 375 to 1300 umol m‘2 s“ over the length of the growing season. Leaf temperature was significantly higher at 51, 72, and 86 DAP, (P s 0.01, 0.05, and 0.05, respectively), in stress plants, (Figure 2) suggesting stomatal closure in the stress treatment. Yet, transpiration did not differ between stress and nonstress treatments (Figure 3). At soil depth 1 to 33 cm, soil moisture content was w 140 m w m a :3 n-E .0543 825300 LOuOEOuQOO 120 Flgure 36 1500- + Stress —o— Nonstress i i d l Ceptometer counts (jimol rn‘2 s") Days After Planting Figure 1.. PAR intercepted by the canopy of eight genotypes of common been grown under stress and nonstress moisture conditions at the Kellogg Biological Station, Hickory Comors, MI. in 1995. Bars indicate standard error of the mean at P s 0.05. Vertical arrow indicates when stress was induced. 20 Flgut 37 + Stress —o— Nonstress Temperatue °C Days After Planting Figure 2. Leaf temperature of eight genotypes of common been grown under stress and nonstress moisture conditions in a rainshelter at the Kellogg Biological Station, Hickory Comors, MI. in 1995. Bars indicate standard error of the mean at P s 0.05. Vertival arrow indicates when stress was induced. 801 m A Tl h-E0 Div cozthnCOuF Figure 38 80‘- + Stress —o— Nonstress 8 B Transpiration (jig cm'2 8") \\\\ ////" 30. 40 50 60 70 80 90 100 Days After Planting Figure 3. Transpiration rate of eight genotypes of common been grown under stress and nonstress moisture conditions in a rainshelter at the Kellogg Biological Station, Hickory Comors, MI. in 1995. Bars indicate standard error of the mean. Arrow indimtes when stress was induced. 3F 39 significantly higher in the nonstress treatment throughout the growing season (Figure 4), except for 48 and 55 DAP. However at soil depth 33 to 63.4 and 63.5 to 91.4 cm there was no significant difference between stress and nonstress soil moisture content (Figure 5 and 6, respectively), although there was a tendency for the nonstress treatment to contain more soil moisture at all sampling dates of the two depths except 48 and 55 DAP at soil depth 33 to 63.4 cm (Figure 5). Monthly mean air temperature ranged from a minimum of 60.1 to a maximum of 83.7 °F (Figure 7). Yield of the eight genotypes in 1995 ranged from 1057 to 1863 Kg ha" under adequate moisture stress with a drought intensity index (Dll) of 0.35 (T able 2), suggesting a moderate moisture stress. Sierra, Lef-2-RB, and their progeny (T 31 10-2 and T3147-2) were among the top four performers (T able 2). When stress and non-stress treatments were combined, Lef-2-RB had the highest yield and was significantly higher than all other genotypes except T3110—2 (Table 2). The genotype Bet 477 was used as the drought resistant check since numerous studies have documented its resistance (CIAT, 1984; Sponchiado et al., 1989). Its yield ranged from 987 Kg ha" under stress to 1431 Kg ha" under sufficient moisture. Based upon previous nonpublished work at MSU, 8-42-M-2 was used as a drought susceptible check. Its yield ranged from 894 Kg ha’1 under moisture stress conditions to 1393 Kglha" under adequate soil moisture conditions (Table 2). Yield reduction for the eight genotypes ranged from 30 to 46%. The genotype, Lef-2-RB had the lowest yield reduction, and T3008-1 had the greatest (Table 2). The geometric mean for the eight 0.26- 0.25 -’ 0.24 4 0.23- 0.22- 0.21 4 0.20 -* Neutron probe counts at depth 1 - 33 cm 0.19 d 40 5 ° + Stress —o— Nonstress 0.18 Figure 4. Days After Planting Neutron probe counts of eight genotypes of common been grown under stress and nonstress moisture conditions in a rainshelter at the Kellogg Biological Station, Hickory Comors, MI. in 1995. Bars indicate standard error of the mean at P s 0.05. Vertiml arrow indicates when stress was induced. 4'1 0.28 - 026 J + Stress E V —o— Nonstress 0'5 to I 8 024 - g E 022. i g ozor O. i 2 0.18 - 0.15 -.. ..... , ........ fl ....... , ........ , ......... W.H.... 40 so so 70 so so 100 Days After Planting Figure 5. Neutron probe counts of eight genotypes of common been grown under stress and nonstress moisture conditions in a rainshelter at the Kellogg Biological Station, Hickory Comors, MI. in 1995. Bars represent standard error of the mean. Vertival arrow indicates when stress was induced. 42 0.20 - + Stress 0.18 - .. " —O— Nonstress 0.10 - . \ “l 'l O 0.14 - .. \¢ 0.12 1 0.10 II\ Neutron probe counts at depth 63.5 - 91.4 cm Days After Planting Figure 6. Neutron poobe counts of eight genotypes of common been grown under stress and nonstress moisture conditions in a rainshelter at the Kellogg Biological Station, Hickory Comors, MI. in 1995. Bars represent standard error of the mean. Vertical arrow indicates when stress was induced. 43 + 1995 avg max monthly temp. ---0--- 1996 avg max monthly temp. + 1995 avg min monthly temp. —v---1996 avg min monthly temp. 90. k/ 80 O ................. o ............... u. °° 70- % /\ g. v—————v’// \ g OO-l K ”A, \ XV 50- \ V 40 I I I I June July August September Average monthly temperature (1995 and 1996) Figure 7. Mean monthly maximum and minimum temperature (°F) recorded at the Kellogg Biological Station, Hickory Comors, MI. in 1995 and 1996. Amie N. So... 2 8:888 c.8563. 848:. <5... «cacao... 832:8 Sea 3.. «.38 8:: 8:888 483.83. :35... 288256 58x am... 08.83.... 38:. 8:: £88 668:8 58x 6.... 2 e6... :8: $8825 5.60:“ F. 88288 992: .: m 8.88:2 e. 5e .6..ch 90.8.8. «8.6: .: 1.0.6:. 00303. 2.. .: .89 03.63 388.2 .:aox u ohm. cascades so...» age... 88.3.. oceans..." .6 8.. Basso: 52% 38: cm. m... 53.8 88 8 3% a. 8m oboe ..omm d... a.» :8 we 33 be :8 come cams 3.3.» .98 o. a: on 8o 98. 33 mass at: 8 $8 on 88 0.8. 58 82.: to. o. 38 e8. :8 come 0.8m «Lei.» 88 8 :3 8 :8 ..ows came 488-. 84 so 88 so 8.... 38 ohm 89?. 3% 8 moo e use 33 can» . 0.3083 .32.. 56.8.8 3:583 9.33:8 2:63 388 2.3.: a 8.5:: a. p n 98 883.8 8 02.2.... a. 528.8 so... :32 8:888 88.88. m 528.8 832:8 £38 .5: 8:888 «.05. 45 cultivars ranged from 849 to 1555 Kg he". Geometric mean was used to assess yield potential, an important factor since a genotype might be low yielding under sufficient moisture conditions, but have minimal yield reduction under stress. Such a genotype would be stress resistant but undesirable. The choice of GM to represent mean productivity is preferred because, when ranking genotypes, GM better accounts for large differences in performance between stress and nonstress environments than does the simple arithmetic mean used by Rosielle and Hamblin (1981 ). The genotype T3008-1 had the highest DSI and Lef-2-RB had the lowest (Table 2). According to this system, the resistant genotypes in order from most to least resistance were Lef-2-RB, T3147-2, Bet 477, Sierra, and T3110-2. The susceptible genotypes in order from most to least susceptible were T3008-1, T3016-1, and 8-42-M-2. STI ranged from 0.322 to 1.055 with the genotype Lef-2-RB having the highest value indicating the greatest resistance and highest yield potential and the genotype T3016-1 having the lowest value indicating susceptibility and low yield potential (Table 2). Arbitrarily using 0.6 as the STI cutoff between resistant and susceptible genotypes, STI and DSI agreed on the genotypes that would be assessed as resistant or susceptible, but the order within categories differs (Table 2). The GM ranked Lef-2-RB, T3110-2, T3147-2, and Sierra in that order, as having the highest yield potential. These results were identical to those of STI. Bet 477 was used as the drought resistant check and the DH and STI both designated it as such, however, its yield potential was less than that of T3110-2 and T3147-2 and their parents, Lef-2-RB and Sierra. Previous work 46 (nonpublished) at MSU indicated that Bet 477 had a lower yield potential than Sierra and Lef-2-RB, but exhibited greater yield stability. The GM, DSI, and STI were each analyzed to determine their degree of correlation with yield under stress conditions, yield under non-stress conditions, and combined yield of the two moisture treatments. The correlation of geometric mean and STI with yield under stress, non-stress, and combined moisture treatments was positive and highly significant, ranging from 0.98“" to 0.99’“ (T able 3). As would be expected, the DSI was inversely correlated with all three yield categories but was only significantly correlated with yield in the stress treatment (-0.72*). The geometric mean and STI were more accurate than the DSI in selecting desirable genotypes based upon yield performance for 1995. 1996 field experiment A significantly greater quantity of PAR was intercepted by the canopy of the nonstress treatment on 50, 78, and 92 DAP (P s 0.01, 0.05, and 0.05, respectively) (Figure 8). The difference in PAR intercepted by the canopy ranged from 656 in the stress treatment to 717 umol rli‘2 s" in the nonstress treatment. Leaf temperature ranged from 21 to 26.5 °C. The stress treatment had a significantly higher (P s 0.10) leaf temperature than the non-stress treatment at 71 and 85 DAP and the tendency was the same on all other sampling dates except 43 and 92 DAP (Figure 9). The non-stress treatment had a higher (P s 0.10) transpiration rate than the stress treatment at 92 DAP (Figure 10). The only difference in soil moisture between stress and non-stress 47 Table 3. Correlations of yield under stress, yield under non-stress, and combined yield for stress and non-stress treatment to geometric mean (GM), drought susceptibility index (DSI), and stress tolerance index (STI). Data from been (Phaseolus vulgaris L.) plants grown at the Kellogg Biological Station in Hickory Comors, MI. In 1995. 19.9.5 GM DSI STI Stress 0.99m -o.72* ’ 0.98“" Non-stress 0.98“" -0.46 0.98“" Combined 0.99“" -O.58 0.98“" “'2 ‘ Indicates significance at P 5 0.001 and 0.05, respectively,.according to DMRT. Ceptometer counts (mol in2 s") 1400- 1200- i L l f 48 7 —O— Stress —o— Nonstress Days After Planting Figure 8. PAR intercepted by the canopy of eight genotypes of common been grown under stress and nonstress moisture conditions at the Kellogg Biological Station, Hickory Comors, MI. in 1996. Bars indicate standard error of the mean at P s 0.05. Vertical arrow indicates when stress was induced. 49 27 - . —e— Stress 2° 2 —o— Nonstress /7 ' 25- 24- Temperature °C 21- 40 50 60 70 80 90 100 Days After Planting Figure 9. Leaf temperature of eight genotypes of common been grown under stress and nonstress moisture conditions in a rainshelter at the Kellogg Biological Station, Hickory Comors, MI. in 1996. Bars indicate standard error of the mean at P s 0.10. Vertical arrow indicates when stress was inbduced. Transpiration (pg crn'2 s") 70- 50 ' -O— Stress —o— Nonstress Days After Planting F igure10. Transpiration rate of eight genotypes of common been grown under stress and nonstress moisture conditions in a rainshelter at the Kelloggs Biological Station, Hickory Corners, MI. in 1996. Bars indicate standard error of the mean at P s 0.10. Vertical arrow indicates when stress was induced. 51 treatmentsoccurrodintho1t033cmdopthat78DAP(Ps0.05)whontl'lenon- stress treatment had a significantly higher soil moisture content than the stress treatment (Figure 11). There was a tendency for higher soil moisture content in the non-stress treatment on all sampling dates for the 33 to 63.4 cm depth (Figure 12). There was no significant difference between the two treatments at the 63.5 to 91.4 cm depth (Figure 13). Average mean temperature ranged from 57.5 (minimum) to 80.4 (maximum) °F (Figure 7) and was higher in 1995 than in 1996. The genotypic yield in 1996 ranged from 1151 to 1411 Kg he" with a Oil of 0.05, indicating no moisture stress (T able 4). Leaf temperature, transpiration, and neutron probe data supported the D11 conclusion of no soil moisture stress in 1996. The lack of moisture stress in 1996 was attributed to consistent malfunctioning of the rainshelter throughout the growing season. The shelter did not close during precipitation and often had to be closed or kept open due to safety hazards associated with its operation. There was a numerical difference in yield between “stress” and “nonstress” treatments, but this was probably due to leaf injury symptoms resulting from sunscald and bronzing. The sunscald appeared to result from afternoon irrigation of the plants and subsequent opening of the rainshelter, subjecting moist leaves to bright sun and high temperatures. The bronzing was typical of ozone damage. In 1996, visual data were collated for sunscald, leaf bronzing, leaf yellowing, and brown veins. Plants were visually scored on a scale of 0 to 5, with 5 being severely damaged and 0 being no visual damage. The sunscald Neutronprobecountsatdepth1-33cm 0.28 '- 020 '1 0.24 1 0.22 - 0.20 '1 0.18 a 0.10 a 0.14 - 0.12 - 0.10 : 52 -O— Stress -0—- Nonstress 0.08 40 IIIIIIIII Days After Planting Figure 11. Neutron probe counts of eight genotypes of common been grown under stress and nonstress moisture conditions in a rainshelter at the Kellogg Biological Station, Hickory Comors, MI. in 1996. Bars indicate standard error of the mean at P s 0.05. Vertical arrow indicates when stress was induced. 53 0.26 - + Stress T —0— Nonstress g 0.24 4 V’ ‘ r' p - 022 - " . 8 P 8 020 - T if j, .. U) E J a g 0.10 - g e 0.101 C 2 S 0 z 0.14 - 0.12 ‘V'VTTVVII— rrrrrrrrr I vvvvvvvvv 'v we I r 1' 40 so 60 70 80 90 Days After Planting Figure 12. Neutron probe count of eight genotypes of common been grown under stress and nonstress moisture conditions in a rainshelter at the Kellogg Biological Station, Hickory Comors, MI. in 1996. Bars represent standard error of the mean. Vertical arrow indicates when stress was induced. E0 '2 Fm I ”-00 Fauna-"U «I 0~E§ 30.50- .anbuaoz Figun 54 0.28 - + Stress g 025 .. -<>- Nonstress ‘1: 5 .. I to. 024 1 . fl 8 .. - 3 5 O 8‘ 022 - u )- iii W g 020 - 0 g 0.18 - ~ 2 " -/ o . z 0.16 0.14 “HIP..- ......... -., ......... , ......... , 40 50 60 70 so 90 Days After Planting Figure 13. Neutron probe counts of eight genotypes of common been grown under stress and nonstress moisture conditions in a rainshelter at the Kellogg Biological Station, Hickory Comers,~Ml. in 1996. Bars represent standard error of the mean. Vertical arrow indicates when stress was induced. 400.0 a. $0.0 0:02 0.800 0:0 830800 803030. 0200:. $0.0 80:05:. 0800:. 0c080..0....< 500x Em... 00030.00 300: .02... 0:0 0.800 6.08:8 500x 8.... 0.. 000: 200000050 5.60:0 .2. 008.580 9.02: .: 0 850:0..2 0. .20 .358 0.0.8.8. 20.5: 5 1.0.62 00320. 2.. .: .80. 9.05:. 58:03. 500x 0 Pom. $082000 50.0” 0.. 0030500 00030.20 .6 30.. 808.5: <.0.0m 2.00: cm. 9.. 80.0.. .00. .0 .2... e. .000 0.000 ...0 0 0.00.2.» ..so . .0 .0: 0 . .000 .000 .00 40......» .000 .s .000 0 .000 0.0.0 .00 0.000 .0... 0 .0.0 so .000 0.000 0.00 .8. .0.» .00. .0 . .000 00 .000 0.000 .000 83.00 .000 -0 .0... 00 .20 .002 0.00 40000-. :8 .0 ..00 0 ..00 .0000 .000 00. .3 .30 s ..0. 0 ..0. 0.0... 0.00 . 0520:. .0320 50.8.00 06:58:. 0:408:00 0303 300:0 2.5.: 0 8.03: 0. .u 0 0.8 0820.3 .0 02.2.... 0. 30088:... $0.0 0:02 80.0.8800 8:0...000. 0 50.00.00 83.0500 $0.0 .33 0.88 0:0 830.88 200.3030. 56 rating for 8-42-M-2 was significantly higher than that of T3147-2 and 13110-2. The genotype 8-42-M-2 had a significantly higher rating for leaf bronzing than all other genotypes except Lef-2-RB (Table 5). Leaf yellowing was significantly greater in T3016-1 than in Lef-2-RB, Sierra or T3110-2 (Table 5). The genotypes, T3016-1, 8-42-M-2, and T3147-2 had a significantly higher yield than T3008-1 and Bet 477 (Table 4). Thus, the drought susceptible bean genotype, 8-42-M-2, had a significantly higher yield than the drought tolerant BAT 477 (Table 4). Although there was no moisture stress, the yield difference between the designated stress and non-stress treatments ranged from -5 to 14%, with a negative number indicating a higher yield in the designated stress than non-stress treatment (Table 4). The genotypes T3110-2 and T3008-1 had the least difference between yield in the two moisture treatments but T3147-2 had the greatest with a 14% yield reduction in the designated stress treatment. Even though the stress was not moisture related, the GM, DSI, and STI were still computed. The geometric mean ranked T301 6-1, 8-42-M-2, T3147-2, and Sierra, in that order as having the highest yield potential. As in 1995, the STI produced the same ranking as the geometric mean with regard to drought resistance and yield potential. The DSI designated three of these same four genotypes as being susceptible, T3016-1, 8-42-M-2, and T3147-2. Ignoring the negative signs, the most tolerant lines, as designated by the DSI, were also the ones with the lowest yield potential. These data indicate that plants did experience a stress in 1996, that the genotypes were differentially affected by it, and the stress was not due to moisture deficit. As in 1995, the correlation of Tab. 700... .0...”me 57 Table 5. White mold, bronzing, and yellowing observed during the 1996 growing season at KBS. Genotypes Sunscald Bronzing Yellowing 8-42—M-2 4.1 a“ 4.1 a” 1.3 abc” T3008—1 3.9 ab 1.6 b 2.8 abc BAT 477 3.4 ab 2.0 b 3.0 ab T3016-1 2.9 abc 1.6 b 3.4 a Lef-Z-RB 2.7 abc 2.5 ab 0.9 bc Sierra 2.6 abc 0.9 b 0.6 c T3147-2 1.9 be 1.3 b 1.8 abc T3110-2 1.0 c 0.9 b 0.9 Do ** Different letters indicates significant difference among means within a column at P s 0.01 according to DMRT. 58 geometric mean and STI with yield from the stress, non-stress, and combined stress and non—stress treatments was positive and highly significant ranging from 0.85“" to 0.99“", however, the correlation batween GM and combined moisture was not valid because the data produced a 1.00 correlation (T able 6). Unlike, 1995, the correlation between yield and DSI was positive in all three yield 2 categories and was significant for nonstress (0.82‘) and combined moisture treatments (0.63?) (T able 6). T3147-2 and Sierra were among the four highest yielding varieties during both years. Greater validity of 1995 data Given the lack of moisture stress and the incidence of leaf injury in 1996, only the 1995 data could be construed as relating to moisture deficit. The 1995 data indicated that T3147-2, Sierra, Lef-2-RB, T3110-2, and BAT 477 were drought resistant and 8-42-M-2, T3016-1, and T3008-1 were drought susceptible. The designation of T3147-2 and T3110—2 was resistant are supported by the work of Schneider et al. (1997), while the designation of BAT 477 as resistant was supported by numerous studies (CIAT, 1984; Sponchiado at al., 1989; Singh, 1995). Similarly, the designation of Sierra and Lef-2-RB as drought resistant is supported by results of Ramirez-Vallejo (1992). However, the 1995 results categorized T3016-1 and T3008-1 as drought susceptible in contrast to the work of Schneider et al. (1997) which categorized them as drought resistant. The designation of 8-42-M-2 as susceptible was supported by the work of Acosta-Gallegos (1988). Genotypic differences in both GM and DSI 59 Table 6. Correlations of yield under stress, yield under non-stress treatment, ' and combined yield for moisture treatments to geometric mean (GM), drought susceptibility index (DSI), and stress tolerance index (STI). Data from bean (Phaseolus vulgaris L.) plants grown at the Kellogg Biological Station in I-lickory Corners, MI. in 1996. 1926 GM DSI STI Stress 0.87“ 0.16 0.85“ Non-stress 0.96“" 0.82' 0.96“" Combined ~— 063‘ 0.99“" “‘5 “, *, * Indicates significance at P s 0.001, 0.01, 0.05, and 0.10, respectively, according to DMRT. 60 have been reported in common bean (Acosta-Gallegos, 1988; Acosta-Gallegos and Adams, 1991; White and Singh, 1991; Schneider et al., 1997) and in wheat (Triticum aesfivum) (Clarke et al., 1992). White end Singh (1991) reported similar limitations in the use of DSI in common bean in that DSl did not differentiate between potentially drought resistant genotypes and genotypes with low yield potential. Conclusion T3147-2, Lef-Z-RB, T3110-2, Sierra, and BAT 477 were drought resistant and T3016—1, T3008-1, and 8-42-M-2 were drought susceptible. Both GM and STI were better predictors than DSI of yield performance under limited moisture stress. 61 Literature cited Acosta-Gallegos, J.A 1988. Selection of common bean (Phaseolus vulgaris I.) genotypes with enhanced drought tolerance and biological nitrogen fixation. PhD. diss. Michigan State University, East Lansing, MI. USA Acosta—Gallegos, J.A, and MW. Adams. 1991. Plant traits and yield stability of dry bean (Phaseolus vulgaris L.) cultivars under drought stress. J. Agric. Sci. (Cambridge) 117:213-219. Amon, I. 1980. Breeding for higher yield. Co-ordinator's report on the first session. In: lntemational Potash Institute (ed.), Physiological Aspects of Crop Productivity. Proceedings of the 15" Colloquium of the lntemational Potash Institute. Wagenningen. The Netherlands pp.77-81. CIAT (Centro Internacional de Agriculture Tropical). 1984. Annual report 1983. Bean Program CIAT, Cali, Columbia. CIAT (Centro Internacional de Agriculture Tropical). 1988. Annual report 1987. Bean Program CIAT, Cali, Columbia. Clarke, J.M., R.M. DePauw, and TE. Townley-Smith. 1992. Evaluation of methods for quantification of drought tolerance in wheat. Crop Science 32:723-728. Fairbaim, J.N. 1993. Evaluation of soils, climate and land use information at three scales: The case of low income bean farming in Latin America. Ph.D. diss. University of Reading, Reading, U.K Fernandez, C.J. G. 1993. Effective selection criteria for assessing plant stress tolerance. In Adaptation of food crops to temperature and water stress: Proceedings of an international symposium, Taiwan, 13-18 August, 1992. AVRDC. pp2257-270. Fischer, RA, and R. Maurer. 1978. Drought resistance in spring wheat cultivars. I. Grain yield responses. Aust. J. Agric. Res. 29:277-317. Food and Agriculture Organization (FAO). 1984. Food balance sheets, 1979- 1981. FAO, Rome, Italy. Kelly, J.D., M.W. Adams, A.W. Saettler, G.L. Hosfield, G.V. Vamer, MA Uebersax, and J. Taylor. 1990. Registration of ”Sierra" Pinto Bean. Crop Sci. 30:745-746. Lynch, JP and J.J. van Beem. 1993. Growth and architecture of seedling roots of common bean genotypes. Crop Sci. 33:1253—1257. 62 Ramirez-Vallejo, P. 1992. Identification and estimation of heritabilities of drought related resistance traits in common bean (Phaseolus vulgaris). PhD. diss. Michigan State Univ., East Lansing (Diss. Abstr. 92-26240). Rosielle, AA and J. Hamblin. 1981. Theoretical aspects of selection for yield in stress and non-stress environments. Crop Sci. 21:943-945. Schneider, KA, R. Rosales-Same, F. lbarra-Perez, B. Cazares-Enriquez, J.A Acosta-Gallegos, P. Ramirez-Vallejo, N.'Wassimi, and JD. Kelly. 1997. Improving common bean performance under drought stress. Crop Science 37:43-50. Schwartz, HF, and MA Pastor-Corrales(eds.). 1989. Bean production problems in the tropics. 2nd ed. CIAT, Cali, Columbia. Singh, SP. 1982. A key for identification of different growth habits of Phaseolus vulgaris L. Bean Improvement Cooperative 25:92-95. Singh, SP. 1995. Selection for water-stress tolerance in interracial populations of common bean. Crop Science 35:118-124. Sponchiado, B.N., J.W. White, J.A. Castillo, and PG. Jones. 1989. Root growth of four common bean cultivars in relation to drought tolerance in environments with contrasting soil types. Exp. Agric. 25:249-257. White J.W., and SP. Singh. 1988. Breeding common beans for adaptation to drought conditions. In: G. Hoogenboom, F. lbarra, S.P. Singh, J.W. White and S. Zuluaga (eds), Research on Drought Tolerance in Common Beans. CIAT, Cali, Columbia. White J.W., and SP. Singh. 1991. Breeding for adaptation to drought. p. 501- 551. In A van Schoonhoven and 0. Voysest (ed.) Common beans: Research for crop improvement. CAB. lntemational. wallingford, UK, and CIAT, Cali, Columbia. Chapter 2 Bean seedling root growth as an indicator of field performance under moisture stress. Introduction Drought stress inhibits root growth (Robertson et al., 1990; Westgate and Boyer, 1985; Sharp, Silk, and Hsiao, 1988). Reports of increased root/shoot (RIS) ratio in droughted plants (Bradford and Hsiao, 1982; Sharp and Davies, 1979; Hubick et al., 1986) indicated that plants may respond to drought stress by preferentially maintaining root growth over shoot growth (Hsiao and Acevedo, 1974). Mild water stress promoted an increase in root elongation (Hsiao and Acevedo, 1974; Jupp and Newman, 1987; Watts et al., 1981). Blum (1988) found that root length density (RLD) and total root length per plant were greater in late maturing than in early maturing isogenic lines of sorghum (Sorghum bicolor) at most growth stages, yet when RLB was calculated versus leaf area per plant, the early lines had a greater RLDIunit leaf area. He interpreted this as meaning the early lines had an advantage inmaintaining a higher leaf water potential at a given soil moisture potential and that this was a drought resistance attribute. Blum (1988) reported that the best yielding maize lines under stress had an improved root length density of 120 to 150 cm. Carrow (1996) concluded that high RLD in the 20 - 60 cm root zone and the ability to maintain 63 64 evapotranspiration in drying soil were important for drought resistance in tall fescue (Festuca arundinaceae). The role of abscisic acid (ABA) in stomatal closure has been documented in many plants (T aiz and Zeiger, 1991), including cowpea ( Vrgna unguiculata) and cassava (Manihot esculenta). Less is known about the effects of ABA on root growth in water stressed environments, although ABA is believed to play a critical role in root elongation during drought-stress (Robertson et al., 1990). ABA may have additional regulatory roles in the adaptation of plants to drought stress (Jones, 1978). ABA levels increased in the roots of water-stressed plants (Hubick et al., 1985; Lachno, 1984; Walton et al., 1978) and this increase did not depend on transport from the shoot (Walton et al., 1976). Similarly, Sharp et al. (1993) reported that ABA promoted root elongation and inhibited shoot elongation in maize (Zea mays) at low water potential. . They also suggested that ABA is involved in the orientation of cell expansion in roots at low water potential. Polyethylene glycol (PEG) has been used to simulate drought in plants. It induced a primary water stress by reducing water availability (lzzo, 1989). The most serious limitation of PEG as an osmoticum has been its toxicity (lzzo, 1989). Kaufman and Eckard ( 1971) concluded that PEG produced changes in plant water relations similar to those caused by drying soil at the same water potential. Such studies have been conducted utilizing many species, including maize (Zea mays) (lzzo et al., 1989), coleus (Krizek, D.T. and Semeniuk. P., 1979), white clover (Trifolium repens) (Robin et al., 1989), and Capsicum annum 65 (Schaefer et al., 1979). These studies all concluded that PEG has the potential to simulate a drought stress environment. Historically, the soil medium has been the single greatest inhibitor to the advancement of knowledge about root growth and development (Waisel et al., 1996). Until recently, there were few suitable nondestructive methods for observing the growth and development of intact root systems. Nondestructive methods of root systems are limited to hydroponic and minirhizotron systems, which are expensive and limit the observation and measurement of the root system (Merhaut et al., 1989). In order to be useful to plant breeding programs, methods must be relatively inexpensive and must permit rapid evaluation of large numbers of gerrnplasm (Brar et al., 1990). The growth pouch method outlined by McMichael et al. (1985) appears to meet this criteria with regard to screening for root growth. McMicheal et al. (1985) using small seeded legumes (alfalfa and clover) found that root growth in pouches correlated to root growth in minirhizotrons and in field grown plants. The objectives of this study were to investigate root morphological response to ABA or PEG in Phaseolus vulgaris L. and to assess the feasibility of using root growth in pouches as a screening tool for drought resistance in common bean. 66 Materials and Methods: Genotypes '. The study used eight common bean genotypes which vary in their response to moisture stress: 1. Sierra, a been developed in Michigan. 2. BAT 477, documented by CIAT (1984) to be drought resistant. 3. 8-42-M-2, a drought susceptible line developed at Michigan State University. 4. Lef-2-RB, a drought resistant line. 5. T3008—1, developed by the Michigan State University bean breeding program. 6. 13016-1, developed by the Michigan State University bean breeding program. 7. T3110-2, developed by the Michigan State University bean breeding program. 8. T3147-2, developed by the Michigan State University been breeding program. (Table 1). Growth chamber study Seedlings were grown in a growth chamber with 23120°C day/night temperatures and a 15 h photoperiod. Photosynthetically active radiation (PAR) measured 523 umol m“2 s’1 at the top of the plant canopy using a Decagon Sunfleck Ceptometer (Pullman, Wash.) The experimental design was a split plot with solution (Half strength Hoagland’s nutrient solution or deionized water) as the main plot, genotypes as the subplot, and four replications. Seeds were germinated four days prior to initiation of the experiment. Uniform sized seeds 67 Table 1. Characteristics of common bean genotypes grown in field experiments at Kellogg Biological Station, Hickory Comers, MI. in 1995 and 1996. Genotypes Pedigree Origin£ Seed¥ Seed Plant: Size Color Type Sierra - Not identified§ MSU M Pinto ll T3110—2 Sierra X Lef-2-RB MSU M Striped lll T3147-2 Sierra X Lef-2-RB MSU M Striped lll Lef-2-RB (Ver 1OIChis INIFAP M Black lll 143)lpue 144 (striped) Bat {177 (51051 X ICA CIAT M Brown ll Bunsi) X (51012 X Cornell 49-242) 8-42-M-2 N81 017 X Lef-2-RB MSU M Tan or Brown lll T3016-1 Sierra X AC 1028 MSU M Tan or Brown lll T3008-1 Sierra x AC 1028 MSU M Tan or Brown lll £ MSU = Michigan State University CIAT = Centro lntemacional de Agriculture Tropical INIFAP = National Institute for Forestry, Agriculture, and Livestock Research, Mexico. ¥ M=Medium. 1: Type II = Indeterminate-bush, erect stem and branches Type Ill = Indeterminate-bush, prostrate main stem and branches 5 Derived from crosses of Durango Race Pinto with Mesoamerican Race Black (Kelly et al., 1990). 68 were selected for inclusion and rinsed in a 1 umol CaSO4 solution for one hour before germination. Seeds were germinated four days prior to initiation of the experiment. Seedlings were transplanted to a CYG growth pouch measuring 15.24 cm x 16.51 cm (MEGA International, Minneapolis, Minn.) at one seed per pouch, an adaptation of a procedure used by McMichael et al. (1985). All pouches contained 50 cc of deionized water and were stapled to black cardboard and placed upright in a specially designed holder with 2.54 cm between pouches. Seedlings were covered with a clear plastic covering for two days. Plants were given four 50 cc applications of half strength Hoagland’s nutrient solution, adjusted to pH 6.14, or deionized water from the sixth day after transplanting (DAT) to the fourteenth day when plants were sampled. Fresh weights were taken for roots, stems and leaves. Fresh roots were placed in a whirlpack bag and stored in 15% (vlv) methanol solution at 4° C. Leaves and stems were oven dried for 48 h at 60° C, weighed, and discarded. Roots were prepared for root imaging according to the procedure developed by Smucker et al. (1990). Root dry weight was then determined. Root quantification and processing was done using a Sun Ultra-based WR-RIPL; V. 3.0 at the root image processing laboratory, Michigan State University (Http:llrootdig.css.msu.edu.). Statistical analysis was done with the aid of MSTAT. 69 Root statistics Roots were divided into 5 classes, based upon root diameter. Root length was determined for each class and a summation was made of root length in all classes. The classes were Class 1 (0.2 mm), Class 2 (0.5 mm), Class 3 (0.9 mm), Class 4 (1.4 mm), and Class 5 (2.1 mm). Root classes 1, 2, and 3 comprised secondary roots and classes 4 and 5 comprised primary roots. Various ratios of secondary to primary roots were determined. The difference between control root length and root length under each treatment (ABA, -0.52 MPa PEG, and -1.07 MPa PEG) (delta value) was calculated. Some delta values were negative so a transformation of the data was done using a logarithmic scale (Au) for statistical analysis of the data. Data were analyzed across treatments to determine treatment effects. ABA experiment Plants were grown in a growth chamber with 23120°C day/night temperatures and a 15 h photoperiod. PAR measured 527 umol mas" at the top of the plant campy using a Decagon Sunfleck Ceptometer. The experimental design was a split plot with solution (ABA + deionized water or ABA + half strength Hoagland’s nutrient solution) as the main plot, genotypes as the subplot, and four replications. Experimental procedures were the same as those of the control experiment. From 6 to 14 DAT, the solutions in the pouches were replaced four times. ABA (cis-trans, :1: ABA, Sigma) was dissolved in deionized 70 water or nutrient solution for a final ABA concentration of 10" m. PEG experiment Two experiments were initiated with polyethylene glycol (PEG 600). The experimental design was a split plot with solution (PEG + deionized water or PEG + half strength Hoagland’s nutrient solution) as the main plot, genotypes as the subplot, and four replications. Plants in the first PEG experiment were grown in 8 PEG solution with a water potential of -1.07 MPa. The water potential was - 0.52 MPa in the second PEG experiment. Day/night temperature regimes for both experiments was 23l20°C with a 15 h photoperiod. PAR measured 524 and 528 ul'l‘lOl m"s“ for the -1.07 MPa and -0.52 MPa experiments, respectively. Water stress was induced at six DAT by adding PEG 600 (Sigma Chemical Co., St. Louis, M0) at 25 mlIL (osmotic potential -1.07 MP8) or 18 mlIL (osmotic potential -0.52 MPa). Solutions were replaced four times between 6 and 14 DAT. ‘ Greenhouse Study Plants were grown in polyvinyl chloride tubes (PVC) for 40 days in a greenhouse at Michigan State University, in East Lansing, MI. The temperature regime was 28°C 1 2°C and a light intensity of 1241 uE m”s“ for the first experiment and a temperature regime of 25°C :t 2°C and a light intensity of 1200 uE m‘zs" for the second experiment. Both experiments had a 15 h photoperiod. 71 Experiment 1 consisted of the medium-sized seeded genotypes, Sierra, T3008- 1, T3147-2, and 8-42-M—2 and was planted on June 18, 1996. Experiment 2 also consisted of the medium-sized seeded genotypes T3016-1, Lef-2—RB, T3110-2, and, BAT 477 and was planted on September 16, 1996. The experimental design was a split plot with water (stressed and nonstressed) as the main plot, genotypes as the subplot, and fourreplications. The PVC tubes were 76.2 cm in length with a diameter of 30.5 cm. To determine root growth at different depths each PVC tube was cut into five 15.2 cm sections. The fire individual sections were taped together to produce one 76.2 cm tube. The bottom section was filled with silica sand. The remainder of the PVC tube was filled with a Kalamazoo sandy loam soil (T ypic Hapludalfs, fine-loamy, mixed, mesic) that had been sieved to remove all stones and packed to a bulk density of 1.31 glcm’. Five seeds per PVC tube were planted and thinned to one plant per PVC tube at 14 days after planting (DAP). Stress was initiated at 14 DAP by reducing the amount of water given to plants in the stress treatment. Plants in the stress treatment received 53% less water than plants in the nonstress treatment. Determination was done by visually observing plants and the soil in the stress environment. Plants were watered when the soil began to crack from lack of water and plants began to wilt. Stress plants were watered approximately once per week.' Plants in the nonstress environment were watered approximately three times per week Plants were sampled at 40 DAP. Stem, leaf and reproductive parts were weighed, and dried at 60°C for 48 h, re-weighed, and discarded. Roots were extracted from each section by sieving the soil through 2 72 mm mesh wire. Roots were prepared for video imaging according to the procedure used by Smucker (1990). Root quantification and processing was I done using a Sun Ultra-based WR-RIPL; V. 3.0 at the root image processing laboratory, Michigan State University (Http:llrootdig.css.msu.edu.). After video imaging, roots were dried at 60°C for 48 h then weighed and discarded. Statistical analysis was done with the aid of MSTAT. Correlations Correlations were determined for each root class of the control, ABA, - 0.52 MPa PEG, and -1.07 MPa PEG experiments and with each root class of PVC experiments 1 and 2. Correlations were determined separately using pouch data from the water solution and pouch data from the nutrient solution and each of these was correlated separately against the stress and non-stress treatment of each PVC experiment. Correlations were determined separately for each soil depth of PVC experiments 1 and 2. Results and Discussion Root length: Control experiment There were no significant genotypic differences for root classes 1 and 5, the smallest diameter of secondary roots measured by this procedure and the widest diameter of primary roots, respectively (Table 2). BAT 477, the resistant .868 M. 408. So. 835 2 86:. 8333 con: ooooafioo con—2388a .: 8 3.3.8.8: 0.83.819. s a m. Noon bag 523838.. 8 o: o:<...o:3o:8_.< 833:3 96$: 0.836812 .3 a .3 m 833. «0.58: 3 38.." «.839... 783.256 3.58: 2 8.3.8.. 88.. 8. N5on .8336... 83888.9 man u .m 3 268.812.. woos o8 ease. as a daemon canoe o: gas assess , 02.6268 .8 «con £29 ...o8. 8o. 5.4m 0.8mm. 88» 08828.8 083293 0883.: 0832»... M828 3.8 be who as o.mo so ..oo o. ..oo o: o.oo be. Poo» am .3. an.» no.3 be won 8 ohm ~...o m Poo mo obs moo o.oo._ abut—s.» 8.3 0 Now ma ohm ..so me o..~o mo o.oo on 98.. n 53er onbo a N3 no Pan ..om mo obs we ob» o 98.. do. .5.» ammo on who no obo ..oo mo ooo on com moo o.oo~ ..wooo... 8.8 m on. m o..: ..3 8 ..oo o o.o.~ o o.oom 488... 8.3 0 abc m oho Nos 8 Poo m 93 m oboe m)... an» 3.8 o ..oo o ob» ._.._o .8 oh» 0 Po» 0 PS. o.<. o mm mm mm om oo 8. 3. r 0.883 .283 528.8 «6:38:08 2:03 Booze i=2: 8 8.2:: m. .u n o.o. one Pom. 8%8928? 883.3 8 025.... am .3288» :o «6:383. 2.8838 383 Boone (.55 m 8.55. m. H 59888 30. 8:9... .3 3888 man 9838.2 3 one... 30. 08mm .3 3....3888. 838928.... 74 check, had a significantly lower total root length than Sierra, T3147-2, T3008-1 and 1'3016-1. BAT 477 also had a lower seed weight than these genotypes (Table 2). Class 2 root length was significantly lower in BAT 477 than in Sierra, T3147-2, T3008-1, and 18016-1. Similarly, the root length for root classes 3 and 4 of BAT 477 were also lower than for Sierra, T3008-1, and T3016-1 (Table 2). Field performance of Sierra and T3147-2 designated them as resistant genotypes but their root length was significantly greater than that of BAT 477, the resistant check, which may be partly explained by their larger seed weight. Gregory's work (1989) showed that BAT 477 had a greater rooting depth than susceptible genotypes under stress but stress and rooting depth were not a part of this treatment. BAT 477 and 8-42-M-2, the susceptible check, did not differ significantly with regard to total root length or root length of any of the five root classes. Fifty-two to 61% of the total root length consisted of class 2 roots, while the percentage of class 1 roots ranged from 11 to 17% of the total root length (Table 3). Secondary root classes 1 and 2 comprised 63 to 75% of the total root length and roOt classes 2 and 3 contained 82 to 86% of the total root length. Ninety-five% of the total root length was comprised of all secondary roots (classes 1—3,Table 3). There were no significant genotypic differences for class 5 roots (Table 3). Seed weight did not affect percentage of roots in the individual root classes. The resistant check BAT 477 had a smaller percentage of its total roots as class 2 than did T3147-2 and Lef-2-RB, two other resistant genotypes, and 75 .838 a. 38388 o. 88 .3 .3288. Bo. 0.388 8.. 0.0.... 8333 383 8303.38 8.3.33.3 .3 3 8.3.3383 0.83.812 A o m. N000 33.. 83883.3 8 o: 3383338.:~ 83.8..3 99...... 0.83812 .0 o .3 3o: 83o... 78383.8 35.83. 8.583 2 88383 8.2 m. ”2800 3838.... 8388888 333 o .m 3 3.8.833. 0832508 .883 .229 0.38. a 088» 0.88 0.83 0880 0.388..» 0888.8 0888.86 .x. 083.3 3.8 o. .3 3... mo 33+ no mo. ..oo 3. o.o~ 38 No man. mm 3... . oo 8 8.3.» 8.8 00 .s 0. e m. 0 ...0 0 0.00 30 o 0. 00 0.80....» 00.8 o .3 00 o 8 mo ...0 0 0.00 8 mo 0» 00 53-8 00.00 a .0 0. o 0.. 0 0.0. 0 0.08 .0 o 00 00 8. .0.» 0.50 on .0 00 0 o. a ..00 ea 0.00 0.. 00 00 00 8000-. 00.00 a .. 0» 0 on o 0.00 o 0..» 00 o 0.. 00 80.0.. 00... o .0 0. mo 8 mo N00 as 0.0 3. mo 00 00 03 .3 00.00 0 .s 0.. 0 00 e ..00 ea 0.00 00 000 0.. 00 o.<. 0 no .. .0 8 .00 0 _ 0 0 .. + 0.88... 8.83 53.88 «63.38... 9.8838 3303 .388 .18... o 83.3.. b. t a com 3.... o..o. «88387.. 888.3 8 02.»... 3a .3988» 8 «83.38... 3.8838 3326 388 5.3... a 8.533. .9 53.8.8 8o. 19.. 0.388 ..m .3 3.53883 6.». oh. o.o. ..s. 3.3 n... 0833985. 76 did not differ significantly from 8-42-M-2, the susceptible check, or the resistant genotype Sierra. The percentage of class 3 roots in BAT 477 was greater than that of T3147-2, but not different from that of 8-42-M-2 or Sierra. The control did not separate resistant and susceptible genotypes, and root growth in half strength Hoagland’s solution did not differ from root growth in deionized water (Table 4). ABA experiment root length There were no significant genotypic differences for root classes 3, 4, and 5 (Table 5). The genotypes T3147-2 and Lef-2-RB had a significantly higher (P s 0.01) total root length than Sierra. Total root length of the resistant genotypes T3147-2 and BAT 477 did not differ significantly from that of the susceptible check 8-42-M-2. The class 1 root length of T3147-2 was significantly higher (P s 0.05) than that of all other genotypes except, 8-42-M-2 and Lef-2-RB (Table 5). The genotypes T3147-2, 8-42-M-2, and Lef-2-RB, had a'significantly greater (P s 0.05) length of class 2 roots than Sierra, T3008-1, and BAT 477 (Table 5). BAT 477 had one of the lowest total root lengths in the control treatment, but was among the group with the highest total root length in the ABA treatment. Seed weight did not affect root length of plants in the ABA experiment. Total root length of plants in the ABA treatment was significantly greater than that of control plants and the same was true for all of the individual root classes (Table 6). Significant genotypic differences existed for percentage of total roots in 77 Table 4. Root growth response to half strength Hoagland’s nutrient solution versus deionized water. Root Classes Controlfi ABA -O.52 MPa PEG -1.07 MPa PEG Class 1 ns ns W < H‘ W < H’ Class 2 ns ns W < H‘ W < H‘ Class 3 ns ns W < H' W < H‘ Class 4 ns ns W < H’ ns Class 5 ns ns ns _ ns Total ns ns W < H' W < H’ Classes 1 + 2 ns ns w < w w < H’ Classes 1+2+3 ns ns ns f ns *, + Indicates significant difference at P s 0.05 and 0.10, respectively. ns Indicate non significant data. W = Water H = Hoagland's nutrient solution 2 Control solution contained half strength Hoagland's nutrient solution or deionized water. ABA solution contained 10‘ m ABA dissolved in half strength Hoagland's nutrient solution or deionized water. PEG solution contained 18 mllL (-0.52 MPa) vlv of PEG 600 and deionized water or half strength Hoagland’s nutrient solution or 25 mllL (-1.07 MPa) vlv of PEG 600 and deionized water or half strength Hoagland’s nutrient solution. 78 ...00.0 0. 40.0. 80. .030... 0. 0.03. 83303 3003 00303.80 0033.30.03 .3 0 00333083 030332 .2 3 3 0. 0000 033 8300.03.03 .0 03 03<.83303.0.... 838.03 08.33 03030010.. .0 3 .3 .05 2. >0) 0. 00.0000 33.3.03. 8388.080 033 0 .0 3 030.8303. 000.0 £08 32.303 .3.0 0 0.00000 .0003 0003 80.3.0308... 0030.800 .00 0003 £20. ._.0.0. 80. 3.30 0.000. .00.» 0.0000 6.0. 0.0000 .00. 0.0003 3.0 0.0000 0.... 0.02.0 00.00 m. 0.000 a! 0.00 a. . 0.00 0. 0.00 30 . 0.0. 30 0.03 30 4.0.. 30.0 00.3.0 00 0.0 m 0.00 0 0.3 00 ..00 0.0 0.00 0.30.3.0 00.3 0 3.00 00 0.00 000 0.03 m ..3. 0.00 0.00 r0..0-x0 00.00 3 .300 m 0.00 00 0.00 0 ..00 0.0 0.00 ._.0._ .00 00.00 00 0.1.0 00 0.0.. 03 3.00 00 ..00 0.0 0.00 40000... 00.00 m 0.300 00 0.0 3 0.00 0 ...0 0.0 0.00 4.00.0... 00....— 0 3.000 3.00 003 0.00 000 ....0 0.0 0.0.. 0)... 30.0 00.00 0 0.0.. 0 ma 0....— 03 0.00 0 . .00 0.: 0.00 0.<. 0 A. ..3 30.00 A. .00 30.00 00.00 00.0.. 3.. 0.3083. .0308 33.8.00 0.03.383. 3.008300 03030 30030 3.3.3 0 8.033 0. 00 0.0. 033 0.00. 8000038.... 0088.30 .0 02.0.... . 30 53.8.00 30 0.03.383. 3.8838 03030 30030 53.3.3 0 8.033. m. a 53.8.00 80. .030.3 .3 30.0.0 033 3.0308. 0.. 0003 80. 0.000 .3 35.30.08. 8000038.... 79 403.0 0. 003003003 0. 80. 830.3 0.0.03. 83303 3003 8303.000 02330.03 .3 0 00.3.3030: 030330. .2 3 3 0. 0000 033 8300.03.03 .0 03 0338330383.. 83.8..03 0.0.0.3 030330. .0. .3 3 0. 00.0000 30...3.03. 83008880 033 0 .0 3 030.8303 .83 .30 .00. 80.3030 .30803. 000.0 88 3.<.303 .3.0 0 0.00000 30003 0003 80. 3.03083 48083.0 40.0. .00. 0.30 0.000. 8.0... 0.0000 8.0. 0.0000 3.0. 0.0003 3.3. 0.0000 .0... 0033.0. 0.0. 3:. 0.33 33 ..0. 33 0.0. 33 0.03 03 0.000 03 )0) ....00 3.000 0.00 ...00 0.000 0.0030 0.00 3.00 000 3.00 0 ..00 0 0.00 3 0.00 0 0.00 3 0.000 3 -. .00 2.10 0mm 0.00 3 0.00 3 3.00 0 0.00 3 0.0 3 0.000 3 O.<. 0. 03 00 30 0. .0. 3 0.883. .0308 53.8.0 0.03.3838 03030 30030 53.3.3 0 8.033 0. .u 0 0.0.. 00023.30 .0 02.04. a... 33.8.00 .8. 830.3 .3 30.0.0 033 .8. 5.3.3 0.00000 .3 33330.20. 8000038.... 0. 003.8. 00.0..03 83.0.303 30.. 0830.3 180.030 30.303. 00.0303 2 30.03.83 0.0.0.. >0) 00.0303 830.303 .00 3 >0) 3.000.83 .3 30.. 0830.3 180.0330 30.303. 00.0..03 0. 30.03.83 8.0.. 000 00.0303 838.303 .0 3.... 70.00 2.00. <3. 0. 000 000 033 30.03.83 $0.0. 0. 30.. 0830.3 180.0330 30.303. 00.0303 2 00 3.... T. .00 2.00. <3. 0. 000 000 03 30.03.83 $0.0. 2 30.. 0830.3 180.0330 30.303. 00.0303. 80 root classes 1-4 of plants grown in exogenous ABA (Table 7). Unlike the control, 32 to 47% of the total root length was comprised of class 1 roots. Root classes 1 and 2 comprised 81 to 90% of the total root length. Root classes 1 through 3 comprised 95 to 99%, as they did in the control treatment. Percentage of total roots in class 1 was significantly greater in the plants from the ABA treatment than in control plants (Table 8). However, the percentage of root length in root classes 2 and 3 was greater in the contrOl plants. Nevertheless, the increase in class 1 roots of ABA treated plants was so much greater than that of control plants that the combination of class 1 + 2 roots comprised a significantly greater percentage of the total root length in ABA treated plants than in control plants (86 vs 71 %, respectively). Seed weight did not affect percentage of total roots in individual root classes. The ABA treatment stimulated the development of the finer secondary roots. Presumably such an occurrence during a moisture deficit would increase the root absorptive surface area. thereby permitting the plant to obtain more water. Simultaneously, a greater percentage of ABA treated plants was in class 5 in comparison to control plants (Table 8). ' This would permit the plant to obtain moisture that might be in the deeper soil depths. These results generated the working hypothesis that ABA provides information about a genotype’s potential for root expansion during moisture stress. The data agree with other work indicating that ABA stimulates root growth (Creelman et al., 1990; Robertson et al., 1990; Sharp et al., 1993) and are exciting in their suggestionthat ABA disproportionately induces development of fine secondary roots. 81 435 q. .uoaoamco R 308 33 .oozacm. 32 among 3 ca...» 8332. oom: 03258 3.3.3.3 .3 m @0235ng 2.53319. 5 a m. nmoo mam 333.38.. 8 m: Ssgoanm...‘ 833:3 03$: oomaooq 8a 3 m m. ”Sosa amigo; 8338.28 moo m 3 3 308338 5. .5... z. >m> 0033.3 ..oo 8... :28 Emma“; 0.3m» . 0.3mm 0.3mm Emmom 0.839..» 0.33%? 0.38.0.3 m... «and ooh m. um moo. mm o. .3 mo. 5.8 m. :5 am 3 o. mm m+ mu no 43 5.» . woo mo 3 m mm on m o fiwo . o 0.3 . mo m . om mo mu «LES.» go o 3 mo 5 moo 3 on ...8 o Poo mm m mm moo mu rovmbw wmb a 3 mo 3 moo m o one o can co m 8 m mm 43 3.» use oo an o .6 m 3 m . 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I o: m» m: »» m... ..mw oo: Pom o... .3 at. mm m: m.» m: >m> 3m .5 o .3 o ».».. mo 98 m mm o cu o m» o .08» 2.3 .umm mo o m. m ..m o ».m» m ob» mo 3 (o mm o mm o u -.b» 2.1m .umm an m mo o m o ..»o o ..o» m mm m mm m mm o o.<. »w .. w. .3 Go a » m t . 0.83:. 8.88 88.88 «835838 maoac Emma (.58 m 883: m. .u m ob. 883.3 8 02.3.. n Gonzo. 88.8: 83883 om: «.88.... .8383...» 258:. 3.58: oq 88:83 <88... >w> 3.58: smm 85 3 >m> 9328.. .3 om: £835 Iomo.m:m.m 25.83. 8.58: o. 88:83 (m8: .umm 8.58: 8:883 ..m 3.... mob» .somv <2 o. .umm moo mam 88:82. ‘88.. on om... «.835 103.286 358:. 3.58: o.. »m 35. A... .3 2.1m. <2 9. .umm moo man 88:82. (m8. oq om: madam... Iomc.m:a.m 2.30:. «0.5.8:. . a ..am8m8m 3o. £85 ammmmm .-m .3 3....3m88 8.». Pm. ob. ..A. man »... 88398.5. 83 -0.52 MPa polyethylene experiment root length Significant genotypic differences were observed for all root length classes in the -O.52 MPa treatment, except class 5 (Table 9). The total root length of T3147-2 was significantly higher (P s 0.05) than that of Lef-2-RB, T3110-2, and Tacos-1 (Table 9). For class 1 roots, 73147-2 root length was significantly higher (P s 0.05) than 8-42-M-2, Lef-2-RB, T3110—2, and 1’3008-1 (Table 9). Class 2 root length for T3147-2 was significantly higher (P s 0.05) than that of Lef-2-RB and T3008-1 (Table 9). Sierra and BAT 477 had a significantly greater (P s 0.01) class 3 root length than T3008-1 (Table 9). Sierra, 8-42-M-2, T3110- 2, and BAT 477 were among the group with the highest (P s 0.10) root length for class 4 roots (Table 9). Root length did not correspond with seed size. As in the ABA treatment, BAT 477 was among the group of plants with the highest total root length when plants were grown in PEG at a w of -0.52 MPa and this was true for all root classes, except class 5 which had no significant genotypic differences (Table 9). Generally, the same situation applied for the resistant genotypes, Sierra and T31‘47-2. The genotype T3008-1 had a lower root length than BAT 477 for all root classes, except class 5. The susceptible check, 8-42-M-2 was among the group with the highest root length in all classes except class 1. Plants grown at a w of -O.52 MPa had a significantly greater total root length than the control plants and the same was true for all root classes, except Class 2 where the two were equal (Table 6). However, total root length of the -O.52 MPa-treated plants was significantly less than that of plants grown in ABA (Table 5), and the same was true for all root classes. Plants .308 0. .88. 30. 8:05 3 0.0:. 8330: 03: 033.03 083.380 .: 8 003.88: 0.83.312 A 0 0. 006 0:0 30.380 8 9: 333338.... 833.80 0.3.... 0.83.812 I 0 8. 00.0090 03.3.0... 83008.53 0:0 9 ..m : 0.880080 .: 0 00.83.88 03.8. comm. 38.8: 2 .0....» 2.08. .80.... 08 0.<.0o0 88 0.0833 0380 00o: Bo. 08388... 032.63 .00 «30 £20. .88. 3. 5:0 083. an.» 083» .9... 0830 .98 0.33 0.3 0.33 a... 8.28 3.8 a. 3 men. n.» men. 9. a... 98 a... 98 a8. 98 8 333 8.8 no N. a 9n a 3 a 98 no 98 en 98 u to...» 8.8 a .8 38 ..N on N... men 9.8 an 9.8 a 98 83-3 8.8 a we 8 9m 8 2 an 9.8 an 98.. an 98 8. 3.» 3.8 8 . 3 a8. 2 an. ..0 man 98 no 98. man 98 488.. 8.8 a ..m a 9a a 9a a . 98 a 98. o 98 488.. 8.2 a 3 88 ..m man 3 mo 98 mo 98.. an 98 m)... 0.3 3.00 c 0.0 3 N0 3 0.0 ma 0.0» m o... .0 3 0.00 o.<. m .98 8.8 3.8 8.8 898 8.8 3. .. 4 0.88:. 8.88 80.88 10:38:. 0.88:3 38:0 333 (0...: e 8.03: e. 0 n 0.0.. 0.0.... 0:0 9.0. 880088? 082080 8 025.... :0 80.88 .3 20:58:. 0.88:3 38:0 333 (.03.: e 883:. a...“ 80.88 3:. 8:0... .: 3083 30 0.9308. 0.“ 3.. Be. 083 .: 3....3083. «30308.... 85 grown in -O.52 MPa PEG solution had a higher percentage of their roots in class 2 (46 to 56%) than in any other class (T able 10) and a larger percentage of roots inclasses1 +2thaninclasse32+3. Thepercentageoftotalrootlength in class 1 was greater in the -O.52 MPa solution than in control plants but less than in the ABA—treated plants (Table 8). The percentage of total root length in class 2 roots equaled that of control plants and was greater than that of ABA-treated plants (Table 8). The percentage of total roots in secondary root classes 1 + 2 of plants in the -O.52 MPa treatment was intermediate to that of control and ABA- treated plants while the percentage of roots in classes 2 + 3 was less than that of control plants, but greater than that of ABA treated plants. The -0.52 MPa treatment was similar to the ABA treatment in that both stimulated the development of class 1 roots and total root length (RL). Percentage distribution in individual root classes did not correspond with seed weight (Table 10). :1 .07 MPa polyethylene glycol experiment There were no genotypic differences for any of the root classes or for total root length in the -1.07 MPa treatment (Table 11). Total root length of plants grown in -1.07 MPa PEG was greater than that of control plants and than plants grown in -O.52 MPa PEG, but less than that of plants grown in ABA (Table 6). The same was true for class 1 roots. Root length of class 2 roots was equal to that of ABA-treated plants and greater than that of the other two treatments. Class 3 root length was equal to that of control plants but less than that of ABA- treated plants and greater than that of plants in the -0.52 MPa experiment. Root 6 8 400.0 3. 00803.30 0. 30.0 .33 30.3000. 30. 0.00000 0. 06:. 00330: .000: 00:02:00 33.60.00 6 0 32:50.6: 90:60.. .2 0 0 0. ~06 0:0 3:020:80 .0 0: 03.33.0305 003.960 03“.: 3030010.. 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BAT 477 had a greater percentage of its roots as class 1 roots than did 8-42-M- 2, T3110-2, and T3008-1 (Table 12). The reverse was true for class 2 roots. BAT 477 had a greater percentage of its roots in classes 1 + 2 than did 8-42-M-2 while the reverse was true for classes 2 + 3 (Table 12). The resistant genotypes. Sierra and T3147-2, did not differ from 8-42-M-2 with regard to classes 1 + 2 and classes 2 + 3. Percentage distribution in individual root classes did not correspond with seed size. The percentage of total root length in class 1 was equal to that of the ABA-treated plants and greater than that of the other two treatments. Percentage of total roots in class 2 was less than that of control plants and plants grown in -0.52 MPa PEG treatment (Table 8). The percentage of total root length in classes 1 and 2 was higher than that of any other treatment. While not identical, the distribution of roots in classes 1 through 5 and the total root length of plants grown in -1.07 MPa was more similar to that of plants grown in ABA than to plants in any of the other experiments. Class 1 root growth was stimulated by ABA and by both PEG concentrations (T able 8). No work in the literature was found comparing the effects of ABA and PEG on root length, but the data concur with previous work indicating that ABA increased root growth (Robertson et al., 1990). 89 400.0 ..~. $83.30 0. .003 .33 302.08. ..00. 0.088 0. 0.0:. 00330.. 000.. 0030200.. 83.30.00 3 0 8.3.8.3.. 9038. .0. s 0 m. nmoo 0.5 8300.03.00 .0 m: o..<.3...3o...m..< 0033.50 9.05.... 2.03.8. .0.. .s 0 .3 m 00.555030 0.30. .pmm moo. «0.5.0... 0. .. .3 zoo m. ”28.6 8.36.... 33003.58 0.... 0 .m .. 2.0.0830... 0030208. 0.08.... 902.0 .8. A?» in...» 83.3 ..u. .0.» 300m-.. duo. m... m>._. s3 0.88» 0.08.. . 0.0%.. 0.3mm . 0.88m...» 9883+?» 0.3886 .x _ . on. not 0m 0.. .. 0.. ..no so . obo so mm on. mm ..m mm on: so moo so moo m moo ..mo 98 mm moo mm mm moo mm oo o. m , 3 m ..so 98 mm o m. on mo s» mo so moo N o 98 9B . mm m mo mo oo mm o msm .. m ..mo . 98 m. oo mm mom mm oo . mm m. .o moo ..mo 98 mm moo mm mm mo s. moo mo mo m oo ..8 98 3 mo 8 mm moo so m so oo o oo ..mo 9so 9 mo 8 as o . :. . 0503... .0303 30.8.0 103.383.220.08 030.6 38.6 3...... n 0033.. m. p m 0.0. 02.0.8. 30000.20? 8803...... .0 025.... ..0 30.8.0 :0 103.383.510.268 030.6 30030 (.3... 0 00.:3... # 50.8.8 3.0. in... 1088...... .3 35.30.03 8.». Po. 0.0. ..s. n...— N... 8080303. Ratios Since there were distinct differences among experiments with regard to percentage of roots as primary or secondary roots, this raised a question about the existence of a pattern between primary and secondary roots among genotypes and across treatments. A number of possible ratios of primary to secondary roots were calculated and analyzed to determine if there was a pattern among the genotypes or across the four experiments (T able 13). Ratios were reported based on genotypic significance and a relatively low coefficient of variation. Several ratios had significant genotypic differences in both the ABA and -1.07 MPa experiments. These primarily involved the ratio of class 1 roots to other root classes and reflect the stimulatory effect that both ABA and -1.07 MPa PEG had on class 1 roots. Root ratios did not correspond with seed weight among the medium-sized seeds in this study. Control ratios No ratio distinguished between resistant and susceptible genotypes. BAT 477 did not differ from T3110—2, T3008-1, or T3016-1 in any of the ratios (Table 14). ' ABA ratios As with the ratios from the control experiment, none of the ABA ratios distinguished between resistant and susceptible genotypes. There was greater Table 13. Various ratios of different root classes in plants grown in the growth 91 chamber in control, ABA or PEG 600 (-O.52 or -1.07 MPa) solutions. Ratios: Control -ABA -O.52 MPa -1.07 MPa ‘15 ns *(26) ns '(23) 1I3 1(41) ns ns ”(37) 114 “(72) “(66) ns ns %+3 ns "(29) ' ns “(24) 1/3+4 *(42) ns ns “(38) 113+5 1(41) ns ns ”(38) 1I4+5 “(73) ns ns “(38) 964-344 ns “(29) ns “(24) . 1A+3+4+5 ns ”(29) ns “(25) 1+213+4 1(29) ns ns *(31) 1+2I3+5 ns ns 1(48) *(31) 1+2/4+5 “(69) ns ns ns 1+2+3I4+5 ns *(58) ns ns 213 ns ns ‘(38) ‘(28) 2/4 ”(71) *(54) ns ns 2/3+4 ns ns ‘(39) ns 213+5 ns ns *(35) 1128) 214+5 “(70) ns ns ns 213+4+5 ns ns *(40) ns ”, ‘, " Indicates significance at P s 0.01, 0.05, and 0.10, respectively among means, according to DMRT. Number in parentheses is coefficient of vanafion. ns Indicate no significant differences. 1 Indicates root width classes 1-5 in millimeters (0.2, 0.5, 0.9, 1.4, and 2.1, respectively). A ' 92 Table 14. Ratios of root classes that had significant genotypic differences in the control experiment of seedlings grown in growth pouches in a hydroponic solution that contained deionized water or half strength Hoagland’s nutrient solution. 69000138 (1)/(3)1 (1)/(4) (1 W314) (1 )l(3+5) (1 )l(4+5) Sierra 0.49 hot 11 bcd‘ 0.47 abc‘ 0.49 bct 11 bc‘ T3147-2 0.63 ab 16 abc 0.60 ab 0.63 ab 18 ab 8-42-M-2 0.71 a 22 ab 0.68 a 0.71 a 21 a Lef-2-RB 0.63 ab 26 a 0.61 ab 0.63 ab 25 a T3110-2 0.43 bc 8 cd 0.41 be 0.43 bc 8 be T3008-1 0.40 c - 6 d 0.34 c 0.36 c 6 0 13016-1 0.50 bc 8 cd 0.46 abc 0.50 bc 8 be BAT 477 0.53 abc 11 bed 0.51 abc 0.53 abc 11 bc c.v. 41 72 42 41 73 Genotypes (1 +2)I(3+4)$ (1 +2)l(4+5) (2)/(4) (2)/(4+5) Sierra 2.4 b" 0.63 ab“ 52 bc“ 52 ab T3147-2. 3.2 a 0.97 ab 81 ab 79 ab 8-42-M-2 2.7 ab 0.87 ab 66 abc 65 ab Lef-2-RB 3.1 a 1.27 a 107 a 102 a T3110-2 2.1 b 0.43 b 37 c 25 b T3008-1 2.5 b 0.33 b 28 c 27 b T3016-1 2.5 b 0.41 b 35 c 33 b BAT 477 2.4 b 0.52 b 42 be 41 b C.V. 29 69 70 70 “, ', + Different letters indicate significant difference among means with a column at P s 0.01, 0.05, and 0.10, respectively, according to DMRT. :1: Indicate root width classes 1-5 in millimeters (0.2, 0.5, 0.9, 1.4, and 2.1, respectively. 93 than a 10-fold ratio between secondary to primary roots (classes 1+2Iclasses 4 + 5) (Table 15 and 16). -0.52 MPa ratios Several of the ratios did separate T3147-2 from 8-42-M-2, but none separated 8-42-M-2 from BAT 477 (Table 17). Generally, T3147-2 and BAT 477 . did not differ from each other and Sierra and BAT 477 did not differ (T able 17). There were no significant genotypic difference between susceptible and resistant genotypes with the ratios that produced significant genotypic differences in the control experiment, but there was a consistent pattern to the ratios of secondary to primary roots in which T3147-2 > BAT 477 > 8-42-M-2 (Table 18). Sierra was somewhat similar to BAT 477. -1.07 MPa Ratios Unlike root length (RL) in the -1.07 MPa experiment, the ratios exhibited significant genotypic differences (Table 19 and 20). The resistant genotypes T3147-2 and BAT 477 did not differ for any of the ratios with class 1 in the numerator while BAT 477 consistently had a higher ratio than the susceptible check 8-42-M-2. These ratios compared class 1 roots to other roots and illustrate the greater proportion of class 1 (fine) roots to other roots in the -1.07 MPa PEG experiment. The data suggest that such a ratio is indicative of a resistant genotype. Nevertheless, Sierra, the other genotype designated as 94 Table 15. Table of all ratios from ABA experiment that had genotypic significance. Genotypes (1)/(2)1 (1)/(4) (2)/(4) (1)/(2+3) Sierra 0.93 ab" 16 c‘ 17 c‘ 0.71 ab‘ T3147-2 1.13a 48ab 41 ab 1.00a 8-42-M-2 0.90 abc 31 abc 33 abc 0.75 ab Lef-2-RB 0.97 ab 52 a 49 a 0.83 ab T3110-2 0.66 c 18 c 25 bc 0.51 c T3008-1 0.78 be 28 be 35 abc 0.63 bc T3016-1 0.86 be 31 abc 36 abc 0.71 ab BAT 477 1.03 ab 22 c 22 be 0.84 ab G.V. 26 66 54 29 Genotypes (1 )I(2+3+4):|: (1 )I(2+3+4+5) (1 +2+3)I(4+5) Sierra 0.66 ab” 0.65 bc‘ 32 b“ T3147-2 0.93 a 0.93 a 78 ab 8-42-M-2 0.73 ab 0.73 ab 58 ab Lef-2-RB 0.81 ab 0.81 ab 88 a T3110-2 0.50 b 0.49 c 38 b T3008-1 0.62 ab 0.61 be 46 ab T3016-1 0.68 ab 0.67 be 62 ab BAT 477 0.80 ab 0.78 ab 39 b C.V. 29 29 58 ”, " Different letters indicate significance among means within a column at P s 0.01 and 0.05, respectively, according to DMRT. 1: Indicates root width classes 1-5 in millimeters (0.2, 0.5, 0.9, 1.4, and 2.1, respectively). 95 dose .5. wagon A33 5o >w> 962.563 53 82.333. 8 So 833. 962.563 «3.2.. 53 :3 Q3338 «635838. 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H 58.0888 400. $.88: 0.88888 ...8 .: 3....38848 .0.». 0.8. 0.0. ..8. 8:8 8..... 488080.285. 488.8 N0. £8.88 .33 .88 .. .04 2:88 8mm 8.684.383 .88. 8.488838 .8 .88 833. 8.682383 48.88 .88. :88 08:828.." 86:58:88. 88882888 0.8.8.8108 0.8.4.88. 38.8.8. 38.8.8. _ 34.8. 8.843 8.88 88. .888. 88 8.88 88.. 8.88 88.. 8.88 88.. 48.848 .88. 888 88.48 8.48 888 8.88 88 8.8 88 8.88.3.8 4.88 8 88.8 8.84 88 8.88 8 8.88 8 88.8.88 ...88 8 .888. 8.44 888 8.88 88 8.88 88 48. .8.8 8.88 88 48.88 8.88 8. 8.88 88 8.8. 8 48888.. 8.88 88 48.88 8.84 , 88 8.88 88 8.88 8 480. 8.. 3.4» 88 40.88 0.48 888 8.88 88 8.80 88 8>4 844 .8.88 88 8. ..8 8.88 8 8.8 8 8.84 8 8.<. 8. 88 88 88 84 3. . 05848:. .8388 58.8.8 10:58:. 85848888 8388.. 388:8 5.3.: 8 8.83:.8. v 8 0.0. 8:8 0.08. 488888.282. 888350 .8 02:4... :8 38.8.8 :8 10:38:. 8:488:88 838:0 388:8 1.8.: 8 8.83:. 8" 58.88.88 38. in... 8.88888 ..-8 _: 35.38.83 .0.~. 0.8. 0.8. ..8. 8:8 u... 488888835. 101 resistant, usually did not differ from 8-42-M-2. Deltas values ABA Deltas The greatest numerical increase of ABA-treated plants over control plants for all genotypes occurred with class 1 roots followed by class 2 roots (Table 21). Class 2 roots in Sierra increased less than class 2 roots of 8-42-M-2 and Lef-2-RB. BAT 477 was.in the group of genotypes with the lowest increase in root length of class 1 and class 3 roots, although its class 2 roots did not differ from the group of genotypes with the greatest increase in root length (Table 21). The increase in total root length of BAT 477 with ABA was intermediate to that of the other genotypes, with T3147-2 and 8-42-M-2 at the high and Sierra at the low and. -0.52 MPa PEG Deltas The PEG concentration of -O.52 MPa increased total root length of all genotypes except T3008-1, which decreased (Table 22). The increase in total root length in T3147-2 and BAT 477 was significantly greater than that of all other genotypes (Table 22). With the -O.52 MPa treatment, T3008-1 decreased its root length in comparison to the control for roots in classes 2, 3, and 4 (Table 22). There was a decrease in class 3 roots in all genotypes except 8-42-M-2 and BAT 477(T able 22), where 8-42-M-2 maintained its class 3 RL and BAT 477 102 ...88.8 0.. 2.88: 3:848:88 882488: >0) 8:8 888.3. 38.8. .84 888... 488. 8.888. 2. 3838848 488488838 >0) 8.684.383 .:8.<.888. 38. 8.88888 3388 .88 888888.88 488. 8.888 .483 .88 888.48. 888.383. 088884888 48.8. ..88. . 0.888. 8" 0.8880 0.88808 0.8888 0.8888 0.80.8 &.M0 8.. N40 0.. ..00 8:. 0.04 o. 0..0 ...8 0.00 :8 48.84.» ...00 8 8.40 8 8.88 88 0.08 888 0...... 0.08 rung.» . ...00 m 0.: 888 who 8 0.4» 8 0.M0 0.00 884.an .M..00 8 0.04 88 0.00 8 0.40 8 0N0 0.00 40.. .0.» 0.00 8 N0» 0 . 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U 0.0M .400. 0:. ..40 8 ...8 88 0.00 88 0.04 00 0.00M U 0.0M 0).. 844 .900 m N... 8 N30 8 0.00 m 0.00 8 0.00 0.<. .00 Am 0 0 . .N 04 . 0588:. .8..83 38.88.88 10:58:. 9:28:88 838:0 388:8 1.2: 8 88.03: 8. .u 8 0.08 8888330 .8 0.5.»... m ..8<8. 8.388.10208838 88.8388 808. 88:88:35.8: 8. 88.8 0830 8 .808:.:3..8 888.8. 8 58.88.88 38. ...8... 8.88888 ..8 .: 30:38.83 .0.». 0.8. 0.0. .... 8:8 8... 38888385. 104 increased. -1.07 MPa PEG Deltas There were no significant genotypic differences in the increase over the control in total root length or in root classes when plants were grown in -1.07 MPa PEG (T able 23). Five of the 8 genotypes had a decrease in class 3 roots when plants were grown in -1.07 MPa PEG (Table 23). Polyvinyl-chloride Experiment 1. Significant genotypic differences were only observed in root class 1 and total root length (T able 24) for the 1 to 15.2 cm depth. In total root length and root class 1, T3147-2 had a significantly higher root length (P s 0.10) than the other three genotypes. The stress treatment had a significantly lower (P s 0.001) root length of class 3 roots than the non-stress treatment and the same was true for class 5 (P s 0.10) roots (Table 25). In the 15.3 to 30.5 cm depth, significant genotypic differences occurred for total root length and for root classes 2, 3, and 5 (Table 24). In root classes 2 and 3, T3147-2 had a significantly higher (P .< 0.05 and 0.01, respectively) root length than 8-42-M-2 but was not significantly higher than Sierra and T3008-1. For class 5, T3147-2 had a significantly higher (P s 0.01) root length than Sierra and 8-42-M-2 (Table 24). For total root length 8-42-M-2 had a significame lower (P s 0.10) root length than Sierra and T3147-2 but was not significantly different 403.0 nu. $255530 3‘8. 3 .3 Emmy no.8 8358639 >__ 3:333 32.2638 3.55103 o_ N' ns ns S > NT Class 2 ns ns S > N‘ ns ns 8 > N” Class 3 S < N'” ns ns ns ns ns Class 4 ns ns ns ns ns ns Class 5 S < N' ns ns ns ns ns Total ns ns 8 > N” ns ns S > N‘ Root dw ns ns S > N‘ S > N" ns ns Percentages Class 1 S > N' ns ns ns ns ns Class 2 S < N‘ ns ns ns ns ns Class 3 ns 8 s N’ S < N‘ ns ns 8 < N’ Class 4 ns ns ns ns ns 8 < Nt Class 5 ns ns ns ns ns ns Class1 +2 S > N" ns S > N’ ns ns S > N' Classz+3 S < N“ ns 8 < Nt ns ns S < N“ ”‘, ”, '. 1 Indicates significant difference at P 3 0.001, 0.01, 0.05, and 0.10, respectively. ns Indicate non significant data. S I Stress treatment, NI Non-stress treatment, RL I root length Depth 'A' I1-15.2 cm, '8' I 15.3-30.5 cm, 'C' I 30.6-45.7 cm, '0' I 45.8-61 cm. '5' I 61.1-76.2 cm. 110 from T3008-1 (Table 24). Moisture status had no effect on root length for roots at the 15.2 to 30.5 cm depth (T able 25). Significant genotypic differences were observed for total root length and for root classes 2, 3, and 5 at a depth of 30.6 to 45.7 cm (Table 24). In root classes 2 and 3 (P s 0.01), 8-42-M-2 had a significantly lower root length than Sierra and T3147-2 (Table 24). Class 5 root length of 8-42-M-2 was significantly lower (P s 0.10) than that of T3008-1 and T3147-2 (T able 24). Total root length of 8-42-M-2 was significantly lower (P s 0.10) than that of the other three genotypes (Table 24). At this depth, root length of class 1 and class 2 roots was significantly higher (P s 0.05) under the stress treatment than under the non-stress treatment (Table 25). The same was true for total root length (P s 0.01) and root dry weight at this depth (Table 25). At a depth of 45.8 to 61 cm, the only significant genotypic differences occurred in root classes 3 and 5 (Table 24). In root class 3, 8-42- M-2 had a significantly lower (P s 0.01) root length than Sierra but did not differ from T3008-1 and T3147-2 (Table 24). However, in root class 5, 8-42-M-2 and Sierra were significantly higher (P s 0.05) than T3008-1 and T3147-2 (Table 24). Root dry weight at this depth was significantly greater (P s 0.10) under stress (Table 25). There were no significant genotypic differences in total root length or in any of the five root classes for depth 61.1 to 76.2 cm (Table 24), and moisture stress did not affect root length at this depth (T able 25). Across the five depths, genotypic differences occurred for total root length 111 and for root classes 2 and 3 (Table 26). The genotype 8-42-M-2 had a significantly lower total root length and lower class 2 root length (P s 0.05) than the other three genotypes (Table 26). In class 3, 8-42-M-2 was significantly lower (P s 0.01) than Sierra and T3147-2 (Table 26). The genotype 8-42-M-2 had a significantly lower seed weight than the other genotypes, suggesting that TRl. corresponded to seed weight (T able 26). Across all depths, stress increased (P s 0.10) total root length and root length in classes 1 and 2 (Table 25). No significant genotypic differences existed for percentages of root length in any of the root classes at depth 1 to 15.2 cm (Table 27), but 58 to 61% of all roots at this depth were class 1 roots and 31 to 33% were class 2 roots (Table 27). At this depth, the stress treatment had a greater percentage (P s 0.05) of total roots as class 1 roots than the non-stress treatment and the reverse (P s 0.05) was true for class 2 roots. The percentage of class 1 plus class 2 roots was greater (P s 0.10) under stress (Table 25). For the 15.3 to 30.5 cm depth, significant genotypic differences were observed for percentage of total roots in classes 1, 2, and 3 and in classes 1 + 2 and classes 2 + 3 (Table 27). Root classes 1 + 2 comprised 93 to 96% of the total root length (Table 27). The genotype 8-42-M-2 had a significantly higher (P s 0.05) percentage of total roots in class 1 than Sierra and T3147-2 (Table 27), but a lower percentage of roots in classes 2 and 3 than Sierra and T3147-2. Consequently, 8-42-M-2 had a significantly higher percentage (P s 0.05) of total roots in classes 1 + 2 than Sierra and T3147-2 and a significantly lower 12 1 333333333 .2 33 a 3. 330033 333.33. 83333.38» 33.. 3 .3 3 333833333 .3 3 «.833 33.. 33.3.38 533333.. 20 $62.33... ...33.3 33. 0:33.333 .23. Bo. 633.3 2 .02 8.3303 3333 3332.63... 33.23 .3 3... .3 1<0 .3333 R 33 33.. 3.3.3.3.. .3 3 03325333 .33 «33.. 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Pom. man 0.3. «83038.5 88293 8 02.3.. . 2.. 528.8. so «6:582 926338 8326 38..."... .55.: m 863:. H 598.8. 32 £33 0.888. fm .3 3....3883 8.». Pm. ob. 99 man NA. .8835: 116 percentage (P s 0.05 and 0.01, respectively) of total roots in classes 2 + 3 than Sierra and T3147-2 (T able 27). Percentage distribution among root classes did not correspond to genotypic seed weight. Stress decreased the percentage of total roots in class 3 (P s 0.10) (T able 25). For depth 30.6 to 45.7 cm, percentage of roots in class 1 ranged from 50 to 63% with 8-42—M-2 having a significantly higher (P s 0.01) percentage than the other three genotypes (Table 27), corresponding with the lower seed weight of 8-42-M-2 in comparison with the other three genotypes. Percentage of total roots as class 2 ranged from 33 to 44%, with 8-42-M-2 having a significantly lower (P s 0.01) percentage than the other three genotypes (Table 27). Root classes 1 + 2 comprised 92 to 96% of the total root length and was significantly higher for 8-42-M-2 than for the other three genotypes (T able 27). Root classes 1 through 3 comprised 99% of all roots. Percentage of total roots in Class 1 at the 45.8 to 61 cm depth ranged from 45 to 52% with 8-42-M-2 having a significantly higher (P s 0.10) percentage than Sierra. The genotype 8-42-M-2 had a significantly lower percentage (P s 0.01) of total roots in classes 2+3 at this depth than all other genotypes except T3147-2 (T able 27). However, the greater percentage of class 1 roots in 8-42- M—2 was such that 8-42-M-2 had a higher percentage of roots in classes 1+2 (P s 0.05) than the other three genotypes (Table 25), again corresponding with the lower seed weight of 8-42-M—2 in comparison to the other three genotypes. At a depth of 61.1 to 76 cm, only 14 to 33% of the total roots were class 1 roots and root classes 1+2 only comprised 32 to 67% of all roots (T able 27). 1 17 There were no genotypic differences. When data for all depths of the 0.7 m PVC column were combined, 8-42- M-2hadahigher(P s 0.05)percentageofitsrootsinclasses1and51hanthe other three genotypes and a lower percentage (P s 0.05) in classes 2 and 3 (T able 28). Consequently, 8-42-M-2 had the highest percentage of roots in classes 1+2 and the lowest in classes 2+3. Stress increased (P s 0.10) the percentage of total root length in classes 1+2 and decreased (P s 0.10) the percentage in classes 3 and 4 (Table 25). In the pouch experiments, ABA and PEG increased total root length and percentage of roots in class 1 during these treatments, which were designed to simulate moisture stress, and also decreased the percentage of class 2 roots, yet had a greater percentage of all roots in classes 1+2. In PVC Experiment 1, moisture stress did exactly that in the top 15 cm of the soil profile. Furthermore, stress increased (P s 0.05) the percentage of class 1+2 roots in the 30.5 to 45.7 cm soil depth and when all soil depths were combined (Table 25). mm regard to actual root length, stress increased RL in root classes 1 and 2 and total root length (P s 0.01) at the 30.5 to 45.7 cm depth. The same was true for class 1, class 2, and total root length across all depths (Table 25). The susceptible check, 8-42-M-2, had a greater root length of class 1 roots and of classes 1+2 than the other three genotypes. if stress increases the roots in classes 1+2, the data indicate that 8-42-M-2 was experiencing a greater degree of stress than the other three genotypes and this may be further evidence of its drought susceptibility in the severe moisture stress of PVC 118 .335 Mm. 3083.38 2 Be.» .3 53.338. ..oo. p.888 £38 88 £8 83358 .2 8.. 83.8 o. m o.» 3 20 .58 c. mo 3. 3.28.! .2 .02 85303 383 830238. 3.33.» 56.6 9.95 .3 m 9.83328 .2 A0 a a. mason.» 8.5.0.... 83.88.58 33.. m ..m 3 330.2838 .3 m «.88 333 3038.38 88.33.. mxvozaoa. .. 832538 0.88...." 0.88» 0.88. 0.88 0.88 0.88.. ...» 0.83 55 0.886 «.28 mm 3. Ac 8. a m. 0.8.. 8 . 9.». 3. mm a. 8 8 AV m: 4.089.. mm a wm m m 0 CAN» 0...: U ow G we AA mu 46.3?» GA 6 mm m V 9 ohm» 9.8 a mm a mu Am ma mAwu—Sfi m. m wA U A a 0.0AN 9.5» m mm m 8 mm U 1.. .. . 0.3963. 5.8..» 53.83 «.63....83. 3.32638 3.3030 .388 5.5.3 m 8533 m. .u m ob... Pom. .333 0...... 388921... 8835c .o 02.2.... 8 53.8.8 30 «63.383. 3.39.38 2303 3.88 5.55 m 8.533. a 53.8.8 3o. (.35 0.888 ...m .3 3....3083 8.». Pa. ob. ..A. ~33 N... 888.225. 119 Experiment 1. However, the data may simply reflect the lower seed weight of 8- 42-M-2 in comparison with the other three genotypes, although all four are medium-sized seeds. PVC Experiment 1 ratios Root class ratios across all soil depths showed that 8-42-M-2 exceeded the other three genotypes with regards to ratio of class 1IClass 3, Class 1Iclasses 3+4, and classes 1+2/classes 3+4 (Table 29). This suggest that 842- M-2 had a greater proportion of its roots as the smaller secondary roots in comparison to the other three genotypes, again possibly suggesting that the genotype was experiencing stress and providing further evidence of the drought susceptibility of this genotype or simply reflecting the smaller seed weight of 8- 42-M-2. Polyvinyl-chloride experiment 2. - Rooting Pattern None of the genotypes in PVC Experiment 2 had roots that reached deeper than 61 cm (Table 30). This experiment was concluded in greenhouse temperatures that were cooler than that of PVC Experiment 1. Thus, these plants experienced a milder moisture stress and that may have been reflected in the more shallow root growth of the plants in PVC Experiment 2 and in the different rooting patterns of PVC Experiment 1 and PVC Experiment 2. 433.3 um. £338 0. 8.3. Be. .0393 838 3.. 3.. 333.38 o. _u Mt ns ns ns ns Classz ns S > N’ ns ns ns ns Class3 S < N' S < N1 ns ns ns ns Class4 ns S < N’ ns ns ns ns Class5 ns ns ns ns ns ns Total ns S < N" ns ns ns ns Root dw ns S < N' ns ns ns ns Percentages Class1 S > N“ ns S < Nt ns ns S > N' Class2 S < N" ns S < N’ ns ns S < N‘ ClassS S < N" S < Nt ns ns ris S < N‘ Class4 ns ns ns ns ns S < Nt Class5 ns ns S < N‘ ns ns ns Class1+2 ns S > N‘ S < Nt ns ns S > N" Class2+3 S < N” ns S < N1 ns ns S < N‘ ”, ', 1' Indicates significant difference at P s 0.01, 0.05. and 0.10, respectively. ns Indicate non significant data. . Sc Stress treatment, N- Non-sum treatment, RL . root length Depth 'A' -1-15.2 cm, '8' . 15.3-30.5 cm, '0' - 30.6-45.7 cm. '0' - 45.8-61 cm. 'E" - 61.1-78.2 CHI. 126 percentage of total roots at the top 15 cm (Table 31). For the 15.2 to 30.5 cm depth T3110-2 had a significantly higher root length of class 1 roots (P s 0.10) than the other three genotypes (Table 31). Stress decreased (P s 0.10) the percentage of class 3 roots, and the percentage of roots in classes 1+2 was significantly greater (P s 0.05) under stress (Table 32). There were no significant genotypic differences at any of the other depths (Table 31). At the 30.6 to 45.7 cm depth, stress decreased the percentage of roots in classes 1 (P s 0.10), 2 (P s 0.10), and 5 (P s 0.05) (Table 32). Cumulative total root length across all depths indicated that T3110-2 had a significantly higher total root length and class 1 root length (P s 0.10 and 0.05, respectively) than Lef-2-RB and BAT 477 (Table 33). Seed weight of T3110-2 was also significantly higher than that of Lef-2-RB and BAT 477, whereas T3110-2 seed weight, TRL and length of class 1 roots did not differ from T3016- 1. With regard to percentage of roots in each class at each soil depth, there were no significant genotypic differences at any of the root depths except 15 to 30 cm (Table 34). At this depth, T3110-2 had a greater percentage of its roots in class 1 than the other three genotypes, a lower percentage in class 2 (P s 0.05) than T3016-1 and Lef-2-RB, and a lower percentage in class 3 than T3016-1 (Table 34). The percentage of roots in classes 1+2 was greater (P s 0.01) in T3110-2 than in T3016-1 and lower (P s 0.05) in root classes 2+3 for T3110-2 than for the other three genotypes (Table 34). 127 ...mEo aw. 053535 88. 32 .039... 3 35 8330: con: 09.523» 9.95 .3 oh 3 p BAT 477 > 8-42-M-2 (Table 18). Sierra was somewhat similar to BAT 477. Total root length of plants grown in -1.07 MPa PEG was greater than that of control plants and than plants grown in -0.52 MPa PEG, but less than that of plants grown in ABA Unlike root length (RL), the ratios exhibited significant genotypic differences. The resistant genotype BAT 477 consistently had a higher ratio than the susceptible check 8-42-M-2. Sierra and T3147-2, the other genotypes designated as resistant, usually did not differ from 8-42-M-2. Analysis of the delta values supports the working hypothesis that the 10" M ABA treatment measured the genetic potential for root length expansion. Root length increased in the -1.07 MPa (PEG) treatment more than in the -0.52 MPa (PEG) treatment and both were less than the ABA treatment. They did not differentiate among genotypes. I None of the genotypes in PVC Experiment 2 had roots that reached deeper than 61 cm. This experiment was conducted in greenhouse temperatures that were cooler than that of PVC Experiment 1. Thus, these plants experienced a milder moisture stress and that may have been reflected in the more shallow root growth of the genotypes and in the different mating patterns exhibited in the two experiments. The total root length of PVC Experiment 1 was fairly evenly divided throughout the first four depths of the study, 1 - 61 cm. Approximately 23% of the total roots were in the top 15 cm; 26% at the 15 to 30.5 cm depth; 26% at the 146 30.6 to 45.7 cm depth; 23% at the 45.8 to 61 cm depth and 2.5% at the 61.1 to 76cmdepth. This maybe partlyexplained bythe largerseedweightof genotypesinPVC1incomparisontoPVC2. Stressdecreasedthepercentage ofroots atthe15to 35.5 cm depth and increased it atthe 30.6 to 45.7 cm depth. The moisture stress of PVC Experiment 1 has been designated as severe due to a fairly high temperature of 28 :l: 2°C and high intensity of sunlight during growth of plants from June 18 through July. In contrast, total root length of PVC Experiment 2 was concentratedin the top two depths of the study, the first 30 cm. Approximately, 64% of the total roots were in the top 15 cm; 30% at the 15.3 to 30.5 cm depth; 6.5% at the 30.6 to 45.7 cm depth; 1.5% at the 45.8 to 61 cm depth, and 0% below 61 cm. As in PVC Experiment 1, stress decreased the percentage of roots at the 15 to 30.5 cm depth and increased the percentage of roots in the top 15 cm. The moisture stress of PVC Experiment 2 was designated as mild due to low temperatures of 25 :t 2°C and lower sunlight intensity during plant growth from September 18 through October. Results suggest that root length of the control and the -1.07 MPa PEG treatments may correlate more closely with the shallower soil depths under mild moisture stress, a situation where the roots are concentrated in the upper soil horizons. Under more severe moisture stress where the roots penetrate more deeply into the soil horizon, the control correlated more closely with the intermediate soil depths and the -0.52 and -1.07 MPa PEG with the deeper soil depths. The data also suggest that seed weight may be an important factor in 147 total root length until at least 40 DAP, may affect root length distribution among the individual root classes, and that root length comparisons among genotypes should only be made among genotypes that have a similar seed weight. 148 Literature cited Blum, A 1988. Plant breeding for stress environments. CRC Press, Boca Raton, Fla. Bradford, KC. and TC. Hsiao. 1982. Physiological responses to moderate water stress. In: O.L. Lange, P.S. Nobel, C.B. Osmond, H. Ziegler, Eds., Encyclopedia of Plant Physiology (New Series), Vol 128. Physiological Plant Ecology ll. Springer-Veflag, Berlin, pp 263-324. Brar, G.S., AG. Matches, H.M. Taylor, B.L. McMichael, and J.F. Gomez 1990. Two methods for characterizing rooting depth of forage-legume seedlings in the field. Crop Science 30:413-417. Carrow, R. 1996. Drought avoidance characteristics of diverse tall fescue cultivars. Crop Science 36:371-377. Gregory, P.J. 1989. The role of root characteristics in moderating the effects of drought. P. 141-150. In: P.W.G. Baker (ed.) Drought resistance in cereals. C.A.B. lnt., Wallingford, England. Hsiao, TC. and E. Acevedo. 1974. Plant responses to water deficits, water use efficiency, and drought resistance. Agricultural Meteorology, 14:59-84. Hubick, KT., J.S. Taylor, D.M. Reid. 1985. The effect of drought on levels of abscisic acid, cytokinins, gibberellins, and ethylene in aeroponically grown sunflower plants. Plant Growth Regul. 16(2):234-241. lzzo, R., F. Navari-lzzo, and MP. Quartacci. 1989. Growth and mineral contents of roots and shoots of maize seedlings in response to increasing water deficits induced by PEG solutions. Journal of Plant Nutrition, 12:1175-1193. Jones, H.G. 1978. How plants responds to stress. Nature 2712610. Jupp, AP., and El. Newman. 1987. Morphological and anatomical effects of severe drought on the roots Lolium perenne L. The New Physiologist, 1 05:393-402. Kaufman, MR. and AN. Eckard. 1971. Evaluation of water stress control with polyethylene glycols by analysis of guttation. Plant Physiol. 47:453-456. Kelly, J.D., M.W. Adams, AW. Saettler, G.L. llosfield, G.V. Vamer, MA Uebersax, and J. Taylor. 1990. Registration of ”Sierra” Pinto Bean. Crop Sci. 30:745-746. 149 Krizek, D.T. and P. Semeniuk 1979. Differential sensitivity of eleven cultivars of coleus to water stress followingapplication of polyethylene glycol 600. HortScience 14(3): 404 (Abstract). Lachno, DR. 1984. Abscisic acid and indole-3-acetic acid in maize roots subjected to water, salt, and mechanical stress. News bulletin: Br Pl Gr Reg Gr Mono 6:16. . McMichael, B.L., J.J. Burke, J.D. Berlin, J.L. Hatfield, and J.E. Ouisenberry. 1985. Root vascular bundle arrangement among cotton strains and cultivars. Environ. and Exp. Bot. 25:23-30. Merhaut, D.J.F., J.G. Latimer, and J.W. Daniell. 1989. Use of transparent polyethylene rhizo-bags to study growth of peach roots. HortScience, 24(6):1038. Robertson, J.M., KT. Hubick, E.C. Yeung, and D.M. Ried. 1990. Developmental responses to drought and abscisic acid in sunflower roots. I. Root growth, apical anatomy, and osmotic adjustment. Journal of Experimental Botany 41 :325-337. Robin, 0., L. Shamsun-Noor, and A Guckert. 1989. Effect of potassium on the tolerance to PEG-induced water stress of two white clover varieties (Trifolium repens L.). Plant and Soil 120:153-158. Schaefer, R.L., D.T. Krizek, and CW. Reynolds. 1979. Relationship between leaf water potential and leaf conductance in Capsicum annuum 'Yolo Wonder. HortScience 14:404 (Abstract). Schneider, KA, R. Rosales-Sema, F. lbarra-Perez, B. Cazares-Enriquez, J.A Acosta-Gallegos, P. Ramirez-Vallejo, N. Wassimi, and JD. Kelly. 1997. Improving common bean performance under drought stress. Crop Science 37:43-50. Sharp, RE. and W.J. Davies. 1979. Solute regulation and growth by roots and shoots of water stressed maize plants. Planta 147:43-49. Sharp, R.E., W.K Silk, and re. Hsiao. 1988.. Growth of the primary root at low water potentials.1. Spatial distribution of expansive growth. Plant Physiology, 87:50-57. Sharp, R.E., G.S. Voetberg, l.N. Saab, and N. Bernstein. 1993. Role of abscicic acid in the regulation of cell expansion in roots at low water potentials. In: T.J. Close and EA Bray (eds), Plant responses to cellular dehydration during environmental stress. Current topics in plant physiology: An 150 American Society of Plant Physiologists Series, 10:57-65. Smucker, AJ.M., AK Srivastava, M.W. Adams, and B.D. Knezek 1991. Secondary tillage and traffic compaction modifications of the growth and production of dry edible beans and soybeans. Applied engineering in agriculture 7(2): 149-1 57. Taiz, L. and E. Zeiger. 1991. Plant Physiology. The Benjamin/Cummings Publishing Company, Inc. Redwood City, California. Waisel, Y., A Eshel, and U. Kafltafi. 1996. Plant Roots: The hidden half. Marcel Dekker, Inc., New York, New York pp. 541 -545. Walton, D.C., M.A Harrison, and P. Cote. 1976. The effects of water stress on abscisic acid levels and metabolism in roots of Phaseolus vulgan's L. And other plants. Planta 147:43-49. Watts, 8., J.L. Rodriguez, S.E. Evans, and W.J. Davies. 1981. Root and shoot growth of plants treated with abscisic acid. Annals of Botany, 47:595-602. Westgate, ME. and J.S. Boyer. 1985. Osmotic adjustment and the inhibition of leaf, root, stem and silk growth at low water potentials in maize. Plants 164:540-549. Chapter 3 The effect of ABA, PEG, and water stress on above ground growth Introduction Growth and development in most crops proceeded completely unimpaired and crop yield 'was maximal only when high water status was maintained throughout the life of the crop (Laing et al., 1984). While the ultimate effect of drought was limitation of growth and yield, specific physiological effects of water stress varied depending on the history of the crop, and timing and intensity of stress (White and Castillo, 1989). In bean, the most sensitive phase of development to water stress was from flowering to early pod set (Dubetz and Mahalle, 1969; Laing et al., 1983 and 1984; Halterlein, 1983; Sheriff and Muchow, 1984). Prolonged stress before flowering restricted canopy development, which in turn limited yield (Laing et al., 1984). The relative sensitivity of different stages of development to stress varied with the degree of stress (Begg and Turner, 1976). The most common effect of water deficit during bean growth was reduction in plant size and yield (Kramer, 1983). Drought stress affected many physiological and morphological characteristics associated ultimately with seed yield. The phonological stage of the crop at the time of the stress as well as the intensity and duration of the water stress determined the amount of damage 151 152 done to the crop and therefore yield (Acosta-Gallegos and Adams, 1991). When drought stress was imposed at the beginning of the reproductive phase in dry bean, seed yield was reduced twice as much as the reduction observed when the stress was imposed at the vegetative phase (Acosta-Gallegos and Shibata, 1989). Stem length, number of branches, pods per plant, seeds per pod and yield were all reduced. Root characteristics were of primary importance in determining drought response of common bean (White and Castillo, 1989). Under conditions of water stress, root growth in the soil surface layer was relatively slow while the growth of new roots in the deeper, wetter layers was hastened (Garay and Wllhelm, 1983; Sponchiado et al., 1989;Trejo and Davis, 1991). Early water deficits reduced the rate of leaf expansion and hence, leaf area accumulation. Reduction of leaf area in common bean was associated with smaller size of individual leaves rather than decreased leaf number (Bonnano and Mack, 1983). Leaf senescence, on the other hand, was considered to be a drought avoidance mechanism that allowed the plant to survive dry periods (Kramer, 1983). Rapid senescence rates, however, may be detrimental to final yield. Abscisic acid (ABA) has been suggested to be one metabolic signal involved in responses to environmental stresses (Zhang and Davies, 1987). ABA is known to regulate stomatal closure (Zeevaart and Creelman, 1988) and has shown to reduce the rate of leaf growth of Phaseolus (Van Volkenburgh and Davies, 1983). Shoot responses to root hypoxia have been reported to be 153 mediated both by changes in leaf water status (Schildwacht, 1989) and by ABA transported from the roots (Zhang and Davies, 1987). Sharp and Davies (1989) have suggested that root signals and shoot water status act together to modulate shoot responses to root stresses. They concluded that in plants with hypoxic roots, leaf expansion rates and stomatal conductance are limited by leaf water status or shoot signals depending on the rate of water loss from the leaves at the time of the imposition of the stress. The objectives of this study were to investigate shoot response P. Vulgan’s to ABA, PEG and moisture deficit. Materials and Methods: Genotypes The study used eight common bean genotypes which vary in their response to moisture stress: 1. Sierra, a been developed in Michigan. 2. BAT 477, documented by CIAT (1984) to be drought resistant. 3. 8-42-M-2, a drought susceptible line developed at Michigan State University. 4. Lef-2-RB, a drought resistant line. 5. T3008-1, developed by the Michigan State University been breeding program. 6. T3016-1, developed by the Michigan State University been breeding program. 7. T3110-2, developed by the Michigan State University bean breeding program. 8. T3147-2, developed by the Michigan State University bean breeding program. 154 (Table 1). Growth chamber study Seedlings were grown in a growth chamber with 23120°C day/night temperatures and a 15 h photoperiod. Photosynthetically active radiation (PAR) measured 523 umol m2 s" at the top of the plant canopy using a Decagon Sunfleck Ceptometer (Pullman, Wash.) The experimental design was a split plot with solution (Half-strength Hoagland's nutrient solution or deionized water) as the main plot, genotypes as the subplot, and four replications. Seeds were germinated four days prior to initiation of the experiment. Uniform sized seeds were selected for inclusion and rinsed in a 1 umol CaSO. solution for one hour before germination. Seeds were germinated four days prior to initiation of the experiment. Seedlings were transplanted to a CYG growth pouch measuring 15.2 cm x 16.5 cm (MEGA lntemational, Minneapolis, Minn.) at one seed per pouch, an adaptation of a procedure used by McMichael et al. (1985). All pouches contained 50 cc of deionized water and were stapled to black cardboard and placed upright in a specially designed holder with 2.54 cm between pouches. Seedlings were covered with a clear plastic covering for two days. Plants were given four 50 cc applications of half strength Hoagland's nutrient solution, adjusted to pH 6.14, or deionized water from the sixth day after transplanting (DAT) to the fourteenth day when plants were sampled. Fresh weights were taken for roots, stems and leaves. Fresh roots were placed in a whirlpack bag and stored in 15% (vlv) methanol solution at 4° C. Leaves and m1 _ 155 Table 1. Characteristics of common been genotypes grown in field experiments at Kellogg Biological Station, Hickory Comers, MI. in 1995 and 1996. Genotypes Pedigree Origin£ Seed¥ Seed Plant: Size Color Type Sierra Not identified§ ’ MSU M Pinto ll 1‘3110-2 Sierra X Lef-2-RB MSU M Striped lll T3147-2 Sierra X Lef-2-RB MSU M Striped lll Lef-2-RB (Ver 1OIChis INIFAP M Black lll 143)lpue 144 (striped) Bat 477 (51051 X ICA CIAT M Brown ll Bunsi) X (51012 X Cornell 49-242) 8-42-M-2 N81017 X Lef-2-RB MSU M Tan or Brown lll T3016-1 Sierra X AC 1028 MSU M Tan or Brown lll T3008-1 Sierra x AC 1028 MSU M Tan or Brown lll £ MSU = Michigan State University CIAT = Centro Internacional de Agricultura Tropical INIFAP = National Institute for Forestry, Agriculture, and Livestock Research, Mexico. ¥ M=Medium. :t Type II = lndeterrninate-bush, erect stem and branches Type III = lndeterrninate-bush, prostrate main stem and branches § Derived from crosses of Durango Race Pinto with Mesoamerican Race Black (Kelly et al., 1990). 156 stems were oven dried for 48 h at 60° C, weighed, and discarded. Root dry weight was obtained after the root imaging process was completed. Statistical analysis was done with the aid of MSTAT. ABA experiment Plants were grown in a growth chamber with 23720°C day/night temperatures and a 15 h photoperiod. PAR measured 527 mol m"s“ at the top of the plant canopy using a Decagon Sunfleck Ceptometer. The experimental design was a split plot with solution (ABA + deionized water or ABA + half strength Hoagland's nutrient solution) as the main plot, genotypes as the subplot, and four replications. Experimental procedures were the same as those of the control experiment. From 6 to 14 DAT, the solutions in the pouches were replaced four times. ABA (as-trans, 1 ABA, Sigma) was dissolved in deionized water or nutrient solution to a final ABA concentration of 10‘ m. PEG experiment Two experiments were conducted using polyethylene glycol (PEG 600). The experimental design was a split plot with solution (PEG 7* deionized water or PEG 4» half strength Hoagland’s nutrient solution) as the main plot, genotypes as the subplot, and four replications. Plants in the first PEG experiment were grown in a PEG solution with a water potential of -1.07 MPa. The water potential was - 0.52 MPa in the second PEG experiment. Day/night temperature regimes for 157 both experiments was 23120°C with a 15 h photoperiod. PAR measured 524 and 528 umol m"s"l for the -1.07 MPa and -0.52 MPa experiments, respectively. Water stress was induced at six DAT by adding PEG 600 (Sigma Chemical Co., St Louis, M0) at 25 mIIL (osmotic potential -1.07 MPa) or 18 mlIL (osmotic potential -0.52 MPa). Solutions were replaced four times between 6 and 14 DAT. Greenhouse Study Plants were grown in polyvinyl chloride tubes (PVC) for 40 days in a greenhouse at Michigan State University, in East Lansing, MI. The temperature regime was 28°C :l: 2°C and a light intensity of 1241 uE m"s°' for the first experiment and a temperature regime of 25°C t 2°C and a light intensity of 1200 HE m‘zs’1 for the second experiment. Experiment 1 consisting of genotypes Sierra, T3008-1, T3147-2, and 8-42-M-2 was planted on June 18. Experiment 2 consisting of genotypes T3016-1, Lef-2-RB, BAT 477, and T3110-2 was planted on September 16, 1996. The experimental design was a split plot with water (stress and nonstress) as the main plot, genotypes as the subplot, and four replications. The PVC tubes were 76.2 cm in length with a diameter of 30.5 cm and cut into five individual sections measuring 15.2 cm. The bottom section was filled with silica sand. The remainder of the PVC tube was filled with a Kalamazoo sandy loam soil (T ypic Hapludalfs, fine-loamy, mixed, mesic) that had been sieved to remove all stones and packed to a bulk density of 1.31 glcm’. Five seeds per PVC tube were planted but plants were then thinned to 158 one plant per PVC tube at 14 days after planting (DAP). Stress was initiated at 14 DAP by reducing the amount ofwater given to plants in the stress treatment Plants in the stress treatment received 53% less water than plants in the nonstress treatment. Drought stress determination was done by visually observing plants and the soil in the stress environment. Plants were watered when the soil began to crack from lack of water and plants began to wilt. Stress plants were watered approximately once per week Plants in the nonstress environment were watered approximately three times per week Plants were sampled at 40 DAP. Stem, leaf and reproductive parts were weighed, and dried at 60°C for 48 h, re-weighed, and discarded. Roots were extracted from each section by sieving the soil through 2 mm mesh wire. After video imaging, roots were dried at 60°C for 48 h then weighed and discarded. The difference between control shoot growth and shoot growth under each treatment (ABA, - 0.52 MPa PEG, and -1.07 MPa PEG) (delta value) was calculated. Some delta values were negative so a transformation of the data was done using a logarithmic scale (Au) for statistical analysis of the data. Statistical analysis was done with the aid of MSTAT. Results and Discussion Control treatment: Leaf, stem, and root dry weight Significant genotypic differences were observed for leaf, stem, and root dry weight (P s 0.01). The genotype BAT 477 had significantly lower leaf dry 159 weight than T3110-2 (a resistant genotype), T3008-1, and T3016-1 (T able 2). However, there was no significant difference in leaf dry weight between BAT 477, a tolerant genotype, and 8-42-M-2, a susceptible genotype (Table 2) and no significant leaf dry weight differences between the resistant genotypes, BAT 477, Sierra and T3147-2. BAT 477 had a significantly lower stem dry weight than T3110-2 (resistant) and T3008-1 (T able 2). Again, there was no significant difference between BAT 477 and 8-42-M-2 or between BAT 477 and the resistant genotypes Sierra, T3147-2, and Lef-2-RB (T able 2). BAT 477 had a significantly lower shoot dry weight than Sierra, T3147-2, T3110-2, T3008-1, and T3016-1 ((P s 0.05) Table 2). BAT 477 had a significantly lower root dry weight than Sierra, T3008-1, and T3016-1 (T able 2). The genotypes Sierra and 8-42- M-2 had a significantly higher RIS ratio (P s 0.05) than T3110-2, T3008-1, and BAT 477 suggesting that the former genotypes imparted a greater percentage of their carbohydrates into root production in comparison to the latter (Table 2). All of the genotypes produced seed in the medium size seed class, although there were significant differences in seed weight among the genotypes (Table 2). Generally, leaf, stem, shoot, and root dry weight and RIS ratio did not follow a pattern with regard to seed weight. For example, both Sierra and T3008-1 had one of the largest seed weight, yet Sierra produced a high RIS ratio due to a relatively lower shoot dry weight in comparison to the genotypes. In contrast, T3008-1 produced a relatively large shoot and root dry weight, resulting in a lower RIS ratio. 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(06:. .0. 0. .0030. 0.030. 0:00.0. 30.0. 0:0 3000:00. 3.6 0. 0.0:. 00330: 000: 00:0.<000 02330.00 .: 0 02330.3: 000302 .2 0 0 0. 00.00 0:0 ...0:00.0:.00 .0 0: 0:<.3:30:.0._< 00:.3..00 03S: 0:0302 .2 .0 0 0. 0200.6 00.36:. 33020830 0:0 0 .0 : 0:0.000000 .: 00.<0.:<.0:0 0.<00. 000 00.5.0: 0. 0.0» 2.00. 00:0...000 .00 0000 £20. ..00. .0. 0.03 .0. 0:00. .0. 200. .0. 20 3..0 0.23 00.00 0. 0..00 0: 0.00 0. 0.000 00.. 0.0.x. 0. 0.000 00... ...0. 0.x.» 00.00 00 0..00 00 0.00. 000 0.0.. 00 0.0.3 0 0.00» 00 0.00.2.» 00.00 0 0.. .0 00 0..00 0 0.000 0 0.000 0 0.0.. 000 00.000 00.00 0 0.000 0 0.000 0 0.00 0 0.000 00 0.000 0 ...0. .0.» 00.00 00 0.00 00 0.00 0 0.0.0 00 0.000 00 0.000 0 40000.. 00.00 0 0.00. 0 0.00. 00 0.00 0 0.000 0 0.0.3 000 400.0; 00.0 0 0.00 0 0.000 00 . 0.0.00 0 0.000 0 0.000 0 0)... 0.3 00.00 0 0..00 0 0.000 00 0.000 00 0.30 0 0.000 000 .... .. . 0503:. .0020 30.00.00 06:...00:. 0...20:00 030:0 300:0 (.3.: 0 00.03: 0. 0 0 0.0.. 0.00. 0:0 0..0. 3000003.... 00020.:0 .0 0.5.»... 166 Delta Significant genotypic differences were observed for -O.52 MPa PEG induced differences in leaf, stem, shoot, and root dry weight and for RIS ratio. The leaf dry weight increased for T3147-2 was significantly higher (P s 0.01) than forT3110-2, 1'3008-1, and T3016-1 but did not differfrom the otherthree genotypes (Table 6). 8-42-M-2 had a significantly higher (P s 0.05) stem dry weight than T3110-2, T3008-1, and T3016-1 but not significantly higher than Sierra, T3147-2, Lef-2-RB, and BAT 477 (T able 6). Nevertheless, the shoot dry weight of T3147-2 was only significame higher (P s 0.01) than that of T3110-2 and T3008-1 (Table 6). Root dry weight showed that the genotype, 8-42-M-2 had a significantly higher (P s 0.10) root dry weight than T3110-2, T3008-1, and T3016-1 but not significantly higher than the other genotypes (T able 6). The genotype T3008-1 had a significantly higher (P s 0.01) RIS ratio than Sierra, 8- 42-M-2, and Lef-2-RB (Table 6). In comparison to the control,the -0.52 MPa PEG treatment increased shoot and decreased root dry weight of Sierra, decreased shoot and root dry weight of Lef-2-RB and T3110-2, increased shoot and root dry weight of T3008.1 and BAT 477. Shoot and root response were independent of the significant differences in seed weight among these genotypes in the medium size seed class. 167 400.0 0. 2.00: 0:33:00 00.5.00: 0.00 2.00 0mm 30.30:. 0:0 00:.3. .0000. .0.. .00.. 0.03. 0000.. 30.. 0:0 3000000. 300 .0. 0.00. 00330: 000: 0302000 000030.00 .: 0 00.3.:0..0: 000300. .0.. 0 0 0. 006 0:0 .3:00.0:.00 .0 0: 0:<.3:30:.0.... 00:.3..00 03.30 000302 .0.. .0 0 0. 00.00..." 00.3.00. 33003830 0:0 0 .0 0 000800000. _ 00:0...000 000. .0. 0.03 .0. . 0000. .0. .000. .0. 3.0 ..0..0 0.0.30 0.000 000. 0.0.0 000. 0.000 000: 0.0.0 000. 0.00 09. 00.0.0.0 0.00 0 0.000 0000 0.0.. 0 0.0.. 000 0.000 00 0.00.2.0 0.000 00 0.000 0 0..0 00 . 0.0.0 0 0..00 0 00.0.30 0.000 000 . 0.000 00 0.000 000 0.0.0 000 .0.. .0 0 ...0. .00 0.000 00 0.0.0 000 .0000 00 0.00. 00 0.00. 00 40000.. 0.00 0 0.000 0 0.00 0 0.000 00 0.03 0 30.0.. 0.000 00 .0000 00 0.0.3 000 .0000 0 0.000 00 0>4 00.. 0.0.0 000 0.000 0000 0.000 000 0.00. 00 0.000 00 8. .. ... 2.33:. .0003 30.00.00 0.030003 0.00.3:00 030:0 300:0 £00.: 0 00.03: 0. 0 m 0.0.. 0.00. 0:0 0..0. 3000003.... 0000350 .0 0.5.04. 168 -1 .07 MPa PEG treatment: Leaf, stem, and root dry weight There were no genotypic differences for leaf, stem, shoot, and RIS (Table 7). Deltas ‘ There was no genotypic difference for leaf, stem, shoot, and root dry weight or for RIS ratio (T able 8). Although not significant, the -1.07 MPa treatment increased shoot and root dry weight in Lef-z-RB and BAT 477, the two genotypes with the lowest seed weight. Response to ABA varied among the genotypes, but the response exhibited no pattern with regard to seed weight. Comparison across experiments There were significant differences among the control, ABA, -O.52 MPa, and -1.07 MPa experiments for leaf, stem, shoot, and root dry weight and for RIS ratio (Table 9). The ABA experiment had a significantly higher (P s 0.01) leaf, shoot, and root dry weight than the other three experiments. It also had a significantly higher (P s 0.01) stem dry weight than the control and -O.52 MPa PEG experiment. The -0.52 MPa PEG experiment had a lower RIS ratio than the control and ABA experiments (Table 9). ABA increased both shoot and root dry weights, while the -O.52 and -1.07 PEG experiments did not significantly differ from the control experiment with regard to root or shoot dry weights (Table 9). This was surprising since root 169 400.0 ... 00. 3.00. 0. .0030. 0.030. 0000.0. 0:0 30.0 0:0 3000000. ..0..0 0:0 .00 0000 3.00. 0. 0.00. 00330: 000: 00:0...000 0020.00.00 .: 0 00.3.0000: 00030010.. 0 0 0. 008 0:0 3:00.0300 .0 0: 0:<.3:30:.0.... 00:.3..00 03.0.... 00030010. .0 0 0. 00.0000 00.3.00. 33003.30 0:0 0 .0 0 000800000 .: 00.35.0000 0.30. 000 00.000: 0. -. .0.. :00. 0032000 . .00 0000 £20. ..00. .0. 0.03 .0. 0000. .0. .000. .0. . E0 3..0 0.03 00.00 0. 0..00 :0 0..00 :0 0.000 :0 0.000 :0 0.000 :0 40.0.0.0 00.00 00 0..00 0..00 0.000 0.000 0.0.. 0.00.3.0 00.00 0 0..0. 0..00 0.000 0.000 0.000 00.0.00 00.00 0 0..00 0..00 0.000 0.000 0.00.. 40. .00 00.00 00 0..0. 0..00 0.00.. 0.00. 0.00. 40000.. 00.00 0 0.00 0.00 0.000 0.000 0.000 400. 0.. 00.0 0 .0....0 0.. .0 0.000 0.000 0.000 0>4 0.... 00.00 0 0.00 0.000 0.000 0.000 0.0. 0 . 0.33:. .0003 30.00.00 0.0:...00:. 0...03:00 030:0 300:0 £00.: 0 00.03: 0. .u m 0.00. 0000330 .0 02.04. :0 :0 0.0:...003 0:33:00 030:0 300:0 £00.: 0 00.03:. 400.0 0. 200: 0.3380 0030: -. .0.. 2.00 0m0 30.30:. 0:0 00:..0. .0000. .0. .00.. 0.03. 0000.. 30.. 0:0 3000000. 3.3.0.060. 00330: 000: 00:0...000 00330.00 3 000.3333: 000300102. 0 0.0000 0:03:003300 .0 0: 0:<.3:30:.0..< 00:.3..00 0330 000300. .0. .0 0 0. 00.005 00.3.00. 33003.30 0:0 0 .0 0 000600000. 030.300 000. .0. 0.03 .0. 0000. .0. .000. .0. 0.0 3.3 0.03 0.00 :0 0.00 :0 0.0. :0 .00. :0 0.00 :0 40.000 0.0. 0.0. 0.0. 0.0. 0.0. 0.00.2.0 0.00 0.00 0.00 0.0. 0.00 m 00.0.00 0.00 0.00 0.0. 0.00 0.00 1 .0. .0.» 0.8 0.8 0.3 .00. 0.0. 40000.. 0.00 0.0. .000 0.0. .00. 4090.. .00. 0.00 0.0. 0.0. 0.0. 0>4 00.. .00. 0.00 0.00 0.00 0.00 :0 30.00.00 :0 0.0:...003 0...0.0:00 030:0 300:... (.3.: 0 00.03:. 171 400.0 0. 00300000: 0. .00.. 0.03. 0000.. .00. 0... £0.00. 0:0 3000000. .000 0. 0.00. 00330: 000: 00:02000 0030.00.00 .: 0 00003000: 000300. .0. 0 0 0. 00.6 0:0 ..0:00.0:.00 .0 0: 0303:3052... 00:.3..00 0.92.0 000300. .0. .0 0 0. 00.0000 03.3.00. 8300.08.00 0:0 0 .0 0 000.000000 ..03 .00 .00. ..00.30:.0 .300000. 4.00.3030 ..00. .0. 0.03 .0. 0000. .0. 000. .0. 0.0 .000 000.40. 9.00 6.3 9o: 08 9NN¢ a! 90...“. 003 9000 0.. E 9.00 m 9.00 m 9000 0 9000 m 900. m .90» 2:00 .umm 9.00 U . 9000 0 9M8 U 980 o 9N2 U ...—.04 300 ..qu 9.0» a 9. .. 00 9wa U 9040 G 90.0 06 0.<. mm mm 00 00 um .... . 00.0.00. .0008 .:0.00.0 0.0:.000000 030:0 300:0 £00.: 0 00.03: 0. 0 a 0.... 0:0 0.00. 3000005.... 0083.00 .0 0.504. 0 000.3. 00.5.0: 00:.0.:00 00.. 0..0:0.0 1000.0:00 :500:. 00.5.0: 0. 00.03000 5.0.0.. >0) 00.5.0: 00:.0.:00 .0.. 3 >0) 0.000200 .: 00.. 0..0:0.0 ...000.0:0.0 :500:. 00.5.0: 0. 00.0:.~00 5.0.0.. 0mm 00.5.0: 00:.0.:00 .0 3.... 70.0» 2.00. <2 0. 0mm 08 0:0 00.0:.~00 (0.0. 0. 00.. 0..0:0.0 ...000.0:0.0 :500:. 00.5.0: 0. 00 3.? .-. .3 2.00. <2 0. 0mm 00.. 0:0 00.03000 (0.0. 0. 00.. 0..0:0.0 1000.0:0.0 :500:. 00.5.0? 172 length data (Chapter 2, Table 5) indicated that total root length of the ABA and PEG experiments was significantly greater than that of the control. However, the rootlengtl'idataalsoindicatedthattl'leincreasewasprimarilytl'latofclass1 roots, often with a corresponding decrease in root classes 2 and 3 (Chapter 2, Table 7). Since class 1 roots are smaller in diameter and dry weight than class 2 and 3 roots, the root dry weight results were reasonable. The -0.52 MPa PEG experiment had a lower RIS ratio than the control and ABA experiments, primarily due to the lower numerical root dry weight in comparison to the control and ABA experiments. The lower RIS ratio of the -0.52 MPa PEG experiment and the lack of significant difference among RIS ratio of control, ABA, and -1.07 MPa PEG experiments was unexpected since ABA and moisture stress treatment, simulated dy both PEG experiments, reportedly increase root growth and inhibit shoot growth. An increased RIS ratio had been hypothesized. Nevertheless, the data does reflect increased total root length under ABA and both PEG experiments (Chapter 2). Again, the increased root length was in the smaller diameter class 1 roots which would be expected to have a lower dry weight than the class 2 and 3 roots which were decreased in the ABA and PEG experiments. BAT 477 maintained a fairly consistent leaf dry weight across all four treatments and its value was almost identical for the control, ABA and -1.07 MPa PEG treatment. The resistant genotype, T3147-2, was second to BAT 477 with regard to consistency of leaf weight across experiments. 173 Effects of Nutrient Solution Versus Water Leaf dry weight of all experiments was significantly greater (P s 0.05) when plants were grown in the nutrient solution, while there was no significant difference for stem dry weight in any of the experiments (Table 10). Shoot dry weight was greater in all treatments except -1.07 MPa PEG when plants were grown in nutrient solution (T able 10). Consequently, the RIS was significantly greater (P s 0.05) in the water solution. Similar to the control experiment, leaf and shoot dry weight of the ABA experiment were significantly greater (P s 0.05 and 0.10, respectively) in nutrient solUtion (Table 10). Consequently, RIS ratio was significantly greater (P s 0.05) in the water solution of the control and ABA experiments (Table 10). Leaf (P s 0.01), shoot (P s 0.05), and root (P s 0.05) dry weight of the -O.52 MPa PEG experiment were significantly greater when plants were grown in nutrient solution. Thus, RIS ratio was greater in water than in nutrient solution for the control and ABA experiments (Table 10). Leaf( (P s 0.05) and root (P s 0.10) dry weight were greater in nutrient solution in the -1.07 MPa PEG experiment, but stem and overall shoot dry weight did not differ between nutrient solution and water. As a result, the RIS ratio did not differ between nutrient solution and water treatments. Insufficient nutrients, as indicated by the water treatment, decreased leaf dry weight in all experiments and decreased shoot dry weight in all experiments except the -1.07 MPa PEG experiment (T able 10). Insufficient nutrients did not affect stem dry weight in any of the experiments. Insufficient nutrients only reduced root dry weight in the PEG experiments while insufficient nutrients 174 Table 10. Leaf, stem, shoot, and root and RIS ratio growth response to half strength Hoagland's nutrient solution versus deionized water. Root Classes Controls ABA -O.52 MPa PEG -1.07 MPa PEG Leafdrywt. W H" W > H‘ ns ns “, *, + Indicates significant difference at P s 0.01, 0.05, and 0.10, respectively. ns Indicate non significant data. W = Water H = Hoagland's nutrient solution a Control solution contained half strength Hoagland’s nutrient solution or deionized water. ABA solution contained 10" m ABA dissolved in half strength Hoagland’s nutrient solution or deionized water. PEG solution contained 18 mlIL (-0.52 MPa) vlv of PEG 600 and deionized water or half strength Hoagland’s nutrient solution or 25 mllL (-1 .07 MPa) vlv of PEG 600 and deionized water or half strength Hoagland’s nutrient solution. 175 increased RIS ratio in the control and ABA experiments. Results suggest that lack of sufficient nutrients reduce leaf dry weight during sufficient and insufficient moisture status, as simulated by PEG, and reduce root growth during moisture stress. Both are undesirable, but the latter would have a compounding effect during moisture stress. BAT 477 maintained a fairly consistent leaf dry weight across all four treatments and the value was almost identical for ABA and the - 1.07 MPa PEG treatment (T able 10). Another resistant genotype, 1'3147-2, was second to BAT 477 with regard to consistency of leaf dry weight across experiments (T able 10). Polyvinyl-chloride experiment 1 Leaf, stem, and root dry weight The four genotypes used in this experiment were Sierra, T3008-1, T3147- 2, and 8-42-M-2. There were no significant differences among the genotypes for leaf, stem, reproductive, and shoot dry weight or for RIS ratio. The susceptible genotype, 8-42-M-2, had a significantly lower (P s 0.10). root dry weight than the other three genotypes (Table 11). This corresponds with the greater percentage of class 1 roots in 8-42-M-2 than in the other three genotypes and the lower percentage of roots in classes 2 and 3 of B-42-M-2 in comparison with the other three genotypes (Chapter 2). It is logical to expect the class 1 roots to have a lower dry weight than roots in classes 2 and 3. 176 ...eEe 3. 02 £06.... 2 .359 «33¢. «:33. can 308 can 30538. 830 2 8a.. 8330: com: @3368 c353 .: n 0302650 3a 3 a n. 5656 can m 2.. ... 308338 .3 m 3.355.95on Eco Bonanza um.» 03 5 .035 can mob a: .3 92:08... 20 06256:. A. 90:03.3 .8 «can £29 52 § «83 6v meoqoacnze 8V mace. § moo. 8v 2m Ego 90:6 3.9.... e. me an we am oh 3» 8a an :8 m» an an .308; 8.8 o m.» uh o.» 9m :8 m S» 3.3.?» 8.3 m we wax Pa 3.; :3 m an «.3.—(5 8.8 a uh Nb 0.» mb 0.3» a 0.: .. a 9:203 .288 5988» «635838 2:26 Boone (.55 m 8.5:: m, _u m Pom man 93. Revenge? 383.3 .oozmfi am 528.3 so £033.83 936838 9326 33?». .535 m 8.55. 177 Polyvinyl-chloride experiment 2 Leaf. stem. and root dry weight The four genotypes used in this experiment were Lef-2-RB, BAT 477, T3016-1, and T3110-2. As with the PVC 1 experiment, there were no significant differences among the genotypes for leaf, stem, reproductive, and shoot dry weight or for RIS ratio. The genotype, T3110-2, had a significantly higher (P s 0.10) root dry weight than BAT 477 and Lef-2-RB but was not significantly higher than T3016-1 (T able 12). Similar to PVC experiment 1, the root dry weight data corresponds well with the root length data from Chapter 2. The total root length of T311Cl-2 was significantly greater than that of Lef-2-RB and BAT 477 (Chapter 3, Table 29) but not than T3016-1 and the same was true for class 1 roots. There were no significant differences among genotypes for percentage of class 1 roots but there was a trend for T3110—2 to be higher than the rest (Chapter 2, Table 31). Effects of water stress Moisture stress decreased (P s 0.10) stem dry weight in PVC experiment 1 and leaf dry weight in PVC experiment 2 and increased RIS ratio in both PVC experiment 1 (P s 0.01) and PVC experiment 2 (P s 0.10) (T able 13). Correlations The two PVC experiments correlated poorly with the four growth pouch .336 an. 02 £063. 2 696m. «33¢. «3003. 333 Be.» 33 305300. 830 2 sec. 8.3363 333 330233 96.23 .3 m 0303388 8a 8 a 2 8.6590 033 e ..m 3 3306.833 .3 3 3.32.31.03.33 Eco Bonanza um.» Q3 .3 5335 can web 93 .3 3.2322. .u N” PVC Experiment 2 Leaf dry wt. ns ns ns — ns ns 8 < N‘ Stern dry wt. ns ns ns ns ns ns Shoot dry wt. ns ns ns ns ns ns Repro. dry wt. ns ns ns ns ns ns Root dry wt. ns S < N‘ ns ns ns ns RIS ratio. ns ns ns ns ns S > N‘ *‘, ', + Indicates significant difference at P s 0.01, 0.05, and 0.10, respectively. ns Indicate non significant data. S = Stress N = Nonstress Depth “A” =1-15.2 cm, '8' = 15.3-30.5 cm, “C” = 30.6-45.7 cm, '0' = 45.8-61 cm, 'E” = 61.1-76.2 cm. 180 experiments and that was true for leaf, stem, shoot, and root dry weight data, and for RIS ratios (Tables14 and 15). Conclusion In the control treatment, there was no significant differences between the resistant genotype BAT 477 and the susceptible genotype 8-42-M-2 for leaf, stem, and root dry weight, but there were significant leaf dry weight differences between the resistant genotypes, BAT 477, and Sierra and T3147-2. The genotypes Sierra and B-42-M-2 had a significantly higher RIS ratio than T3110- 2, T3008-1, and BAT 477 suggesting that the former genotypes imparted a greater percentage of their carbohydrates into root production in comparison to the latter. For the ABA treatment, significant genotypic differences were observed for leaf, stem, shoot, and root dry weight. Sierra, a resistant genotype, had a significantly higher RIS ratio than all other genotypes except BAT 477, suggesting that a higher proportion of carbohydrates was partitioned to the roots. There was no significant difference between BAT 477 and T3147-2 (both resistant) and the susceptible genotype 8-42-M-2. Sierra and T3147-2 (both resistant) differed in their RIS ratio. In the -O.52 MPa PEG treatment, there was no significant difference between BAT 477 and 8-42—M-2 for leaf, stem, shoot, and root dry weight and RIS ratio. BAT 477 and 8-42—M-2 were among the group with the highest RIS ratio. . There were no genotypic differences for leaf, stem, shoot, and RIS in the 181 Table 14.Ccrrelaticn coefficient for leaf, stem, shoot, and RIS ratio among control, ABA, -0.52 MPa PEG, and -1.07 MPa PEG experiments for common bean in a greenhouse for 40 d at 28 :l: 2°C day/night temperatures and a 15 h photoperiod in PVC tubes. PVC Experiment 1. Treatment Leaf Stem Shoot Root RIS ratio ~ Score Stress Control 0.56 -0.82 -O.63 0.36 0.44 ABA -0.60 -0.39 -0.70 -0.70 -0.35 -0.52 MPa PEG -0.16 0.52 -0.07 -0.89* 0.30 -1.07 MPa PEG 0.05 -0.40 _-0.70 -0.06 -0.14 Non-stress Control -0.56 0.01 0.1 0.64 0.07 ABA 0.82 -0.63 0.36 -0.38 0.42 -0.52 MPa PEG 0.51 -0.40 -0.77 0.26 0.25 -1.07 MPa PEG -0.29 -0.08 0.25 0.47 -0.42 Combined Control 0.43 -0.47 -0.5 0.72 -0.25 ABA -0.25 -0.44 -0.37 -0.63 0.55 -0.52 MPa PEG -0.16 0.54 -0.22 —0.72 -0.118 -1.07 MPa PEG 0.00 -0.13 -0.45 -0.65 0.23 1' Significant at 0.10 probability level. 182 Table 15. Correlation coefficient for leaf, stem, shoot, and RIS ratio among control, ABA, -0.52 MPa PEG, and -1.07 MPa PEG experiments for commonbean inagreenhousefor40dat2532°Cdaylnight temperatures and a 15 h photoperiod in PVC tubes. PVC Experiment 2. Treatment Leaf Stem Shoot Root RIS ratio Score Stress Control 0.98“ -0.75 -0.56 0.73 0.50 ABA -0.57 0.75 -0.56 0.1 1 0.47 -0.52 MPa PEG 0.49 0.14 0.61 0.70 0.65 -1.07 MPa PEG 0.55 -0.69 -0.35 0.10 -0.31 Non-stress Control 0.1 1 -0.41 0.24 0.70 0.66 ABA -0.91* 0.47 -0.98** 0.27 0.29 -0.52 MPa PEG -0.78 0.57 0.18 -0.60 0.50 -1.07 MPa PEG -0.38 0.17 0.07 0.917 0.12 Combined Control 0.72 -0.64 -0.23 0.75 0.59 ABA -0.80 0.64 -0.87* 0.17 -0.34 -0.52 MPa PEG -0.62 0.24 0.47 0.74 -0.04 -1.07 MPa PEG 0.03 -0.44 -0.30 0.20 0.66 *‘, 1‘ Significant at 0.01 and 0.10 probability level, respectively. 183 -1.07 MPa PEG treatment. Compariscnacrosstreatmentsshcwedthattl'oeABAexperimenthada significantly higher leaf, shoot, and root dry weight than the other three experiments and a significantly higher stem dry weight than the control and -0.52 MPa PEG experiment but was not significantly higher than the -1.07 MPa PEG experiment. ABA increased both shoot and root dry weights, while the -0.52 and -1.07 MPa PEG experiments did not significame differ from the control experiment with regard to'root or shoot dry weights. This was surprising since root length data indicated that total root length of ABA. and both PEG experiments was significantly greater than that of the control. The -0.52 MPa PEG experiment had a lower RIS ratio than the control and ABA experiments, primarily due to the lower numerical root dry weight in comparison to the control. BAT 477 maintained a fairly consistent leaf dry weight across all four treatments and the value was almost identical for control, ABA and -1.07 MPa PEG treatment. Another resistant genotype, T3147-2, was second to BAT 477 with regard to consistency of leaf weight across treatments. Leaf and shoot dry weight of the control experiment were significantly greater in the nutrient solution than in deionized water, while there was no significant difference for stem or root dry weight. Insufficient nutrients, as indicated by the water treatment decreased leaf dry weight in all experiments and decreased shoot dry weight in all experiments except the -1.07 MPa PEG experiment, while insufficient nutrients did not affect stem dry weight in any of 184 the experiments. Insufficient nutrients only reduced root dry weight in the PEG experiments while insufficient nutrients increased RIS ratio in the control and ABA experiments. In PVC Experiment 1 there were no significant differences among the genotypes for leaf, stem, reproductive, and shoot dry weight or for RIS ratio. The susceptible genotype, B-42-M-2, had a significale lower root dry weight than the other three genotypes. I In PVC Experiment 2 there were no significant differences among the genotypes for leaf, stem, reproductive, and shoot dry weight or for RIS ratio. The genotype, T3110-2, had a significantly higher root dry weight than BAT 477 and Lef-2-RB but was not significantly higher than T3016-1. Moisture stress decreased stem dry weight in PVC experiment 1 and leaf dry weight in PVC experiment 2 and increased RIS ratio in both PVC experiment 1 and PVC experiment 2. The two PVC experiments correlated poorly with the four growth pouch experiments and that was true for leaf, stem, shoot, and root dry weight data, and for RIS ratios. 185 Literature cited Acosta-Gallegos, J.A., and J.K Shibata. 1989. Effect of water stress on growth and yield of indeterminate dry bean (Phaseolus vulgaris L.) Cultivars. Field Crops Res. 20:81-93. Acosta-Gallegos, J.A, and MW. Adams. 1991. Plant traits and yield stability of dry bean (Phaseolis vulgaris L.) cultivars under drought stress. J. Agric. Sci. (Cambridge) 117:213-219. Begg, J.E. and MC. Turner. 1976. Crop water deficits. Adv. Agron. 28:161-217. Bonanno, AR. and H.J. Mack 1983. Yield components and pod quality of snap beans growth under differential irrigation. J. Amer. Soc. Hort. Sci. 105:869-873. CIAT (Centro lntemacional de Agricultura Tropical). 1984. Annual report 1983. Bean Program CIAT, Cali, Columbia. Dubetz, S. 1969. An unusual photonastism induced by drought in Phaseolus vulgaris L. Can. J. Bot. 47:1640-1641. Dubetz, S. and RS. Mahalle. 1969. Effect of soil water stress on bush beans (Phaseolus vulgaris L.) At three stages of growth. J. Amer. Hortic. Sci. 94:479-481. Garay, AF., and WW. Wilhelm. 1983. Root system characteristics of two soybean isolines undergoing water stress conditions. Agro. J. 75:973- 975. - Halterlein, AJ. 1983. Bean water requirements, root system, irrigation, drought behavior in kidney beans. In: Crop-water relations. I.D. Tesar and MM. Peat (Eds). John Wiley Press, New York. Kelly, J.D., M.W. Adams, AW. Saettler, G.L. Hosfield, G.V. Vamer, MA Uebersax, and J. Taylor. 1990. Registration of “Sierra” Pinto Bean. Crop Sci. 30:745-746. Kramer, P.J. 1983. Water relations of plants. Academic Press, Inc. Pp.342-389. Laing, D.R., P.J. Kretchmer, S. Zuluaga, and PG. Jones. 1983. Field bean. In: W.H. Smith and S.J. Banta (Eds), Symposium on potential productivity of field crops under different environments. Los Banos, Phillippines, 1980 (Proceedings) IRRI pp.227-248. 186 Laing, D.R., P.G. Jones, and J.H.C. Davis. 1984. Common bean (Phaseolus vulgaris L.) In: P.R. Goldsworthy and NM. Fisher (Eds), The physiology of tropical crops. John Vlfiley 8 Sons Ltd. Pp.305-351. McMichael, B.L., J.J. Burke, J.D. Berlin, J.L Hatfield, 8 J.E. Quisenben'y. 1985. Root vascular bundle arrangement among cotton strains and cultivars. Environ. and Exp. Bot. 25:23-30. Schildwacht, P. 1989. Is a decreased water potential after withholding oxygen to roots the cause of the decline of leaf elongation rates in Zea mays and Phaseolus vulgaris L.? Ibid 177:178-184. Sharp, R. E., and W.J. Davies. 1989. Regulation of growth and development of plants growing with a restricted supply of water. In: H.G. Jones, T. L. Flowers, and MB. Jones (eds). Plants under stress. Cambridge University Press. London. Pp:72-93. Sheriff, D.W. and RC. Muchow. 1984. The water relations of crops. In: P.R. Goldsworthy and NM. Fisher (Eds.), The physiology of tropical field crops. John Wiley 8 Sons Ltd. Pp.39-83. Sponchiado, B.N., J.W. White, J.A. Castillo, and PG. Jones. 1989. Root growth of four common bean cultivars in relation to drought tolerance in environments with contrasting soil types. Expl. Agric. 25:249-257. Trejo, OJ and W.J. Davis. 1991. Drought induced closure of Phaseolus vulgaris L. Stomata precedes leaf water deficit and any increase in xylem ABA concentration. J. Expt. Botany 42: 1 507-1 51 5. Van Volkenburgh, E., and W.J. Davies. 1983. Inhibition of light stimulated leaf expansion by ABA. Journal of Experimental Botany 34:835-845. White, J.W. and J.A Castillo. 1989. Relative effect of root and shoot genotypes on yield of common been under drought stress. Crop Sci. 29:360-362. Zeevaart, J.A, and RA Creelman. 1988. Metabolism and physiology of abscisic acid. Annual Review Plant Physiology Plant Molecular Biology 39:439-473. Zhang, J., and W.J. Davies. 1987. ABA in roots and leaves flooded plain plants. Ibid. 37:649-659. 187 Summary and conclusion Geometric mean and STI were better predictors than DSI of yield performance under limited moisture. The yield performance of T3147-2, Sierra, Lef-2-RB, T3110-2, and BAT 477 under moisture stress conditions in the field met the criteria for categorization as drought resistant while 8-42-M-2, T3008-1, and T3016-1 were categorized as drought susceptible. ABA increased total root length and root length of all root classes except class 2 when plants were grown in 15.2 x 16.5 cm growth pouches. The -0.52 and -1.07 MPa PEG experiments increased total root length and root length of root classes 1, 3, 4, and 5. ABA and both PEG experiments shifted the percentage of total roots heavily towards class 1 roots. Nutrient solution had no advantage over deionized water with regard to root length and morphology of the control and ABA experiments, however, the lack of nutrients decreased total root length and root length of root classes 1, 2, and 3 when plants were grown in - 0.52 and -1.07 MPa PEG solutions. When plants grown in 0.76 cm PVC tubes were subjected to a severe moisture stress, total root growth was fairly evenly distributed throughout the 5 equal sections of the PVC tube. When the stress was mild, root growth was concentrated in the top 30 cm. Severe moisture stress increased root length in classes 1 and 2 and total root length, and the increase was more pronounced at the 30 to 45 cm soil depth. Severe stress increased percentage of class 1 roots and decreased the percentage of class 2 roots in the top 15 cm of the soil depth. The ABA, -0.52, and -1.07 MPa PEG pouch experiments increased the root 188 Iengtha'ndpercentageofclass1 roots (thefinestroots), asdid moisturestress inthe PVC experiments. Theratiocfsecondaryto primaryrootsappearedtobe important in mm resistance and the -1.07 MPa experiment produced ratios that separated the resistant genotypes T3147-2 and BAT 477 from the susceptible genotype 8-42-M-2. ABAincreasedbothrootendshootdryweightsoRIS ratiodidnot increase in comparison to the control. The -0.52 MPa experiment decreased RIS ratio and no change occurred with the -1.07 MPa PEG experiment. In contrast to the susceptible genotype 8-42-M-2, the resistant genotypes T3147-2 and BAT 477 maintained fairly consistent leaf, stern, and root dry weights and RIS ratios across the control, ABA, and both PEG experiments. When root growth was distributed somewhat evenly across all soil depths during severe'moisture stress, the control experiment, conducted in growth pouches, was a good predictor of total root length in the 15 to 30 cm soil depth and the -1.07 MPa PEG treatment predicted root length at the 30 to 45 cm depth. The ABA and -1.07 MPa PEG treatments, conducted in the growth pouches, were the best predictors of root growth at the 45 to 60 and the -1.07 MPa PEG at 60 to 75 cm soil depths. When roots were shallow as in the mild moisture stress of PVC experiment 2, the -1.07 MPa PEG experiment of the growth pouch study was the best predictor of root growth in the PVC tubes. A larger number of correlations occurred between plants in pouch and PVC experiments when plants in the growth pouches were grown in nutrient solution as opposed to deionized water. Clearly, a greater number of cultivars must be 189 studied beforethegrowtl'lpouchmethodcanbeacceptedorrejected. Thedata is promising in thatitsupportsfurtherstudyratl'lerthan rejection oftheconcept Thedata suggestthatseedweight maybean importantfactor in total root length until at least 40 DAP.-that it may affect root length distribution among root classes, and that root length comparisons should only be made among genotypes that have a similar seed weight Recommendations 1. When assessing bean root growth via the growth pouch method, plants should be grown in half-strength Hoagland’s nutrient solution. 2. Genotypes of similar seed weight should be used when attempting to assess drought resistance or susceptibility of been genotypes via quantification of root length. 3. A minimum rooting depth of 1.0 meter is needed when attempting to assess rooting depth of drought resistant and drought susceptible bean genotypes.