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' x 3 ‘Wfi, I? ,Ii3r ‘ ‘1’.“ .49: . 3,.“ , is: in :12: THESE; SITY LIBRARIES \ll'll i ll ‘llll l \\ will" \llljl \lelH This is to certify that the dissertation entitled Evaluation of Physiological Parameters and Nitrogen Partitioning and Remobilization in Beans (Phaseolus v aris L. an Cow eas Vi n un iculata a1 uégr stress ans nonBstreés oil mgisture con 1tRons.) presented by Mmasera Manthe has been accepted towards fulfillment of the requirements for Doctoral Crop Physiology dqgeehi Major professor [)ate "2;/42Z5?}//;7j9/ : MS U is an Affirmative Action/Equal Opportunity Institution 0-12771 LIBRARY Michigan State University this checkout!” Y” M' me: u RETURN 90"” "mm W dd. dd.- TO AVOID FINES Mum 0" °' DUE DATE DUE DATE DUE DATE AWWW‘WWT ‘- r-..AMmfifi a‘fi. BY MMASERA MANTHE A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Crop Physiology - Crop and Soil Science 1 994 _ the a: influe Clami duct Carbo' 'Condu wfilter Soil, 1 8mm “3815:; ABSTRACT Evaluation of Physiological Parameters and Nitrogen Partitioning and Remobilization in Beans (Bhaseolm Maris L.) and Cowpeas (Zigna W (walp) L.) Under Stress and Non-stress Soil Moisture Conditions. by Mmasera Manthe Soil moisture stress adversely affects crop growth and porductivity. Crop canopy, the amount of light intercepted, assimilate production and nitrogen accumulation are also influenced by variations in water regimes in the soil. This study was conducted to examine the effect of terminal drought on yield— and yield components, root growth and distribution, leaf water status, photosynthesis, stomatal conductance, transpiration ratio, carbon isotope discrimination, and nitrogen partitioning and remobilization in beans (Phaseolus Maris L.) and Cowpeas (1mm W (walp) L.). The research was conducted in Michigan using either a rainshelter or black polyethylene plastic to impede water on a mixed mesic aeric ochraqualfs soil or a mixed mesic glossoboric hapluidulfs soil, respectively. Moisture stress was imposed at the late vegetative stage (V,) of plant growth Four categories of beans and cowpeas were used in these studies: 1) drought resistant and high yielding; 2) drought resistant and low yielding; 3) drought susceptible and high yielding, and 4) drought susceptible and low yielding. Moisture stress reduced bean yield by up to 50% and pods per plant by 36%. Leaf water retention capacity and leaf water content were significantly reduced by I’CS gc: WC. moisture stress in both beans and cowpeas. Relative water content was not influenced by moisture stress but varied among genotypes. Drought stress decreased root growth rate. resistant bean genotypes had a lower reduction in root growth rate than the susceptible genotypes. Photosynthetic rate was reduced by moisture stress in beans and cowpeas but there were no genotypic differences. Stomatal conductance was not affected by moisture stress in beans but was decreased by stress in cowpeas. Soil moisture stress did not affect carbon isotope discrimination (CID) in either beans or cowpeas, but drought resistant bean genotypes had lower CID values. Soil moisture stress decreased the proportion of 1"’N in the roots, stem and leaves in beans and com. Drought resistant bean genotypes maintained their N remobilization levels under stress. Nitrogen concentration and dry weight were decreased by moisture stress. Dedicated to my grandmother MORWADI EMILY MANTHE iii ACKNOWLEDGEMENTS I would like to express my sincere appreciation to my major professor Dr Eunice Poster for her continuous academic and moral support, patience, advice and faith in me to undertake this study. I would also like to thank the members of my guidance committee, Dr Alvin Smucker, Dr James Flore and Dr Patrick Hart for their time, valuable suggestions and review of this manuscript. A very special thanks to Dr Lucas Gakale, Director of the Agricultural Research Station in Botswana for his support and for helping secure financial assistance for my studies from Botswana Government. Thanks goes to Clifford Akujobi, Anny Kakuzi, Dave Harris, Brian Graff and Tom Galecka for their assistance with field work and data processing. Most importantly, I want to thank my family for their love and support. This degree is as much as theirs as mine. TABLE OF CONTENTS LIST OF TABLES ................................................................... viii LIST OF FIGURES ................................................................... xiv INTRODUCTION ....................................................................... 1 LITERATURE REVIEW .............................................................. 7 Effect of drought stress on yield and yield components .......................... 7 Effect of drought stress on leaf water relations .................................... 8 Effect of drought stress on photosynthesis and Stomatal conductance .............................................................................. 9 Effect of drought stress on carbon isotope discrimination ...................... 11 Effect of drought stress on root growth ............................................ 13 Effect of drought stress on nitrogen partitioning and remobilization ........................................................................... 14 References ............................................................................... 16 CHAPTER 1. The Effect of Soil Moisture Stress on Dry Beans W115 mm L.) and Cowpeas (Xigna W L. (walp)). 1. Yield and Yield Components, Leaf Water Status and Root Growth. Abstract ..................................................................................... 21 Introduction ................................................................................. 22 Materials and Methods .................................................................... 23 Results and Discussion .................................................................... 27 Conclusion .................................................................................. 59 References ................................................................................... 61 v CHAPTER 2. The Effect of Soil Moisture Stress on Dry Beans Bhaseglns Wis L.) and Cowpeas 01ng mm L. (walp)). II. Photosynthesis, Radiation Interception, Stomatal Conductance, Transpiration Ratio and Carbon Isotope Discrimination Abstract ........................................................................................... 63 Introduction ...................................................................................... 64 Materials and Methods ......................................................................... 65 Results and Discussion ......................................................................... 68 Conclusion ........................................................................................ 91 References ........................................................................................ 93 CHAPTER 3. The Effect of Soil Moisture Stress on Dry Beans (flasgohts Means L.) and Com Mans unguieulata L. (walp)). 111- Nitrogen Partitioning and Remobilization Abstract .......................................................................................... 94 Introduction ..................................................................................... 95 Materials and Methods ........................................................................ 96 Results and Discussion ....................................................................... 100 Conclusion ...................................................................................... 126 References ...................................................................................... 127 CHAPTER 4. The Effect of Leafhopper Damage on Dry BeamQhaseolus $112335 L.) and cowpeas (Elma unguigulata L. (walp)). IV. Yield, Physiological Parameters, Nitrogen Partitioning and Remobilization Abstract ........................................................................................ 128 Introduction .................................................................................... 129 Materials and Methods ...................................................................... 129 Results and Discussion ...................................................................... 136 1. Yield and Yield Components. Leaf Water Status and Root Growth ............................................................................. 136 II. Photosynthesis, Stomatal Conductance, Transpiration Ratio and Carbon Isotope Discrimination .............................................. 156 III. Nitrogen Partitioning and Remobilization ................................. 167 vi Conclusion ................................................................................ 183 References ................................................................................ 190 APPENDIX A ........................................................................... 191 APPENDIX B ........................................................................... 197 APPENDIX C ........................................................................... 200 vii LIST OF TABLES CHAPTER 1 . Yield and Yield Components of Bean Genotypes in a Rainshelter at the MSU Agronomy Farm, East Lansing. MI. 1990 ..................................... 31 . Yield and Yield Components of Bean Genotypes in a Rainshelter at the MSU Agronomy Farm, East Lansing. MI. 1992 ..................................... 32 . Yield and Yield Components of Bean Genotypes Using Plastic at the MSU Agronomy Farm, East Lansing. MI.1992 ............................................. 33 . Bean Yield and Yield Component Correlations ............................................. 35 . Bean Drought Index, 1990 & 1992 ........................................................... 36 . The Effect of Soil Water Changes on Relative Water Content in Beans in the Rainshelter at the MSU Agronomy Farm, East Lansing. MI. 1990 ............................................................................................... 38 . The Effect of Soil Water Changes on Relative Water Content in Beans Using Plastic at the MSU Agronomy Farm, East Lansing MI. 1992 ............................................................................................... 39 . The Effect of Soil Water Changes on Leaf Water Retention Capacity in Beans Using Plastic at the MSU Agronomy Farm, East Lansing. MI. 1992 ............................................................................................... 41 9. The Effect of Soil Water Changes on Leaf Water Content in Beans Using Plastic at the MSU Agronomy Farm, East Lansing. MI. 1992 .............................................................................................. 42 10. Root Growth Rate of Bean Genotypes at the MSU Agronomy Farm, East Lansing. MI. 1990 ............................................................................................ 43 11. The Effect of Soil Water Changes on Relative Water Content in Cowpeas in the Rainshelter at the MSU Agronomy Farm, East Lansing. MI. 1990 ......................................................................................... 50 viii 12. The Effect of Soil Water Changes on Relative Water Content in Cowpeas Using Plastic at the MSU Agronomy Farm, East Lansing. MI.1992 .......................................................................................... 51 13. The Effect of Soil Water Changes on Leaf Water Content in Cowpeas Using Plastic at the MSU Agronomy Farm, East Lansing. MI. 1992 .............................................................................................. 52 14. The Effect of Soil Water Changes on Leaf Water Retention Capacity in Cowpeas Using Plastic at the MSU Agronomy Farm, East Lansing. MI. 1992 .............................................................................................. 53 15. Root Growth Rate of Cowpea Genotypes at the MSU Agronomy Farm, East Lansing. MI. 1992 ................................................................................................ 54 CHAPTER2 1. The Effect of Soil Water Changes on CO2 Assimilation Rate in Beans in the Rainshelter at the MSU Agronomy East Lansing. MI. 1990 .................................................................................................. 7O 2. The Effect of Soil Water Changes on CO2 Assimilation Rate in Beans Using Plastic at the MSU Agronomy Farm, East Lansing. MI. 1992 ................................................................................................... 71 3. The Effect of Soil Water Changes on Light Intercepted by Beans Using Plastic at the MSU Agronomy Farm, East Lansing. MI. 1992 .................................................................................................. 72 4. The Effect of Soil Water Changes on Transpiration Ratio in Beans in the Rainshelter at the MSU Agronomy Farm, East Lansing. MI. 1990 .................................................................................................. 74 5. The Effect of Soil Water Changes on Transpiration Ratio in Beans Using Plastic at the MSU Agronomy Farm, East Lansing. MI. 1992 .................................................................................................. 76 6. The Effect of Soil Water Changes on Stomatal Conductance in Beans in the Rainshelter at the MSU Agronomy Farm, East Lansing. MI. 1990 .................................................................................................. 77 7. The Effect of Soil Water Changes on Stomatal Conductance in Beans Using Plastic at the MSU Agronomy Farm, East Lansing. MI. 1992 .................................................................................................. 78 8. The Effect of Soil Water Changes on Carbon Isotope Discrimination in Beans Using Plastic at the MSU Agronomy Farm, East Lansing. MI. 1992 .................................................................................................. 79 9. The Effect of Soil Water Changes on Co2 Assimilation Rate in Cowpeas in the Rainshelter at the MSU Agronomy Farm, East Lansing. MI. 1990 .................................................................................................. 81 10. The Effect of Soil Water Changes on CO2 Assimilation Rate in Cowpeas Using Plastic at the MSU Agronomy Farm, East Lansing. MI. 1992 ................................................................................................. 82 11. The Effect of Soil Water Changes on Light Intercepted by Cowpeas at the MSU Agronomy Farm, East Lansing. MI. 1992 ................................................................................................. 83 12. The Effect of Soil Water Changes on Transpiration Ratio in Cowpeas in the Rainshelter at the MSU Agronomy Farm, East Lansing. MI. 1990 ................................................................................................. 85 13. The Effect of Soil Water Changes on Transpiration Ratio in Cowpeas Using Plastic at the MSU Agronomy Farm, East Lansing. MI. 1992 ................................................................................................. 86 14. The Effect of Soil Water Changes on Stomatal Conductance in Cowpeas in the Rainshelter at the MSU Agronomy Farm, East Lansing. MI. 1990 ................................................................................................. 87 15. The Effect of Soil Water Changes on Stomatal Conductance in Cowpeas Using Plastic at the MSU Agronomy Farm, East Lansing. MI. 1992 ................................................................................................. 88 16. The Effect of Soil Water Changes on Carbon Isotope Discrimination at the MSU Agronomy Farm, East Lansing. MI. 1992 ................................................................................................. 89 CHAPTER3 l. The Effect of Soil Water Changes on 15N Content in Bean Roots in the Rainshelter at the MSU Agronomy Farm, East Lansing. MI. 1990 ................................................................................................ 101 2. The Effect of Soil Water Changes on 15N Content in Bean Stems in the Rainshelter at the MSU Agronomy Farm, East Lansing. MI. 1990 ................................................................................................ 102 3. The Effect of Soil Water Changes on 1“N Content in Bean Leaves in the Rainshelter at the MSU Agronomy Farm, East Lansing. MI. 1990 ................................................................................................ 103 4. The Effect of Soil Water Changes on 15N Content in Bean Reproductive Parts in the Rainshelter at the MSU Agronomy Farm, East Lansing. MI. 1990 ................................................................................................ 105 5. The Effect of Soil Water Changes on 15N Content in Bean Roots Using Plastic at the MSU Agronomy Farm, East Lansing. MI. 1992 ................................................................................................ 106 6. The Effect of Soil Water Changes on 15N Content in Bean Stems Using Plastic at the MSU Agronomy Farm, East Lansing. MI. 1992 ................................................................................................ 107 7. The Effect of Soil Water Changes on 15N Content in Bean Leaves Using Plastic at the MSU Agronomy Farm, Lansing. MI. 1992 ................................................................................................ 108 8. The Effect of Soil Water Changes on 15N Content in Bean Reproductive Parts Using Plastic at the MSU Agronomy Farm, East Lansing. MI. 1992 ................................................................................................ 109 9. The Effect of Soil Water Changes on N Concentration in Bean Roots and Stems in the Rainshelter at the MSU Agronomy Farm. East Lansing. MI. 1990 ................................................................................................ 1 11 10. The Effect of Soil Water changes on N Concentration in Bean Leaves in the Rainshelter at the MSU Agronomy Farm. East Lansing. MI. 1990 ............................................................................................... 112 xi l6. ' 11. The Effect of Soil Water Changes on N Concentration in Bean Reproductive Parts in the Rainshelter at the MSU Agronomy Farm. East Lansing. MI. 1990 ............................................................................................... 113 12. The Effect of Soil Water Changes on N Concentration in Bean Roots Using Plastic at the MSU Agronmy Farm, East Lansing. MI. 1992 ............................................................................................... 115 13. The Effect of Soil Water Changes on N Concentration in Bean Stems Using Plastic at the MSU Agronomy Farm, East Lansing. MI. 1992 ............................................................................................... 116 14. The Effect of Soil Water Changes on N Concentration in Bean Leaves Using Plastic at the MSU Agronmy Farm, East Lansing. MI. 1992 ............................................................................................... 1 17 15. The Effect of Soil Water changes on N Concentration in Bean Reproductive Parts Using Plastic at the MSU Agronomy Farm, EastLansin.MI. 1992 .......................................................................... 119 16. The Efect of Soil Water Changes on 1"‘N Content in Cowpea TVX 3236 in the Rainshelter at the MSU Agronomy Farm, East Lansing. MI. 1990 ............................................................................................ 123 17. The Effect of Soil Water Changes on N Concentration in Cowpea TVX 3236 in the Rainshelter at the MSU Agronomy Farm, East LansingMI.1990 .............................................................................. 124 18. The Effect of Soil Water Changes on Cowpea TVX 3236 Dry Weight in the Rainshelter at the MSU Agronomy Farm, East Lansing. MI. 1990 ............................................................................................. 125 CHAPTER 4 1. Yield and Yield Components of Bean Genotypes Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991 ............................................................................ 138 2. Yield and Yield Component Correlation in 1991 .......................................... 140 3. Relative Water Content in Beans Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991 .............................. 141 xii . Leaf Water Retention Capacity in Beans Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991 ...................................................................................... 142 . Leaf Water Content in Beans Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991 ...................................................................................... 143 . Root Growth Rate of Bean Genotypes Sujected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991 ...................................................................................... 144 . Yield and Yield Components of Cowpea Genotypes Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991 ..................................................................... 148 . Relative Water Content in Cowpeas Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991 ...................................................................................... 150 Leaf Water Content in Cowpeas Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991 ..................................................................................... 151 10. Leaf Water Retention Capacity in Cowpeas Subjected to 11. 12. 13. 14. Leafhopper Infestation at the MSU Agronomy Farm in East Lansing.MI. 1991 ............................................................... 152 Root Growth Rate of Cowpea Genotypes Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991 ..................................................................................... 153 C02 Assimilation Rate in Beans Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East lansing. MI. 1991 ..................................................................................... 157 Transpiration Ratio in Beans Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991 ..................................................................................... 158 Stomatal Conductance in Beans Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991 ..................................................................................... 159 xiii 15. l6. 17. 18. 19. 20. 21. 22. 23. 24. 25. Carbon Isotope Discrimination in Beans Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991 ..................................................................................... 161 C02 Assimilation Rate in Cowpeas Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991 ..................................................................................... 162 Transpiration Ratio in Cowpeas Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991 ..................................................................................... 163 Stomatal Conductance in Cowpeas Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991 ..................................................................................... 164 Carbon Isotope Discrimination in Cowpeas Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991 ..................................................................................... 166 15N Content in Bean Roots Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991 ..................................................................................... 167 15N Content in Bean Stems Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991 ..................................................................................... 168 15N Content in Bean Leaves Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991 ..................................................................................... 170 15N Content in Bean Reproductive Parts Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991 ..................................................................................... 171 N Concentration in Bean Roots Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991 ..................................................................................... 172 N Concentration in Bean Stems Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East lansing. MI. 1991 ..................................................................................... 173 xiv 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. N Concentration in Bean Leaves Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991 ..................................................................................... 175 N Concentration in Bean Reproductive Parts Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991 ................................................................... 176 1"N Content in Cowpea Roots and Stems Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East LAnsing. MI. 1991 ..................................................................................... 179 15N Content in Cowpea Leaves Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991 ..................................................................................... 180 15N Content in Cowpea Reproductive Parts Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991 ................................................................... 181 N Concentration in Cowpea Roots and Stems Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991 ................................................................... 182 N Concentration in Cowpea Leaves Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991 ..................................................................................... 184 N Concentration in Cowpea Reproductive Parts Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991 ................................................................... 185 Dry Weight of Cowpea Roots and Stems Subjected to Leafhopper Infestation at the MSU Agonomy Farm in East lansing. MI. 1991 ..................................................................................... 186 Dry Weight of Cowpea Leaves Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991 ..................................................................................... 187 Dry Weight of Cowpea Reproductive Parts Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991 ................................................................... 188 1.50 2. So 3. RC 4. RC LIST OF FIGURES CHAPTER 1 1. Soil Water Content in 1990 .................................................. 28 2. Soil Water Content in 1992 .................................................. 29 3. Root Distribution of Beans at 9 DAS in 1990 ............................ 44 4. Root Distribution of Beans at 50 DAS in 1990 ........................... 45 5. Root Distribution of Beans at -6 DAS in 1992 ............................ 47 6. Root Distribution of Cowpeas at -1 DAS in 1990 ......................... 48 7. Root Distribution of Cowpeas at 27 DAS in 1990 ......................... 55 8. Root Distribution of Cowpeas at -6 DAS in 1992 ......................... 56 9. Leaf and Soil Temperature of Cowpeas in 1992 ........................... 58 CHAPTER 2 1. Leaf and Soil Temperature of Beans in 1992 ............................. 73 CHAPTER 3 1. Total Bean Plant Dry Weight in 1990 ........................................ 120 2. Total Bean Plant Dry Weight, 1992 .......................................... 121 CHAPTER 4 1. Soil Water Content in 1991 .................................................... 137 2. Root Distribution of Beans at 13 DAS in 1991 .................................. 146 3. Root Distribution of Beans at 27 DAS in 1991147 4. Root distribution of Cowpeas at 13 DAS in 1991 ........................ 154 5. Root Distribution of Cowpeas at 27 DAS in 1991 ........................ 155 6. Total Bean Plant Dry Weight in 1991 ................................... 177 xvii INTRODUCTION Beans (Phaseclns mustn't L.) and com (Elma minute (walp) L.) are important grain legume crops in many countries around the world. They are used mainly in the grain form, however, green immature pods and leaves are also consumed as a vegetable. They are a source of essential proteins (22-24 %), vitamins and minerals (Bressani, 1985). While these crops play a significant role in the diets of many developing countries, their importance is limited by their high cost relative to cereals due to low yield production. Global estimates indicate that unpredictable periods of drought occurring within the normal rainy season may account for an average production loss of 15% in tropical areas (Fischer et al., 1983). Christiansen (1982) estimated that production on 26% of the world’s 14 billion hectares of arable land is limited by drought stress and that 85% of global cropland is rainfed. Drought stress. as defined here, is when the amount of water available to the plant is insufficient to suStain growth and development. Drought stress may be terminal in which there is a gradual decrease of water through plant maturation, or it may be intermittent. Intermittent drought may be of short duration up to 1 week or of long duration, 3-4 weeks. and occurs at one or more times throughout the season. Drought resistance is defined as the ability of a genotype to survive drought stress with minimal yield loss. Drought resistant mechanisms have been discussed at great length by Levitt (1956, 1972, 1980). As soil moisture stress increases, growth will be retarded relative to the degree of “tolerance“ of the tissues or the ”avoidance” of the whole plant system. Wi Fi SUE of , this ela_< the} CID; the 2 At a critical level of stress, growth will drop to zero. Levitt suggested that the mechanisms for drought adaptation be defined as drought escape, avoidance and tolerance. Drought escape tends to minimize the interaction of drought with crop growth and yield. Tolerance gives the ability to produce despite loss of plant water status. Avoidance increases the ability to maintain relatively high plant water status despite a shortage of moisture in the environment (Fischer and Turner, 197 8; Fischer and Sanchez, 1979; O’Toole and Chang, 1979). DROUGHT ESCAPE Early maturing varieties are known to escape the effects of late drought and this confers yield advantage (Levitt, 1972). Drought escape is often the most important and successful form of drought adaptation and is usually imparted through the combination of genotype maturity and planting date. Ludlow (1989) defined four main features with this strategy: 1) Short phenology which results in low yield potential, 2) developmental elasticity which is good for survival, 3) photoperiod insensitivity in native species so that they can flower and produce seed whenever rain falls, and 4) photoperiod sensitivity in crop plants so that the time of flowering coincides with the average date of the end of the rainy season. Due to the unpredictability of drought, drought adaptation through escape is generally not feasible. Drought adaptation through escape also fails to meet the farmer’s needs for longer maturing varieties which will provide leaves for vegetable use. This need can be met through drought adaptation by avoidance or tolerance. DROUGHT AVOIDANCE Ludlow (1989) has explained the main features of dehydration avoidance as 1) 3 sensitivity of the plant tissues to dehydration, a mechanism which has no penalty for growth if water uptake is maximized; 2) maximization of water uptake by developing roots, a mechanism which has a short term but no long term cost for growth if water loss is reduced by elastic responses; 3) minimization of water loss by stomatal control, leaf movement, smaller leaves and the shedding of older leaves; and 4) low osmotic adjustment, little Stomatal adjustment and photosynthetic adjustment. Drought avoidance will result from increased resistance to water flux in the plant or from improved control over vapor transfer at the leaf surface. Resistance to water flux in the-plant is greater in the root (Newman, 1974). Increased root resistance may be achieved through increased axial resistance or increased radial resistance. The ability of the root to adjust osmotically to increased soil moisture stress may also be an important component of drought avoidance (Hsaio and Acevedo, 1974; Newman, 1974). Increasing soil water deficits near the soil surface seems to induce compensatory extension of the roots deeper into the unexploited soil layers. The deep rooting system characterizes plants that are drought avoiders because they are able to exploit soil moisture in the lower soil profiles (Newman, 1974). However, developing a deep root system may not necessarily be a beneficial strategy when soil moisture reserves are unavailable in the deeper levels because the plant then wastes assimilates. Increased root development comes at the expense of shoot growth so shoot growth is at a disadvantage when rain resumes. Drought avoidance promoted by a large, well branched, deep root system with efficiency of soil water extraction is desirable as long as there is moisture to be extracted from the volume of soil contacted by the roots. However, when the water sup dc: wi di. T8 of lo Ur. 4 supply is exhausted below the crop water requirement, the plant may rapidly suffer desiccation injury. Reduction in leaf expansion is probably the first indicator of the plant’s response to drought stress. A drought susceptible genotype will attain low leaf area which in turn will limit canopy photosynthesis leading to lower productivity (Hsaio, 1973). If drought becomes more severe, the stomata may close in order to minimize loss of water through transpiration. Stomata act as regulators for both carbon dioxide exchange and water loss in plants. So the closure of stomata may directly lead to greater resistance to carbon dioxide uptake and therefore affect photosynthesis and subsequent productivity. DROUGHT TOLERANCE The response and tolerance of any plant to reduction in leaf water potential is complex. It may involve any number of physiological and metabolic processes. It can be measured at the individual process level or at an integrated level. Growth as an integrated response can serve as a measure of plant tolerance under stress if and when maintainance of growth under stress is required (Berg and Turner, 1976; Blum, 1970). When the tissue is not protected from dehydration by avoidance mechanisms, cells lose turgor and dehydrate. Several basic physiochemical events occur at the cellular level under the effect of dehydration such as reduction in the chemical activity of water, concentration of solutes and macromolecules, removal of water of hydration from macromolecules and alterations in the cellular membrenes (Blum, 1988). Ludlow (1989) described dehydration tolerance as a measure of the plant’s capacity to withstand severe dehydration defined in terms of leaf water potential (LWP), or relative water content lOV Ct exz 0L Bl Di 5 (RWC) of the last surviving leaf on a plant subjected to a slow, continuous soil drying cycle (lethal value). Osmotic adjustment results from the accumulation of solutes within cells, which lowers the osmotic potential and helps maintain turgor of both shoots and roots as plants experience water stress. This allows turgor driven processes such as stomatal opening and expansion growth to continue, although at reduced rates, to progressively lower water potentials. Ludlow (1989) contends that dehydration tolerance has moderate to high osmotic adjustment which is a good long term leaf and plant survival mechanism. On the other hand, Levitt (1980) noted that osmotic adjustment is an avoidance mechanism. Blum (1988) reported that when dehydration avoidance is expressed in terms of the maintainance of a higher water or turgor potential under conditions of water stress, osmotic adjustment as a means of retaining a higher turgor at a given tissue water potential is a component of dehydration avoidance. Ludlow and Muchow (1989) concluded that osmotic adjustment is positively correlated with dehydration avoidance and tolerance only if soil water is not exhausted and is negatively correlated with dehydration avoidance if soil water is exhausted. At present the best and ultimate indicator of drought resistance used in brwding programs is grain yield measured under well-watered and water-stressed conditions. It would greatly aid the plant breeding process if a physiologically based drought resistance indicator could be found that breeders could use as a selection tool in large segregating populations or to screen potential parental lines. One approach to searching for such a physiological screening tool is to compare genotypes of the same species and of known but Pbl' tesi Stilt 3551 ICU 6 but differing levels of drought resistance. This research study was conducted to evaluate physiological characteristics in beans and cowpeas and to determine the characteristics that can be used as screening tools in a breeding program designed to develop drought resistant lines. Most studies often look at the physiological parameters individually. This study was designed to simultaneously study physiological characteristics such as CO; assimilation rate, stomatal conductance, transpiration ratio, carbon isotope discrimination, radiation interception, leaf water, root growth, and nitrogen partitioning and remobilization. pr 11L SC 31 69 0b Sh We LITERATURE REVIEW E Efi E l l . l l l . l l Drought stress which occurs during the growth of beans and cowpeas affects many physiological and morphological characteristics associated ultimately with seed yield. The duration and intensity of drought stress as well as the phenological stage of the crop at the time the stress occurs will determine the amount of damage done to the crop and therefore yield. The yield of beans and cowpeas may be considered as the product of their components: number of pods per plant, number of seeds per pod, number of plants and individual seed weight. There is general agreement in the literature that the reproductive stage is the most sensitive to water suess in legumes, affecting seed yield by reducing pod set and single seed weight (Diputado and Rosario, 1985; Acosta-Gallegos and Shibata, 1989; Acosta- Gallegos and Adams. 1991; Gwathmey and Hall, 1992; Herbert and Baggerman, 1983). Shouse et al. (1981) reported yield reduction by moisture stress of 35 % at flowering and 69% at the pod fill stage in cowpeas. ln beans, when drought stress was imposed at the beginning of the reproductive phase. it reduced seed yield 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. The number of pods per plant was the yield component most affected by water stress. Summerfield et al. (1985) noted that in cowpeas under moderate water stress, determinz tt flower When mt stomatall led to sul leaf area (Gwathm 8 determinate cultivars produced close to normal seed yield in spite of the stress imposed at flowering because the plants matured their fruits before the stress became severe. When more severe stress was imposed at different times of the reproductive period, stomatal closure and reductions in leaf area combined to limit dry matter production and led to substantial decreases in seed yield. Concurrent reduction in pod production and leaf area in cowpeas and beans due to drought stress has been reported by others also (Gwathmey and Hall, 1992; Acosta-Gallegos and Adams, 1991). WWW Plant water deficit is described in terms of water content or the energy status of the water in the cell. The water content is usually expressed as relative to that at full saturation. The relative water content and the' energy status of the water is usually expressed as the total water potential (Turner, 1982). The ability of plants to retain water is important particularly under drought conditions. Leaf water content estimates the capacity of water retention by detached leaves at the time of detachment. Leaf water retention capacity measures percentage moisture lost after 24 or 48 hours of leaf detachment. The degree to which plants withstand desiccation, expressed as relative water content or water potential at which leaves die is called the critical or lethal value (Ludlow and Muchow, 1989). Low lethal water status influences the plant’s survival by contributing to dehydration tolerance and leaf survival during intermittent drought stress and therefore to yield stability. Walker (1983) observed that cowpea genotypes which previously had been found to have a high biomass production potential under drought conditions also had high leaf water I 942161 1 hence: (Wallet constant energet water 0 mamas drought ll drought reductior capacity Ithtive v been Obs: E3361 of 9 water retention capacity, suggesting that this trait can be used to improve swd yield of water stressed plants. Significant differences for leaf drying have also been detected between genotypes and for the interaction between genotype and time after detachment (Walker and Miller, 1986). Cowpeas exposed to drought stress maintained a fairly constant level of relative water content when drought was imposed at 20 to 50 days after emergence (Nagarajah and Schulze, 1983). When the stomates started to close, relative water content was as high under drought stress as in well watered controls. The maintanance of a high relative water content in the leaves characterized cowpea as a drought avoiding species (Bates and Hall, 1982). In beans, leaf water content and leaf water retention capacity increased under drought stress (Acosta-Gallegos and Adams, 1991). Ramirez-Vallejo (1992) found a reduction in relative water content under stress and an increase in leaf water retention capacity in beans. There were also genotypic differences in leaf water content and relative water content. Genotypic differences in relative water content in wheat have also been observed (McCraig and Romagosa, 1991; Ritchie et al., 1990). 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 of higher plants is derived from CO2 assimilated by photosynthesis (Zelith, 1982). Zelith contends 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 plants. Elia TIL—"I depres respon control When i stresses plant bl In “ a rest proCess lower s when 10 It is now well established that the rate of CO, assimilation in the leaves is depressed at moderate leaf water deficits or even before leaf water status is changed in response to a drop in air humidity or in soil water potential. In such cases stomatal control of C02 diffusion plays the most important role in controlling photosynthesis. When drought period is lengthened, dehydration is more severe or other environmental stresses are superimposed. Changes may occur in metabolic functions and/or in whole plant behavior (Chaves, 1991). CO, assimilation and stomata responded fairly independently, in spite of a certain degree of coupling, to short term variations of environmental factors (Kuppers et 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 CO2 assimilation and stomatal conductance during soil drying was fairly independent of the water status of the leaf. Similar observations by Bates and Hall (1981) indicated that stomatal closure due to soil water depletion was not associated with changes in leaf water status. Studies on cotton (59mm 111131121111 L.) have shown that 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). Stomata limited the photosynthetic process in well-watered plants or in mildly stressed plants while mesophyll resistance was the main factor reducing it under more severe moisture stress. Early stress treatments had lower stomatal resistance and higher photosynthetic rates than the late stressed treatments. prior to select g biomass photosy‘. Similarlj conduct: conclude 1 1 Peng et al. (1991) observed that photosynthesis measured at the single leaf level prior to flowering in sorghum (Seaman 1119919: L.) was a trait which can be used to select genotypes for higher productivity. They observed that leaf photosynthesis, total biomass and grain production were significantly reduced by limited water supply. Leaf photosynthesis was positively correlated with total biomass and grain production. Similarly, Hamdani et al. (1991) showed genotypic reduction in water potential, stomatal conductance and CO2 assimilation. rate with decreasing available soil water. They concluded that stomatal conductance and photosynthesis have the potential to be used as screening tools for drought resistance of sorghum genotypes at the vegetative stage of growth. E ill I l l l . l' . . . Stable carbon isotopic composition is a potentially valuable characteristic for evaluating breeding lines for productivity and water use efficiency (WUE) on the basis of integrated plant responses (Johnson et al., 1990; Ehleringer et al., 1991). As water becomes limiting for a plant, the stomata eventually exhibit some degree of closure. If this closure restricts water loss from the leaf proportionately more than the decrease in photosynthetic rate (A) then intercellular CO2 (ci) is reduced (Cowan and Troughton, 1971). This response results in water savings to the plant and a subsequent increase in WUE. Because ribulose biphosphate carboxylase oxygenase (Rubisco) discriminates against 1"CO,” the proportion of 13CO2 to 12CO2 increases within the leaf. With this increased concentration of 13CO2 in the interior of the leaf compared to 12C0,, Rubisco has less opportunity to discriminate against l3C0,. Consequently, 13CO2 discrimination u... .1 . -‘-__ decrca procedr inform; carbon therefor develoo measure physiolc l were no and so 1 Sigmfiea 12 decreases as stress becomes more pronounced (Johnson et al. , 1990). Although Cl and WUE can be reliably and accurately measured by gas exchange procedures, these are generally instantaneous measurements that do not provide information over an extended period of time. Because carbon is continually being fixed, carbon isotope discrimination can be used to provide a long term indication of ci, and therefore measurements of CID reflect the combination of 13C and 12C over the development of the particular tissue being analysed. This combining ability suggests that measurements of CID may differentiate between genotypes better than most instantaneous physiological assays (Johnson et al. , 1990). Hall et al. (1992) in their review concluded that genotypic differences in CID were more consistent than differences in A/ g, photosynthetic rate or stomatal conductance and so should be easier to select for in breeding. Ismail and Hall (1992) indicated significant correlations for WUE, CID, specific leaf weight, biomass, water use and leaf area per plant in cowpeas. Similar observations have also been made in beans (White et al. , 1990). White et al. (1990) found a positive correlation between root length density and CID, concluding that leaf physiology (as measured by CID) was not independent of root activity and rooting density. Ehleringer et al. (1991) reported that CID is significantly correlated with transpiration efficiency estimates in beans. In coffee (£9113 arabiea L.), photosynthetic rates and stomatal conductance have had a positive correlation with CID (Meizner et al., 1990). Studies were made to evaluate CID on the leaves as well as the grain. In cowpea, leaf CID detected genotypic differences more readily than grain CID (Hall et al., 1990). This study also concluded that sci conditit 13 that selection based upon CID in cowpeas should be equally effective under wet or dry conditions. WWW Roots play an important role in the growth and survival of plants during periods of drought stress. Under drought, the root is characterized by a low root density in the dry surface layer and a higher root proliferation in the deeper, wetter soil layers. However, under non-stress conditions, roots proliferate in the soil zone with the lowest soil water retention (Garay and Wilhelm, 1983). In Peanuts (Amhis W L.) root growth from 20 to 50 days after planting was significantly reduced in the upper 40 cm of the soil profile by drought stress, but recovered upon rewatering (Meisner and Karnok, 1992). - Box et al. (1989) reported a 37% reduction in roots in the top 20 cm during an 18 day drought period and a 50% increase in root number at 60 to 150 cm depth in wheat (Tritium mum L.). The response to short term drought suggests that large quantities of photo-assimilated carbon may have been lost to the rhizosphere at the depth of shallow roots. Additionally, new allocations of plant carbon were required for the new growth of roots at greater soil depth. It is generally agreed that there is more root growth at greater depths under drought stress (de Vries et al.. 1989; Smucker et al., 1991; Stofella et al., 1979; Obisesan, 1986: O’Toole and Bland, 1987). In cowpeas under mild drought stress, Nagarajah and Schulze (1983) showed an increase in absolute root growth. In the early stages of soil drought, root weight in the stressed plants was greater than that of the ‘_. assim. 1985) influe differ: numb: SUEHU 13km; txhibn l4 Nitrogen metabolism is essential for crop growth and development. The assimilation and distribution of nitrogen in the vegetative and reproductive parts of edible grain legumes is an important process in determining seed yield (Westerman et al., 1985). Nitrogen assimilation and distribution during seed filling have a significant influence on the final seed nitrogen concentration and yield in beans. Evidence of differences in nitrogen accumulation, partitioning and remobilization among the limited number of species and cultivars studied to date supports the concept of studies to more strenuously evaluate differences among cultivars which vary in their resistance to drought (Chapman and Muchow, 1985; DeVries et al., 1989; Sinclair and Horie, 1989). The literature indicates that a great proportion of the total nitrogen is translocated to the reproductive parts (pods and seeds) of grain legumes. Under water stress, cowpeas translocated a greater proportion of the total nitrogen to the pods than did well watered control plants (Wein et al. , 1979). Similarly, Lynch and White (1992) reported that total nitrogen allocation to the seeds dominated the reproductive nitrogen budget in beans. They concluded that the relatively small nitrogen allocation to leaves as opposed to swds suggested that carbon gain during reproductive growth may be limited by seed nitrogen demand. Yield is positively associated with the seed filling duration and negatively associated with seed protein concentration. In general, high seed protein genotypes exhibit faster nitrogen partitioning and dry matter allocation into seeds, shorter seed 15 filling duration and lower yield (Navaro et al, 1985). On the other hand, Boon-Long et al.(1983) suggested that neither the maximum level of total nitrogen in the leaf nor the rate of redistribution seems to be closely related to the final seed yield. The contribution of redistributed nitrogen to seed nitrogen varies among cultivars and is increased by nitrogen stress applied during the reproductive growth. Egli et al. (1983) reported that moisture stress did not consistently alter the contribution of redistributed nitrogen to the nitrogen in the seed. In soybeans (Glycine max L.), nitrogen accumulation in the roots and nodules was much less affected by irrigation treatment than was nitrogen accumulation in the shoots (Sinclair et al. , 1987). In beans, the susceptible genotype utilized nitrogen less efficiently than the resistant genotype (Foster et al. , 1991). The results also indicated that the shoot may be a greater determiner than the root with regard to nitrogen concentration and efficiency. Aeosra‘r of lodei Aoosu' _ Bates L with Ch Bars 1. of conp‘ Blum A. REFERENCES Acosta-Gallegos J. A. A. , Shibata J. K. 1989. Effect of water stress on growth and yield of indeterminate dry bean (Phaseolus mm L.) cultivars. Field Crops Res. 20:81-93. Acosta-Gallegos J. A. A., Adams M. W. 1991. Plant traits and yield stability of dry bean (2min mm L.) under drought stress. J. Agric. Sci. 117:213-219. Bates L. M., Hall A. E. 1981. Stomatal closure with soil water depletion not associated with changes in bulk leaf water status. Oecologia (Berl) 50:62-65. Bates L. M., Hall A. E. 1982. Relationships between leaf water status and transpiration of cowpea with progressive soil drying. Oecologia (Berl) 53:285-289. Begg J. E., Turner N. C. 1976. Crop water deficits. Adv. Agron. 28:161-217. Blum A. 1988. Plant breeding for stress environments. CRC Press, Inc. Buca, Florida. Blum A. 1970. The effect of plant density and growth duration on sorghum yield under limited water supply. Agrn. J. 62:333-336. Boon-Long P., Egli D. B., Leggett J. E. 1983. Leaf nitrogen and photosynthesis during reproductive growth in soybeans. Crop Sci. 23:617-620. Box J. E., Smucker A. J. M., Ritchie J. T. 1989. Minirhizotron installation techniques for investigating root responses to drought and oxygen stresses. Soil Sci. Am. J. 53: 1 15- 118. Bressani R. 1985. Nutritive value of cowpeas. In Cowpea research, production and utilization. eds, S. R. Singh and K. O. Rachie. John Wiley & Sons Ltd. NY. Chapman A. L., Muchow R. C. 1985. Nitrogen accumulated and partitioned at maturity by grain legumes grown under different water regimes in a semiarid and tropical environment. Field Crops Res. 11:69-79. Chaves M. M. 1991. Effects of water deficits on carbon assimilation. I. Expt. Bot. 42:1- 16. Christiansen M. N. 1982. World environmental limitations to food and fibre culture. In Breeding plants for less favourable environments. eds, M. N. Christiansen and C. F. Lewis. Wiley Interscience. Cowan I. R., Troughton J. H. 1971. The relative role of stomata in transpiration and assimilation. Planta 97:323-336. 16 Vr‘ LIA: 1.". v t I a DCV; nitro water 17 DeVries J. D., Bennett J. M., Albrecht S. L., Boote K. J. 1989. Water relations, nitrogenase activity and root development of three grain legumes in response to soil water deficits. Field Crops Res. 21:215-226. Diputado Jr. M. T., del Rosario D. A. 1985. Responses of cowpea (Xigna (walp) L.) to moisture stress and seed treatment. Crop Sci. Soc. Philippines 10:51-56. Egli D. B., Meckel L., Phillips R. E., Radcliff D., Leggett J. E. 1983. Moisture stress and nitrogen redistribution in soyabeans. Agron. J. 75: 1027-1031. Ehleringer J. R., Klassen 8., Clayton C., Sherill D., Holbrook M. F., Cooper T. A. 1991. Carbon isotope discrimination and transpiration efficiency in common bean. Crop Sci. 31:1611-1615. Ephrath J. E., Mavani A., Bravdo B. E. 1990. Effects of moisture stress on stomatal resistance and photosynthetic rate in cotton (QQSMIILIII hjmmun) I. Controlled levels of stress. Field Crops Res. 23:113-117. Fischer K. S., Johnson E. C., Edmeads G. O. 1983. Breeding and selection for drought resistance in tropical maize. Centro Internacional de Mejopamiento dc Tropical Maize. CIMMYT.E1 Batan, Mexico. 19p. Fischer R. A., Turner N. C. 1978. Plant productivity in the arid and semi arid zones. Ann. Rev. Plant Physiol. 29:227-317. Fischer R. A., Sanchez M. 1979. Drought resistance in spring wheat cultivars. II. Effects on plant water relations. Aust J. Agric Res. 30:801-814. Foster E. F., Carmi A., Nunez-Barrios A., Manthe M. 1991. Drought effects on N concentration and water use in reciprocal grafts of beans with differing drought adaptation. Bean Improvement Cooperative 34; 108-109. Garay A. F. , Wilhelm W. W. 1983. Root system characteristics of two soybean isolines undergoing water stress conditions. Agron. J. 75:973-975. Gwathmey C. 0., Hall A. E. 1992. Adaptation to mid-season drought of cowpea genotypes with contrasting senescence traits. Crop Sci. 32:773-778. Hall A. E., Mutters R. G., Hubick K. T., Farquhar G. D. 1990. Genotypic differences in carbon isotope discrimination. Crop Sci. 30:300-305. Hall A. E., Mutters R. G., Farquhar G. D. 1992. Review and Interpretation: Genotypic and drought induced differences in carbon isotope discrimination and gas exchange of cowpea. Crop Sci. 32(1)1-6. 18 Hamdani S. H. A., Murphy J. M., Todd G. W. 1991. Stomatal conductance and C0, assimilation as screening tools for drought resistance in sorghum. Can. J. Plant Sci. 71:689-694. Herbert S. J., Baggerman F. D. 1983. Cowpea response to row width, density and irrigation. Agron. J. 75:982-986. Hsaio T. C. 1973. Plant response to water stress. Ann. Rev. Plant Physiol. 24:519-570. Hsaio T. C. , Acevedo E. 1974. Plant responses to water deficits, water use efficiency and drought resistance. Agric. Meteorl. 14:59-84. Ismail A. M. , Hall A. E. 1992. Correlation between water use efficiency and carbon isotope discrimination in diverse cowpea genotypes and isogenic lines. Crop Sci. 32:7-12. Johnson D. A., Asay K. H., Tuszen L. T., Ehleringer J. R., Jefferson P. G. 1990. Carbon isotope discrimination: potential in screening cool season grasses for water limited environments. Crop Sci. 30:338-343. Kuppers B. I. L., Kuppers M., Schulze E. D. 1988. Soil drying and its effect on leaf conductance and CO2 assimilation of mm mm (L) walp). I. The response to climatic factors and to the rate of soil drying in young plants. Oecologia 75:99-104. Levitt J. 1956. The hardiness of plants. pp 278. New York and London: Adcademic. Levitt J. 1972. Responses of plants to environmental stresses pp 697. New York and London: Academic. Levitt J. 1980. Responses of plants to environmental stresses. 2" ed vol 2. Academic Press. New York. Ludlow M. M. 1989. Strategies of response to water stress. In structural and functional responses to environmental stresses. edited by K. H. Kreeb, H. Richter and T. M. Hinckley. SPB Academic Publishing bv, The Hague, The Netherlands. Ludlow M. M. , Muchow R. C. 1989. Critical evaluation of the possibilities of modifying crops for high production per unit of precipitation. Aust. J. Plant Physiol. 179-211. Lynch J., White J. W. 1992. Shoot nitrogen dynamics in tropical common bean. Crop Sci. 32:392-397. McCraig T. N. , Romagosa l. 1991. Water status measurements of excised leaves: Position and age effects. Crop Sci. 31:1583-1588. 19 Meisner C. A., Karnok K. J. 1992. Peanut root response to drought stress. Agron. J. 84:159-165. Meizner F. C., Goldstein G., Grantz D. A. 1990. Carbon isotope discrimination in coffee grown under limited water supply. Plant Physiol. 92: 130-135. Nagarajah S., Schulze E. D. 1983. Responses of Eigna mm (L) walp. to atmospheric and soil drought. Aust. J. Plant Physiol. 10:385-394. Navarro L. R. S., Hinson K., Sinclair T. R. 1985. Nitrogen partitioning and dry matter allocation in soyabean with different md protein concentration. Crop Sci. 25:451-455. Newman E. K. 1974. In plant root and its environment. (E. W. Carson ed.) pp 363-440: Charlottesville. Univ. Press of Virginia. Nunez-Barrios A. N. 1991. Effect of soil water deficits on the growth and development of dry beans (Phaseolus mm L.) at different stages of growth. PhD Diss. Michigan State Uniniversity. Obisesan I. O. 1986. Exploratory tendencies of roots in the soil: Assessment and effects on grain yield of cowpea (Vigna W (L) walp). Nigerian J. Agron. 1:25-29. O’Toole J. C., Chang 1‘. T. 1979. Stress physiology in crop plants. pp 373-405. Willey Interscience. New York. O’Toole J. C., Bland W. L. 1987. Genotypic variation in plant root systems. Advances in Agron. 41:91-95. Peng S., Krieg D. R., Girma F. S. 1991. Leaf photosynthetic rate is correlated with biomass and grain production in grain sorghum lines. Photosynthesis Res. 28:1-7. Ramirez-Vallejo R. P. 1992. Identification and estimation of heritabilities of drought related resistance traits in dry beans (Phaseolus mm L.). Ph.D Dissertation. Michigan State University. Ritchie S.W., Nguyen H. T., Holaday A. S. 1990. Leaf water content and gas exchange parameters of two wheat genotypes differing in drought resistance. Crop Sci. 30: 105-1 11. Shouse P., Dasberg 8.. Jury W. A., Stolzy L.H. 1981. Water deficits effects on water potential, yield and water use of com. Agron. J. 73:333-336. Sinclair T.R., Muchow R. C., Bennett J. M., Hammond L. C. 1987. Relative sensitivity of nitrogen and biomass accumulation to drought in field grown soyabean. Agron. J. 79: 986-991 . Fun-Al LC. v Sloth cffoci Smuej envirc Stoffe. of his: 830. Turner plant v Banos. Summe cowpea Rachie. Walker in coop. Tm; drought i Weir H. Under no simples. thterma mObUizati White J. I grow] an “51.1. Pi Zi‘ith. r. BIOSCICDCe 20 Sinclair R. R., Horrie T. 1989. Leaf nitrogen, photosynthesis and crop radiation use effeciency. Crop Sci. 29:90-98. Smucker A. J. M., Barrios A. N., Ritchie J. T. 1991. Root dynamics in drying soil environments. Below ground Ecol. Spring pp 4-5. Stoffella P. J., Sandsted R. F., Zobel R. W., Hymes W. L. 1979. Root characteristics of black beans. I. Relationships of root size to lodging and seed yield. Crop Sci. 19:823- 830. Turner N. C. 1982. Techniques and experimental approaches for the measurement of plant water status. In Drought resistance in crops with emphasis on rice. IRRI. Los Banos. Phillipines. Summerfield R. J., Pate J. J., Roberts E. H., Wein H. C. 1985. The physiology of cowpeas: In cowpea research, production and utilization. eds S. R Singh and K. O Rachie. John Wiley and Sons. Ltd. New York. Walker D. W. 1983. Influence of genotype on drought resistance and nitrogen fixation in cowpea (Vim W (L) walp) Ph.D diss. Texas A & M Univ. Collage Station. Texas. - Walker D. W., Miller, Jr. J. C. 1986. Rate of water loss from detached leaves of drought resistant and susceptible genotypes of cowpeas. Hortsci. 21(1):l3l-132. Wein H. C., Littleton E. J., Ayanaba A. 1979. Drought stress of cowpea and soybean under tropical conditions. In Stress physiology in crop plants. eds H. Mussel and R. C. Stapples. Willey Interscience. New York. pp 284-301. Westerman D. T., Porter L. K., O’Deen W. A. 1985. Nitrogen partitioning and mobilization patterns in bean plants. Crop Sci. 25:225-228. White J. W., Castillo J. A., Ehleringer J. 1990. Associations between productivity, root growth and carbon isotope discrimination in Bhaseclus mlgarjs (L) under water deficits. Aust. J. Plant Physiol. 17:189-195. Zelith, I. 1982. The close relationship between net photosynthesis and crop yield. Bioscience (10)32:796-802. CHAPTER] THE EFFECT OF SOIL MOISTURE STRESS ON DRY BEANS (Bhascalns mums L.) AND COWPEAS (Elana W L. (walp)). I. Yield and Yield Components, Leaf Water Status and Root Growth. ABSTRACT Soil moisture stress adversely affects the growth of different plant organs and hence crop productivity. This study was conducted to examine the effect of terminal drought on yield, pods per plant, seeds per pod, leaf water, and root growth and distribution of beans (Phaseolus Maris L.) and cowpeas (Zigzag mm L. (walp)) under field conditions. The research was conducted in Michigan using either a rainshelter or black polyethylene plastic to impede water on a mixed mesic aeric ochraqualfs soil or a mixed mesic glossoboric hapluidulfs soil, respectively. Moisture stress was imposed at the late vegetative stage (V9), 37 and 55 DAP in 1990 and 1992 respectively. Drought stress reduced seed yield by up to 50% in beans. Pods per plant were significantly reduced under stress by 36% in beans, but seeds per pod were not sensitive to a decrease in soil water content. Pods per plant and yield maintained a significant, consistent correlation in 1990 and 1992. Soil moisture had no effect on relative water content. Leaf water retention capacity and leaf water content were significantly reduced by moisture stress. Plants maintained high relative water content, leaf water retention 21 moat: growth Ill I007. 22 capacity and leaf water content throughout each season. Drought stress decreased root growth rate in both beans and cowpeas. Resistant bean genotypes had a lower reduction in root growth rate than susceptible genotypes. INTRODUCTION Soil moisture stress occurring at flowering or pod filling stages has a detrimental effect on yield, but the effect is greatly influenwd by the rate and duration of moisture stress. Akycampong and Steponlcus (1981) reported a 30% yield reduction when stress was imposed at flowering and an 80% yield reduction when stress was imposed at the pod filling stage in cowpeas (Vigna Whiz L. (walp)). Yield reductions were largely due to a decrease in the number of pods per plant. Muchow (1985) showed similar results in 30be (Gimme max L.), pigeon pea (,Qajanus gajan L.), lablab bean, green gram, black gram and cowpeas. The degree to which plant parts withstand desication is often expressed in terms of leaf water content at the time when the leaves die, thus the critical or lethal value. In excised wheat CLriticmn m L.) leaves, drought resistant genotypes lost water at a slower rate than the less resistant genotypes (Clarke and McCaig, 1982). A significant genotype x environment interaction has also been reported (Clarke, 1983). Roots play an important role in the growth and survival of plants during periods of drought stress. Root characteristics are of primary importance in determining drought response of common beans (White and Castillo, 1989). Under conditions of water stress, root growth in the surface soil layers is relatively slow while the growth of new roots in the de. andTi compo $3888. 23 the deeper, wetter layers is hastened (Garay and Wilhelm, 1983; Sponchiado et al. , 1989; and Trejo and Davis, 1991). The objective of this study was 1) to investigate the response of yield and yield components to drought stress, 2) to evaluate the potential use of leaf water status as a screening tool, and 3) to evaluate root growth and distribution in response to drought stress. MATERIALS AND METHODS A field study was conducted at the Agronomy Research Farm at Michigan State University in East Lansing during the summers of 1990 and 1992. In 1990 a rainshelter was used to impose moisture stress during the late stage of vegetative of growth (V,) at 37 DAP. In 1992, black polyethylene plastic was used to impose moisture stress during the late stage of vegetative growth (V,) at 55 DAP. The plastic was placed between rows and on non-rainy days it was rolled inside so that the soil surface was exposed for drying- The soil type for the 1990 experiment was a fine loamy, mixed mesic aeric ochraqualfs with a slope of 0-3% (USDA Soil Conservation Service Classification). For the 1992 experiment, it was a fine loamy, mixed mesic glossoboric hapluidalfs with a slope of 2-6%. The rainfall and temperature data are presented in Fig 1 and Table l of Appendix A. The experimental design was a modified split plot with four replications. The main plot was the moisture level and genotypes were the subplots. The moisture factor 24 was confounded by site difference in that all stressed plots were grouped together and all non-stressed plots were grouped together. Each plot had four rows of 2 m length. The beanspacingwasSOx lOcmandthecowpeaspacingwas 75x20cmwhichresulted in a plant density of 20 plants per m2 for beans and 10 plants per tn2 for cowpeas. In 1990 two bean genotypes (9-39-1 and 8-42-M-2) and two cowpea genotypes (TVX 3236 and BOOS-C) were used. In 1992 four bean genotypes (9-39-1, 8-42-M-2, N81017 and 8-25- 2) and four cowpea genotypes (TVX 3236, Blackeye, ER." and IT838-742-2) were used. The bean genotypes were chosen based upon their previous performance in the MSU bean breeding program and their subsequent designation as either drought resistant or susceptible. The cowpea genotypes were chosen based upon their performance from a preliminary growth chamber study conducted in 1989 and their performance in field studies at IT'I‘A and in Botswana. Genotypic descriptions are presented in Table 2 of Appendix A. Plots were hand planted using a hoe to open rows and 40 or 20 seeds were planted per row for beans and cowpeas respectively, along with abundant inoculant. The bean inoculum was Magnum phasmli and the cowpea inoculum was 311mm Cowpea miscellany nitrogen EL. Wedges 1220 Both beans and cowpeas were planted on June 25 but because of poor germination the cowpeas were replanted on July 18. Fertilizer was applied as 19-19-19 at the rate of 40 Kg N/ha before planting. Three days after planting on June 28 all plots received 30 25-Oc 131301 applied of irrig growinp applied fitsblis 25 mm of irrigation to facilitate germination. Total rainfall during the growing season (June 25-0ct 5) was 287.6 mm. On July 31, Sevin (Carbaryl insecticide) was applied at the rate of 4 teaspoons per gallon of water to control Mexican bean beetle and leathopper. 19.22 Planting occurred on June 12. The fertilizer 21-7-14 with 4% Mn and 1% Zn was applied at the rate of 40 Kg N/ha before planting. All plots received a total of 283.3 mm of irrigation in four applications before stress was imposed. The total rainfall during the growing season (June 12-Sept. 16) was 309.0 mm. A greater amount of irrigation was applied in 1992 in order to break the soil cntst and enhance germination and plant stand establishment. Sevin was applied on July 29 to control leafhopper. Soil moisture was monitored regularly in all plots at three depths in 1990 (0-30, 30-60, 60-90 cm) using a neutron probe. In 1992 readings were only recorded at the 0-30 and 30-60 cm depth because the field had a high water table. Undisturbed soil core samples were taken at the same depths to develop a soil moisture desorption curve which was used to convert the volumeu'ic moisture content into matric potential. In 1992 leaf temperature, using the infrared thermometer and soil temperature were monitored. Leaf temperature was recorded on a single leaf per plant and on three plants per plot. Soil temperature was recorded from the center row of each plot. Wm Relative water content (RWC) was determined in 1990 and RWC, leaf water content (LWC) and leaf water retention capacity (LWRC) were determined in 1992. Weather permitting, measurements were made every two weeks after stress was imposed. 26 Three plants per plot at the same growth stage were tagged and marked A, B and C. The center leaflet of the youngest fully developed leaf was placed 'in a plastic bag marked A,, B, or C, depending on whether it was from plant A, B or C respectively. With the leaf face-up, the leaflet on the right was labelled A5, B3 or C3 and the leaflet on the left was labelled A1, B1 or C,. The RWC, LWC and LWRC measurements were made on samples marked number 1, 2 and 3 respectively. Immediately after leaf detachment, the samples were placed in ziplock bags and stored on ice in a cooler until their fresh weight was recorded. REC: Each sample was weighed and placed in a petri dish and covered with distilled water. After 4 hrs, turgid weight was recorded. The leaves were then oven dried at 70° C for 24 hrs to determine the dry weight. The RWC was computed as: (Fw-Dw)/(Tw- Dw) * 100. LEG: The fresh weight was recorded. Then, leaves were oven dried as described above. The LWC was computed as: (Fw-Dw)/Dw * 100. mg: After the fresh weight was recorded, samples were left uncovered in a dark environment at room temperature for 48 hrs. After 48 hrs, air dry weight (Dw,) was recorded, leaves were oven dried at 70° C for 72 hrs, and the dry weight (Dw,) was recorded. The LWRC was computed as: (Fw-Dw,)/(Fw-Dw,) * 100. mamas Root measurements were made using a minirhizotron camera. Only live roots were counted. This provided information on root distribution along the soil profile. Root growth rate was calculated from root counts of two successive recording dates as follows; [W00 Mahler 0110’ Oct and Iainfa reSllll mm a) Cm dep 27 (root count on date 1 - root count on date 2)/ number of days between date 1 and date 2, which was reported as number of roots/ cm’l day. Each plot had one 6 foot x 2 inch inside diameter tube inserted at a 45° angle into the center row to a depth of 3 feet and measurements were taken, weather permitting, every 30 days. At physiological maturity seed yield and yield components were recorded on the two center rows. The drought intensity index (DII) for the site and the drought susceptibility index (DSI) of each genotype was determined by the method of Fischer and Maurer (1978) (Appendix A). All measured parameters were analysed by MSTAT microcomputer statistical package for agricultural sciences or by the SAS package. RESULTS AND DISCUSSION 5 'l l I . The rainshelter used in 1990 provided moderate moisture stress. Soil water content decreased with increasing drought for the stress and non-stress treatments at all depths (F ig 1). The soil water content was lower for the stress than the non-stress treatment only at the 30 cm depth. At the 60 and 90 cm depths the stress treatment had higher moisture than the non-stress treatment. In 1992, the field had a high water table and rainfall was frequent and excessive during the season. Consequently the access tubes were usually full of water, making it impossible to take readings as scheduled. As a result only two readings were recorded. The stress treatment had higher moisture at the 60 cm depth (Fig 2). There was no difference at the 30 cm depth. Soil Moisture Content (7%) 28 FIG I. VOLUMETRIC SOIL MOISTURE CONTENT IN 1990 0-30 cm depth 2B- Soll Water Content (2) T I I I r I T I r I I I I I 30— 60 cm depth 26 32 28- 5011 Moisture Content (2) r "r T f 'T U T V r I I I' j j 60-90 cm depth HNON-STRESS HSI'RESS 26 t f r ' rrrr'r rr'1 30405060708090100 DAYS AFTER PLANTING Soil Moisture Content (7:) Soil Moisture Content (2.) so, 28- 26 29 FIG 2. VOLUMETRIC SOIL MOISTURE CONTENT IN 1992 0-30 CM DEPTH 301} 28- 'TerW UT—TTj T'fi'TI 30— 60 CM DEPTH \\ \ 26 60 “TV/EFT ’ah' ’ “9‘0 DAYS AFTER PLANTING o—o NON-STRESS o—o STRESS mum 1220 Moisture stress significantly reduced yield of 8-42-M-2 by 51.4 % but had no significant yield reduction on 9-39-1 (Table 1). The genotype 8-42-M-2 yielded significantly higher due to the greater yield of 8-42-M-2 under non-stress conditions. Pods per plant were significantly reduced by stress but seeds per pod did not differ between moisture treatments or genotypes. 1222 In the rainshelter, the genotypes N 81017 and 8-25-2 did not show any differences between stress and non-stress. The drought intensity index was 0.07, indicating that there was essentially no stress. N81017 yielded significantly higher than 8-25-2 (Table 2). When plastic was used, the stress treatment had a significantly higher yield than the non- stress treatment (Table 3), due mainly to 9-39-1 which had a significantly reduced yield under the non-stress treaunent. 1992 was an excessively wet year and the plastic did help to retard moisture penetration. Most of the time the soil was saturated. Often when soil moisture or minirhizotron readings were recorded, water had to be pumped out of the tubes prior to taking readings. The reduced yield of 9-39-1 under non-stress conditions may be due to excess moisture. The low yield of 9-39-1 under the non-stress treatment is considered reduced because the higher yield under stress is consistent with the yield that was obtained for 9-39-1 in 1990 and previous studies (unpublished results). Thus, 9-39-1 may be more susceptible to excess moisture than the other genotypes. The 30 31 firm—rm _. 5.":— E San COB—cocoa.» cm was: 0253.8 5 w woman—.25. w. an Km: arm—6:25. menu 5 m8" 585m. 7:. $8. Omogmflan & imrc RE mmmUm vmw 2:5 mm” 536 EA. ~50 352A. mL~-Z-~ av a a a $8; a 989 a Z w quuh w 9.8..— Amv e m a 530 a 2va e 8 w Bach a a * a. omzavm mL~-Z-~ m c with w Ewe; e c 33b 3 a a G! €>fimw madam a q a 3.: .m a 23-38» a Z w H: _ re a a ** §* No8.— mfg 53b Pa mu manna ZmUH 28.38“ Eu :2 mam—.583 a... s 0523» .39.“ 33:: o 8:55 5:38 «5:583 32288 w. en 93 2. Pa non—c835"; woooamem 8 Dean»: Zea—.5 go do...” 32 45me N. 5a..— Ea 5o:— Oeavoega c... was: 0253.8 5 m worsen—8H a: :5 Km: >m8=e8< 35: 3 m8. 583m. 7:. $3. www.cm vmw 100m 3....” 5916 OmOZmflw—O & Mam—10 E .50 E52... E52. 2394 Amy M a 3 Emma 939 u a 5 Emma 33b 5b «bu-» Amv u a Z Bab 953 a w 5 Saab 536 Pu— + a . 8 094355 2393 u 3 w 33.x w «huh u 3 a Seek a a an * «55mm mnnmm m c 3 32b 28.38..“ a e Z ammuu s B 8 mu manna 756" 28-3% Bu no. finance—z s. + 0533. 582a SEE a 8:55 3&8? amamowa $2238 a: en 93 Q. P— angaea—V. 883mg 8 Dean»: Zane—o ”meme #8". 33 .5»me u. in... BE <55 08:68:88 cm was: 038368 deem 2an a: 9o 75: >m3=o§< $5: 8 m8" 585m. 7:. $3. mmmUm mm” VOUw mm” <=mrU OmOZmfiW—O «a <=wEV E vow 3524. «mama Empz ”mmanEz mL~-Z-~ Amv m o Swab w 2mg u m 53.. as some as who; Amv u 5 53.0 an 959 a a _ mum; a $9— 3.... 23¢: Amv a 3 $38 so 939 u 2 33.8 so 3.3; Pa. m-~m-~ Amv u m 03.4 8 969 m m Eum.m man :28 warm 8 B + Omzoaficm «15-39 m c we Noah w Pub; u q a «arm n 233.» a 5 e 8.3.... we «bub u m a Saab an a an a. «55mm, macaw u 8 m 33.5 a 23.323 u m a $8; 3 EM! * * mu mega ZmUu 23.30% H ecuémmamnwa s. + D522: .32.... £88 a 8:55 5:88 “Liam—8:» Ease—.2: w" on 98 on c._ now—c828? 8838a 8 63—5.. 34 genotypes 8-42-M-2 and N81017 were high yielding and had a low yield reduction under stress. 9-39-1 had the highest yield reduction (Table 3), but it occurred in the non-stress treatment. As reported by others, a significantly high correlation was observed between yield and pods per plant for both seasons (Table 4), (Acosta-Galegos and Shibata, 1989; Acosta—Gallegos and Adams, 1991; Neinhuis and Singh, 1986; Ramirez-Vallejo, 1992). Originally, 8-42-M-2 was thought to be drought resistant and 9-39-1 drought susceptible. The 1990 and 1988 (unpublished) results indicated that 9-39-1 is actually resistant but low yielding and that 8-42-M-2 is high yielding, but susceptible (Table 5), based upon the Fischer drought susceptibility index (DSI). Since no stress occurred in the rainshelter in 1992, only results from the plastic were used to categorize the genotypes. N 81017 was categorized as resistant and 8—25-2 was categorized as susceptible (Table 5). Based on the Fischer index, the geometric mean, the arithmetic mean and % yield reduction under stress a new classification was developed to define all genotypes as follows; 1. Resistant with high yield potential (RH) 2. Resistant with low yield pctential (RL) 3. Susceptible with high yield potential (SH) 4. Susceptible with low yield potential (SL) When the Fischer index was pooled for both seasons, N81017 ranked as a resistant genotype with a high yield potential and 9-39-1 as an average resistant genotype with low “D‘s. I1" ‘ 35 TABLE 4. Yield and Yield Component Correlations Yield PPS Yield -- 0.65 ” PPP -- SPP 1222 Plastic Expt. Yield - -- 0.68'” PPP - SPP Shelter Expt. Yield --- 0.69‘ PPP «- SPP SPP -0.05 -0.23 0.41 0.40 0.27 -0. 12 PPP= Pods per plant SPP= Seeds per pod at: p: 0.05 ** p: 001 *** p= 0.001 36 TABLE 5. Drought Susceptibility Index and Drought Intensity Index RAIN SHELTER PLASTIC EXPT. RAIN SHELTER GENOTYPE 1990 1992 1992 DII 0.36 0.17 0.07 DSI N81017 0.23 1.43 9-39-1 0.14 -... ...- 8—42-M-2 1.42 -_.. «.- 8-25-2 --- 2.06 0.04 DSI: 0.0= Maximum Resistance 1.0= Average Resistance > 1.0= Susceptible - DII: 0.0= No stress 1.0= Maximum stress Pooled Drought Susceptibility Index, 1990 and 1992 N81017 0.8 Resistant 9-39-1 -- 8-42-M-2 2.3 Susceptible 8-25-2 2.2 Susceptible 37 yield potential. 8-42-M-2 ranked as a susceptible genotype with high yield potential and 8-25-2 as a susceptible genotype with low yield potential (Table 5). This classification of genotypes allows for easy evaluation of physiological parameters and determination of yield potential which is important in selecting for high yield. W 1229 RWC was the only leaf water measurement taken. The effect of soil moisture stress on RWC was measured at 19 days after stress was imposed, at flowering and pod development (R,/ R2) stage (Table 6). Subsequent measurements were made at early pod fill stage (R.) and at late pod fill stage (R6), 34 and 47 days after stress was imposed respectively. There were no significant differences between stress and non-stress treatments or between genotypes. The RWC values were generally high, between 83 and 93%. 1222 There was a significant reduction in RWC under stress 13 days after stress was imposed (DAS) and also a genotypic difference at 27 DAS, R,S (Table 8). At 27 DAS, N81017 (resistant and high yielding) had a lower RWC than 8-25-2 (susceptible and low yielding). The other two genotypes. 9-39-1 (resistant and low yielding) and 8-42-M-2 (susceptible and high yielding) were not significantly different from N81017 and 8-25-2. These results suggest that RWC as determined here with a 4 hour imbibition procedure may not distinguish between drought susceptible and resistant genotypes. Results are not conclusive with regard to moisture stress because there was only minimal stress in 1992. .Ll T‘n 7'u-i. I r 38 TABLE 6. The Effect of Soil Water Changes on Relative Water Content in Beans in the Rainshelter at the MSU Agronomy Farm in East Lansing. MI. 1990. W W 1.91 342 47° % 8-42-M-2 (S) 86.5 86.6 89. 1 9-39-1 " 88.3 87.9 88.8 8-42-M-2 (NSD) 85.0 83.4 90.3 9—39-1 " 90.3 86.8 95.2 - ns ns ns GENOTYPE 8-42-M-2 85.6 85.0 89.7 9-39-1 89.3 87.4 92.0 ns ns- ns WATER Stress 87.4 87.3 89.0 Non-stress 87 .6 85. 1 92. 8 ns ns ns S= Stress NSD= Non-stress ns= not significant ‘ Flowering and pod development stage (R1/RQ) 2 Early pod filling stage (R4) 3 Late pod filling stage (R6) .1...— . 39 TABLE 7. The Effect of Soil Water Changes on Relative Water Content in Beans Using Plastic at the MSU Agronomy Farm in East Lansing. MI. 1992. W TREATMENT 2l 132 273 n % N81017 (S) 89.1 80.2 85.8 9-39-1 " 85.8 85.3 89.1 ‘ 8-42-M-2 " 86.7 81.9 86.4 8-25-2 " 89.6 87.7 88.4 N81017 (NSD) 91.5 83.9 88.9 9—39—1 " 92.2 85.9 94.7 8-42-M-2 " 89.6 86.4 93.2 8-25-2 " 88.7 88.4 97.9 ns ns ~ ns GENOTYPE N81017 90.3 82.1 87.3 b 9-39-1 89.0 85.6 91.9 ab 8-42-M-2 88.2 84.1 89.9 ab 8-25-2 89.2 88.0 93.2 a n5 n3 *8! WATER Stress 87.8 83.8 87.4 Non-stress 90.5 86.2 93.7 n5 n5 ltd! S= Stress NSD= Non-stress ns= not significant ***, ", + Different letters within a column indicate significant difference at p= 0.001, 0.01 or 0.1 respectively according to Duncan Multiple Range Test. ‘ Late vegetative stage (V I,) 2 Flowering and pod development stage (Rlle) 3 Pod filling stage (R,/R6) 40 There were also no differences between stress and non-stress treatments or between genotypes in LWRC and LWC (Tables 8 and 9). These parameters need to be assessed in plants grown under greater stress conditions and with an imbibition time that exceeds 4 hours. 399mm Soil moisture stress did not significantly reduce root growth rate (Table 10) but there was a tendency for root growth rate to be reduced under stress in 1990 (14%). The genotype 9-39-1 maintained its root growth rate under stress while 8-42-M-2 had a 25 % reduction. This may partially explain the low yield reduction (4.6%) observed for 9—39-1 compared to the 51% yield reduction for 8-42-M—2 in 1990. Genotypically, 9—39—1 had a lower root growth rate than other genotypes in 1990. It appears that the resistant genotype, 9—39—1 had a lower root growth rate than the susceptible genotype, 8-42- M-2. Figures 3 and 4 show root distribution of 9-39-1 and 8-42-M-2 at 9 and 50 DAS, respectively, in 1990. There was a tendency for more roots under non—stress treatment at all soil depths for both genotypes. At 9 DAS root count was greater in the top 30 cm of the soil for both genotypes. A150 DAS, moisture stress greatly reduced root count at 60-90 cm depth in both genotypes. In 1992 the minirhizotron tubes were placed only up to 60 cm depth because the rocky subsoil made it impossible to push the tubes down. Due to the high water table in this field and excessive rainfall later on, only one reading was taken during the season. At the 30 cm depth, all genotypes except N81017 had greater root count under the non-stress treatment. 9-39-1 and 8-42-M-2 had the same root 41 TABLE 8. The Effect of Soil Water Changes on Leaf Water Retention Capacity in Beans Using Plastic at the MSU Agronomy Farm in East lansing. MI. 1992. W TREATMENT 21 132 2f % N81017 (S) 95.3 96.6 96.8 9-39-1 " 94.6 97.6 97.1 8-42—M—2 " 94.6 94.7 97.6 8-25-2 " 95.1 97.1 98.1 N81017 (NSD) 94.1 97.7 97.5 9-39-1 " 94.6 97.2 98.2 8-42-M-2 " 95.8 97.8 97.8 8-25-2 " 95.6 97.6 97.2 ns ns - ns GENOTYPE N81017 94.7 97.2 97.1 9-39-1 94.6 97.4 97.6 8-42-M-2 95.2 96.2 97.7 8—25-2 95.4 97.6 97.2 ns ns ns WATER Stress 94.9 96.5 97.4 Non-stress 95.0 97.6 97.7 ns ns ns S= Stress NSD= Non-stress ns= not significant ‘ Late vegetative stage (V 5) 2 Flowering and pod development stage (R,/R,) 3 Pod filling stage (Rs/Ra) 42 TABLE 9. The Effect of Soil Water Changes on Leaf Water Content in Beans Using Plastic at the MSU Agronomy Farm in East Lansing. MI. 1992. W 2‘ 132 21’ % N81017 (S) 79.4 82.1 82.8 9-39-1 " 78.3 81.2 81.7 8-42-M-2 " 80.9 82.0 82.5 8-25-2 " 79.7 81.3 81.2 N81017 (NSD) 79.6 81.0 82.7 9-39-1 " 78.8 83.3 83.6 8-42-M-2 " 79.3 81.6 82.8 8-25-2 " 76.9 81.5 82.4 ns ns -- ns GENOTYPE N81017 79.5 81.6 82.8 9-39-1 78.6 82.2 82.7 8-42-M-2 80. 1 81.8 82.6 8-25-2 78.3 81.4 81.8 ns ns ns WATER Stress 79.6 81.7 82.1 Non-stress 78.7 81.9 82.9 ns ns ns S= Stress NSD= Non-stress ns= not significant 1 Late vegetative stage (V 3) 2 Flowering and pod development stage (R,/R,) 3 Pod filing stage (R,/R,) 43 TABLE 10. Root Growth Rate of Bean Genotypes at the MSU Agronomy Farm in East Lansing. MI. 1990. TREATMENT W # of rootslcm’lday 8-42-M-2 (S) 1.28 9-39-1 " 0.94 8-42-M-2 (NSD) 1.72 9-39-1 " 0.86 ns GENOTYPE 8-42-M-2 1.50 9—39-1 0.90 ns WATER - Stress 1.11 Non-stress 1.29 ns S= Stress NSD= Non-stress ns= not significant 44 noun: 3. BEAN ROOT 01511113011011 AT 9 DAS IN 1990 90-1 82- 74-: 66-: 53$ 50; 42-: 345 255- 1a; 101 2.‘ ' - — ED— 821" 9—39-1 roots (count/cmz) 74': 8-42-M-2 ._ .55- 53: so: 1 42.1 34.3 roots (count/cmz) ‘ . :3 Stress 2.. Non-Stress 0-30 30-60 ' 60-80 soil depth (cm) . . - 4S . FIGURE 4. BEAN ROOT DISTRIBUTION AT 50 DAS IN 1990 9-39-1 7/////////////////////////////.1/1/V/////. 7/////////////////////////////////////////////////////////////é 7 t . Z///////////////////////////////////////////42/2 8-42-M-2 12:: Stress L Non-Stress 60-90 F— . 7//////////////////////////////////////////////. d .J u 5 8 O 2 4 5 6 5 5 4. 5 2 m ANEo\ucaooV 300.. e.&...u..h....4.n....r.n...m. 5 5 5 4. 5 2 4| 4| ANEo\uc:oov 300.. 30-60 soil depth (cm) 0-30 46 count under the stress and non-stress treatment at the 60 cm depth. At 6 days before stress was imposed the treatment designated as stress had a reduced root count in N 81017 and a slightly increased root count in 8-25-2 (Fig 5) at 60 cm. As the season progressed, excessive rainfall made it impossible for the plastic to impede moisture so stress could not be maintained and a high water table prevented additional root measurements. None of the root count measurements were significantly different mainly due to the high coefficient of variation that was found. In order to eliminate this problem, more than one tube has to be used per treatment. This was not possible to do in this study because of the small plot size that was used. XielsLdata In 1990, planting occurred late on June 25, in order to obtain a warmer soil temperature. However, cowpea germination was still very poor so they were replanted on July 18. Consequently, their growth period was shortened so they did not reach maturity because frost occurred when the plants had just flowered. Similarly, the 1992 growing season was generally cool and plant growth was slow. Again, frost occurred when the plants were flowering. As a result, there was no yield data for cowpeas in 1990 and 1992. The genOtype BOOS-C was n01 planted in 1992 because of its long maturity. It was a late maturing variety which could not mature during the Michigan growing 8838011. 47 FIGURE 5. BEAN ROOTDIS'TRIBUTION AT -6 DAS IN 1992 9-39-1 4.9.. 8-25-2 7////////////////////////////////////////////// 1 4 - -1- ANEo\u::ooV 33.. .w.w.n a 3-42-11-2 N81017 30-60 soil depth (cm) 0-30 150-80, soil depth (cm) 0-30 cud-d-qqq-dfiqmuz- « a.» a u u 1 1. .ANEo\E:oov 300.. CDSI'RESS m 11011-311133 . . 48 ' ., , FIG 6. COWPEA ROOT DISTRIBUTION AT -‘I DAS IN 1990 TVX 3236 BOOS-C [:21 Stress . Non-Stress 30-60 I soil depth (cm) 32- . . _ 4. 5 2 4| ANEo\E:ooV 300.. . .ANEo\E:ooV 300.. 60-80 0-30 49 mm In 1990 RWC was measured at three growth stages; early vegetative (V,), late vegetative (V 9) and flowering (R1) stages under stress and non-stress soil moisture conditions. No differences were observed with the water treatments or the water x genotype interaction (Table 11). TVX 3236 had a significantly higher RWC than BOOS-C 4 days before stress was imposed. In 1992 stress significantly reduced RWC only at the pod filling stage, 27 DAS (Table 12). There were genotypic differences at all sampling dates. Blackeye consistently had lower RWC than the other genotypes. Similarly, stress significantly reduced LWC only at 27 DAS. There were genotypic differences at all sampling dates (Table 13). Soil moisture stress decreased LWRC at 13 DAS (Rlle) and at 27 (Rs/R.,) days after stress was imposed (Table 14). There were no genotypic differences. There was no pattern in the response of the genotypes in RWC or LWC. TVX 3236 had a significantly higher RWC and LWC than Blackeye at all sampling dates. W In 1990, BOOS-C had a significantly higher root growth rate than TVX 3236 (Table 15). Figures 6 and 7 show root distribution a day before stress was imposed and at 27 DAS respectively, in 1990. Both genotypes had more roots under the non-stress treatment at all depths except BOOS-C at the 80 cm depth at 27 DAS (Fig 7). None of the differences was statistically significant. In 1992, 6 days before stress was imposed there were more roots under the treatment designated as stress at 60 cm for all genotypes (Fig 8). The soil was highly saturated. it was not possible to take soil moisture or “‘1' 50 TABLE 11. The Effect of Soil Water Changes on Relative Water Content in Cowpeas in the Rainshelter at the MSU Agronomy Farm in East Lansing. MI. 1990. W TREATMENT -41 112 243 % BOOS-C (S) 89.7 91.7 93.7 TVX 3236 " 95.2 93.9 95.9 B005-C (NSD) 92.7 91.9 90.9 TVX 3236 " 95.8 94.7 95.1 - ns ns ns GENOTYPE BOOS-C 91.2 91.8 92.3 TVX 3236 95.5 94.3 95.5 It 113 - n3 WATER Stress 92.4 92.8 94.8 Non-stress 94.2 93.3 93.0 ns ns ns S = Stress NSD= Non-stress ns= not significant ** p(0.01) ‘ Early vegetative stage (V,) 2 Late vegetative stage (V a) 3 Flowering and pod development (RI/R9 TAI 51 TABLE 12. The effect of Soil Water Changes on Relative Water Content in Cowpeas Using Plastic at the MSU Agronomy Farm in East Lansing. MI. 1992. W 22 TREATMENT 2‘ 132 % TVX 3236 (S) 87.0 89.4 90.3 ab BLACKEYE " 80.9 83.1 82.1 c ER, " 81.4 84.4 87.1 bc IT838-742-2 " 81.9 86.5 84.4 c TVX 3236. (NSD) 88.5 87.7 92.2 ab BLACKEYE " 80.9 79.9 94.1 a ER7 " 82.8 84.2 95.4 a IT83S-742-2 " 88.9 87.0 91.8 ab ns ns * GENOTYPE TVX 3236 87.8 a 88.5 a 91.2 a BLACKEYE 80.9 b 81.5 c 88.1 b ER, 82.1 ab 84.3 be 91.2 a IT83S-742-2 85.4 ab 86.8 ab 88.1 b It *** *1 WATER Stress 82.8 85.9 86.0 Non-stress 85.3 84.7 93.4 n3 n3 till! S= Stress NSD= Non-stress ns= not significant ' ***, **, *, * Different letters within a column indicate significant difference at p= 0.001, 0.01, 0.05 or 0.1 respectively according to Duncan Multiple Range Test. 1 Late vegetative stage (V 8) ’ Flowering and pod development stage (R1/Ra) 3 Pod filling stage (R,/R,) TAB If? 1111 131.11 E117 11835 wx BLAC ER, 11333 T171 : BLAC £11, 0835 Stress Non-S1 52 TABLE 13. The Effect of Soil Water Changes on Leaf Water Content in Cowpeas Using Plastic at the MSU Agronomy Farm in East Lansing. MI. 1992. IREAIMENT 21 132 27: % TVX 3236 (S) 85 .4 86.1 85.1 BLACKEYE " 81.6 84.3 83.9 ER, " 81.8 84.1 84.4 IT83S-742-2 " 82.1 83.5 84.4 TVX 3236 (NSD) 85.3 85.9 85.8 BLACKEYE " 80.1 84.0 84.6 ER, " 81.8 84.7 85.5 IT83S-742-2 " 82.8 84.6 85.9 ns ns ns GENOTYPE TVX 3236 85.3 a 86.0 a 85.4 a BLACKEYE 80.9 b 84.1 b 84.3 b ER, 81.8 b 84.4 b 84.9 ab IT83S-742-2 82.4 ab 84.0 b 85 .1 a t t 4- WATER Stress 82.7 84.5 84.4 Non-stress 82.5 84.8 85 .4 n5 n5 *8! S= Stress NSD- Non-stress ns= not significant *"', 1‘, 1 Different letters within a column indicate significant difference at p= 0.01, 0.05 or 0.1 respectively according to Duncan Multiple Range Test. 1 Late vegetative stage (V8) 1 Flowering and pod development stage (R,/R,) 1 Pod filling stage (R.,/R6) 53 TABLE 14. The Effect of Soil Water Changes on Leaf Water Retention Capacity in Cowpeas at the MSU Agronomy Farm in East Lansing. MI. 1992. TREATMENT 21 1i 27’ % TVX 3236 (S) 96.7 96.0 97.4 BLACKEYE " 96.7 97.7 96.0 ER. " 96.6 95.4 97.5 IT838-742-2 " 97 .7 96.8 96.4 TVX 3236 (NSD) 97.4 98.2 97.6 BLACKEYE " 96.3 98.2 97.8 ER, " 96.8 97.9 98.3 IT83S-742-2 " 97.2 98.7 98.3 ns ns ns GENOTYPE ~ TVX 3236 97.0 97.1 97.5 BLACKEYE 96.5 98.0 96.9 ER, 96.7 96.6 97.9 IT83S-742-2 97.5 97.8 97.4 ns ns ns WATER Stress 96.9 96.5 96.8 Non-stress 96.9 98.3 98.0 ns #11! IN”! S= Stress NSD= Non—stress ns= not significant 1""- p(0.001) 1 Late vegetative stage (V ,) 1 Flowering and pod development stage (R1/R¢) 3 Pod filling stage (R,/Rg) 54 TABLE 15 . Root Growth Rate of Cowpea Genotypes at the MSU Agronomy Farm in East Lansing. MI. 1990. IREAIIMENT REMED— BOOS-C (S) 2.77 TVX 3236 " 0.98 BOOS-C (NSD) 3.71 TVX 3236 " 1.57 ns GENOTYPE BOOS-C 3.24 TVX 3236 1.28 * WATER Stress 1.88 - Non-stress 2.64 ns S= Stress NSD= Non-stress ns= not significant * p= 0.05 55 FUZWRWTWHfiMSNIM a,” a . M m . M 1m, r 11 1 Fl wrct g? m éeéééwm m H HI! w .w m..w. w . m. m .J.. w.w.w.w.w.m.w.m.m.mfl Aqu>cae$ 302 ANEobeaeov 33.. 4 2 8 a 1 ANEO\¢CJOOV .500”. 4.. 2 8.. - a... 1 AN.E0\~C300V DuOOK O. 56 flG 6. COWPEA ROOT DISTRIBUTION AT -6 DAP IN 1992 "335-742-2 321 24- 11s- a 1 24- ANEo\E:ooV 300m DSTRESS -NON-STRESS BA”) mm b .n. m M... Ma... mm .w .5 (w .h. .... m n .1 Mn... m Ea a q — I - “.1 .r 8 O 2 1 QEo\ucaoov 300m 57 minirhizotron readings without first pumping out the water. MW At 13 and 41 DAS (68 and 86 DAP respectively) the non-stress treatment had a lower leaf temperature than the stress treatment and had a lower soil temperature 2 days before stress was imposed and at 25 DAS. Both probably contributed to the slow plant growth rate that was observed in 1992 (Fig 9). The arrows in the graphs indicate when moisture stress was imposed (55 DAP). SUMMARY RESPONSE UNDER MOISTURE STRESS EARAMEIER BEANS - COWPEAS Yield components PPP1 * SPP2 ns Leaf water (RWC, LWRC, LWC) * * Root growth ns ns 1 PPP= Pods per plant 1 SPP= Seeds per pod Temperature (00) Temperature (°C) 58 FIG 9. COWPEA SOIL AND LEAF TEMPERATURE IN 1992 241 Sell Temp. 16 f t f r *1 24.-1 Leaf Temp. 4 13" H NON-STRESSED H STRESSED 16 F I 1 f j 50 60 7O 80 90 100 Days After Planting CONCLUSIONS Soil moisture sn'ess decreased seed yield, especially through decreased number of pods per plant in beans. The number of seeds per pod was insensitive to water stress. It seems that bean yield can best be improved by maximizing the number of pods per plant. The wwpea genotype, Blackeye consistently had a lower RWC in 1992. The high yielding resistant genotype (N81017) had the lower RWC in beans on the last sampling date of 1992. Leaf water content provided genotypic and stress treatment differences in bean and cowpea in 1992. Results are inconclusive with regard to the use of these measurements as screening tools for drought resistance due to minimal moisture stress in 1992. The tests need to be repeated in an environment which can guarantee moisture stress. ' Soil moisture stress in 1990 reduced root growth rate in both bean and cowpeas. Resistant bean genotypes had a lower reduction in root growth rate than susceptible genotypes. In general, root count decreased with increasing soil depth and stress. In beans, resistant genotypes had more roots than susceptible genotypes. There was no pattern between root growth and yield potential of the genotypes. There was no genotypic pattern of root growth in cowpeas. Root growth analysis can be a useful tool when used to explain the response of a genotype in beans; however, the minirhizotron technique does not make it feasible to be used on a large number of cultivars because of the amount of work and time involved with the minirhizotron installation and data collection. The minirhizotron technique also requires that a large number of tubes be installed for each 59 60 plot in order to reduce the coefficient of variation. This is not practical for examining large numbers of lines. The resistant genotypes performed better than the susceptible genotypes in terms of yield and root growth. This shows the need to categorize genotypes according to their resistance and yield potential in order to successfully evaluate parameters that can be used as screening tools. Others have used plastic to impose moisture stress successfully. However, in this study the use of plastic to impose moisture stress was not effective. The plastic conserved moisture and therefore did not impose moisture stress. Thus, when the plastic was pulled back, there was moisture on the soil surface. Water also went in between the plants since that space was not covered with plastic. The plastic only covered between the rows and not between plants within a row. REFERENCES Acosta-Gallegos J. A. A., Shibata J. K. 1989. Effect of water stress on growth and yield of indeterminate dry beans (2mm mm L.) cultivars. Field Crops Res. 20:81-93. Acosta-Gallegos I. A. A., Adams M. W. 1991. Plant traits and yield stability of dry bean (Ehasmlns mans L.) under drought stress. J. Agric. Sci. 117:213—219. Akyeampong M. P., Steponkus P. L. 1981. Yield responses of cowpeas to a drought stress. Agron Abstracts. 73"1 Ann. Meeting. Am. Soc. Agron. 78. Bonanno A. R., Mark H. J. 1983. Yield components and pad productivity of snap beans grown under differential irrigation. J. Amer. Soc. Hort. Sci. 108(3):832-836. Clacke J. M., McCaig T. 1982. Excised-leaf water retention capability as an indicator of drought resistance of 112111911111 genotypes. Can. J. Plant SCi. 62:571-578. Clarke J. M. 1983. Differential excised leaf water retention capabilities of 112111911111 cultivars grown in field and controlled environments. Can. J. Plant Sci. 63:539-541. Garay A. F., Wilhelm W. W. 1983. Root system characteristics of two soyabean isolines undergoing water stress conditions. Agro. J. 751973-975. Meckel L., Egli D. 8., Phillips R. E., Radcliffe D., Leggette J. E. 1984. Effect of moisture stress on seed growth in soyabean. Agron. I. 76:647-650. Muchow R. C. 1985. Phenology. seed yield and water use of grain legumes grown under different soil water regimes in a semi-arid tropical environment. Field Crops Res. 11:81- 97. Niehuis 1., Singh S. P. 1986. Combining ability analysis and relationships among yield, yield components, and architectural traits in dry bean. Crop Sci. 26:21-27. Ramirez-Vallejo R. P. 1992. Identification and estimation of heritabilities of drought related resistance traits in dry bean (2113301115 2111231115 L.). Ph.D Dissertation. Michigan State University. Sponchiado B. N., White I. W., Castillo l. A., Jones P. G. 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 C. J., Davis W. I. 1991. Drought induced closure of 13225291115 Maris L. Stomata preceeds leaf water deficit and any increase in xylem ABA concentration I. 61 62 Expt. Botany 42:1507-1515. White J. W. , Castillo J. A. 1989. Relative effect of root and shoot genotypes on yield of common bean under droughtstress. Crop Sci. 29:360-362. CHAPTER2 THE EFFECT OF SOIL MOISTURE STRESS ON DRY BEANS (Ehamlns Mantis L.) AND COWPEAS (liens W L. (walp)). II. Photosynthesis, Light Interception, Stomatal Conductance, Transpiration Ratio and Carbon Isotope Discrimination. ABSTRACT Soil water changes affect crop canopy and hence the amount of light intercepted by a crop and assimilate production. The objective of this study was to investigate the effect of soil water deficit on changes in light interception, photosynthesis, stomatal conductance, transpiration ratio and carbon isotope discrimination. The study was carried out in the field using either a rainshelter or black polyethylene plastic to impose terminal drought stress at the late vegetative growth stage (V 9). Photosynthetic rate was reduced by severe water stress in both beans (Phaseohrs yulgaris L.) and cowpeas (Kim W L. (walp)). Stomatal conductance was not affected by moisture stress in beans but was reduced by 33 % in cowpeas. There were no genotypic differences for photosynthetic rate in beans or cowpeas but there were genotypic differences for stomatal conductance. Moisture stress decreased transpiration ratio in beans but increased it in cowpeas. Soil moisture stress did not affect carbon isotope discrimination in either species but there were genotypic differences in beans. Drought resistant bean genotypes had lower CID values than drought susceptible bean 63 64 genotypes and CID was positively correlated to yield in beans. INTRODUCTION Photosynthesis plays an important role in dry matter production and subsequently yield. Genotypic variability in photosynthesis per unit leaf area may be useful in increasing gross productivity of crop plants and as a screening tool if it can be demonstrated to be measurable and related to growth in field studies and if it is physiologically linked to compensating differences in leaf area production (Mahon, 1990). 1 Although severe drought affects plant growth in many ways, the response of photosynthesis to water deficits has gained special attention. The main reason is that the stomates respond very early to changes in humidity or water stress and thereby often decrease the rate of photosynthesis long before the leaf water status has changed (Kaiser, 1987). Stomatal movements provide the leaf with opportunity to change both the partial pressure of CO2 at the sites of carboxylation and the rate of transpiration. In turn, changes in transpiration rate can cause changes in the temperature and water potential of the leaf (Farquhar and Sharkey, 1982). Studies have shown that leaf conductance decreased with decreasing soil water content in wheat (Ifitigun mm L.) and sunflower (Helm mm; L.) (Gollan et al, 1986). Blackman and Davis (1985) reported similar observations in maize (Zea mays L.). The objective of this study was to investigate the effect of soil water changes on photosynthesis, stomatal conductance, transpiration ratio, light interception, and carbon 65 isotope discrimination in beans and cowpea. MATERIALS AND METHODS A field study was conducted at the Agronomy Research Farm at Michigan State University in East Lansing during the summers of 1990 and 1992. In 1990 a rainshelter was used to impose moisture stress at 37 DAP. In 1992, black polyethylene plastic was placed between the rows to impose moisture stress at 58 DAP. Moisture stress was initiated at the late vegetative growth stage (V 9) for both years but this stage occurred at different DAP due to the different environmental conditions each year. The soil type for the 1990 experiment was a fine loamy, mixed mesic aeric ochroqualfs with a slope of 0-3 % (USDA Soil Conservation Service Classification). For the 1992 experiment, it was a fine loamy, mixed mesic glossoboric hapluidalfs with a slope of 2-6%. The rainfall and temperature data are presented in Fig 1 and Table 1 of Appendix A. The experimental design was a modified split plot with four replications. Moisture stress was the main plot and genotypes were the subplot. The moisture factor was confounded by site difference in that all stressed plots were grouped together and all non- stressed plots were grouped together. Each plot had four rows of 2 m length. The bean spacing was 50 x 10 cm and the cowpea spacing was 75 x 20 cm which resulted in a plant density of 20 plants per m1 for beans and 10 plants per m1 for cowpeas. In 1990, two bean genotypes (9-39-1 and 8-42-M-2) and two cowpea genotypes (TVX 3236 and B005-C) were used. In 1992 four bean genotypes (9-39-1, 8-42-M-2, N81017 and 8-25- 1m». v.4" I' .- a 66 2) and four cowpea genotypes (TVX 3236, Blackeye, ER-,, IT838-742-2) were used. The bean genotypes were chosen based upon their performance in the MSU bean breeding program as either being drought reSistant or susceptible. The cowpea genotypes were chosen based upon their performance from a preliminary growth chamber study conducted in 1989 and based upon their performance at IITA and in Botswana. Genotypic description are presented in Table 2 of Appendix A. All plots were hand planted using a hoe to open rows. Party or 20 swds per row were planted for beans and cowpeas respectively, with abundant inoculant. The bean moculumwasngbmmphmliandmecowpeamoculumwasRhimbimncowpea miscellany nitrogen EL. BMW 1 12%) Both beans and cowpeas were planted on June 25 but because of poor germination, cowpeas were replanted on July 18. Fertilizer was applied as 19-19-19 at the rate of 40 Kg N/ha before planting. Three days after planting, on June 28 all plots received 30 mm of irrigation to facilitate germination. The total rainfall during the growing season (June 25-Oct 5) was 287.6 mm. On July 31, Sevin (Carbaryl insecticide) was applied at the rate of 4 teaspoons per gallon of water to control Mexican bean beetle and leafhopper. 1222 Planting occurred on June 12. The fertilizer (21-7-14) with 4% Mn and 1% Zn was applied at the rate 42 pounds N per acre before planting. All plots received a total 67 of 283.3 mm of irrigation in four applications before stress was imposed. The total rainfall during the growing season (June lZ-Sept. 16) was 309.0 mm. A greater amount of irrigation was applied in 1992 in order to break the soil crust, enhance germination and facilitate stand establishment. Sevin was applied on July 29 to control leafhopper. Soil moisture was monitored regularly in all plots at three depths in 1990 (0-30, 30—60, 60-90) using a neutron probe. In 1992 readings were only recorded at the 0-30 and 30-60 cm depths because the field had a high water table. Undisturbed soil core samples were taken at the same depths to develop a soil moisture desorption curve which was used to convert the volumetric moisture content into matric potential. W Three plants per plot were tagged and measurements were taken from these plants on the uppermost fully expanded leaf. The ADC-LCA 2 photosynthesis system (The Analytical Development Co. Ltd.. Hoddesdon. UK) was used under the following conditions (flow rate= 400 ml m", leaf temperature= 30:1;2 °C, vapor pressure deficit (VPD)= 3 kPa, ambient CO,;t10 ml 1‘, and photosynthetically active radiation (PAR)21000 nmol m“2 s"). The leaf was enclosed in a leaf chamber and exposed to incoming solar radiation. All readings were recorded at approximately the same photosynthetically active radiation (PAR). Each reading took approximately 30 seconds before a stable value was recorded. Measurements were taken between 10 am and 2 pm EDT on a cloudless day. Photosynthesis, stomatal conductance and transpiration ratio were calculated from a program developed by Moon and Flore (1986), (Appendix Bl). Liam. Devic: rcflec1 or 2.01 intero 2 pm Stages M grow each leave drier 1110 i ”U /.~;r W111 68 I . I I . Light interception was measured in 1992 using the Sunfleck Ceptometer (Decagon Devices, Inc. Pullman. Wa). The amount of incident radiation transmitted to and reflected by the crop canopy were measured by placing the ceptometer horizontally below or above the crop canopy and calculations were made to determine the fractional light intercepted by the canopy (Appendix B2). Measurements were taken between 10 am and 2 pm EDT on a cloudless day at flowering (R1) and early pod development (R1) growth stages. C l I D' . . . Samples for carbon isotope discrimination were taken during the pod filling growth stage (R,) on five plants per plot only in 1992. Five leaves were sampled from each plant so 25 leaves were sampled from each plot. The uppermost fully expanded leaves were detached and samples were bulked for each plot. The samples were oven dried at 60°C for five days before grinding. The samples were sent to Isotope Services, Inc in Los Alamas, NM, USA for analysis via mass spectrometry. RESULTS AND DISCUSSION W In 1990, moisture stress did not affect photosynthetic rate until later in the season when the stress period had been in effect for 41 days (Table 1). Drought stress reduced .r—ml-‘m-Iea. .g. VI .' v 69 photosynthesis by 38 % . Comic et al. (1987) demonstrated that when bean plants were exposed to a rapid or slow drought cycle, photosynthetic rate declined and upon rewatering it increased. Similarly a 40 % decrease in net photosynthetic rate with decreasing soil water potential has been reported in cotton (fiassynium hm L.) (Plant and Federman, 1990). There were no genotypic differences in the rate of photosynthesis (Table 1). There were no differences between the stress and non-stress treatments or between genotypes in 1992 (Table 2). The drought intensity index (Fischer Index) in 1992 was 0.17, indicating that there was mild drought stress. Light interception was significantly higher under the plastic covered stress treatment at 11 DAS (Table 3). Nunez-Barrios (1991) observed a reduction in light interception during drought in beans. The observed increase in light interception understress is probably related to the fact that there was minimal moisture stress in 1992 and because the plastic covered stress plots had an added advantage of warmer soil temperature (Fig 1) during the latter part of the season (25 DAS), helping facilitate growth. Arrows in Figure 1 indicate the time when stress was imposed (55 DAP). The stress treatment also had a slightly higher leaf temperature at 47 DAS. The genotype 8-42-M-2 intercepted more light than the other genotypes. I . . B . In 1990, at 41 DAS (Table 4), the stress treatment had a significantly lower transpiration ratio than the non-stress treatment. This corresponds with the lower photosynthetic rate in the stress treatment at 41 DAS (Table 1). In 1992 there were no significant differences between stress and non-stress treatments except at l DAS where 70 TABLE 1. The Effect of Soil Water Changes on CO2 Assimilation Rate in Beans in the Rainshelter at the MSU Agronomy Farm in East Lansing. MI. 1990. W TREATMENT 61 271 411 pmols m'1 s‘1 8-42-M-2 (S) 10.8 8.1 6.0 9-39-1 " 11.0 7.9 4.6 8-42-M-2 (NSD) 13.5 6.9 8.4 9-39-1 " 10.5 7.2 8.9 ns ns ns . GENOTYPE _ 8-42-M-2 12.1 7.5 7.2 9-39-1 10.8 7.5 6.8 ns ns ns WATER - Stress 10.9 8.0 5.3 Non-stress l 1.9 7.0 8.6 ns ns * S= Stress NSD= Non-stress ns= not significant * p= 0.05 1 Late vegetative stage (V9) 1 Flowering and pod development stage (RI/R2) 1 Pod filling stage (R5) ESPE SQPS Sgbg 71 TABLE 2. The Effect of Soil Water Changes on CO2 Assimilation Rate in Beans Using Plastic at the MSU Agronomy Farm in East Lansing. MI. 1992. W TREATMENT 11 152 nmols m‘1 s'1 8-42-M-2 (S) 12.4 7.9 9-39-1 " 13.9 9.1 N81017 " 13.3 6.5 8-25-2 " 14.3 8.8 8-42-M-2 (NSD) 12.0 8.3 9-39-1 . " 11.4 6.9 N81017 " 11.1 9.3 8-25-2 " ' 14.9 9.7 ns ns GENOTYPE - 8-42-M-2 12.2 8. 1 9-39-1 12.6 8.0 N81017 12.2 7.9 8-25-2 14.6 9.2 ns ns WATER Stress 13.5 8.1 Non-stress 12.3 8.5 ns ns S== Stress NSD= Non-stress ns= not significant ‘ Late vegetative stage (V9) 1 Flowering and pad development (Rlle) N 811 9-39- 8-42‘ N8lI 9-39 8-25 N811 9-39 842 8-25 8065 Non. ‘72 TABLE 3. The Effect of Soil Water Changes on Light Intercepted by Beans at the MSU Agronomy Farm in East Lansing. MI. 1992. W TREATMENT 41 112 % N81017 (S) 67.4 83.3 9-39-1 " 74.3 81.4 8-42-M-2 " 82.3 89.7 8-25-2 " 70.8 80.8 N81017 (NSD) 77.9 76.8 9-39-1 " 66.5 74.4 8-42-M-2 " 81. 1 87.0 8-25-2 " 74.9 79.0 ns - ns GENOTYPE N81017 72.6 80.1 b 9-39-1 70.4 77.9 b 8-42-M-2 81.7 88.4 a 8-25-2 72.8 79.9 b n8 III WATER Stress 73.7 83.8 a Non-stress 75.1 79.3 b m + S= Stress NSD= Non-stress ns= not significant *, 1 Different letters within a column indicate significant difference at p= 0.05 or 0.1 respectively according to Duncan Multiple Range Test. 1R1 2 R2 24 ”a c 2 «1H AUOV Quay—01.00505. II . 2 2 A00» 0L3~OL0QEUF 1 Temperature (°C) Temperature (00) ' 22- 24- 22- 20- 16- I6 . 73 FIGURE 1. BEAN SOIL AND LEAF TEMPERATURE IN 1992 51:11 Temp. 241 20- 18- Leaf Temp. 1' F T r _‘I 60 70 so 90 100 Days After Planting 1 74 TABLE 4. The Effect of Soil Water Changes on Transpiration Ratio in Beans in the Rainshelter at the MSU Agronomy Farm in East lansing. MI. 1990. W W 61 271 413 mol H,O/ mol CO2 8-42-M-2 (8) 417.6 644.4 268.8 9-39-1 " 481.3 531.3 227.0 8-42-M-2 (NSD) 403.2 482.2 384.0 9-39-1 " 469.0 527.2 445.2 - ns ns ns GENOTYPE 8-42-M-2 410.4 563.3 324.9 9-39-1 475.1 529.2 336.1 ns -ns ns WATER Stress 449.5 587.8 247.9 Non-stress 436. 1 504.7 414.6 ns ns * * P= 0.05 S= Stress NSD= Non-stress ns= not significant 1 Late vegetative stage (V9) 1 Flowering and pad development (R,IR:) 1 Pod filling stage (R5) —— ”la FE $118. the und SUE. sea: res; any 11011 diff soy] and USC 33 d 1ndl< Cart 75 stress increased the transpiration ratio (Table 5). amalgam: In 1990 soil moisture stress had no effect on stomatal conductance and there were no genotypic differences. A water x genotype interaction was significant at 6 DAS (Table 6). The resistant genotype, 9-39-1 maintained stomatal conductance under stress while the susceptible genotype, 8-42-M-2, significantly decreased its stomatal conductance under stress. This may have contributed to the high yield reduction for 8-42-M-2, suggesting that stomatal conductance was limiting under moisture stress early in the season. Trejo and Davis (1991) showed an early reduction in stomatal conductance in response to soil drying in beans. In young bean seedlings stomata started to close before any leaf water deficit was detected. In 1992 there were no differences between stress and non-stress treatments or between genotypes (Table 7). C I I 11° . . . Carbon isotope discrimination was not affected by water stress but genotypic differences were observed (Table 8). Genotypic variability in CID has been reported in soybeans (Glycine mg; L.) (Ashley, 1991) and peanuts (Armenia hymgaea L.) (Brown and Bryd, 1991). In 1992, 9-39-1 had a lower CID value than N81017 and 8-25-2. The use of CID as a determining factor would have selected 9-39-1, a low yielding genotye, as desirable whereas N 81017 is the more desirable genotype. These results, seem to indicate that CID can not separate low yielding genotypes from higher yielding ones. Carbon isotope discrimination was positively and significantly correlated to yield. 76.1 TABLE 5 . The Effect of Soil Water Changes on Transpiration Ratio in Beans Using Plastic at the MSU Agronomy Farm in East Lansing. MI. 1992. W IREATMENI 11 111 mol HZOI mol CO2 8-42-M-2 (S) 349.5 488.7 9-39-1 " 275.9 325.7 N81017 " 370.9 867.3 8-25-2 " 317.7 375.4 8-42-M-2 (NSD) 294.7 347.7 9-39-1 -" 297.6 351.4 N81017 " 310.9 296.3 8-25-2 " 261.4 284.6 ns ns GENOTYPE - 8-42-M-2 322. 1 418.2 9-39-1 286.8 338.6 N81017 340.9 581.8 8-25-2 289.5 330.0 ns ns Stress 328.5 514.3 Non-stress 291 .2 320.0 * ns S= Stress NSD= Non-stress ns= not significant 1 p= 0.1 1 Late vegetative stage (V 9) 1 Flowering and pod development (R,/R,) TABLE (1 77 TABLE 6. The Effect of Soil Water Changes on Stomatal Conductance in Beans in the Rainshelter at the MSU Agronomy Farm in East Lansing. MI. 1990. W TREATMENT 61 27; 411 mmols m’1 s’1 8-42-M-2 (S) 169.9 b 79.9 66.9 9-39—1 " 209.9 ab 64.8 45.0 8-42-M-2 (NSD) 250.5 a 46.8 87.7 9-39-1 " 170.1 b 61.8 72.9 . * ns ns GENOTYPE 8-42-M-2 210.2 63.4 77.3 9-39-1 190.0 63.3 59.0 ns -ns ns WATER Stress 190.0 72.3 56.0 Non-stress 210.3 54.3 80.3 ns ns ns S= Stress NSD= Non-stress "‘ Different letters within a column indicate significant difference at p= 0.05 ns= not significant according to Duncan Multiple Range Test 1 Late vegetative stage (V9) 1 Flowering and pad development (RI/R.) 3 Pod filling stage (R5) TABLE :1 (T1 3’13 l. 842M- 139-1 N81017 1.25.2 3-42-M-1 9-39-1 N81017 8-25-2 842-111 1391 N81017 8252 311635 Non'Sfl’eS 7,8 TABLE 7. The Effect of Soil Water Changes on Stomatal Conductance in Beans Using Plastic at the MSU Agronomy Farm in East lansing. MI. 1992. WW TREATMENT 11 151 mmols m’1 s‘1 8-42-M-2 (S) 133.1 . 85.6 9-39-1 " 132.1 69.5 N81017 " 151.0 73.4 8-25-2 " 140.4 78.5 8-42-M-2 .(NSD) 128.5 83.9 9-39-1 " 115.8 71.1 N81017 " 120.0 81.6 8-25-2 " 144.9 80.3 ns - ns GENOTYPE 8-42-M-2 130.8 84.7 9-39-1 123.9 70.3 N81017 135.5 77.5 8-25-2 142.7 79.4 ns ns WATER Stress 139.1 76.7 Non-stress 127. 1 79.2 ns ns S= Stress NSD= Non-stress ns= no significant 1 Late vegetative stage (V 9) 1 Flowering and pod development (kl/R2) TA 79 TABLE 8. The Effect of Soil Water Changes on Carbon Isotope Discrimination in Beans Using Plastic at the MSU Agronomy Farm in East Lansing. MI. 1992. TREATMENT Delta N81017 (S) 20.5 9-39-1 " 20.0 8—42-M-2 " 20.4 8-25-2 " 20.5 N81017 (NSD) 21.4 9-39-1 " 19.1 8-42-M-2 " 20.1 8-25-2 " 21.1 ns GENOTYPE N81017 21.0 a - 9-39-1 19.6 b 8-42—M-2 20.2 ab 8-25-2 20.8 a WATER Stress 20.4 Non-stress 20.4 ns S= Stress NSD= Non-stress ns= not significant * Different letters within a column indicate significant difference at p= 0.05 according to Duncan Multiple Range Test I; O (Tal The pho red1 in 11 gem and in re Whe: light 1111811 Bhnmnthssis In 1990, moisture stress significantly reduced photosynthetic rate at 4 and 18 DAS (Table 9). TVX 3236 had significantly higher photosynthetic rate than BOOS-C at 4 DAS. The genotype x water level interaction was significant only at 18 DAS (Table 9). The genotype TVX 3236 was more sensitive to moisture stress with a 46 % reduction in photosynthetic rate while BOOS-C had a 23 % reduction. Littleton et al. (1981) found reduced photosynthetic rate in cowpeas under water shortage. A 59% reduction in photosynthetic rate by cowpeas due to moisture stress has also been reported by Hall et al. (1992): In 1992, there were no differences between stress and non-stress treatments but genotypic differences were observed at 15 DAS (Table 10). Blackeye had the lowest photosynthetic rate. I . I I . There were no differences between the stress and non-stress treatments in 1992 in the amount of light intercepted, but Blackeye intercepted more light than the other genotypes at 11 DAS (Table 11). A14 DAS under the non-stress treatment, TVX 3236 and IT83S-742-2 had negative light interception. This is because they performed poorly in terms of canopy development. They were upright with very little canopy cover so when the readings were recorded for the amount of light reflected above and below the canopy, there was very little difference between the two readings. This translated as high light transmission through the canopy and low light interception. Therefore when light interception was calculated (Appendix 82) it was negative. Blackeye had a low 80 TA] JCT? 31.- TABLE 9. The Effect of Soil Water Changes on CO2 Assimilation Rate in Cowpeas in the Rainshelter at the MSU Agronomy Farm in East Lansing. MI. 1990 W TREATMENT -171 41 181 umols m'1 S'1 BOOS-C (S) 12.0 11.7 10.1 c TVX 3236 " 12.5 17.2 8.9 c BOOS-C (NSD) 13.2 17.5 13.1 b TVX 3236 " 13.1 19.8 16.6 a - ns ns * GENOTYPE BOOS-C 12.6 14.6 b 11.6 TVX 3236 12.8 18.5 a 12.7 as r "' ns WATER Stress 12.2 14.4 b 9.5 b Non-stress 13.1 18.6 a 14.9 a ITS I: It S= Stress NSD= Non-stress *, * Different letters within a column indicate significant difference at p= 0.05 ns= not significant or 0.1 respectively according to Duncan Multiple Range Test 1 Early vegetative stage (V 3) 1 Late vegetative stage (V7) 1 Flowering stage (R1) 82 1' TABLE 10. The Effect of Soil Water Changes on CO2 Assimilation Rate in Cowpeas Using Plastic at the MSU Agronomy Farm in East lansing. MI. 1992. W EBATMENT 11 151 umols m‘1 s1 TVX 3236 (S) 14.7 14.6 BLACKEYE " 11.9 4.5 BR, " 12.8 9.7 TT83S-742-2 " 13.9 10.6 TVX 3236 (NSD) 14.2 12.0 BLACKEYE " 12.6 6.0 BR, " 13.2 8.6 TT83S-742-2 " 1 1.6 10.2 ns ns . GENOTYPE TVX 3236 14.4 13.3 a BLACKEYE 12.2 5.3 c ER, 13.0 9.2 b IT838-742-2 12.7 10.4 ab “5 *tdI WATER Stress 12.9 9.2 Non-stress 13.3 9.8 ns ns S= Stress NSD= Non-stress ns= not significant *** Different letters within a column indicate significant difference at p= 0.001 according to Duncan Multiple Range Test. TABLE 83' TABLE 11. The Effect of Soil Water Changes on Light Intercepted by Cowpeas at the MSU Agronomy Farm in East lansing. MI. 1992. W WENT 41 111 % TVX 3236 (S) 21.0 a 1.6 c BLACKEYE " 8.7 a 18.7 ab ER, " 5.7 a 11.3 bc IT838-742-2 " 5 .7 a 18.7 ab TVX 3236 (NSD) -42.0 b 5.1 c BLACKEYE " 7.2 a 30.7 a ER, " 15.3 a -l.7 c TT83S-742-2 " -3.3 a 6.8 be + - + GENOTYPE TVX 3236 -10.5 3.3 b BLACKEYE 8.0 24.7 a ER, 10.5 4.8 b TT83S-742-2 1.2 12.8 ab US it WATER Stress 10.3 12.6 Non-stress -5.7 10.2 ns ns S = Stress NSD= Non-stress ns= not significant 1‘", 1 Different letters within a column indicate significant difference at p= 0.01 or 0.1 respectively according to Duncan Multiple Range Test. photosyr a highs: 85110111) 2111011111 tended 1 8.4 photosynthetic rate, but intercepted the highest amount of radiation while TVX 3236 had a higher photosynthetic rate and low interception. Blackeye was the most prostrate genotype. There appeared to be a negative relationship between photosynthesis and the amount of light intercepted suggesting that light was not being efficiently utilized. I . . E . Moisture stress significantly increased transpiration ratio at 4 days after stress was imposed in 1990. At 18 DAS, BOOS-C had a significantly higher transpiration ratio than TVX 3236 (Table 12). In 1992 there were no differences between stress and non-stress treatments. TVX 3236 had lower transpiration ratio than Blackeye at 15 DAS in 1992 (Table 13). WW ' Moisture stress reduced stomatal conductance by 33 % at 18 DAS in 1990 (Table 14), consistent with other reports of reductions up to 71% in cowpeas (Hall et al. , 1992). The genotype BOOS-C had a significantly lower stomatal conductance than TVX 3236 at 4 DAS which correlates with its lower photosynthetic rate (Table 9). There were no differences between stress and non-stress treatments in 1992 (Table 15), but Blackeye had lower stomatal conductance than TVX 3236 and IT83S-742-2 at 15 DAS. C I I E' . . . There was no difference between the stress and non-stress treatments or between genotypes in carbon isotope discrimination in 1992 (Table 16). However, Blackeye tended to have low CID under stress. 85; TABLE 12. The Effect of Soil Water Changes on Transpiration Ratio in Cowpeas in the Rainshelter at the MSU Agronomy Farm in East Lansing. MI. 1990. W -171 41 181 mol H20! mol CO2 BOOS-C (S) 431.3 535.5 291.6 TVX 3236 " 400.4 556.8 251.6 B005-C (NSD) 393.9 399.5 346.1 TVX 3236 " 352.4 370.3 252.1 . ns ns ns GENOTYPE BOOS-C 412.6 467.5 318.8 TVX 3236 376.4 463.6 251.8 ns ns - 1 WATER Stress 415.8 546.1 271.6 Non-stress 373.2 384. 9 299. 1 ns 1‘ ns * p= 0.05 “ p= 0.1 S= Stress NSD= Non-stress ns= not significant 1 Early vegetative stage (V3) 1 Late vegetative stage (V7) 1 Flowering stage (R.) TA. 86. TABLE 13. The Effect of Soil Water Changes on Transpiration Ratio in Cowpeas Using Plastic at the MSU Agronomy Farm in East Lansing. MI. 1992. W W L1 151 mol H,O/ mol CO2 TVX 3236 (S) 252.6 311.7 BLACKEYE " 270.7 601.9 ER, " 271.0 380.9 IT83S-742-2 " 267.3 365.8 TVX 3236. (NSD) 211.3 299.3 BLACKEYE " 272.3 433.7 ER, " 243.5 381.3 IT838-742-2 " 306. 1 41 1.9 ns - ns GENOTYPE TVX 3236 231.9 305.5 b BLACKEYE 271.5 517.8 a ER, 257.3 381.1 ab TT83S-742-2 286.7 388.8 ab "5 lull!“ WATER Stress 265.4 415.1 Non-stress 258.3 381.5 ns ns S= Stress NSD= Non-stress ns= n0t significant *1" Different letters within a column indicate significant difference at p= 0.001 according to Duncan Multiple Range Test. 1 Late vegetative stage V, 1 Flowering and pad development (R,/R,) TABLE .87 TABLE 14. The Effect of Soil Water Changes on Stomatal Conductance in Cowpeas in the Rainshelter at the MSU Agronomy Farm in East Lansing. MI. 1990. W W -171 41 183 mmols m'1 s‘1 BOOS-C (S) 205.9 101.1 c 75.4 TVX 3236 " 172.9 184.9 a 65.7 BOOS-C (NSD) 162.2 135.1 b 109.4 TVX 3236 " 144.6 143.6 b 103.7 . ns "' ns GENOTYPE BOOS-C 184.0 118.1 b 92.4 TVX 3236 158.8 164.2 a 84.7 ns - * ns WATER Stress 189.4 143.0 70.6 b Non-stress 153.4 139.4 106.6 a ns ns * S= Stress NSD= Non-stress ns= non-significant * Different letters within a column indicate significant difference at p= 0.05 according to Duncan Multiple Range Test 1 Early vegetative stage (V3) 1 Late vegetative stage (V,) 1 Flowering (R1) 38 TABLE 15. The Effect of Soil Water Changes on Stomatal Conductance in Cowpeas Using Plastic at the MSU Agronomy Farm in East Lansing. MI. 1992. W W 11 151 mmols In1 S‘1 TVX 3236 (S) 117.3 122.5 BLACKEYE " 96.3 61.5 ER, " 108.5 85.1 IT83S-742-2 " 122.0 100.8 TVX 3236 (NSD) 100.3 113.9 BLACKEYE " 115.7 71.2 ER, " 121.9 92.5 TT83S-742-2 " 1 16.4 127.6 ns - as GENOTYPE TVX 3236 108.8 118.2 a BLACKEYE 106.0 66.3 c ER, 115.2 88.8 bc IT83S-742-2 119.2 114.2 ab ns *t* WATER Stress 111.0 92.5 Non-stress 113.6 101.3 ns ns S= Stress NSD= Non-stress ns= not significant 1'" Different letters within a column indicate significant difference at p= 0.001 according to Duncan Multiple Range Test. 1 Late vegetative stage (V g) 1 Flowering and pad development (Rlle) 89 TABLE 16. The Effect of Soil Water Changes on Carbon Isotope Discrimination in Cowpeas Using Plastic at the MSU Agronomy Farm in East Lansing. MI. 1992. TREATMENT Delta TVX 3236 (S) 20.6 BLACKEYE " 19.9 ER7 " 20.6 IT83S-742-2 " 20.4 TVX 3236 (NSD) 21.3 BLACKEYE " 20.1 ER, " 20.2 lT83S-742-2 " 20.3 ns GENOTYPE TVX 3236 20.9 BLACKEYE 20.0 ER, 20.4 llT83S-742-2 20.3 ns WATER Stress 20.5 Non-stress 20.4 ns S= Stress NSD= Non-stress ns= not significant Slflwlfl severe P110108) Underg uIlder 5 a scree SUMMARY RESPONSE UNDER MOISTURE STRESS IN 1990 BEANS COWPEAS Photosynthesis * at RS - 41 DAS * at V7 - 4 DAS "‘ at R1 - l8 DAS Transpiration "‘ at R, - 41 DAS * at V7 - 4 DAS Ratio Stomatal Conductance ns ns CID ns ns * significant at p=0.05 ns= not significant DAS = Days after stress was imposed CONCLUSIONS Water stress decreased photosynthesis late in the season when the stress was severe while stomatal conductance was affected earlier in the season in both beans and cowpeas. Genotypic differences were found only for stomatal conductance but not for photosynthesis. The resistant bean genotype, 9-39-1 maintaned its stomatal conductance under stress while the susceptible genotype significantly decreased stomatal conductance under stress. This suggests that stomatal conductance may have potential to be used as a screening tool in a bean or cowpea improvement program. More work is needed on a wide have observ from s the po .9; wide range of genotypes. Carbon isotope discrimination was not affected by stress, contrary to reports that have been made that CID decreased with increasing stress. Genotypic differences were observed in beans only. CID values were not effective in separating resistant genotypes from susceptible ones in either beans or cowpeas. The high cost of CID analysis limits the potential use of CID in breeding programs. REFERENCES Ashley D. A. 1991. Water use efficiency and tolerance to moisture stress in soybeans. Agron. Abstracts pp 122. Blackman P. G., Davis W. J. 1985. Root to shoot communication in maize plants of the effects of soil drying. J. Expt. Botany 36:39-48. Brown R. H., Bryd G. T. 1991. Water use efficiency and 13C isotope discrimination in peanut. Agron. Abstracts pp 123. Cornic G. , Papgeorgiou I. , Louason G. 1987. Effect of a rapid and a slow drought cycle followed by rehydration on stomatal and non-stomatal components of leaf photosynthesis in [Mus m L. J Plant Physiol. 126:309-318. Farquhar G. D., Sharkey T. D. 1982. Stomatal conductance and photosynthesis. Ann. Rev. Plant Physiol. 33:317-345. Gollan T., Passioura J. B., Munns R. 1986. Soil water status affects the stomatal conductance of fully turgid wheat and sunflower leaves. J. Plant Physiol. 13:459-464. Hall A. E., Mutters R. G., Farquhar G. D. 1992. Review and Interpretation: Genotypic and drought induced differences in carbon isotope discrimination and gas exchange of cowpea. Crop Sci. 32(1):1-6. Ismail A. M., Hall A. E. 1993. Carbon isotope discrimination and gas exchange of cowpea accessions and hybrids. Crop Sci. 33:788-793. Kaiser W. M. 1987. Effects of water deficits on photosynthetic capacity. Physiol. Planatarum 17:142-149. Littleton E., Dennett M. D., Elston 1., Monteith J. L. 1981. The growth and development of cowpeas (Minn W (L) walp) under tr0pical field conditions. 3.Photosynthesis of leaves and pods. J. Agric. Sci. 91:539=550. Mohan JD 1990. Photosynthetic carbon dioxide exchange, leaf area and growth of field grown pea genotypes. Crop Sci. 30: 1093-1098. Moon I. W. Jr., Flore .l. A. 1986. A BASIC computer program for calculation of photosynthesis, stomatal conductance, and related parameters in an open gas exchange system. Photosynthesis Res. 7:269-279 92 93 Plant Z. , Federman E. 1990. Acclimation of CO2 assimilation in cotton leaves to water stress and salinity. Plant Physiol. 97:515-522. Trejo C. 1., Davis W. J. 1991. Drought induced closure of My: mm L. Stomata preceeds leaf water deficit and any increase in xylem ABA concentration. I. Expt. Botany 42(245):1507-1515. CHAPTER3 THE EFFECT OF SOIL MOISTURE STRESS ON DRY BEANS (Phaseolus mm: L.) AND COWPEAS (Mina ungnjculm (walp) L.). III. Nitrogen Partitioning and Remobilization. ABSTRACT Nitrogen accumulation and partitioning in grain legumes is important in terms of both the physiology of pod filling and the nutritive value of the grain. Soil water deficits affect nitrogen accumulation. The objective of this study was to determine the effects of soil water changes on nitrogen accumulation, partitioning and remobilization in bean (flaming 3011241213 L.) and cowpea (Eigna unguilata (walp) L.). This study was carried out in the field using a rainshelter or black polyethylene plastic to impose terminal drought stress at the late vegetative stage (V,). A moderate moisture stress with a drought intensity index of 0.36 decreased the proportion of 1’N in the roots, stem and leaves in beans and cowpeas. Resistant genotypes remobilized more N to the seeds and other plant parts than susceptible genotypes suggesting that N remobilization may contribute to yield stability. N concentration and dry weight were reduced by moisture stress. 94 INTRODUCTION Nitrogen management is one of the greatest challenges in crop production. To realize higher yield of grain legumes with high protein requires higher rates of nitrogen fixation by legumes and increased partitioning of nitrogen into the seeds. A thorough understanding of nitrogen partitioning during growth and development may facilitate efforts to achieve higher yield, especially in moisture limiting environments. In soybean (9mm max L.), leaf nitrogen contributed 45-64 % of the total N that was remobilized to seeds and the stem N contributed 19-27 % (Zeiher et al. , 1982). Severe moisture stress decreased N concentration in soybean leaves and the proportion of seed nitrogen coming from remobilization was not related to yield since moisture stress did not consistently alter the contribution that remobilized N made to seed N (Egli et a1. , 1983). Navarro et al (1985) in soybean studies concluded that high seed protein genotypes exhibited faster nitrogen partitioning and dry matter allocation into seeds. When three bean lines were labelled with 1"N at the early pod fill stage, they displayed an increase in nitrogen content in flowers and fruits (Dubois and Burris, 1986). In cowpeas, nitrogen fixed after flowering contributed 40% of the fruit’s intake of nitrogen. The mobilization of nitrogen fixed before flowering contributed 60 % (Peoples et al. , 1983). Muchow et al. (1993) reported no differences in N partitioning to leaves in soybean, mungbean and cowpea grown under wet and dry water regimes. Biomass accumulation was positively correlated to nitrogen accumulation. The objective of this study was to determine the effect of water stress on nitrogen partitioning and remobilization in beans and cowpeas. ’95 MATERIALS AND METHODS A field study was conducted at the Agronomy Research Farm at Michigan State University in East Lansing during the summers of 1990 and 1992. In 1990 a rainshelter was used to impose moisture stress at 37 DAP. In 1992 a black polyethylene plastic was placed between the rows at 55 DAP, to impose moisture stress. Moisture stress was imposed at the late vegetative stage (V 9) each year, but different environmental conditions led to different growth rates for each year, hence the late vegetative stage did not occur at the same number of DAP. The soil type for the 1990 experiment was a fine loamy, mixed mesic aeric ochraqualfs with a slope of 0-3 % (USDA Soil Conservation Service Classification). For the 1992 experiment it was a fine loamy, mixed mesic glossoboric hapluidalfs with a slope of 2—6%. The rainfall distribution and temperature data area presented in Fig l and Table 1 of Appendix A. The experimental design was a modified split plot with four replications. Moisture level was the main plot and genotypes were the subplot. The moisture factor was confounded by site difference in that all stressed plots were grouped together and all non- stressed plots were grouped together. Each plot had four rows of 2 m length. The bean spacing was 50 x 10 cm and the cowpea spacing was 75 x 20 cm which resulted in a plant density of 20 plants per in2 for beans and 10 plants per m2 for cowpeas. In 1990 two bean genotypes, 9-39-1 and 8-42-M-2, and two cowpea genotypes, TVX 3236 and B005-C, were grown. In 1992 four bean genotypes, 9-39-1, 8-42-M-2, N81017 and 8-25- 2, and four cowpea genotypes, TVX 3236, Blackeye, ER., and IT83S-742-2, were grown. 96 9.7. The bean genotypes were choosen based upon their previous performance in the MSU bean brwding program and their subsequent designation as either drought resistance or susceptible. The cowpea genotypes were choosen based upon their performance from a preliminary growth chamber study conducted in 1989 and their performance in field studies at IITA and in Botswana. Genotypic descriptions are presented in Table 2 of Appendix A. All plots were hand planted using a hoe to open rows. Forty or 20 seed were planted for beans and cowpeas respectively, with abundant inoculant. The bean inoculum was Rln'zolznun mu and the cowpea inoculum was thngjmn cowpea miscellany nin'ogen EL. 21W ~ 1220 Both beans and cowpeas were planted on June 25 but because of poor germination the cowpeas were replanted on July 18. Fertilizer was applied as 19-19-19 at the rate of 40 Kg N/ha before planting. Three days after planting on June 28, all plots received 30 mm of irrigation water to facilitate germination. The total rainfall during the growing season (June 25-Oct 5) was 287.6 mm. On July 31, Sevin (Carbaryl insecticide) was applied at the rate of 4 teaspoons per gallon of water to control Mexican beetle and leafhopper. 1222 Planting occurred on June 12. The fertilizer 21-7-14 with 4% Mn and 1% Zn was applied at the rate of 40 Kg N/ha before planting. All plots received a total of 283.3 mm -98 of irrigation in four applications before stress was imposed. The total rainfall during the growing season (June 12-Sept. 16) was 309.0 mm. A greater amount of water was applied by irrigation in 1992 in order to break the crust and enhance germination and stand establishment. Sevin was applied on July 29 to control leafhopper. Soil moisture was monitored regularly in all plots at three depths in 1990 (0-30, 30-60, 60-90) using a neun'on probe. In 1992 readings were only recorded at the 0-30 and 30-60 cm depths because the field had a high water table. Undisturbed soil core samples were taken at each depth to develop a soil moisture desorption curve which was used to convert the volumetric moisture content into matric potential. W In 1990 ten plants per plot from the border rows were labelled with 1“N on August 10. Five plants of approximately the same growth stage were tagged from each border row then designated as 1 to 10 in alternating rows so that the odd numbered plants were in one row and the even numbered plants were in another row. In 1992 eight plants per plot were labelled with "N on August ll. Each year plants were labelled at the late vegetative stage (V 9). WW l"N-urea was used to label the plants. Plants were labelled in the morning between 8 am and 12 noon. Upon labelling. each plant was covered with plastic so that the entire trifoliate was separated from the rest of the plant. The trifoliate was dipped into the solution of 0.35 % N and 0.001% ortho L-77 surfactant for a few seconds then removed. The plastic around the plant prevented the solution from dripping onto the plant or the _99 soil. Control plants were treated with surfactant only. As soon as the leaf was dry, the plastic was removed, rinsed with water, and dried in the sun. The petiole of the labelled leaf was tagged and a flag was placed in front of the plant for easy identification. After a minimum of two hours, the labelled plant was recovered with plastic as before and the leaf was dipped in water to remove all urea from the outside of the leaf. W A screw driver was used to loosen the soil around the labelled plant and the plant was pulled from the soil with as much root as possible. The plant was cut at the soil line to separate-the roots. The labelled leaf and its petiole were separated from the rest of the plant, washed with water to remove all soil, and placed in a bag for dying. A separate container was used to wash soil from the remainder of the plant. A tape measurer was used to determine the height of each plant and to determine the middle of the plant for separation into upper and lower leaves, upper and lower stems, and upper and lower reproductive parts (flowers and/or pods). Each plant part was bagged separately for drying- Two labelled plants were sampled the day after treatment in order to determine how much l’N-urea entered the plant. In 1990 two labelled plants were subsequently sampled at flowering and pod development (RI/RQ), pod filling (R,) and physiological maturity (R.,). In 1992 labelled plants were subsequently sampled only at pod filling and physiological maturity. W The samples were oven dried for 48 hrs at 72°C before grinding in a Udy mill 100 grinder. The dry weight was also recorded. Extreme care was taken not to contaminate plant parts. Whirlpak bags were used to collect samples from the grinder. After each sample was ground, the entire grinder, working surface, and the instruments were carefully cleaned. Compressed air was used to clean the grinder. Samples were analyzed for N and 1’N using a gas chromatography mass spectrometer (AN CA-MS , Europa Scientific, Crewe. U.K) after conversion of sample N to N2 by Dumas combustion in a roboprep CN analyzer. Ammonuim sulfate (0.3663 atom % 15N) Whatman number 1 filter paper was used as a reference standard. RESULTS AND DISCUSSION BEANS Mitten: 1220 Moisture stress did not significantly reduce 1’N content in the portion of the root that was retrieved but there was a tendency for lower 1’N content under stress. There were no genotypic differences (Table 1). There was a tendency for a higher "N content under the non-stress treatment in the lower stem and a tendency for a lower 1"N content under the non-stress treatment in the upper stem at pod filling and physiological maturity (Table 2). At 65 DAS (R2), 9-39-1 contained a significantly greater proportion of total "N than 8—42-M-2 in the lower stems, possibily indicating less N remobilization to seeds or other plant parts. Moisture stress significantly decreased 1’N content in the lower leaves at 29 DAS (Table 3). 8-42-M-2 contained significantly more 1"’N than 9-39-1 in 1.01 TABLE 1. The Effect of Soil Water Changes on "N Content in Bean Roots in the Rainshelter at the MSU Agronomy Farm in East Lansing. MI. 1990 W W 211 292 653 % 8-42-M-2 (S) 0.71 0.79 0.53 9-39-1 " 0.34 0.55 0.75 8—42-M-2 (NSD) 1.57 1.26 0.55 9-39-1 " 1.06 1.10 0.71 ns ns ns . GENOTYPE 8-42-M-2 1.14 1.03 0.54 9-39—1 0.70 0.83 0.73 ns ns ns WATER - Stress 0.52 0.67 0.64 Non-sn'ess l .31 1. 18 0.63 ns ns ns S= Stress NSD= Non-stress ns= not significant ‘= R¢IR3 Flowering and early pod development ’= R, Pod filling 3= R7 Physiological maturity 102 TABLE 2. The Effect of Soil Water Changes on 1’N Content in Bean Stems in the Rainshelter at the MSU Agronomy Farm in East Lansing. MI. 1990. WW TREATMENT 11‘ 292 1553 Mm % 8-42-M-2 (S) 10.29 a 6.85 1.74 9-39-1 " 5.11 b 6.19 3.70 8-42-M—2 (NSD) 9.12 a 12.58 2.34 9-39-1 " 10.56 a 11.06 6.95 * ns ns GENOTYPE 8-42-M—2 9.79 9.31 2.00 9-39-1 7.83 8.62 5.33 ns ns * WATER Stress 7.70 - 6.52 2.72 Non-stress 9.94 11.71 4.97 ns """ ns Wm 8-42-M-2 (S) 5.82 4.09 2.21 9-39—1 " 2.25 4.97 2.07 8-42-M-2 (NSD) 4.34 3.50 0.98 9-39-1 " 5.05 3.73 2.02 ns ns ns GENOTYPE 8-42-M-2 5.08 3.84 1.59 9—39—1 3.65 4.35 2.04 ns ns ns WATER Stress 4.04 4.52 2.15 Non-stress 4.70 3.63 1.50 IE ns ns_ S= Stress NSD= Non-stress ns= not significant **, " * Different letters within a column indicate significant difference at p= 0.01, 0.05 or 0.1 respectively according to DMRT. 1: Rle3 2: Rs 3: R7 103 TABLE 3. The Effect of Soil Water Changes on 1"‘N Content in Bean Leaves in the Rainshelter at the MSU Agronomy Farm in East Lansing. MI. 1990. W TREATMENT 211 292 653 Malays: % 8-42-M-2 (S) 9.06 5.71 0.81 9-39-1 " 11.37 1.09 3.40 8~42-M-2 (NSD) 9. 13 23.07 1.32 9—39—1 " 22.24 9.94 2.37 ns ns ns - GENOTYPE 8-42-M-2 9.09 14.39 1.06 9—39-1 16.81 5.51 2.81 ns * ns WATER Stress 10.21 3.40 2.11 Non-stress 16.62 16.50 1.92 ns ** ns 111221122295 8-42-M-2 (S) 18.02 13.14 2.49 9-39-1 " 7.89 11.00 1.22 8—42—M-2 (NSD) 14.02 10.61 1.66 9-39-1 " 11.11 11.05 0.95 ns ns ns GENOTYPE 8-42-M-2 16.31 12.06 2.28 9-39-1 9.50 11.03 1.10 " ns ns WATER Stress 12.95 12.07 1.76 Non-stress 12.36 10.86 1.13 1'15 IE 115 S= Stress NSD= Non-stress ns= not significant ** p= 0.01 a p= 0.05 ‘= R2/R3 2: R5 104 , the lower leaves at 29 DAS (R,) and in the upper leaves at 21 DAS (R5). This indicates that by these dates, 8-42-M-2 was remobilizing less N from the leaves to developing seeds or other plant parts than 9-39-1. Although not significant, the differences between 1“N content in the upper and lower reproductive structures under stress and non-stress were quite interesting. 9-39-1 maintained the level of 1"’N remobilization to the upper and lower reproductive structures under stress and non-stress n’eatments at 65 DAS, but the level of remobilization was reduced under stress in 8-42-M-2 (Table 4). In addition, 9- 39-1 remobilized 1’N to the seeds at a faster rate under the stress than non-stress treatment. The ability of 9-39-1 to increase its N remobilization rate under stress and its ability to maintain the amount of N remobilized may partly explain its greater yield stability (4.6% yield reduction due to stress) over 8-42-M-2 (51.4% yield reduction). 1222 Eventhough four genotypes were planted in 1992, only two were analyzed for 1’N because of lack of funds to analyze all four genotypes. The genotypes N81017 (resistant and high yielding) and 8-25-2 (susceptible and low yielding) were choosen for analysis because they had not previously been used in "N studies and because 9-39-1 and 8-42-M- 2 were used in another study in 1988. Thus, the 1988 and 1990 results would provide information about the latter two genotypes and the 1991 and 1992 results would provide information about the former two genotypes. There were no differences between stress and non-stress treatments or between genotypes in IN content in the roots, stems, leaves or reproductive structures (Tables 5- 8). This was to be expected since there was only a mild drought stress in 1992. 105 TABLE 4. The Effect of Soil Water Changes on "N Content in Bean Reproductive Parts in the Rainshelter at the MSU Agronomy Farm in East Lansing. MI. 1990. W TREATMENT 211 292 653 mm % 8-42-M-2 (S) 4.44 20.81 26.07 9-39-1 " 4.37 16.20 34.14 8-42-M-2 (NSD) 5 .50 22.39 40.64 939-] " 3.75 5.83 34.52 ns ns ns GENOTYPE 8-42-M—2 5.00 21.60 32.31 9-39-1 4.06 11.02 34.33 ns + ns WATER Stress 4.41 18.50 30.10 Non-stress 4.63 14.11 37.14 ns ns ns Wm 8-42-M-2 (S) 5.62 3.71 13.89 9-39-1 " 1.27 4.42 10.18 8-42-M-2 (NSD) 2.80 5.03 18.76 9-39-1 " 1.39 2.02 10.74 ns ns ns GENOTYPE 8-42-M-2 4.21 4.37 16.33 9-39-1 1.32 3.22 10.46 ns ns ns WATER Stress 3.44 4.06 12.03 Non-stress 2.20 3.53 14.75 115 113 [IL— S= Stress NSD= Non-stress ns= not significant * p= 0.1 ‘= R2/R3 2= R, 3= R7 106 TABLE 5. The Effect of Soil Water Changes on 1’N Content in Bean Roots Using Plastic at the MSU Agronomy Farm in East lansing. MI. 1992. W MATMENT 371 472 % N81017 (S) 1.22 0.56 8-25-2 " 0.75 0.55 N81017 (NSD) 1.23 0.66 8-25-2 " 1.63 0.60 ns ns GENOTYPE N81017 1.23 0.61 8-25-2 1. 19 0.58 ns ns WATER - Stress 0.99 0.56 Non-stress 1 .43 0.63 ns ns S= Stress NSD= Non-stress ns= not significant 1= R, Pod filling 2= R7 Maturity .107 TABLE 6. The Effect of Soil Water Changes on ”N Content in Bean Stems Using Plastic at the MSU Agronomy Farm in East Lansing. MI. 1992. W TREATMENT 371 47’ Wm % N81017 (S) 9.42 8.97 8-25-2 " 8.44 9.63 N81017 (NSD) 7.52 9.28 8-25-2 " 11.16 10.51 . ns ns GENOTYPE N81017 8.47 9.13 8-25-2 9.80 10.07 ns ns WATER Stress 8.93 9.30 Non-stress 9.34 9.90 ns ns 1109:me N81017 (S) 3.35 1.88 8-25-2 " 1.53 2.37 N81017 (NSD) 2.61 1.95 8-25-2 " 2.82 9.48 ns ns GENOTYPE N81017 2.98 1.91 8-25-2 2.17 5 .93 ns ns WATER Stress 2.71 2.12 Non-stress 2.44 5.71 11L n5 S= Stress NSD= Non-stress ns= not significant 1= 2: R., 108 TABLE 7. The Effect of Soil Water Changes on 1"N Content in Bean Leaves Using Plastic at the MSU Agronomy Farm in East lansing. MI. 1992. W TREATMENT 37l 47“ Inseam N81017 (S) 11.11 6.98 8-25-2 " 13.95 6.54 N81017 (NSD) 10.60 3.23 8-25-2 " 13.20 9.44 ns ns GENOTYPE N81017 10.86 5.11 8-25-2 13.57 8.00 ns ns WATER Stress 12.53 6.76 Non-stress l 1.90 6.34 ns ns llamecs N81017 (S) 13.92 9.21 8-25-2 " 4.44 18.56 N81017 (NSD) 6.17 18.46 8-25-2 " 18.47 8.00 ns ns GENOTYPE N81017 9.49 14.49 8-25-2 11.46 14.04 ns ns WATER Stress 8.50 14.55 Non-stress 12.32 13.98 115 115—— S= Stress NSD= Non-stress 1: R5 2: R7 ns= not significant 109 TABLE 8. The Effect of Soil Water Changes on ”N Content in Bean Reproductive Parts Using Plastic at the MSU Agronomy Farm in East Lansing. MI. 1992. W MTMENT 37‘ 472 W N81017 (S) 59.08 54.06 8-25-2 " 66.30 55.64 N81017 (NSD) 70.74 57.67 8-25-2 " 42.81 76.98 ns ns GENOTYPE N81017 64.91 55.87 8—25-2 54.56 66.31 ns ns WATER Stress 62.69 54.85 Non-stress 56.77 67.33 ns ns W N81017 (S) 7.78 10.01 8-25-2 " 6.75 20.92 N81017 (NSD) 7.00 13.63 8-25-2 " 27.37 8.47 ns ns GENOTYPE N81017 7.39 11.82 8-25-2 17.06 14.70 ns ns WATER Stress 7. 19 15.47 Non-stress 17. 19 1 1.05 115 I'll S= Stress NSD= Non-stress ns= not significant 1: R5 2: R7 1 19 In 1990, moisture stress tended to reduce ”N content in the roots, lower stem and lower leaves indicating that there was greater N remobilization to the seeds under stress. The resistant genotype, 9-39-1, remobilized more N to the mds and other plant parts than the susceptible genotype, 8-42-M-2. There were no differences in 1992 because there was minimal stress. The difference in N remobilization between resistant and susceptible genotypes, and between stress and non-stress indicate that N remobilization may contribute to yield stability. "N content for most plant parts was not statistically different even though numerical differences existed. This is due to the very high coefficient of variation which ranged from 60 to 200%. Harris (1993) also reported very high coefficient of variation ranging from 107 to 171% in "N recovery in red clover. 11' C . 1220 Moisture stress significantly decreased N concentration in the roots at 29 DAS (Table 9) The stress treatment significantly reduced N concentration at 21 and 29 DAS in the lower and upper stems (Tables 9) and in the lower and upper leaves (Tables 10). These results may be due to greater N remobilization from the roots, stems and leaves under stress and/or reduced N fixation under stress or greater nitrogen use efficiency. Moisture stress reduced N concentration in the lower reproductive structures at 29 and 65 DAS and in the upper reproductive structres at 29 DAS (Table 11). Egli et al. (1983) reported decreased N concentration in soybean leaves in response to moisture stress. At physiological maturity, the resistant and low yielding genotype 9-39-1 had a significantly 111 flaw—rm w. .35 mag. om mo: £82 0558 o: z nonoaanwaoa 5 ma»: woos Ba mama 5 Sn ”warn—8n 3 9o Km: arm—.825. 12.8 3 m8" 585? 7:. $8 wooam rbfimw mHmK EI' Ea BE: 2. LR as B. 8» a. N: we. a. a mL~-Z-~ Amy :3 #3 #8 rd .8 row 9% :3 rue Pma ob?— .. _. B 98 #5 #3 a fee #8 r3 #3 rue mtfi-§-~ 2mg r8 _ 3 98 . Ems we #3 Pme who ram 93 v-3; .. _Lu _ _N _ 3 New w ram _.~o Pun _ mu raw 8 8 a _.. a a a B B szoafiem m5~-§-~ fine _ cm a we #3 _ um 93 _ 3 73 ohq Paw; ru— _ 3 r5 #3 fine #5 _ 8 #8 rue B 8 + B a s a a 1.... £513” manna run 98 fee #3 fee 9mm :3 rum #3 28-38“ rug #3 r8 r8 r3 row Pg _.8 rue a * a {i is. a ** ** a m u wanna ZmUu 28.396 8" =2 amines" 2...... t... s. + U322: E83 393 a 8:55 3&88 «5:533 manage,“ a an PS. 98 2. A: now—c8363. vegan—Em 8 USES Esau—o Ema 4.8.. .fl ”Kuwu n" N... u" we 1'12 ' TABLE 10. The Effect of Soil Water Changes on N Concentration in Bean Leaves in the Rainshelter at the MSU Agronomy Farm in East Lansing. MI. 1990. WP. TREATMENT ZL‘ 292 653 mum % 8-42-M-2 (S) 4.33 2.90 b 1.06 9-39-1 " 3.76 2.44 c 1.66 8-42-M-2 (NSD) 4.57 3.68 a 1.22 9-39-1 " 4.39 3.56 a 1.87 ns + ns GENOTYPE b 8-42-M-2 4.45 3.29 1. l4 ' 9-39-1 4.07 3.00 1.76 It fit 18 WATER Stress 4.05 - 2.67 1.40 Non-stress 4.43 3.62 1.59 I! *** n3 napalm 8-42-M-2 (S) 4.48 4.04 1.08 9-39-1 " 5.22 3.21 1.73 8-42-M-2 (NSD) 5.66 4.81 0.99 9-39-1 " 5.47 4.58 1.60 ns ns GENOTYPE 8-42-M-2 5.07 4.41 1.05 9-39—1 5.34 3.89 1.67 ns ** ns WATER Stress 4.85 3.61 1.45 Non-stress 5.56 4.70 1.45 4' *** as S= Stress NSD= Non-suess ns= not significant "*, **, *, * Different letters within a column indicate significant differences at p= 0.001, 0.01, 0.05 or 0.1 respectively according to DMRT 1: Rz/Ra 2: Rs 3: R7 - 113- TABLE 11. The Effect of Soil Water Changes on N Concentration in Bean Reproductive Parts in the Rainshelter at the MSU Agronomy Farm in East lansing. MI. 1990. hummmmmmumummma flmmflM' W 2? EL. LEMflmmwm % 8-42-M-2 (S) 4.71 2.37 2.14 b 9-39-1 " 4.48 2.30 1.91 b 8-42-M-2 (NSD) 4.66 3.11 2.74 a 9-39-1 " 4.40 3.87 3.03 a ns ns * .GENOTYPE 8-42-M-2 4.69 2.74 2.44 9-39-1 4.44 3.09 2.47 1 ns ns WATER Stress 4.59 2.34 2.02 Non-stres 4.53 3.49 3.88 ns *4! tilt WWEMMME 8-42-M-2 (S) 4.13 3.14 2.38 9-39-1 " 4.19 2.59 2.71 8-42-M-2 (NSD) 4. 12 3.93 2.29 9-39-1 " 4.20 4.20 2.53 ns ns ns GENOTYPE 8-42-M-2 4.13 3.53 2.34 9-39-1 4.19 3.40 2.62 ns ns ns WATER Stress 4.16 2.87 2.55 Non-stress 4.17 4.06 2.41 m * m__ S = Stress NSD = Non-stress significant differences at p= 0.001, 0.01 or 0.1 respectively according to DMRT 3: R7 %&® EK ns= not significant ***, **, * Different letters within a column indicate 1 1 4 higher N concentration than 8-42-M-2, the susceptible and high yielding genotype in the roots, lower and upper stems, and lower leaves indicating that 939-] may have remobilized less N to the seeds and other plant parts or may have utilized nitrogen less efficiently than 8-42-M-2. There was a significant reduction in N concentration under stress in the lower leaves at 21 and 29 DAS (Table 10), in the upper leaves at 29 DAS (Table 10) and in the lower reproductive sn'uctures at 29 and 65 DAS (Table 11). 1222 Since there was a mild drought stress in 1992, there were no differences between stress and non-stress treatments except at 47 DAS in the lower leaves (Table 14), where the stress n'eatment had a significantly higher N concentration than the non-stress treatment. N81017 had a sigificantly higher N concentration than 8-25-2 at 37 DAS in the upper leaves. Although not significant, there was a tendency for N81017 to have a lower N concentration than 8-25-2 in the roots, stems, leaves and reproductive structures (Tables 12-15). In 1990 moisture suess reduced N concentration in the roots, stem, 1eaves and reproductive structures, indicating that the utilization of N under stress was probably more efficient than under the non-stress treatment. The resistant genotype, N81017 had lower N concenn’ation in the seeds than the susceptible genotype, 8-25-2 which may partly explain its greater yield potential. Lynch and White (1992) reported that total N allocation to the seeds dominated the reproductive N budget in beans. 115 TABLE 12. The Effect of Soil Water Changes on N Concentration in Bean Roots Using Plastic at the Agronomy Farm in East Lansing. MI. 1992. W TREATMENT 371 472 % N81017 (S) 1.05 0.88 8—25-2 " 1.21 0.99 N81017 (NSD) 1.18 0.98 8-25-2 " 1.24 1.04 ns ns - GENOTYPE N81017 1.12 0.93 8-25—2 1.22 1.01 ns ns WATER - Stress 1.13 0.94 Non-stress 1 .2 1 1.01 ns S= Stress NSD= Non-stress ns= not significant 116 TABLE 13. The Effect of Soil Water Changes on N Concentration in Bean Stems Using Plastic at the MSU Agronomy Farm in East Lansing. MI. 1992. W W 37‘ 43 mm % N81017 (S) 1.49 1.69 8-25-2 " 1.69 2.02 N81017 (NSD) 1.56 1.69 8-25-2 " 1.98 2.25 ns ns GENOTYPE N81017 - 1.52 1.69 8-25-2 1.84 2.13 ns ns WATER . Stress 1.59 - 1.85 Non-stress 1 .77 1 .97 ns ns limit/em N81017 (S) 1.65 1.66 8-25-2 " 2.02 1.96 N81017 (NSD) 1.93 1.85 8-25-2 " 1.89 2.41 ns ns GENOTYPE N81017 1.79 1.75 8—25-2 1.96 2.19 ns ns WATER stress 1.84 1.81 Non-stress 1 .91 2. 13 ns n_s S= Stress NSD= Non-stress ns= not significant 1: R, 2: R7 117- TABLE 14. The Effect of Soil Water Changes on N Concentration in Bean Leaves Using Plastic at the MSU Agronomy Farm in East lansing. MI. 1992. W TREATMENT 371 472 mm % N81017 (S) 4.03 3.51 8-25-2 " 4.13 3.44 N81017 (NSD) 3.75 2.88 8-25-2 " 3.84 3.07 ns ns GENOTYPE N81017 - 3.89 3.19 8-25-2 3.98 3.26 ns ns WATER Stress 4.08 - 3.47 Non-stress 3.79 2.98 1‘15 4- Umukmm N81017 (S) 4.81 3.46 8-25-2 " 4.32 4.11 N81017 (NSD) 4.86 4.17 8-25-2 " 4.32 4.11 ns ns GENOTYPE N81017 4.84 3.82 8-25-2 4.32 4.11 1 ns WATER Stress 4.57 3.92 Non-stress 4.59 4. 14 m 115 S= Stress NSD= Non-stress ns= not significant +p=o1 an, 2=m 1,1,8 TABLE 15 . The Effect of Soil Water Changes on N Concentration in Bean Reproductive Parts Using Plastic at the MSU Agronomy Farm in East Lansing. MI. 1992. W TREATMENT 37‘ 472 W % N81017 (S) 3.63 3.62 8-25-2 " 3.93 3.88 N81017 (NSD) 3.67 3.63 8-25-2 " 3.88 4.29 ns ns GENOTYPE N81017 . 3.65 3.62 8-25-2 3.90 4.09 ns ns WATER Stress 3.78 - 3.75 Non-stress 3.78 3.96 ns ns 1112mm N81017 (S) 3.67 3.80 8-25-2 " 4.05 4.29 N81017 (NSD) 3.72 3.88 8-25-2 " 3.79 4.31 ns ns GENOTYPE N81017 3.70 3.84 8-25-2 3.92 4.30 ns ns WATER Stress 3.86 4.05 Non-stress 3 .76 4. 10 J11 115 S= stress NSD= Non-stress ns= not significant 1 = R5 2: R7 1 19 E. E l . Total plant dry weight increased with plant growth but was reduced by moisture stress in most cases although the reduction was not statistically significant. In 1990, there was a tendency for the dry weight of 9-39-1 to decrease under stress and that of 8-42-M- 2 to increase under stress at physiological maturity (Fig 1). There was a significant difference between the harvest index (HI) of 9-39-1 (HI= 0.64) and 8-42-M-2 (HI= 0.74) which may partly explain the low yield potential of 9-39-1 and the high yield potential of 8-42-M-2. In 1992, the dry weight of N81017 and 8-25-2 was decreased by stress at 37 DAS. The total dry weight decreased with time which could be due to excessive moisture that increased with time in 1992. The harvest index of N81017 and 8-25-2 were not significantly different in 1992.‘ In 1992 it was 0.56 for N81017 and 0.5 3 for 8-25-2. The actual numbers for dry matter accumulation of the different plant parts are shown in appendix C (Tables 1-7). As would be expected, within each growing season the genotype that accumulated the most biomass also tended to accumulate the most nitrogen. Muchow et a1 (1993) reported similar results in the accumulation and partitioning of biomass and nitrogen in soybean, mungbean and cowpea. comm In 1990 cowpeas were replanted because of poor germination and the genotype B005-C was late maturing. As a result it flowered late in the season so it was not labelled with "N-Urea. Only TVX 3236 was labelled. In 1992 excess moisture and low temperature delayed plant growth and cowpeas were more affected than beans. DRY WEIGHT (groms/ plant) DRY WEIGHT (grams/plant) 120 no. 1. TOTALPLANT DRY WEIGHT 111 1990 ' 9-39-1 30- 20- ‘10- O TrrTrTrfirlrIUTlI‘fTr1V1U TTIII so so 70 so so 160 110 8-42-M—2 20- H NON-STRESSED H STRESSED O ‘Trrrilrrr‘UUUIrtrTl’TU so so 70 so so riboniio DAYS AFTER PLANTING 121 FIG. 2. TOTAL DRY WEIGHT IN BEANS IN 1992 0 1.1 1 1 .0 TO 1 1 4. .o 5 r9 2 I _ 8 O Tuna-cucu-daqudu-uda O O O O O 5 4 3 2 1 cco_a\m583 Eon; Ea O 1 1 r 0 T0 1 + 1 7 o m r9 1| 8 4 N 1 r O Wanda-caucuqqdq-uuuda O O o O O 5 4. 3 2 4| ccgfimses Eon; Ea DAYS AFTER PLANTING H NON-STRESSED HSTRESSE) 1 22 Consequently, they flowered late and were not labelled. 2mm There was no significant difference in the "N content between the stress and non- stress treatments of TVX 3236 in 1990 except in the lower stem at flowering (Table 16) where the non-stress treatment contained a greater proportion of "N than the stress treatment. There was a tendency for a reduction of "N content in plant structures under stress except in the reproductive structures where stress tended to increase the proportion of "N content. These results support the theory of more N being remobilized from other plant parts -to the seeds under stress. Mutation There were no significant differences between the stress and non-stress treatment in the upper stem, lower leaves, and lower and upper reproductive structures in TVX 3236 (Table 17) in 1990. At 49 DAS in the roots, the stress treatment had a significantly higher N concentration than the non-stress treatment. Similarly, the upper leaves had a higher N concentration under stress at 13 DAS but the lower stem had reduced N concentration under stress at 33 DAS. BiomasLAccumulm Moisture stress decreased plant dry weight but only significantly in the upper leaves at 13 DAS (Table 18) in 1990. However, the reproductive structures tended to have more dry weight at 33 DAS under stress. There was no reproductive data at 49 DAS because cowpea pods were damaged by frost. 123 TABLE 16. The Effect of Soil Water Changes on "N Content in Cowpea TVX 3236 in the Rainshelter at the MSU Agronomy Farm in East lansing. MI. 1990 WP. WT 131 332 493 % Roots (S) 7.59 5.87 5.16 (NSD) 2.22 6.01 5.29 ns ns ns Upper Stem (S) 8.89 6.52 8.01 (NSD) 8.82 21.95 5.53 ns ns ns Lower Stem (S) 7.55 16.39 8.98 (NSD) 13.80 34.64 27.61 * ns ns Upper Leaves (S) 6.90 3.20 3.40 (NSD) 4.63 6.32 4.74 ns ns ns Lower Leaves (S) 11.58 10.23 1.35 (NSD) 14.52 25.00 9.01 ns ns ns Upper Reproductive (S) 8.69 14.99 -- (NSD) 4.33 7.42 -- ns ns Lower Reproductive (S) 6.36 20.99 -- (NSD) 6.42 4.38 -- IE IE * p(0.05) S = Stress NSD= Non-stress ns= not significant ‘= R1 Flowering 2= R3,,4 Early pod filling stage 3= R,,, Late pod filling stage 124 TABLE 17. The Effect of Soil Water Changes on N Concentration in COWpea TVX 3236 in the Rainshelter at the MSU Agronomy Farm in East lansing. MI. 1990 W IREAIMENT 13‘ 332 493 % Roots (S) 1.79 1.92 3.21 (NSD) 2.01 2.19 1.86 ns ns * Upper Stem (S) 1.67 1.50 2.40 (NSD) 2.57 2.64 1.65 ns ns ns Lower Stem (S) 1.49 1.19 2.16 (NSD) 2.50 2.46 1.93 ns * ns Upper Leaves (S) 3.63 2.51 2.24 (NSD) 3.41 3.60 2.84 * ns ns Lower Leaves (S) 3.61 2.86 2.54 (NSD) 3.81 3.79 2.94 ns ns ns Upper Reproductive (S) 3.47 3.00 -- (NSD) 3.24 3.14 -- ns ns Lower Reproductive (S) 3.91 3.25 -- (NSD) 3.94 3.66 -- 115 IE S= Stress NSD= Non-stress *, I p= 0.05 or 0.1 respectively I ._ 2 _ 3 _. - R1 - R3/4 - R5l6 ns= not significant 1_25. TABLE 18. The Effect of Soil Water Changes on Cowpea TVX 3236 Dry Weight in the Rainshelter at the MSU Agronomy Farm in East Lansing. MI. 1990. W W 13‘ 332 493 grams/plant Roots (S) 1.21 1.34 1.01 (NSD) 1.95 2.90 2.66 ns ns ns Upper Stem (S) 1.50 1.41 1.20 (NSD) 1.65 2.05 2.43 ns ns ns Lower Stem (S) 7.36 13.25 4.19 (NSD) 16.69 28.06 29.86 ns ns ns Upper Leaves (S) 1.18 1.05 2.41 (NSD) 1.94 2.65 1.16 + ns ns Lower Leaves (S) 4.66 7.05 1.18 (NSD) 13.63 18.93 8.25 ns ns ns Upper Reproductive (S) 0.45 1.96 -- (NSD) 0.27 0.48 -- Lower Reproductive (S) 1.26 9.10 -- (NSD) 1.46 4.58 -- TEL 115 S= Stress NSD= Non-stress ns= not significant + p= 0.1 1_ 2— — R1 - R314 R516 CONCLUSIONS Differences were found between the stress and non-stress treatments and between resistant and susceptible genotypes in "N content, N concentration and dry weight in beans and cowpeas. In general, moisture stress reduced "N content in the stems and leaves of in both beans and cowpeas. These results suggest that beans and cowpeas remobilized more N from the leaves and stems to the seeds under moisture stress. N remobilization in the resistant genotypes (9-39-1 and N81017) was not affected by stress. N remobilization was reduced under stress for the susceptible and high yielding genotype, 8-42-M-2 and increased under stress for the susceptible and low yielding genotype, 825- 2. These findings suggests N remobilization may contribute to yield stability. Soil moisture stress decreased N concentration in beans and cowpeas. The high yielding bean genotypes (8-42-M-2 and N 81017) utilized nitrogen more efficiently than the low yielding genotypes. "N studies may therefore be useful in estimating or explaining the plant’s response to stress. However, because of the difficulty and time involved in labelling plants, sampling and analysis, it is not feasible to do many replications. Therefore "N would not be useful in evaluating a large number of genotypes. 126 REFERENCES Dubois J. D., Burris R. H. 1986. Comparative study of N uptake and disn'ibution in three lines of common bean (1211mm mans L.) at early pod filling stage. Plant and Soil 93:79-86. Egli D. B., Meckel L., Phillips R. E., Radcliffe D., Leggett J. E. 1983. Moisture stress and N redistribution in soybean. Agron. J. 75: 1027-1031. Foster E. F., Carmi A., Nuriez-Barrios A., Manthe M. 1991. Drought effects on N concentration and water use in reciprocal grafts of beans with differing drought adaptation. Bean Improvement Cooperative 34: 108-109. Harris G. H. 1993. N in'ogen cycling in animal- legume, and fertilizer based cropping systems. Dissertation. Michigan State University. Lynch 1., White J. W. 1992. Shoot nitrogen dynamics in tropical common bean. Crop Sci. 32:392-397. Muchow R. C., Robertson M. 1., Pergelly B. C. 1993. Accumulation and partitioning of biomass and nitrogen in soybean, mungbean and cowpea under contrasting environmental conditions. Field Crops Res. 33:13-36. Navarro L. R., Hison K., Sinclair T. R. 1985. Nitrogen partitioning and dry matter allocation in soybeans with different seed protein concentration. Crop Sci. 25:451-455. Peoples M. B., Pate J. S., Atkins C. A. 1983. Mobilization of nitrogen in fruiting plants of a cultivar of cowpea. J. Expt. Bot. 34(142):563-578. Zeiher C., Egli D. B., Leggett I. E.. Reicosky D. A. 1982. Cultivar differences in N remobilization in soybeans. Agron. I. 74:375-379. 127 CHAPTER4 THE EFFECT OF LEAFHOPPER DAMAGE ON DRY BEANS mm mm L.) AND COWPEAS Mata misnlata (walp) L.)- ABSTRACT Soil moisture stress adversly affects crop growth and productivity. This study was conducted to examine the effect of moisture stress on yield and yield components, leaf water, root growth, physiological parameters, and nitrogen partitioning and remobilization in beans (Phaseolus mlgarjs L.) and cowpeas (Xigna W (walp) L.) under field conditions. The research was conducted in Michigan using a black plastic to impede water on mixed mesic ochroqualfs soil. Moisture stress was imposed at the late vegetative stage (V9), 48 DAP. Leafhopper damage decreased seed yield by decreasing the number of pods per plant in both beans and cowpeas. Leaf water retention capacity, leaf water content and root growth were also decreased by leafhopper damage in beans and cowpeas. Leafhopper damage decreased photosynthetic rate and stomatal conductance in both beans and cowpeas. Genotypic differences were found only in cowpeas. Carbon isotope discrimination was not affected by leafhopper damage but genotypic differences were observed in both beans and cowpeas. Leafhopper damage increased the amount of "N in the plant structures indicating less N remobilization under leafhopper stress. Leafhopper damage decreased N concentration and dry weight in both beans and 128 1'29 cowpeas. INTRODUCTION The leafliopper (Empoasca spp) is one of the most important pest in beans and cowpeas. Damage is most severe during hot, dry climatic conditions and during flowering and pod setting growth periods (Kornegay and Temple, 1986). Symtoms of leafhopper damage in beans are yellowing and dowan curling of the leaves, followed by necrosis at the leaf tip and margins. Plant growth is stunted and pod number and seed weight are reduced. Under severe infestation the plant may die. In cowpeas, losses of 60 % or more in seed yield have been reported due to leafhopper damage (Jackai and Daoust, 1986). - The objective of this study was to evaluate the effect of leafhopper damage on yield and yield components, leaf water status, root growth, photosynthesis, stomatal conductance, transpiration ratio, carbon isotope discrimination, and nitrogen partitioning and remobilization. MATERIALS AND METHODS A field study was conducted at the Agronomy Research Farm at Michigan State University in East Lansing during the summer of 1991. The soil type was a fine loamy, mixed mesic aeric ochraqualfs with a slope of 0-3% (USDA Soil Conservation Service Classification). The rainfall and temperature data are presented in Fig 1 and Table l of Appendix A. 13.9 The experimental design was a modified split plot with and with four replications. The main plot was the leafhopper infestation and genotypes were the subplots. The leafhopper factor was confounded by site difference in that all stressed plots were grouped together and all non-stressed plots were grouped together. Each plot had four rows of 2 m length. The bean spacing was 50 x 10 cm and the cowpea spacing was 75 x 20 cm which resulted in a plant density of 20 plants per 1112 for beans and 10 plants per in2 for cowpeas. Four bean genotypes (9-39-1, 8-42-M-2, N81017 and 8-25-2) and four cowpea genotypes (TVX 3236, Blackeye, ER-,, and I'I‘83S-742-2) were used. The bean genotypes were chosen based upon their previous performance in the MSU bean breeding program and their subsequent designation as either drought resistant or susceptible. The cowpea genotypes were chosen based upon theirperformance from a preliminary growth chamber study conducted in 1989 and their performance in field studies at ITTA and in Botswana. Genotype description is presented in Table 2 of Appendix A. Plots were hand planted using a hoe to open rows and 40 or 20 mds were planted per row for beans and cowpeas respectively, along with abundant inoculant. The bean inoculum was Mum 1211355211 and the cowpea inoculum was thzahinm Cowpea miscellany nitrogen EL. r ic The experiment was planted on June 15. Fertilizer was applied as water soluble Pro-sol (20-20-20) on July 27 and August 14 at the rate of 27 pounds per 450 gallons of water. All plots received a total of 116.4 mm of irrigation on June 21 and July 15 before stress was imposed. On August 27 the non-stressed plots received 42.7 mm of irrigation. i31 The total rainfall during the growing season (June 15-Oct 20) was 294.9 mm. Sevin was applied on June 23 and August 15 to alleviate a severe leafhopper problem. Soil moisture was monitored regularly in all plots at three depths (0-30, 30-60, 60-90 cm) using a neutron probe. Undisturbed soil core samples were taken at the same depths to develop a soil moisture desorption curve which was used to convert the volumetric moisture content into water potential. W Relative water content (RWC) , leaf water content (LWC) and leaf water retention capacity (LWRC) were determined. Weather permitting, measurements were made every two weeks after stress was imposed. Three plants per plot at the same growth stage were tagged and marked A, B and C. The center leaflet of the youngest fully developed leaf was placed in a plastic bag marked A,, B2 or C2 depending on whether it was from plant A, B or C respectively. With the leaf face-up, the leaflet on the right was labelled A5, B3 or C3 and the leaflet on the left was labelled A,, B, or C,. RWC, LWC and LWRC measurements were made on samples marked number 1, 2 and 3 respectively. Immediately after leaf detachment, the samples were placed. in ziplock bags and stored on ice in a cooler until their fresh weight was recorded. RWC: Each sample was weighed and placed in a petri dish and covered with distilled water. After 4 hrs, turgid weight was recorded. The leaves were then oven dried at 70° C for 24 hrs to determine the dry weight. RWC was computed as: (Fw-Dw)/(Tw-Dw) * 100. 1.319: The fresh weight was recorded. Then, leaves were oven dried as described aboVe. 132 LWC was computed as: (Fw-Dw)/Dw * 100. LWRC: After the fresh weight was recorded, samples were left uncovered in a dark environment at room temperature for 48 hrs. After 48 hrs, air dry weight (Dw,) was recorded, leaves were oven dried at 70° C for 72 hrs, and the dry weight (Dw,) was recorded. LWRC was computed as: (Fw-Dw,)/(Fw-Dw,) * 100. W The stressed plots were located next to another bean field which was heavily infested with leafhopper. Severe leafhopper damage was done to the plots which were next to the-infested field. As a result, the stressed plots were due to leafhopper damage. This was not initially planned as part of the experiment. W ‘ Root measurements were made by using a minirhizotron camera. Only live roots were counted. This provided information on root distribution along the soil profile. Root growth rate was calculated from root counts of two successive recording dates as follows: (root count on date 1-root count on date 2)/number of days between date 1 and date 2 which was reported as number of rootslcm‘lday. Each plot had one 6 inch diameter tube inserted at a 45° angle into the center row to a depth of 3 feet and measurements were taken, weather permitting, every 30 days. Two readings were taken during the season. At physiological maturity seed yield and yield components were recorded. All measured parameters were analysed by MSTAT microcomputer statistical package for agricultural sciences or by the SAS package. 133 Wis Three plants per plot were tagged and measurements were taken from these plants on the uppermost fully expanded leaf. The ADC-LCA 2 photosynthesis system (The Analytical Development Co. Ltd. , Hoddesdon. UK) was used under the following conditions (Flow rate= 400 m1 m", Leaf temperature= 30:1:2°C, Vapor pressure deficit= 3 KPa, ambient C02= 350:1; 10 pl 1", and photosynthetically active radiation (PAR)21000 umol m'2 s"). The leaf was enclosed in a leaf chamber and exposed to incoming solar radiation. Readings were recorded at approximately the same photosynthetically active radiation (PAR). Each reading took approximately 30 seconds before a stable value was recorded. Measurements were taken between 10 am and 2 pm EDT on a cloudless day. Photosynthesis, stomatal conductance and transpiration ratio were calculated from a program developed by Moon and Flore (1986), (Appendix B1). 2 I I E' . . . Samples for carbon isorope discrimination were taken during the pod filling growth stage (R,) on five plants per pict. Five leaves were sampled from each plant so 25 leaves were detached from each plot. The uppermost fully expanded leaves were sampled and samples were bulked for each plot. The samples were oven dried at 60°C for five days before grinding. The samples were sent to the laboratory of Dr James Ehleringer at the University of Utah. Salt Lake City, UT, USA for analysis via mass spectrometry. 134 MW Ten plants per plot from the border rows were labelled with "N on August 2. Five plants of approximately the same growth stage were tagged from each border row then marked 1 to 10 in alternating rows so that the odd numbered plants were in one row and the even numbered plants were in another row. Plants were labelled at the late vegetative stage (V 9). "N-urea was used to label the plants. Plants were labelled in the morning between 8 am and 12 noon. Upon labelling, each plant was covered with plastic so that the entire trifoliate was separated from the rest of the plant. The trifoliate was dipped into the solution of 0.35 % N and 0.001% ortho L-77 surfactant for a few seconds then removed. The plastic around the plant prevented the solution from dripping onto the plant or the soil. Control plants were heated with surfactant only. As soon as the leaf was dry, the plastic was removed, rinsed with water, and dried in the sun. The petiole of the labelled leaf was tagged and a flag was placed in front of the plant for easy identification. After a minimum of two hours, the labelled plant was recovered with plastic as before and the leaf was dipped in water to remove aTl urea from the outside of the leaf. Windlass A screw driver was used to loosen the soil around the labelled plant and the plant was pulled from the soil with as much root as possible. The plant was cut at the soil line to separate the roots. The labelled leaf and its petiole were separated from the rest of the plant, washed with water to remove all soil, and placed in a bag for dying. A separate 1 3'5 container was used to wash soil from the remainder of the plant. A tape measurer was used to determine the height of each plant and to determine the middle of the plant for separation into upper and lower leaves, upper and lower stems, and upper and lower reproductive parts (flowers and/or pods). Each plant part was bagged separately for drying- Two labelled plants were sampled the day after treatment in order to determine how much "N-urea entered the plant. Two labelled plants were subsequently sampled at flowering and pod development (R,/R,), pod filling (R5) and physiological maturity (R.,). W The samples were oven dried for 48 hrs at 72°C before grinding in a Udy mill grinder. The dry weight was also recorded. Extreme care was taken not to contaminate plant parts. Whirlpak bags were used to collect samples from the grinder. After each sample was ground, the entire grinder, working surface, and the instruments were carefully cleaned. Compressed air was used to clean the grinder. Samples were analyzed for N and "N using a gas chromatography mass spectrometer (AN CA-MS, Europa Scientific, Crewe. U.K) after conversion of sample N to N2 by Dumas combustion in a roboprep CN analyzer. Ammonuim sulfate (0.3663 atom % "N) Whatman number 1 filter paper was used as a reference standard. RESULTS AND DISCUSSION 1. YIELD AND YIELD COMPONENTS, LEAF WATER STATUS AND ROOT GROWTH S '1 l l . Soil moisture content decreased with increasing number of days after planting for both the stress and non-stress treatments at all depths (Fig l). The leafhopper stress treatment had lower moisture content than the non-stress treatment at the 30 and 60 cm depth. There were no significant differences between the stress and non-stress treatment at the 90 cm depth. BEANS Xiellelata There was a significant difference in yield between the leafhopper stress and non- stress treatment (Table 1). Leaflioppers damage bean plants by extracting plant juices, plugging vascular tissue and possibly injecting a toxin into the plant. Leaf margins turn yellow while leaves are crinkled and reduced in size. Heavy attacks may result in stunted growth (van Schoonhoven et al., 1978). All of these symptoms were noted in the leafhopper-stressed plots and none occurred in the control plots. Pods per plant were significantly reduced by leafliopper damage (Table 1). The genotypes 8-42-M-2 and N81017 were higher yielding than 9-39-1 and 8-25-2. Stress significantly reduced yield. These results agree with previous reports indicating that leafhopper affected yield by 136‘ i137 nstavoumncsmmconmutm O-SOGJW'I'H JO-IOGIEPTH r V r T r i V T T'- I GO-GOGIDEP‘I'H am 3 d a m m w .358 9.2.8: 4.8 E8 ami? 4.0m 138 Haw—1m r 5%— 85 Sea Ochcaoaa 3. was: $3.568 98.88; 8 gov—can _amamsaoa A: :5 Km: agave—5. 3:8 5 m8" Ema—m. Zr 53. mmmUm mm” 86m mm” <_m_..U QmOZmflw—O fl 5510 E... mob wEv Zm>z wmccodoz mL~-Z-~ Amy a 2 Each 959 a 5 8ch “38.; web Paw; 6V u w Sub 969 a 5 Emma 28.x 3.x ZmSS Amy m 2 Snub 969 a 3 mafia Nawub 3b «hub Amv u 8 39... 963 m S 3un 52; 3b a 8 8 omzoqfium m$~-z_-~ a 5 Mafia w 9%.— u S Ewe; a ZmSS a 3 new?» a m-~u-~ u 2 Each a a a ** 533.5%me manna m S a Sam; A. 28.38“ a 8 a 33; a a + ** m u madam ZmU u 28.398 8 .1. co. amino»... .3... + 05.22: 588 33:: p 8:55 5383 amazon... manna—.8 w" u" Po— c~ c; Ham—c8355 8833” 8 07:5,. 1 39 reducing the number of pods per plant, seeds per pod, 100 seed weight and the number of empty pods per plant (van Schoohoven et el. , 1978; Kornegay and Temple, 1986; Jackai and Daoust, 1986). The genotype 9-39-1 had a higher yield reduction (38.8%) than 8-42-M-2 (29.2%). This suggests that 9-39-1 may be more sensitive to leafhopper damage than is 8-42-M-2. A significantly high correlation was observed between yield and pods per plant (Table 2). W There were no differences between genotypes but leafhopper damage decreased RWC at 38, 52 and 80 days after planting (Table 3). Leafhopper damage also significantly decreased LWRC at 38, 52 and 66 DAP (Table 4). The two low yielding genotypes, 9-39-1 and 8-25-2 had a higher RWC than the high yielding, drought susceptible genotype (N81017) at 66 DAP. The drought susceptible and low yielding genotype, 8-25-2 had a higher LWRC than 9-39-1 at 80 DAP. LWC was significantly lower under leafhopper damage at 66 DAP (Table 5). W Leafliopper damage did not significantly reduce root growth rate (Table 6) but there was a tendency for mat growth rate to be reduced under stress (52%). The resistant genotypes (9-39-1 and N81017) had a lower root growth rate than the susceptible genotypes (8-42-M-2 and 8-25-2). Figures 1 and 2 show root distribution of four bean genotypes at 61 and 75 days after planting. There was a tendency for more root growth under the non-stress treatment 1 40 TABLE 2. Yield and Yield Component Correlations, 1991. Yield PPP SPP Yield -- 0.65'” 0.001 PPP -- -0. l6 SPP -- PPP= Pods per plant SPP= Seeds per pod *""" p= 0.001 141 - TABLE 3. Relative Water Content in Beans Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991. W TREATMENT 38‘ 52’ 66’ 80‘ % N81017 (S) 81.5 85.1 be 86.1 85.8 9-39-1 " 80.6 88.4 b 82.7 86.9 8-42-M-2 " 81.5 82.5 c 86.9 87.9 8-25-2 " 81.9 86.6 be 85.8 85.5 N81017 (NSD) 89.1 94.4 a 90.8 91.4 9-39-1 " 90.6 88.1 b 89.2 90.6 8-42-M-2 " 91.7 94.5 a 90.4 89.5 8-25-2 " 96.0 94.8 a 82.1 91.5 ns * ns ns GENOTYPE N81017 85.3 88.2 88.4 88.6 9-39-1 85.6 88.3 86.0 88.8 8-42-M-2 86.6 86.5 88.7 88.7 8-25-2 88.9 90.7 83.9 88.5 ns ns ns ns LEAFHOPPER Stress 81.4 85 .7 85.4 86.5 Non-stress 91.8 93 .7 88. 1 90. 8 #4111! *4"! n5 tilt S= Stress NSD= Non-stress ns= not significant ***, * Different letters within a column indicate significant difference at p= 0.001 or 0.1 respectively according to Duncan Multiple Range Test. ‘ Early vegetative stage (V 5) 2 Late vegetative stage (V ,) 3 Flowering and pod development stage (R,/R,) ‘ Pod filling stage (R,/R,) 142 TABLE 4. Leaf Water Retention Capacity in Beans Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East lansing. MI. 1991. W TREATMENT 38‘ 522 663 80‘ % N81017 (S) 95.1 93.4 92.6 c 98.0 9-39-1 " 95.0 96.1 96.2 ab 93.8 8-42-M-2 " 92.4 93.3 94.6 b 95.5 8-25-2 " 91.2 95.0 96.2 ab 98.6 N81017 (NSD) 97.3 97.7 97.1 a 97.2 9-39-1 " 97.1 96.6 97.5 a 96.4 8-42-M-2 " 97.6 96.2 97.7 a 95.5 8-25-2 " 95.8 96.8 96.7 a 97.7 ns ns + ns GENOTYPE N81017 96.2 95.6 94.8 b 97.6 ab 9-39-1 96.0 96.4 96.8 a 95.1 b 8-42-M-2 95.0 94.7 96.1 ab 95.5 ab 8-25-2 93.5 95.9 96.4 a 98.5 a n5 “S + * LEAFHOPPER Stress 93.4 94.5 94.9 96.5 Non-stress 97.0 96.8 97 .2 96.7 813* 3* *** ITS S= Stress NSD= Non-stress ns= not significant ***, **, *, * Different letters within a column indicate significant difference at p= 0.001, 0.01, 0.05 or 0.1 respectively according to Duncan Multiple Range Test. ‘ Early vegetative stage (V 5) 2 Late vegetative stage (V 3) 3 Flowering and pod development stage (R,/R,) ‘ P0d filling Stage (Rs/R6) 143 TABLE 5 . Leaf Water Content in Beans Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991. _DW TREATMENT 38‘ 523 663 80‘ % N81017 (S) 76.3 ab 82.1 81.3 81.4 ab 9-39-1 " 75.3 ab 82.3 82.9 79.0 bc 8-42-M-2 " 75.2 ab 81.5 81.3 80.2 abc 8-25-2 " 78.4 a 81.8 80.7 79.9 abc N81017 (NSD) 78.2 a 83.6 86.4 82.5 a 9-39-1 " 78.3 a 83.1 85.0 82.3 a 8-42-M-2 " 76.5 ab 83.7 85.2 78.4 c 8-25-2 " 72.7 b 81.3 84.5 81.3 ab * ns ns " GENOTYPE N81017 77.3 82.9 83.8 81.9 a 9-39-1 76.8 82.7 84.0 80.6 ab 8-42-M-2 75.9 82.6 83.2 79.3 b 8-25-2 75.6 81.6 82.6 80.6 ab ns ns ns ” LEAFHOPPER Stress 76.3 81.9 81.5 80.1 Non-stress 76.4 82.9 85.5 81. 1 ns ns “" ns S= Stress NSD= Non-stress ns= n0t significant 3'“, *, 3 Different letters within a column indicate significant difference at p= 0.001, 0.05 or 0.1 respectively according to Duncan Multiple Range Test. ‘ Early vegetative stage (V 5) 3 Late vegetative stage (V8) 3 Flowering and pod development stage (R,/R,) * Pod filing stage (R,/R,) 144 TABLE 6. Root Growth Rate of Bean Genotypes Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East lansing. MI. 1991. TREATMENT M # roots/cm’lday 8-42-M-2 (S) 1.36 9-39-1 " 0.64 N81017 " 1.24 8-25-2 " 2.73 8-42-M-2 (NSD) 4.32 9-39-1 " 1.30 N81017 " 2.45 8-25-2 " 4.45 ns GENOTYPE 8-42-M-2 2.84 9-39-1 0.97 N81017 1 .93 8-25-2 3.59 ns LEAFHOPPER Stress 1 .51 Non-stress 3. 13 ns S= Stress NSD= Non-stress ns= not significant 145 for all genotypes except 8-42-M-2 at 61 DAP at the 30 cm depth. At the 60 cm depth there were more roots under stress in 9-39-1 and N81017 , both resistant genotypes. 8-25- 2 had more roots under stress at the 90 cm depth (Fig 1). At 75 DAP, all genotypes had more root growth under the non-stress treatment at the 30 cm depth. At the 60 cm depth, root count was similar for both the stress and non-stress treatment except for N81017 which had more roots in the non-stress treatment. The high yielding and resistant genotype, N 81017 had the same root count at the 80 cm depth under stress and non-sn'ess treatments. 9-39-1 and 8-25-2 both low yielding had decreased roots under stress at the 80 cm depth and 8-42-M-2, high yielding and susceptible (Fig 2). 1112151132 There were significant reductions in seeds per pod, pods per plant and yield due to leafhopper damage (Table 7). IT838-742-2 had a high number of seeds per pod, pods per plant, and the highest yield. Blackeye had the lowest number of seeds per pod, pods per plant and the lowest yield. Nevertheless, TT83S-742-2 had a higher (72%) yield reduction than Blackeye (61%) which was due to a low number of pods per plant under stress with IT83S-742-2. Significant differences in the levels of leafhopper damage between cowpea cultivars have been reported (Parh, 1983). Jackai and Daoust (1986) showed yield losses up to 60% in cowpeas due to leafhopper damage. TVX 3236 and Blackeye are considered to be drought resistant lines and 13R7 and IT838-742-2 to be drought susceptible lines. .146 FIGURE 2. BEAN ROOT DISTRIBUTION AT 81 DAP IN 1991 s-25-2 I— in ggéééégfi FIEII l- 9-39-1 Egg/egg”. F 5 ‘ u I a a u a. 5 4 u” 3 2 1 3505.508 300.. 2 . u a 4 L. t r- 111:. 1 . .._.. .. ._. m N gr??? . ......_.. n a s a a a n .. ANE0\E:3V 300.. 60-80 soil depth (cm) 0-30 150-60 150-50 OO-BO soil depth (cm) 0—30 [:3 Strum -Non-5W 147 FIGURE 3. BEAN ROOTDISI'RIBU'I'ION AT 75 DAP IN 1991 5-25-2 9-39-1 aqua-u- magnum Aqu\«caooV 300.. . 2 5-42-M-2 i 0-30 30-50 60-00 casua- mum-3U.“ soil depth (cm) N51017 0-30 30-50 50-50 soil depth (cl-n) . ANE0\E:3V £00.. 148 .5»me q. 505 25 52a COB—58:8 cm not?» 03on8 wagons.— 8 5:532. 548828 2 Bo ch >m8=o8< 35: S we..." gram. 7:. GS. mmmUm _uOUm Eur—w fiat—u QmOZmfldn a «am—16 E... em” .50 F524 Rama Kmpz mefiHEz a unue Amy 5 a N qr— 2. 2mg 2 w 3 H3... a -m.m cob wr>nfimm=0vwmw manna m a a a Rub a Zoamcduu 8 e 3 u «3.0 w ii iii {*5 mt. mega ZmUu 23235 Bu :2 finance—c. 2...... .3... a. + 222.2: _283 25:: a 8:53 32:88 amazon—2 $22.38 we" PS? PE. 98 2 o; 8.68220? 882:5 8 62:5,. 149 W Leafhopper damage significantly decreased RWC at 38 and 66 days after planting (Table 8). There were genotypic differences at all sampling dates except at 52 DAP. Blackeye consistently had a significantly lower RWC than all other genotypes. This may partly explain the low yield observed with Blackeye. Stressed plants had a significantly lower LWC at 66 and 80 DAP (Table 9). There were also genotypic differences at 52, 66 and 80 DAP. For LWRC, the difference with the stress treatment was significantly lower than the non-stress treatment at 52 and 66 DAP (Table 10). TVX 3236 had a significantly lower LWRC than other genotypes at 66 DAP and Blackeye had a lower LWRC at 80 DAP. mm There were no differences between genotypes but there was a significantly higher root growth rate under the non-stress treatment (Table ll). Blackeye had more roots at the top 30 cm under stress at 61 DAP (Fig 3). Blackeye and TVX 3236 had more roots under stress at the 60 cm depth at 61 DAP. At 75 DAP only Blackeye had more roots under stress at the 30 cm depth (Fig 4). In general, root count decreased with increasing soil depth. 150 TABLE 8. Relative Water Content in Cowpeas Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East lansing. MI. 1991. W TREATMENT 38‘ 522 663 fit. % TVX 3236 (S) 88.5 96.0 a 90.8 91.7 BLACKEYE " 74.9 82.0 a 80.3 89.3 ER, " 85.8 87.8 a 89.2 91.8 IT838-742—2 " 82.4 93.7 a 91.1 94.1 TVX 3236 (NSD) 95.5 91.4 a 94.4 94.3 BLACKEYE " 74.0 90.3 a 88.5 88.1 ER-, " 88.2 96.4 a 95.0 92.2 IT838-742-2 " 92.0 65.0 b 93.2 94.6 ns * ns ns GENOTYPE TVX 3236 91.5 a 94.2 92.6 a 93.1 a BLACKEYE 74.4 b 84.8 84.4 b 88.7 b ER7 87.0 a 90.7 92.1 a 92.0 ab IT83S-742-2 86.6 a 84.1 92.2 a 94.4 a *** n3 3* ** LEAFHOPPER Stress 82.9 89.5 87.9 91.7 Non-stress 86.5 85.8 92.8 92.3 * ns ** ns S= Stress NSD= Non-stress ns= not significant **"', **, *, " Different letters within a column indicate significant difference at p= 0.001, 0.01, 0.05 or 0.1 respectively according to Duncan Multiple Range Test. 1 Early vegetative stage (V 5) 2 Late vegetative stage (V8) 3 Flowering and pod development stage (R,/R¢) ‘ Pod filling stage (R,/R6) 151 TABLE 9. Leaf Water Content in Cowpeas Subjected to Leafliopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991. W W 381 522 66a 80‘ % TVX 3236 (S) 73.4 b 84.9 83.9 b 80.9 BLACKEYE " 80.8 a 84.4 85.2 ab 82.4 ER, " 79.2 a 81.3 84.9 b 80.2 I'I‘83S-742-2 " 76.9 ab 82.2 81.2 c 81.5 TVX3236 (NSD) 77.9 ab 85.4 87.4a 82.6 BLACKEYE " 77.8 ab 83.9 84.7b 84.5 ER, " 73.2 b 82.9 85.8 ab 81.2 I'I‘83S-742-2 " 76.6 ab 82.5 85.4 ab 80.8 * as + ns GENOTYPE TVX 3236 75.6 85.1 a 85.7 a 81.7 ab BLACKEYE 79.3 84.1 ab 84.9 a 83.4 a 13R7 76.2 82.1 b 85.3 a 80.7 b IT83S-742-2 76.7 82.3 b 83.3 b 81.1 ab “5 a. + I"! LEAFHOPPER Stress 77.6 83.2 83.8 81.2 Non-stress 76.4 83.7 85.8 82.3 n5 “S II + S= Stress NSD= Non-stress ns= not significant *"‘, *, * Different letters within a column indicate significant difference at p= 0.01, 0.05 or 0.1 respectively according to Duncan Multiple Range Test. ‘ Early vegetative stage (V,) 2 Late vegetative stage (V a) 3 Flowering and pod development stage (R,/R2) ‘ Pod filling stage (R,IR6) 152 TABLE 10. Leaf Water Retention Capacity in Cowpeas Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991. W TREATMENT 381 522 663 80‘ % TVX 3236 (S) 97.4 91.4 78.2 d 91.0 BLACKEYE " 96.5 92.3 88.9 c 82.6 ER., " 97.4 94.0 90.6 be 91.6 IT83S-742-2 " 97.3 95.5 92.6 abc 97.4 TVX 3236 (NSD) 97.1 96.1 90.2 be 93.1 BLACKEYE " 97.7 97.1 93.2 abc 89.9 ER7 " 98.3 95.6 96.3 a 94.4 IT83S-742-2 " 95.3 94.0 94.4 ab 92.8 ns ns + ns GENOTYPE TVX 3236 97.3 93.8 84.2 b 92.1 a BLACKEYE 97.1 94.6 91.0 a 86.2 b ER, 97.9 94.8 93.4 a 93.0 a IT83S-742-2 96.3 93.3 93.5 a 95.1 a n5 ns *t* I LEAFHOPPER Stress 97 . 1 92.5 87.6 93.5 Non-stress 97 . l 95 .7 93.5 92.5 US a“!!! #3.! ns S= Stress NSD= Non-stress ns= not significant “"3 *, +Dfimmmammmfim¢p= can, 0.05 or 0.1 respectively according to Duncan Multiple Range Test. ‘ Early vegetative stage (V 5) 2 Late vegetative stage (V 8) 3 Flowering and pod development stage (R,/R¢) 4 Pod filling stage (R.,/R.) 153 TABLE 11. Root Growth Rate of Cowpea Genotypes Subjected to Leafliopper Infestation at the MSU Agronomy Farm in East lansing. MI. 1991. WT MIL-.8122. # rmts/cm’lday TVX 3236 (S) 0.64 BLACKEYE " 1.59 ER, " 2.05 IT83S-742-2 " 0.86 TVX 3236 (NSD) 3.25 BLACKEYE " 2.50 ER7 " 3.70 IT83S-742-2 " 3.87 ns GENOTYPE TVX 3236 2.13 BLACKEYE 2.05 ER7 2.88 IT83S-742-2 2.38 ns LEAFHOPPER Stress 1.33 Non-stress 3.34 * S= Stress NSD= Non-stress ns= not significant * p= 0.05 154 "335-742-2 //////////////////// FIG 4. COWPEA ROOT DiSTRlBUTION AT 61 DAP IN 1991 HI 11 J A :1 d a J J - n l. 5 a O 2 cl ANEo\ucaoov Boo. W 0—30 30-80 50-80 soil depth (cm) m-m-,w . u. m a. \W 6 m r... M... p m .m “1...... gage/j. .wi..-.._...; . ANEo\uc:oov 300.. 155 FIG 5. OOWPEA ROOT DISTRIBUTION AT 75 DAP IN 1991 _ m . an... w M. a m m 2 mg??? m. m. d géééé/ZZ/x/Z/Z % m. .2. a- __2_ W _ a ,w w w W a? m gag/gain»... .0 mm. Egg/WE... w.w-w.w-m.a v...«..m.m..m.m.w.._. 3505.503 300.. . ANEo\ucaoov 300.. II. PHOTOSYNTHESIS, STOMATAL CONDUCTAN CE, TRANSPIRATION RATIO AND CARBON ISOTOPE DISCRIMINATION. Wis Leafhopper damage decreased the rate of photosynthesis at 40 and at 70 days after planting (Table 12). At 57 DAP, the genotype 8-25-2, susceptible and low yielding, had the highest photosynthetic rate (Table 12) although it was not significantly different from that of N81017 (resistant and high yielding). Both 8-42-M-2, drought susceptible and high yielding, and 9-39-1, resistant and low yielding had a lower photosynthetic rate than 8-25-2. I . . B . There were no significant differences between stress and non-stress treatments in the transpiration ratio. Genotypic differences were found only at 57 days after planting. The susceptible and low yielding genotype, 8-25-2 had a lower transpiration ratio than the other genotypes (Table 13). Stomatalflm There were no differences between stress and non-stress treatments except at 40 days after planting (Table 14) where the stress treatment had a lower stomatal conductance than the non-stress treatment. There were no genotypic differences. 156 157 TABLE 12. CO, Assimilation Rate in Beans Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991. W WM 401 572 703 pmols m‘2 s'1 8-42-M-2 (S) 9.8 17.4 d 12.2 9-39-1 " 5.5 20.8 acbd 12.7 N81017 " 6.6 17.8 cd 15.5 8-25-2 " 7.6 21.1 abc 15.6 8-42-M-2 (NSD) 8.8 18.1 bcd 16.9 9-39-1 " 8.5 16.6 d 16.0 N81017 " 13.3 22.3 ab 17.2 8-25-2 " 10.0 22.5 a 15.7 ns " ns GENOTYPE 8-42-M-2 9.3 17.7 b 16.2 9-39—1 6.9 18.7 b 14.4 N81017 9.9 20.0 ab 14.7 8-25-2 8.8 21.8 a 15.7 ns ' ns LEAFHOPPER Stress 7.4 19.2 14.0 Non-stress 10.2 19.9 16.5 t ns . S= Stress NSD= Non—Stress ns= not significant * Different letters within a column indicate significant difference at p= 0.05 according to Duncan Multiple Range Test 2 Early vegetative stage (V 5) 2 Late vegetative stage (V9) 3 Flowering and pod development stage (Rile) 158 TABLE 13. Transpiration Ratio in Beans Subjecmd to Leafliopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991. W TREATMENT 401 572 70’ mmols H20/mmols CO2 8-42-M-2 (S) 449.0 334.7 abcd 456.4 9-39-1 " 777.9 304.5 bcd 532.8 N81017 " 600.3 384.8 a 455.6 8-25-2 " 3240.1 276.3 d 396.6 8-42-M-2 (NSD) 421.8 356.3 abc 417.5 9-39-1 " 456.0 380.0 ab 425.8 N81017 " 391.8 316.0 abcd 408.2 8-25-2 " 491.1 280.9 cd 473.5 ns * ns GENOTYPE 8-42-M-2 435.4 345.5 a 436.9 9-39-1 616.9 342.2 a 497.3 N81017 496.1 350.4 a 431.9 8-25-2 1865.6 278.6 b 435.1 ns * ns LEAFHOPPER Stress 1266.8 325 .1 460.3 Non-stress 440.2 333.3 431.3 ns ns ns S= Stress NSD= Non-stress ns= not significant 2‘, + Different letters within a column indicate significant difference at p= 0.05 or 0.1 respectively according to Duncan Multiple Range Test. 2 Early vegetative stage (V 5) 2 Late vegetative stage (V 9) 3 Flowering and pod development stage (Rlle) 159 TABLE 14. Stomatal Conductance in Beans Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing MI. 1991. W IREAIMENT $03 572 703 mmols m’2 s‘1 8-42-M-2 (S) 82.7 157.5 265.2 9-39-1 " 82.8 176.2 235.6 N81017 " 77.7 192.9 187.7 8-25-2 95.2 161.9 218.8 8-42-M-2 (NSD) 137.7 160.3 244.8 9-39-1 147.0 153.7 234.8 N81017 180.4 191.0 233.8 8-25-2 150.0 164.6 270.7 ns ns ns GENOTYPE 8-42-M-2 110.2 159.9 225.0 9-39-1 114.9 164.9 235.2 N81017 129.0 191.9 210.7 8-25-2 122.6 163.2 244.7 ns ns ns LEAFHOPPER Stress 84.6 172.6 226.8 Non-stress 153.8 167.4 246.0 * ns ns S= Stress NSD= Non-stress * p=0.05 3 Early vegetative stage (V 5) 2 Late vegetative stage (V 9) 3 Flowering and pod development stage (RI/R1) ns = not significant 1 6O - C l I D' . . . Carbon isotope discrimination was not reduced by leafliopper damage but genotypic differences were observed (Table 15). Genotypic variability in CID has been reported in soybeans comm max L.) (Ashley. 1991) and peanms (am Inmates L.) (Brown and Bryd, 1991). 9-39-1 (resistant and low yielding) had a lower CID value than N 81017 (resistant and high yielding) and 8-42-M-2 (susceptible and low yielding). MAS maxnthcsis At 57 days after planting, there was a difference between the stress and non-stress treatment (Table 16). Leafhopper damage reduced photosynthesis by 24 % . Genotypic differences were observed at 57 and 70 DAP. Blackeye had the lowest photosynthetic rate. This may explain the low genotypic yield reported for Blackeye (76 Kg/ha). There was no difference between the stress and non-stress treatments except at 40 days after planting where the transpiration ratio was higher due to leafhopper damage (Table 17). Blackeye had the highest transpiration ratio at 57 DAP. WW Leafhopper damage decreased stomatal conductance by 40 % at 40 days after planting, by 20% at 57 DAP and by 15% at 70 DAP (Table 18). At 57 DAP Blackeye had the lower stomatal conductance than TVX 3236. This corresponds with a low photosynthetic rate at 57 DAP (Table 16). 161‘ ° TABLE 15. Carbon Isotope Discrimination in Beans Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991. IREAIMENT DELTA N81017 (S) 20.4 9-39-1 " 19.6 8-42-M-2 " 20.6 8-25-2 " 20.0 N81017 (NSD) 20.4 9-39-1 " 19.9 8-42-M-2 " 20.4 8-25-2 " 20.3 ns GENOTYPE N81017 20.4 a 9-39-1 19.7 b 8-42-M-2 20.5 a 8-25-2 20.2 ab * LEAFHOPPER Stress 20.2 Non-Stress 20.3 ns S= Stress NSD= Non-stress ns= not significant "‘ Different letters within a column indicate significant difference at p= 0.05 according to Duncan Multiple Range Test. 162 TABLE 16. CO2 Assimilation Rate in Cowpeas Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991. W IREAIMENT 4O1 572 703 umols tn‘2 5'1 TVX 3236 (S) 2.8 b 29.7 17.1 ab BLACKEYE " 4.4 ab 9.7 15.1 bc ER, " 11.0 a 15.4 16.1 bc IT83$-742-2 " 6.1 ab 17.7 13.4 bc TVX 3236 (NSD) 9.9 ab 26.6 19.0 ab BLACKEYE 6.1 ab 11.8 10.6 c ER, " 5.3 ab 19.6 17.4 ab IT838-742-2 " 6.5 ab 25.4 22.8 a t IIS 1! GENOTYPE TVX 3236 6.3 23.7 a 18.1 a BLACKEYE 5.3 10.8 c 12.9 b ER, 8.1 17.5 b 16.7 a IT83S-742-2 6.3 21.5 ab 18.1 a [IS 43* It LEAFHOPPER Stress 6.9 18.1 15.4 Non-stress 6. 1 20.9 17.5 ns *lllk us S= Stress NSD= Non-stress ns= not significant ***, 3"“, "' Differentt letters within a column indicate significant difference at p= 0.001, 0.01 or 0.05 respectively according to Duncan Multiple Range Test. 3 Early vegetative stage (V 5) 2 Late vegetative stage (V 9) 3 Flowering and pod development (R1/R2) 163 2 TABLE 17. Transpiration Ratio in Cowpeas Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East lansing. MI. 1991. _DAXW IREAIMENT 40’ 572 703 mol H,O/ mol CO, TVX 3236 (S) 3297.9 a 292.1 370.3 BLACKEYE " 781.8 b 478.8 408.2 ER, " 407.7 b 330.3 384.2 IT83S-742-2 " 853.3 b 286.2 440.7 TVX 3236 (NSD) 421.1 b 240.0 411.3 BLACKEYE " 649.8 b 589.4 886.6 ER, " 717.1 b 350.5 424.1 IT83S-742—2 " 763.7 b 266.9 342.5 " ns ns GENOTYPE TVX 3236 1859.5 266.0 b 390.9 BLACKEYE 715.8 534.1 a 647.1 ER, 562.4 340.4 b 391.6 IT83S-742-2 808.5 276.6 b 391.6 ns " ns LEAFHOPPER Stress 1335.2 346.8 400.9 Non-stress 637.9 361.7 516.0 ‘ ns ns S= Stress NSD= Non-stress ns= not significant ‘2", *, * Different letters within a column indicate significant difference at p= 0.001, 0.05 or 0.1 respectively according to Duncan Multiple Range Test. 3 Early vegetative stage (V 5) 2 Late vegetative stage (V9) 3 Flowering and pod development stage (R,/R,) 164 TABLE 18. Stomatal Conductance in Cowpeas Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East lansing. MI. 1991. W REATMENT 401 572 703 mmols m‘2 8'1 TVX 3236 (S) 66.0 156.4 230.0 bc BLACKEYE " 67.3 110.9 218.3 bc ER, " 51.4 128.4 222.7 bc 1'1'838-742-2 " 78.0 127.4 193.9 c TVX 3236 (NSD) 132.6 167.6 270.8 ab BLACKEYE " 117.3 139.0 200.5 c ER, " 92.2 159.0 250.1 abc IT83S-742-2 " 93.8 164.5 295.9 a ns ns * GENOTYPE TVX 3236 99.3 162.0 a 250.4 BLACKEYE 92.3 125.0 b 209.4 ER, 71.8 143.7 ab 236.4 IT83S-742-2 85.9 145.9 ab 244.9 ms * ns LEAFHOPPER Stress 65.7 130.8 216.2 Non-stress 108.9 157.5 254.3 Illlls *4! #3 S= Stress NSD= Non-stress ns= not significant “"2, **, * Different letters within a column indicates significant difference at p= 0.001, 0.01 or 0.05 respectively according to Duncan Multiple Range Test. 2 Early vegetative stage (V 5, 2 Late vegetative stage (V 9) 3 Flowering and pod development stage (R1/R2) 165 C l I D. . . . Carbon isotope discrimination was not reduwd by leafhopper damage but genotypic differences were observed (Table 17). Blackeye and IT838-742-2 had a significantly lower CID value than ER,. CID values have been proposed for predicting drought resistance and not resistance to leafhopper damage but it is interesting to note that CID did not separate the highest (IT838-742-2) and the lowest (Blackeye) yielding genotypes. III. NITROGEN PARTITIONING AND REMOBILIZATION Mm Even though four genotypes were planted, only two were analysed for 13N because of lack of funds to analyze all four genotypes. N81017 and 8-25-2 were chosen for analysis because they had not previously been used in 13N studies, because N81017 was resistant and high yielding and 8-25-2 was susceptible and low yielding, and because two years of 13N data had already been collected for 9-39-1 and 8-42-M-2. 13N content in the roots was not significantly affected by stress or genotype (Table 20). Leafhopper stress significantly increased 13N content in the lower stems during pod development and pod filling (69 and 86 DAP) by 48% and 53 % respectively (Table 21). At physiological maturity (93 DAP) although not significant, 13N content was increased by 32 % under stress. leafhopper stress significantly increased 13N content in the upper .166 7 TABLE 19. Carbon Isotope Discrimination in Cowpeas Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991. TREATMEL—DELIA— TVX 3236 (S) 19.5 BLACKEYE " 19.6 ER, " 20.1 IT83S-742-2 " 19.0 TVX 3236 (NSD) 19.6 BLACKEYE " 19.1 ER, " 19.7 IT83S-742-2 " 19.2 ns GENOTYPE TVX 3236 19.5 ab BLACKEYE 19.4 b ER, 19.9 a 1’1‘838-742-2 19.1 b ** LEAFHOPPER Stress 19.5 Non-stress 19.4 ns S= Stress NSD= Non-stress ns= not significant """ Different letters within a column indicate significant difference at p= 0.01 according to Duncan Multiple Range Test 167- TABLE 20. “'N Content in Bean Roots Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East lansing. MI. 1991. W TREATMENT 691 862 933 % N81017 (S) 2.29 1.05 0.95 8-25-2 " 1.95 0.57 0.96 N81017 (NSD) 1.14 0.76 0.65 8-25-2 " 1.13 1.36 0.71 ns ns ns GENOTYPE N81017 1.71 0.91 0.80 8-25-2 1.54 0.97 0.83 ns ns ns LEAFHOPPER Stress 2.12 0.81 0.95 Non-stress 1 4 1.06 0.68 ns ns ns S= Stress NSD= Non-Stress ns= not significant 3= R,/R3 Flowering and early pod development 2= R, Pod filling 3 = R, Maturity 168 TABLE 21. 13N Content in Bean Stems Subjecwd to Leahopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991. W TREATMENT 691 862 963 Wm % N81017 (8) 29.90 25.34 12.15 8-25-2 " 27.90 22.91 15.67 N81017 (NSD) 12.49 10.57 10.62 8-25-2 " 17.47 11.65 8.16 ns ns ns GENOTYPE N81017 21.20 17.95 11.38 8-25-2 22.68 17.28 11.91 ns ns ns LEAFHOPPER Stress 28.90 24.13 13.91 Non-stress 14.98 11.1 1 9.39 I!!! # ns Wm N81017 (S) 13.75 6.41 1.90 8-25-2 " 8.16 3.59 2.18 N81017 (NSD) 3.96 7.32 0.97 8-25-2 " 5.49 8.20 0.60 ns ns ns GENOTYPE N81017 8.86 6.87 1.43 8-25-2 6.82 5.89 1.39 ns ns ns LEAFHOPPER Stress 10.96 5.00 2.04 Non-stress 4.73 7.76 0.79 ns " * S= Stress NSD= Non-stress + p(0.1) * p(0.05) 3= Rama 2: Rs ns= not significant ** p(0.01) 3= R7 169 stem at 69 and 93 DAP. This suggests that more N was being remobilized to the stem from the labelled leaf under stress. There were no genotypic differences in 13N content in the lower or upper stems. There was a significant increase of 61% and 62 % in 13N content in the lower 1eaves under stress at 86 and 93 DAP (Table 22). Stress significantly increased 13N content in the upper leaves at 69 and 93 DAP. The genotype N81017 contained a significantly higher level of 13N than did 8-25-2 in the upper leaves under stress conditions at 93 DAP indicating less N remobilization to seeds. There were no differences between stress and non-stress in the lower or upper reproductive structures, or between genotypes (Table 23). However, the leafhopper x genotype interaction was significant in the upper reproductive structures at 86 DAP. Stress increased 13N content by 560% in 8-25-2 indicating greater N remobilization under stress. Leafhopper damage increased ”N content in the stem and leaves. 13N content for most plant parts was not statistically different even though numerical differences existed. This is due to the very high coefficient of variation which ranged from 60 to 200%. Harris ( 1993) also reported very high coefficient of variation ranging from 107 to 171 % in 13N recovery in red clover. 11° C . There was no significant difference in N concentration between the leafhopper stress and non-stress treatment in the roots but N81017 tended to have a lower root N concentration than 8-25-2 (Table 24). The stress treatment significantly increased N concentration at 86 and 93 DAP in the lower stem (Table 25). The drought susceptible genotype, 8-25-2 had a significantly higher N concentration than the drought resistant 170‘ TABLE 22. 13N Content in Bean Leaves Subjected to Leaflropper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991. W TREATMENT 691 862 933 mm % N81017 (8) 41.01 32.92 16.04 8-25-2 " 47.02 32.26 11.38 N81017 (NSD) 32.70 19.56 4.79 8-25-2 " 23.60 5.71 5.50 ns ns ns GENOTYPE N81017 36.86 26.23 10.41 8-25-2 35.29 18.99 8.44 ns ns ns LEAFHOPPER Stress 44.02 32.59 13.71 Non-stress 28.43 12.63 5 . 14 US + 4- 11212113212: N81017 (S) 20.20 8.49 4.21 a 8-25-2 " 17.50 4.96 1.65 b N81017 (NSD) 5.50 7.99 1.28 b 8-25-2 " 9.19 5.28 1.53 b ns ns * GENOTYPE N81017 12.85 8.24 2.54 8-25-2 13.35 5.12 1.60 ns as + LEAFHOPPER Stress 18.85 6.73 2.75 Non-stress 7.34 6.64 1.39 *2: i * S= Stress NSD= Non-stress ns= not significant **, *, + Different letters within a column indicate significant difference at p= 0.01, 0.05 or 0.1 respectively according to DMRT 3=R2/Ra 2=Rs 2=R7 171- TABLE 23. ”N Content in Bean Reproductive Parts Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991. W IREAIMENT 69‘ 862 933 W % N81017 (8) 12.84 28.46 41.83 8-25-2 " 11.18 18.02 46.91 N81017 (NSD) 17.34 29.64 36.91 8-25-2 " 23.04 33.57 33.93 ns ns ns GENOTYPE N81017 15.09 29.05 39.37 8-25-2 17.11 25.79 40.03 ns ns ns LEAFHOPPER Stress 12.01 23.24 43.99 Non-stress 20.19 31.60 35.42 ns ns ns W N81017 (S) 3.29 1.66 ab 7.05 8-25-2 " 1.39 4.87 a 5.91 N81017 (NSD) 2.24 4.01 ab 6.87 8-25-2 " 3.00 0.87 b 6.61 ns * ns GENOTYPE N81017 2.77 3.00 6.96 8-25-2 2.20 2.58 6.26 ns ns ns LEAFHOPPER Stress 2.34 2.44 6.48 Non-stress 2.62 3.27 6.74 115 41$..___DS___ S= Stress NSD= Non-stress ns= not significant * Different letters within a column indicate significant difference at p= 0.05 according to Duncan Multiple Range Test. 1: Rama 2: R5 3: R7 172 TABLE 24. N Concentration in Bean Roots Subjected to leafhopper Infestation at the Agronomy Farm in East Lansing. MI. 1991. W WNT 69‘ 862 933 % N81017 (S) 1.33 1.43 1.01 8-25-2 " 1.88 1.36 1.17 N81017 (NSD) 1.37 1.13 0.91 8—25-2 " 1.75 1.36 1.17 ns ns ns GENOTYPE N81017 1.35 1.28 0.96 8-25-2 1.82 1.32 1.10 Ilnlt n3 n3 LEAFHOPPER Stress 1.61 1.40 0.96 Non-stress 1.56 1 .21 1 .09 ns ns ns Se: Stress NSD= Non-stress 3‘“ p= 0.01 1: Rama 2___ R5 3: R, ns= not significant 173 TABLE 25. N Concentration in Bean Stems Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991. W TREATMENT 69‘ 862 933 mm % N81017 (S) 2.49 2.50 1.57 8-25-2 " 3.15 3.00 2.32 N81017 (NSD) 1.81 1.23 1.27 8-25-2 " 2.82 2.36 1.79 ns ns ns GENOTYPE N81017 2.15 1.87 1.42 8-25-2 2.99 2.68 2.06 d! t * LEAFHOPPER Stress 2.82 2.75 1.95 Non-stress 2.32 1.80 1.53 IIS Int: '1- W N81017 (S) 3.31 2.73 1.85 8-25-2 " 4.58 3.05 3.06 N81017 (NSD) 3.20 3.12 1.64 8—25-2 " 3.98 3.42 1.95 ns ns ns GENOTYPE N81017 3.25 2.93 1.74 8—25-2 4.28 3.23 2.50 ns ns * LEAFHOPPER Stress 3.94 2.89 2.46 Non-stress 3.59 3.67 1.79 ns ns + S= Stress NSD= Non-stress ns= not significant **, 2‘, " p= 0.01, 0.05 or 0.1 respectively I: R2/R3 2: R5 3: R7 .124 - genotype, N81017 at all sampling dates suggesting that 8-25-2 was probably not utilizing N as efficiently as N81017. Leafhopper stress significantly increased N concentration in the upper stem at physiological maturity. The resistant and high yielding genotype, N81017 had lower N concentration than the susceptible and low yielding genotype 8-25-2 at 93 DAP in the upper stem (Table 25). Stress significantly increased N concentration in the lower leaves at 69 and 86 DAP and in the upper leaves at 86 DAP (Table 26). 8- 25-2 had a significantly higher N concentration in the lower leaves at 69 and 93 DAP. There was a significant increase in N concentration in the lower and upper reproductive structures at 69 DAP under stress (Tables 27). 8-25-2 had a significantly higher N concentration than N81017 at 69 and 93 DAP in the lower reproductive structures (Table 27). Leafhopper damage increased N concentration in the roots, stem, leaves and reproductive structures. This suggests that the utillization of N was less efficient due to leafhopper damage. The resistant genotype, N81017 had a lower N concentration in the seeds than the susceptible genotype, 8-25-2. This suggestion of greater N use efficiency may explain its greater yield performance. E' ! I . Total plant dry weight increased with plant growth but was reduced under stress. Leafhopper damage decreased the dry weight of both N81017 and 8-25-2 (Fig 6). The harvest index of N81017 was 0.61 and that of 8-25-2 was 0.64. The actual numbers for dry matter accumulation of the different plant parts are shown in Appendix C (Tables 1- 7). 1 75 TABLE 26. N Concentration in Bean Leaves Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991. '3'“, *, " p= 0.01. 0.05 or 0.1 respectively 3: R7 ‘= 12./R. 2= R. W TREATMENT 691 862 933 W % N81017 (S) 4.54 3.97 2.73 8-25-2 " 4.82 4.53 3.26 N81017 (NSD) 3.79 3.43 2.62 8.25-2 " 4.26 3.45 3.13 ns ns ns GENOTYPE N81017 4.16 3.70 2.68 8-25-2 4.54 3.99 3.19 4' n5 *2! LEAFHOPPER Stress 4.68 4.25 2.99 Non-stress 4.03 3.44 2.88 it + n5 112211.329: N81017 (S) 5.14 4.84 2.23 8-25-2 " 6.48 4.92 1.10 N81017 (NSD) 4.77 3.56 1.28 8-25-2 " 5.91 3.55 2.30 ns ns ns GENOTYPE N81017 4.96 4.20 1.76 8-25-2 6.19 4.23 1.61 ns ns ns LEAFHOPPER Stress 5.81 4.88 1.67 Non-stress 5.34 3.55 1.72 ns lit n5 S= Stress NSD= Non-stress ns= not significant 176 TABLE 27. N Concentration in Bean Reproductive Parts Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI.1991. W IREATMENT 69‘ 862 933 MW % N81017 (S) 4.87 4.39 3.26 b 8-25-2 " 5.81 4.54 4.46 b N81017 (NSD) 3.76 3.34 3.40 b 8-25-2 " 4.78 4.05 3.46 a ns ns + GENOTYPE N81017 4.31 3.86 3.33 8-25-2 5.30 4.29 3.96 *8! ns * LEAFHOPPER Stress 5 .34 4.46 3.86 Non-stress 4.27 3.69 3.43 ** ns ns MW N81017 (S) 5.13 3.45 3.16 8.25-2 " 5.02 3.71 4.01 N81017 (NSD) 4.02 3.51 3.27 8-25-2 " 4.48 3.63 3.44 ns ns ns GENOTYPE N81017 4.58 3.48 3.22 8-25-2 4.75 4.17 3.73 ns ns ns LEAFHOPPER Stress 5 .08 4.08 3.59 Non-stress 4.25 3.57 3.36 * 115—__IIL_ S= Stress NSD= Non-stress ns= not significant 3““, *, * Different letters within a column indicate significant difference at p= 0.01, 0.05 or 0.1 respectively according to DMRT 1"" Rama 2: Rs 3: R7 177 FIG. 6. TOTAL DRY WEIGHT IN BEANS IN 1991 8-25-2 O fluo 1 r r IO 9 r .I TO r8 .- r .m r r r a O o- I I I - I I I Io-I I I ImIII I I06 5 w 3 2 1 0223323 Eon... Ea N81017 HNON-STRESS HSTRESS r I I 1 T r [KTTV 90 ITfTT' 100 80 7'0 DAYS AFTER PLANTING qldu d-qu-qudu-udéq O 6 d d - 0 0 O m m. a .. .. cco_..\m523 Emma .55 ENQQntent Stress significantly increased the proportion of ”N that was in the root at 86 DAP but there were no genotypic differences (Table 28). There was no significant difference between percentage of ”N in the stress and non-stress treatment of the lower stems, but TVX 3236 contained a higher proportion of ‘3N than IT83S-742-2 at physiological maturity suggesting that TVX 3236 remobilized less N from the lower stem. At 69 DAP, the stress treatment contained a greater proportion of ”N the upper stem, and TVX 3236 contained more ”N than IT‘83S-742-2 (Table 28). There was a significant increase in the propotion of ‘3N under stress at 86 DAP in the lower leaves and at 69 and 86 DAP in the upper leaves (Table 29). TVX 3236 contained more ”N in the lower leaves than IT83S-742-2 at physiological maturity. There were no differences between the stress and non-stress treatments in the lower or upper reproductive structures with regard to ”N content (Table 30). IT83S-742-2 contained a greater proportion of ”N in the lower reproductive structures than TVX 3236 at 86 DAP. These results suggest that IT83S-742- 2 remobilized greater amount of N to the seeds. Mammalian Leafhopper damage significantly increased N concentration at 69 and 93 DAP in the roots and upper stems, and at all sampling dates in the lower stem (Table 31). At 93 DAP, TVX 3236 had a significantly higher N concentration than IT838-742-2 in the roots, lower and upper stems. There was a significant increase in N concentration in the lower and upper leaves at 69 and 86 DAP under stress, and TVX 3236 had a higher leaf 178 179 .5me Nm. :2 02.8.: 5 0°52. ”88 B... MES... 93.8.2. 8 5983.. .3885: 2 5... 3m: >m8=e5< 35: 3 m8. $8.5m. 7... $3. ._..~m>...7.mz... gm rDEmw mamK vamw Maw... 62: em. mm. mm. aw. mm. mm. me. me. 3. x ....u..0.u.um.~ manna who 93 we. .93 ~95 5.8 .~.u~ ab. Poe 28.36% ..m.. N. .m who .93 .ubo .98 93 So. a. .. B ... B B B B 2.... a a... mu manna ZmUn 23.38... Bu .5. «£3325. 3...... a. + .71. 98.. 9cm 2. P. 8.6896... .u $522.3 9.. .u m8... .2. w... 9». an .88 .2. w... E 180‘ TABLE 29. 1’N Content in Cowpea Leaves Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991. W— W 691 862 933 W % TVX 3236 (S) 26.55 44.15 20.38 I'I‘83S-742—2 " 21.42 41.68 8.90 TVX 3236 (NSD) 33.34 24.61 14.92 IT83S-742-2 " 1 1. 87 15 .30 7.76 ns ns ns GENOTYPE TVX 3236 29.94 32.99 18.04 IT83S-742-2 15.96 28.49 8.41 ns ns * LEAFHOPPER Stress 24.35 42.74 14.64 Non-stress 22.60 19.96 1 1.34 ns "‘ ns Wm TVX 3236 (S) 16.53 9.19 7.24 IT83S-742-2 " 14.97 7.44 1.30 TVX 3236 (NSD) 9.71 4.68 2.76 I'I‘83S-742-2 " 3.70 4.05 1.42 ns ns ns GENOTYPE TVX 3236 13.12 6.93 5.32 IT83S-742-2 9.33 5.75 1.34 ns ns ns LEAFHOPPER Stress 15.75 8.31 4.27 Non-stress 6.70 4.37 2.33 II! + m 8: Stress NSD= Non-stress ns= not significant *, + p= 0.05 or 0.1 respectively 1= R, 2= R3 3_ 181 TABLE 30. 1"’N Content in Cowpea Reproductive Organs Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991. W IREATMENT 691 862 933 W % TVX 3236 (S) 0.53 4.06 2.38 IT838-742-2 " 2.37 18.77 15.70 TVX 3236 (NSD) 2.20 5.59 8.54 IT83S-742-2 " 6.62 7.66 28.04 ns ns ns GENOTYPE TVX 3236 1.48 4.82 5.46 IT83S-742-2 4.50 13.22 23.93 ns * ns LEAFHOPPER Stress 1.58 11.42 9.04 Non-stress 4.41 6.63 21.54 ns ns ns W TVX 3236 (S) 0.70 0.18 -- IT83S-742~2 " 0.84 0.79 -- TVX 3236 (NSD) 1.68 6.27 -- IT83S-742-2 " 0.79 3.79 -- ns ns GENOTYPE TVX 3236 1.29 3.22 -- IT83S-742-2 0.82 2.79 -- ns ns LEAFHOPPER Stress 0.80 0.49 -- Non-sness 1 .23 4. 62 -- ns ns " p(0.1) ‘= R. ’= R3 R6 S= Stress NSD= Non-stress ns= not significant ...>.w.tm u. . z manna—fine: .: fiasco: woos :2. 92:: $388: 8 ram—Eccvnn .3883: m. :5 Km: .52.:95~ mun: .: m3. 182 58.5. 2.. $3. ....~m>...z.mz... woo.“ Efimw mHmK cmwmm mnmz. RUDE 3. mm» o”. am. mm» 88 me. mo: 8. x ....u..O...um.~ manna Nb. .6: .6: u...» Pom Pom 94m 93 who 288.8% ....o rue .bu Paw Pm: ram Pu. Pun Pu: {i a i :33. *ii $3.... * a i m u mag: ZmU H 23.36% B u :2 gnaw—8:. 3.... t... u. + 0508:. .288 2.9.: w 8.5:: 3388 gnaw—8:. @3238 a. .YI. 98.. 9b.. 98 on P. 882:5 8 62.”... .H W. n" Wu u" ”a 183- lower and upper leaves at 69 and 86 DAP under stress, and TVX 3236 had a higher leaf N concentration than IT83S-742-2 in the lower leaves at 69 and 86 DAP (Table 32). Leafhopper stress significantly increased N concentration in the lower reproductive sn'uctures at 86 and 93 DAP, and upper reproductive structures at 93 DAP (Table 33). There were no genotypic differences in N concentration. 5' E l . Leafhopper damage significantly reduced dry weight of the roots and lower stem at 69 and 86 DAP (Table 34). TVX 3236 had a higher dry weight than IT83S—742-2 in the lower stem at 86 and 93 DAP. There were no differences between the stress and non- stress treatments or between genotypes in the upper stem. Leafhopper stress did not significantly decrease dry weight in the lower and upper leaves except at 69 DAP in the lower leaves (Table 35). TVX 3236 had a higher dry weight than IT83S-742-2 at 93 DAP in the lower and upper leaves. There was a significant decrease in dry weight at all sampling dates in the lower reproductive structures due to leafhopper damage (Table 36). IT83S-742-2 had a significantly higher dry weight than TVX 3236 in the lower reproductive structures at all sampling dates. CONCLUSION Leafhopper damage decreased seed yield by decreasing the number of pods per plant in both beans and cowpeas. Cowpeas were more susceptible to leafhopper damage than beans. Leafhopper damage decreased LWRC and LWC in beans and cowpeas. Genotypic differences in LWRC and LWC occurred in beans and cowpeas but did not 184 TABLE 32. N Concentration in Cowpea Leaves Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East Lansing. MI. 1991. W WENT 69‘ 862 933 W TVX 3236 (S) 7.16 6.31 4.74 IT83S-742-2 " 6.07 5.77 4.77 TVX 3236 (NSD) 5.41 4.51 4.06 IT838-742-2 " 5. 10 4.05 4.04 ns ns ns GENOTYPE TVX 3236 6.29 5.41 4.45 IT83S-742-2 5.58 4.91 4.40 + + ns LEAFHOPPER Stress 6.62 6.04 4.76 Non-stress 5.25 4.28 4.05 *1! 38* 113 mm TVX 3236 (S) 6.18 5.79 4.26 IT83S-742-2 " 6.49 5 .92 4.46 TVX 3236 (NSD) 5.14 4.38 3.58 IT838-742-2 " 5. 17 3.88 3.64 ns ns ns GENOTYPE TVX 3236 5.66 5.09 3.97 lT83S-742-2 5.88 4.90 4.05 ns ns ns LEAFHOPPER Stress 6.33 5.85 4.36 Non-stress 5.16 4.13 3.61 *1!!! ** HS S= Stress NSD= Non-stress ns= not signifcant am n, *, + p= 0.001, 0.01, 0.05 or 0.1 respectively 1: it. 2: R3 3=R6 185 TABLE 33. N Concentration in Cowpea Reproductive Organs Subjected to Leafhopper Infestation at the MSU Agronomy Farm in East lansing. MI. 1991. W IREATMENT 69‘ 862 933 W % TVX 3236 (S) 4.83 5.09 4.51 IT838-742-2 " 5.46 4.94 4.20 TVX 3236 (NSD) 5.02 4.32 3.97 IT838-742-2 " 5.19 4.12 3.31 ns ns ns GENOTYPE TVX 3236 4.94 4.70 4.28 IT83S-742-2 5.33 4.53 3.75 ns ns ns LEAFHOPPER Stress 5.19 5.02 4.35 Non-stress 5.1 1 4.22 3.59 ns ** 4' Wm TVX 3236 (S) 5.08 3.45 4.08 IT83S-742-2 " 4.77 4. 10 4.43 TVX 3236 (NSD) 4.20 4.02 3.65 IT83S-742-2 " 4.71 3.69 3.49 ns ns ns GENOTYPE TVX 3236 4.55 3.73 3.82 IT83S-742-2 4.74 3.86 3.89 ns ns ns LEAFHOPPER Stress 4.87 3.72 4.29 Non-stress 4.46 3.86 3.5 ns___.ns * S= Stress NSD= Non-stress ns= not significant **, * p= 0.01 or 0.1 respectively 1: R1 2_.= R3 3= R6 186 ...»..rm NP DJ. ‘88... 3 0:388 .308 8:: m8Bu 9388.. 8 598.8... .3883: 8. ..8 75: >388... 1.5: .: m8. ...»:«Em. 2... $6.. ...wm>...?.mz... WORM rDEmw mHME Ewan—W munmz .026. mm. mm» 88 .6. mos mu. am. mg 3. «88.38:. .../D. Nu... 6. 9m ..a N... Nb Go a Na... ... ..N ..m ....mum..§N-N .. 9m . N N... ..N .m... .. .ub ... ..a ..m ....._oz A33. .mmol.oom So. So.“ .8.“ Go.U .20.. 1.8.... Got. .8... .001 mol. 1 .mmN 333: III .mm. 3.33: ole .mmo 3.2.0: J U0 q d d a q 4 - Bum? §>< ..CZm ..Cr< >CO. mmfl... 00... 196 TABLE 2. GENOTYPE DESCRIPTION GENOTYPE SOURCE SEED COLOR SEED SIZE 9-39-1 MSU1 white small 8—25-2 “ brown medium N81017 " white " 8-42-M-2 " ‘ off white " TVX 3236 IITEB tan medium IT838-742-2 " " " ER7 " off white small BOOS-C BOTSWANA maroon medium BLACKEYE " white " 1 MSU- Michigan State University Bean Breeding Program. USA. 2 IITA- International Institute of Tropical Agriculture, Ibadan. Nigeria. APPENDIX B 198 Appendix Bl: Photosynthesis Calculations C02 Assimilation Rate (A) A = 178 (Ce - Co) [(l-Xe)/(l-Xo)] Transpiration Rate (E) E = f/s [(Xo-Xe)/1-Xo)] Stomatal Conductance (g) g. = E / (X813 -X0) Where 3 = leaf area Ce = Mole fraction of CO2 at chamber entrance Co=" " " "" “ outlet X0 = Mole fraction of water vapor at chamber outlet Xe="""""”"entrance Xs= " " " " " " saturation f = air flow rate T = Temperature recorded during measurement 199; Appendix B2: Light Interception Calculations Variables measured S - PAR reading from an upfacing ceptometer above crop canopy R - Reflected PAR above canopy (ceptometer inverted above canopy) T - Par reading from an upfacing ceptometer below crop canopy U - Reflected PAR below canopy (ceptometer inverted below canopy) Calculations t = T / S = light transmitted by the canopy r = R / S = light reflected to a sensor above the canopy r, = U / T = reflectance of the soil surface Light Intercepted (f) f = l-t-r-tr, APPENDIX C 201 Calculations for 15N data Atom % and %N were obtained from the mass spectrometer data. 1. a.e = atom % excess = atom % in labelled plant - atom % in control 2. mg l’N enrichment = (a.e/100) * (%N/100) "‘ (Dw) * 1000 a.e and %N were divided by 100 because they are percents. Multiplying by 1000 converts grams to milligrams since the dry weight (Dw) is in grams. 3. % "N recovery = (mg N enrichment/ mg "N applied) "‘ 100 The amount applied was obtained when the plant was sampled one day aftr labeling. The total 1’N in the plant at that time was the total amount of 1"'N that was applied. vabm H. efim mmmoon 0m moww zman numsmmm on moon mun mnoE.UH< zmmen w: woman on «so ZmG rumouoaw mmna. mmmn bmbmwam. 3H. Home. 202 wooam» IIIIIIbeMWIMHMBIII IllllmmmmmIMngll mebHBMZH imp .wwl mm .ww llwm mm «INH Nm mm mHmam\UHw=n mnoNuzuN .m. o.qm o.me H.oN ».pH m.um ».om o.mq H.HN H.um muwmuu = o.mm H.¢N H.Hm w.mw m.mm m.pN H.mo H.mm v.9» mleazuN .Zmu. H.0N H.Ho o.mm m.mw m.Nm m.om H.mo N.ou o.mH m-w-H a o.mH H.Hm H.u» m.om q.mH m.wm H.Nm N.uw H.»m + am 5m 5m am am am so am mmsonwvm mupNaan o.mo o.mq o.mm m.mq m.mH p.mq H.om H.mm H.Hw mlwmup o.mu H.om _H.Nm p.mH m.mm ..um H.uw H.mm 9..» am am am . am 5m 5m 5m 5m zvamw mnnmmm o.mN o.wu H.om ».Hq m.mo m.Nm H.ou H.wm H.»o zosumnnmmm o.mH H.HN H.Ho m.ow q.mm m..H H.pp N.mm H.Hq w» + cm s» 44 am am 4 5m . w.o.p. 4 o.o.om. s. o.o.op. mu mnnmmm ZmUu zosnmnnmmm on" son mwmbwnwnwsn 203 TABLE 2. The Effect of Soil Water Changes on Leaf Dry Weight Dry Weight in Beans in the Rainshelter at the MSU Agronomy Farm in East Lansing. MI. 1990 W W 21 23 65 LQE§I_LEBXBS grams/plant 8-42-M-2 (S) 3.69 4.31 1.09 9-39-1 " 4.86 4.74 1.96 8-42-M-2 (NSD) 6.05 5.39 0.63 9-39-1 " 5.57 6.52 1.91 ns ns ns Genotype 8-42-M-2 4.87 4.85 0.83 9-39-1 5.22 5.63 1.92 ns ns ns Water STRESS 4.28 4.53 1.44 NON-STRESS 5.81 5.96 1.28 * * ns We 8-42-M-2 (S) 0.87 1.46 0.97 9-39-1 " 0.97 2.22 0.69 8-42-M-2 (NSD) 2.33 2.77 0.22 9-39-1 " 2.10 3.68 0.38 ns ns ns Genotype 8-42-M—2 1.60 2.12 0.52 9-39-1 1.54 2.95 0.48 ns * ns Water STRESS 0.92 1.84 0.83 NON-STRESS 2.21 3.22 0.31 it * " S= Stress NSD= Non-stress ns= not significant '** i * , , p=0.001, 0.05 or 0.1 respectively 204 TABLE 3. The Effect of Soil Water Changes on Reproductive Parts Dry Weight in Beans in the Rainshelter at the MSU Agronomy Farm in East Lansing. MI. 1990. .QAXE_AEIEB_RLANIIN§_______ TREATMENT Z1. 29 55 W Emma/plant 8-42-M-2 (S) 0.44 3.52 18.67 9-39-1 " 0.59 4.00 13.24 8-42-M—2 (NSD) 0.45 3.13 15.70 9-39-1 " 0.62 1.63 21.28 ns ns ns Genotype 8-42-M-2 0.43 3.32 17.19 9-39-1 0.60 2.81 17.26 ns ns ns Water STRESS 0.50 3.76 15.96 NON-STRESS 0.53 2.38 18.49 ns ns ns W 8-42-M-2 (S) 0.15 0.54 4.75 9-39-1 " 0.17 0.86 2.26 8-42-M-2 (NSD) 0.14 0.54 5.33 9-39-1 " 0.14 0.49 3.34 ns ns ns Genotype 8-42-M-2 0.14 0.54 5.04 9—39-1 0.16 0.68 2.80 ns ns ns Water STRESS 0.16 0.70 3.50 NON-STRESS 0.14 0.52 4.33 ns ns ns S= Stress NSD= Non-stress ns= not significant 205 TABLE 4. The Effect of Soil Water Changes on Bean Roots Dry Weight Using Plastic at the MSU Agronomy Farm in East Lansing. MI. 1991-92. 1991 1992 TREATMENT .121 38 45 .137 .47 grams/plant grams/plant N81017 (S) 1.20 1.29 1.53 1.57 1.58 8-25-2 " 0.80 0.94 1.16 0.98 0.86 N81017 (NSD) 0.96 0.96 1.05 1.95 1.56 8-25-2 " 0.74 0.87 0.96 0.96 0.70 ns ns ns ns ns Genotype N81017 1.08 1.13 1.29 1.76 1.57 8-25-2 0.77 0.90 1.06 0.97 0.77 + 118 + ** + Leafhopper STRESS 1.00 1.12 1.34 1.28 1.22 NON-STRESS 0.85 0.91 1.00 1.45 1.13 ns * ns ns ns 8: Stress NSD= Non-stress *, * p=0.05 or 0.1 respectively ns= not significant 206‘ TABLE 5. The Effect of Soil Water Changes on Bean Stem Dry Weight Using Plastic at the MSU Agronomy Farm in East Lansing. MI. 1991-92. 1991 19gz_____ TREATMENI;___________21 38 .45 37 ._41_ W grams/plant grams/plant N81017 (S) 8.26 10.11 9.08 8.21 9.22 8-25-2 " 6.36 5.74 7.21 6.69 9.69 N81017 (NSD) 7.07 7.92 8.17 9.57 11.27 8-25-2 " 5.41 7.36 6.31 7.42 8.01 ns ns ns ns * Genotype N81017 7.67 9.01 8.62 8.89 10.24 8-25-2 5.89 6.55 6.76 7.06 8.85 ns ns * ns ns Leafhopper Water STRESS 7.31 7.93 8.14 7.45 9.46 NON-STRESS 6.24 7.64 7.24 8.50 9.64 ns ns ns ns ns W N81017 (S) 1.42 1.66 1.26 1.49 1.47 8-25-2 " 1.29 1.35 1.11 1.00 1.31 N81017 (NSD) 1.74 1.47 1.40 1.25 1.28 9-25-2 " 1.42 1.15 1.03 1.12 1.63 ns ns ns ns ns Genotype N81017 1.58 1.56 1.33 1.37 1.37 8-25-2 1.36 1.25 1.07 1.06 1.47 * * * ns ns Leafhopper Water STRESS 1.36 1.50 1.18 1.24 1.39 NON-STRESS 1.58 1.31 1.21 1.19 1.46 * ns ns ns ns 8: Stress NSD= Non-stress ns= not significant *. * p= 0.05 or 0.1 respectively 267 TABLE 6. The Effect of Soil Water Changes on Bean Leaf Dry Weight Using Plastic at the MSU Agronomy Farm in East lansing. MI. 1991-92. 1991 1992___ TREATMENT 21 38 45 37 4] LoEe_LeaEea grams/plant gramS/Plant N81017 (S) 6.96 6.12 3.24 6.01 4.64 8-25-2 " 6.73 3.41 2.68 6.38 3.19 N81017 (NSD) 7.23 5.56 5.38 7.18 5.82 8-25-2 " 7.24 5.76 2.93 4.84 3.06 ns ns ns ns ns Genotype N81017 7.09 5.84 4.31 6.59 5.23 8-25-2 6.98 4.58 2.81 5.61 3.10 ns ns ns ns * Leafhopper STRESS 6.84 4.76 2.96 6.19 3.92 NON-STRESS 7.24 5.66 4.15 6.01 4.41 ns ns ns ns ns unner_Leaxea N81017 (S) 1.75 1.79 1.28 1.99 1.15 8-25-2 " 1.66 1.47 2.30 1.67 1.12 N81017 (NSD) 2.48 1.78 2.23 1.84 1.21 8-25-2 " 2.26 1.44 1.10 1.43 1.48 ns ns ns ns ns Genotype N81017 2.11 1.78 1.76 1.91 1.18 8-25-2 1.96 1.45 1.61 1.55 1.30 ns ns ns ns ns Leafhopper Water STRESS 1.71 1.63 1.72 1.83 1.13 NON-STRESS 2.67 1.61 1.67 1.64 1.35 * ns ns ns ns S= Stress NSD= Non-stress ns= not significant * p: 0.05 208, TABLE 7. The Effect of Soil Water Changes on Bean Reproductive Parts Dry Weight Using Plastic at the MSU Agronomy Farm in East Lansing. MI. 1991-92 1991 199z_______ IEEAJMENT 21 38 45 37 41— W grams /plant grams /p1ant N81017 (S) 6.29 15.71 28.98 16.66 21.76 8-25-2 " 4.86 13.48 27.29 16.56 20.09 N81017 (NSD) 1.63 6.36 19.06 18.42 24.42 8-25-2 " 0.95 10.82 15.89 13.06 13.82 ns ns ns ns ns Genotype N81017 3.96 11.04 24.02 17.54 23.09 8-25-2 2.90 12.15 21.59 14.81 16.95 ns ns ns ns ns Leafhopper Water STRESS 5.58 14.60 28.13 16.61 20.93 NON-STRESS 1.29 8.59 17.48 15.74 19.12 *** t * ns ns WW N81017 (S) 0.71 5.02 1.87 2.14 3.07 8-25-2 " 0.53 3.02 3.78 1.20 2.57 N81017 (NSD) 0.33 3.80 1.39 1.54 2.56 8-25-2 " 0.23 2.07 0.46 1.65 1.78 ns ns ns ns ns Genotype N81017 0.52 4.41 1.63 1.84 2.81 8-25-2 0.38 2.55 2.12 1.42 2.17 ns * ns ns ns Leafhopper Water STRESS 0.62 4.02 2.83 1.67 2.82 NON-STRESS 0.28 2.94 0.92 1.59 2.17 * ns ns ns ns S= Stress NSD= Non-stress ns= not significant 1' * 'k * . p= 0.001 or 0.05 respectively nrcurcnn STATE UNIV. LIBRQRIES 1|HI111N)1|)”“1111”NWIN1|1|||111||||1H|| 31293010222531