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Katsvairo has been accepted towards fulfillment of the requirements for _lLS_.__degree in __Cmp_&_5n11 Sciences C’Sygmag 2 JW Major professor Date 2/26/99 0-7639 MS U is an Affirmative Action/Equal Opportunity Institution PLACE IN RETURN BOX to remove this checkout from your record. . To AVOID FINES return on or before date due. MAY BE RECALLED with'eariier due date if requested. DATE DUE DATE DUE DATE DUE mo mu YIELD, YIELD COMPONENTS AND NITROGEN PARTITIONING IN BAMBARA GROUNDN UT (Vigna subterranea), COMMON BEAN (Phaseolus vulgaris), AND COWPEA (Vigna unguiculata) GROWN UNDER STRESS AND NON-STRESS SOIL MOISTURE CONDITIONS Tawainga Witman Katsvairo A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Crop and Soil Sciences 1999 ABSTRACT YIELD, YIELD COMPONENTS AND NITROGEN PARTITIONING IN BAMBARA GROUNDNUT( Vigna subterranea),COMMON BEAN (Phaseolus vulgaris L.), AND COWPEA (Vigna unguiculata) GROWN UNDER STRESS AND NON-STRESS SOIL MOISTURE CONDITIONS By Tawainga Winnan Katsvairo Globally, moisture stress is a major constraint in agricultural production resulting in millions of dollars in economic losses. A study was conducted in the rainshelter at the Kellogg Biological Research Station, Hickory Corners, Michigan, in 1995 and 1996 to evaluate the efi‘ect of moisture stress on yield, yield components and N partitioning in Bambara groundnut (Vigna subterranea) genotypes ZVSS30 and ZV8564; common bean (Phaseolus vulgaris) genotypes Carioca, Natal Sugar and T3147-2; and cowpea (Vigna unguiculata) genotypes IT82D-889 and 475/89. The experiment was a split-plot in a randomized complete block design with moisture status as the main effect and species as the sub—plot. Moisture stress reduced yield by as much as 79% in common bean and 46% in cowpea. Cowpea genotypes aborted more seeds per pod than the other species Significant species difi‘erences were observed in seed weight, number of seeds per pod, number of pods per plant, and in N concentration of the different plant parts. Moisture stress did not significantly affect N concentration in any structures. ACKNOWLEDGMENTS I wish to express my sincere gratitude to my major professor Dr. Eunice F. Foster for her invaluable support, advice , encouragement and for fieely giving up a lot of her time throughout the study. I would also like to thank Drs. George Bird, Russell Fred and Richard Harwood for their suggestions and review of this thesis in their capacity as members of my guidance committee. The assistance of Greg Parker and all those who helped with the irrigation, and maintaining the rainshelter at the Kellogg Biological Research Station is greatly appreciated. I am grateful to Norm Blakely, Jerry Taylor, Brian Graff and Tom Galecka at the Crops Barn for their assistance with the processing of the samples and ensuring that I was able to conduct the experiments smoothly. Dr. Oliver Schabenberger’s assistance with the statistical analysis and Dr Anil Shrestha’s proof reading of the thesis are much appreciated. I thank Maurice Yabba, Kerri Gorentz, Patrick Karnbewa, Pete Zugger, Tamara, Tamika, Ryan Rowiniski, Angie Eichom, Heidi Nemeth, Mike Carroll, Ester Nobles, Marvin Gruszka, Maurice Hill, Angela Kovton, Jason Gross and Eric Baka for all their assistance with the planting, weeding, Kjeldahl analysis and data entry. I am indebted to all the fiicnds who helped either through moral support, encouragements or in one way or the other. My special thanks goes to WK. Kellogg Foundation for providing me an opportunity to pursue my studies and iii administering my stay in the United State of America. iv TABLE OF CONTENTS Page LIST OF TABLES .............................................. v LIST OF FIGURES ............................................. vii INTRODUCTION ............................................... 1 LITERATURE REVIEW ......................................... 3 The efl‘ect of moisture stress on plant growth and development ......... 3 Recovery from drought ........................................ 5 Strategies of response to water stress .............................. 6 Drought escape .............................................. 6 Avoidance .................................................. 7 Drought tolerance ............................................ 8 Osmotic adjustment ........................................... 9 Quick screening methods for drought tolerance ...................... 9 Screening method for drought tolerance using growth boxes ........... 10 Criteria for evaluating the effect of moisture stress.on.yield .......................... 10 Mean productivity ........................................... 10 Geometric mean ............................................. 11 The drought susceptibility index ................................ 11 The stress tolerance index ..................................... 11 Nitrogen and its efiect on drought tolerance ....................... 12 Nitrogen contribution of legumes to subsequent non-legume crop ....... 13 Efl‘ect of moisture stress on N fixation ............................ 14 Nitrogenase activity following moisture stress ...................... 15 Nitrogen utilization, partitioning, and remobilization ................. 15 Nitrogen partitioning and remobilization .......................... 16 Moisture stress in Zimbabwe .................................. 20 Origin and history of Bambara groundnut ......................... 21 Nutritional value ............................................ 22 Problems associated with Bambara groundnut production ............. 24 Status of Bambara groundnut production in Zimbabwe ............... 25 C0wpea ................................................... 25 References ................................................. 27 CHAPTER 1 MOISTURE STRESS EFFECTS ON YIELD AND YIELD COMPONENTS OF BAMBARA GROUNDNUT, COMMON BEAN, AND COWPEA Abstract ............................................................ 3 7 Introduction ................................................... 39 Materials and Methods .......................................... 41 Field.stud.y ..................................................................................................... 41 Separate analysis of Bambara groundnut ....................................................... 42 Greenhouse study to assess drought tolerance ............................................... 42 Results and Discussion .......................................... 43 Yield ..................................................... 43 D81, STIandGM .......................................................................................... 46 Yield components of common bean, cowpea, and soybean ............ 50 Bambara groundnut ....................................................................................... 61 Greenhouse study ........................................... 64 Conclusions ................................................ 69 References ................................................... 73 CHAPTER 2 EFFECT OF MOISTURE STRESS ON NITROGEN PARTITIONWG AND REMOBILIZATION IN BAMBARA GROUNDNUT, COWPEA, AND COMMON BEAN Abstract ...................................................... 75 Introduction ................................................... 77 Materials and Methods .......................................... 78 Results and Discussion .......................................... 81 Nitrogen partitioning ......................................... 81 Leaves .................................................... 81 Stems ..................................................... 85 Reproductive structures ....................................... 88 Conclusions ................................................ 93 References ................................................... 94 Conclusions .................................................. 96 LIST OF TABLES CHAPTER 1 l. Arithmetic mean, percent yield reduction, geometric mean, drought susceptibility index (D81), and stress tolerance index (STI) of two cowpea and two common bean genotypes grown under stress and non- stress soil moisture conditions at the Kellogg Biological Station in Hickory Corners, MI in 1995. ........................... 47 2. Arithmetic mean, percent yield reduction, geometric mean, drought susceptibility index (D81), and stress tolerance index (STI) of two cowpea and two common bean genotypes grown under stress and non- stress soil moisture conditions at the Kellogg Biological Station in Hickory Corners, MI in 1995. ........................... 48 3. Potential drought tolerance screening method measuring days to permanent wilting for Bambara groundnut ( Vigna subterranea), common bean (Phaseon vulgaris), and cowpea (Vigna unguiculata) grown in a 1:1 sandzsoil media in growth boxes (1.5 x 1.5 x 12 and 1.5 x 1.5 x 20 cm) in a greenhouse, at the Michigan State University from June 18, 1996 to July 26, 1996. .............................................. 7O 4. Potential drought tolerance screening method measuring days to permanent wilting for Bambara groundnut ( Vigna subterranea), common bean (Phaseolus vulgaris), and cowpea (Vigna unguiculata) grown in a 1:1 sandzsoil media in growth boxes (1.5 x 1.5 x 12 and 1.5 x 1.5 x 20 cm) in a greenhouse, at the Michigan State University fiom August 20, 1996 to October 26, 1996 .......................................... 71 CHAPTER 2 l. Leaf-N concentration (°/o) at the vegetative, flowering and podfill stages of Bambara groundnut (Vigna subterranea), common bean (Phaseolus vulgaris), cowpea (Vigna unguiculata) and soybean (Glycine max) grown under non stress and stress soil moisture conditions at the Kellogg Biological Research Station, MI in 1995 and 1996 .................................................. 82 2. Species contrasts for leaf-N concentration of Bambara groundnut ( Vigna subterranea), common bean (Phaseolus vulgaris), cowpea vii (Vigna unguiculata), and soybean (Glycine max) grown under non- stress and stress soil moisture conditions in a rainshelter at the Kellogg Biological Research Station, MI in 1995 and 1996 . . . . . . . . . . .....83 3. Stem-N concentration of Bambara groundnut (Vigna subterranea), common bean (Phaseolus vulgaris), cowpea (Vigna unguiculata) and soybean (Glycine max) grown under non-stress and stress soil moisture conditions in a rainshelter at the Kellogg Biological Research Station, MI in 1995 and 1996 ................................... 86 4. Species contrasts for stem-N concentration of Bambara groundnut (Vigna subterranea), common bean (Phaseolus vulgaris), cowpea (Vigna unguiculata) and soybean (Glycine max) grown under non-stress and stress soil moisture conditions in a rainshelter at the Kellogg Biological Research Station, MI in 1995 and 1996 ................... 87 5. Reproductive-N concentration (%) of Bambara groundnut (Vigna subterranea), common bean (Phaseolus vulgaris), cowpea (Vigna unguiculata), and soybean (Glycine max) grown under non-stress and stress soil moisture conditions in a rainshelter at the Kellogg Biological Research Station, MI in 1995 and 1996 .................. 89 6. Species contrasts for reproductive-N concentration of Bambara groundnut (Vigna subterranea), common bean (Phaseolus vulgaris), cowpea (Vigna unguiculata), and soybean (Glycine max) grown under non-stress and stress soil moisture conditions in a rainshelter at the Kellogg Biological Station, MI in 1995 and 1996 ................... 90 7. N concentration of leaves, stems, and reproductive structures of common bean(Phaseolus vulgaris L.) grown under non-stress (NS) and stress (S) soil moisture conditions in a rainshelter at the Kellogg Biological Station in Hickory Comets, MI in 1995. .......................... 92 8. N concentration of leaves, stems, and reproductive structures of common bean(Phasequs vulgaris L.) grown under non-stress (NS) and sness (S) soil moisture conditions in a rainshelter at the Kellogg Biological Station in Hickory Corners, MI in 1995. ................................ 92 viii LIST OF FIGURES CHAPTER 2 1. Yield of common bean (Phaseolus vulgaris), soybean (Glycine max) and cowpea (Vigna unguiculata) grown under non-stress and stress soil moisture conditions in a rainshelter at the Kellogg Biological Research Station, MI. 1995 ................................... 44 2. Yield of common bean (Phaseolus vulgaris), cowpea (Vigna unguiculata), and soybean (Glycine max) grown under non-stress and stress soil moisture conditions in a rainshelter at the Kellogg Biological Research Station, MI. 1996. .......................... 45 3. Seed weight per 100 seeds of common bean (Phaseolus vulgaris), cowpea ( Vigna unguiculata and soybean (Glycine max) grown under non-stress and stress soil moisture conditions in a rainshelter at the Kellogg Biological Research Station, MI. 1995 .................... .51 4. Seed weight per 100 seeds of common bean (Phaseolus vulgaris), cowpea (Vigna unguiculata and soybean (Glycine max) grown under non-stress and stress soil moisture conditions in a rainshelter at the Kellogg Biological Research Station, MI. 1996 .................... 52 5. Seeds per pod of common bean (Phaseolus vulgaris), cowpea (Vigna unguiculata) and soybean (Glycine max) grown in a rainshelter at the Kellogg Biological Station, MI. 1995. Data are combined for non-stress and stress soil moisture conditions .............................. 53 6. Seeds per pod of common bean (Phaseolus vulgaris), cowpea (Vigna unguiculata), and soybean (Glycine max) grown under non stress and stress soil moisture conditions in a rainshelter at the Kellogg Biological Station in Hickory Comers, MI. 1996. ........................... 54 7. Number of pods per plant of common bean (Phaseolus vulgaris), cowpea (Vigna unguiculata), and soybean (Glycine max) grown under non—stress and stress soil moisture conditions in a rainshelter at the Kellogg Biological Research Station, MI. 1996. .................... 56 10. ll. 12. l3. 14. 15. l6. 17. Number of seeds aborted per pod of common bean (Phasealus vulgaris), cowpea (Vigna unguiculata), and soybean (Glycine max) grown under in a rainshelter at the Kellogg Biological Research Station, MI. 1995. Non-stress and stress data combined. ............................ Number of seeds aborted per pod of common bean (Phaseolus vulgaris), cowpea (Vigna unguiculata), and soybean (Glycine max) grown under non- stress and stress soil moisture conditions in a rainshelter at the Kellogg Biological Station, MI. 1995 ............................ Shelling percentage of common bean (Phaseolus vulgaris), cowpea (Vigna unguiculata), and soybean (Glycine max) grown under non- stress and stress soil moisture conditions in a rainshelter at the Kellogg Biological Station, MI. 1995 ................................... Shelling percentage of common bean (Phaseolus vulgaris), cowpea (Vigna unguiculata), and soybean (Glycine max) grown under non-stress and stress soil moisture conditions in a rainshelter at the Kellogg Biological Station, MI. 1996 ................................... Yield of Bambara groundnut (Vigna subterranea) grown in a rainshelter at the Kellogg Biological Station, MI. 1995. Data are combined for non- stress and stress soil moisture conditions ......................... Yield of Bambara groundnut (Vigna subterranea) grown at the Kellogg Biological Research Station, MI. 1996. Data are combined for non-stress and stress soil moisture conditions .............................. Shelling percentage of Bambara groundnut (Vigna subterranea) grown in a rainshelter at the Kellogg Biological Station, MI. 1995. Data are combined for non-stress and stress soil moisture conditions ........... Shelling percentage of Bambara groundnut (Vigna subterranea) grown in a rainshelter at the Kellogg Biological Research Station, MI. 1996. Data are combined for non-stress and stress soil moisture conditions Seed weight per 100 seeds Bambara groundnut (Vigna subterranea) grown in a rainshelter at the Kellogg Biological Research Station, MI. 1995. Data are combined for non-stress and stress soil moisture conditions ................................................ Seed weight per 100 seeds of Bambara groundnut (Vigna subterranea) X 57 58 59 6O 62 63 65 .66 grown in a rainshelter at the Kellogg Biological Research Station, MI. 1996. Data are combined for non-stress and stress soil moisture conditions ................................................ 68 INTRODUCTION Grain legumes are an important dietary component of many people in the ‘developing world.’ Grain legumes provide essential protein and vitamins and are an important source of fiber and calories in the human diet. In Zimbabwe, gain legumes are particularly important to the communal area and small scale farmers. Grain legumes are grown for their leaves, immature pods, and dry gain which are consumed in various preparations: fresh green leaves, dried and stored leaves, green peas, dry gain boiled with maize and various pastes (Nleya, 1992). Grain legumes store well and are often stored by farmers for domestic consumption. Only the excess production is sold for cash. The role of gain legumes in meeting human nutritional needs in Zimbabwe is likely to increase with the increasing cost of animal protein. World wide, gain legumes are generally grown under rainfed conditions and often experience moisture stress during the growing season (Ehleringer et al., 1991). White and Singh (1991) estimated that more than 60% of common beans (Phaseolus vulgaris) gown in Latin America, Asia, and Afiica suffer from water stress during crop gowth. In Latin America alone, 93% of the common bean gowing areas experience moisture stress (Fairbairn, 1993). Nearly one third of the world's common beans are produced in the central highlands of Mexico and northeastern Brazil, areas where drought is a common occurrence. Yield losses 1 caused by drought result in the economic loss of millions of dollars for the common bean producing regions of the world. The intensity of drought stress and the phenological stage of development at which drought occurs is unpredictable and difiem for each year and region. Thus, moisture stress influences crop yield in difl‘erent ways in difi‘erent regions (Acosta-Gallegos and Adams, 1991). Various authors have proposed definitions of drought. Hall (1993) defines drought as occurring when water supply in the soil is sumciently less than the maximum tendency of plants to lose water, as determined by the evaporative demand of the atmosphere. Drought stress in this review is defined as insufiicient soil moisture to sustain plant gowth and development. Drought may be terminal, when there is a gadual decrease of soil moisture as the plant matures, or intermittent in which moisture stress persists for seven days or longer and occurs once or several times in the gowing season (Levitt, 1972). Most communal area and small scale farmers in Zimbabwe are located in areas that experience inadequate and ineffective rainfall for crop production. Some of the rainfall occurs outside the gowing season and is subsequently lost through evapotranspiration, while rainfall during the season ofien comes as sporadic storms and results in excessive mofi. LITERATURE REVIEW The effect of moisture stress on plant growth and development Moisture stress afi‘ects cell membrane structure, modifying viscosity and permeability (1220 et al., 1989) and results in decreased cell elongation (Hsiao, 1973). Above gound biomass and leaf area index are reduced due to reduced leaf-area expansion and premature senescence (Acosta-Gallegos and Shibata, 1989). Moisture stress interferes with nutrient uptake and alters plant hormone levels (Bradford and Hsiao, 1982). Moisture stress has the gcatest effect on the plant tissue which is gowing most rapidly at the time the stress occurs (Aspinall et al., 1964). The eflect of moisture stress on seed yield depends on the phenological stage of development during the moisture deficit and on the intensity and duration of the deficit. In legumes, the reproductive stages from flower set through pod development and maturity are the most sensitive to moisture stress (Acosta- Gallegos and Shibata, 1989). Moisture stress in common beans during the reproductive stage reduced yield twice as much as moisture stress during the vegetative phase (Acosta-Gallegos and Shibata, 1989). In cowpea, (Vigna unguiculata), a 35% reduction in yield was observed when moisture stress was imposed at flowering and a 69% reduction when it was imposed at the pod fill stage (Shouse et al., 1981). Meckel et al. (1984) reported that the vegetative stage of soybean (Glycine max) was more sensitive to moisture stress than the seed development stage. However, diflerences in seed yield between stressed and non- stresscd plants of the same variety vary markedly from year to year, depending upon the phenological stage at which moisture stress occurs (Hoogenboom et al., 1987) Inhibition of photosynthesis at low water potential coupled with low carbohydrate reserves at pollination caused developmental failure of the reproductive tissue due to a lack of substrate (Schussler and Westgate, 1991). With maize (Zea mays), Westgate and Grant (1989) showed that low water potential occurred in ovaries of water-deficient plants. At leaf water potentials that completely inhibited photosynthesis, ovary water potential was low enough to affect cell division, cell expansion, and metabolism of assimilates (Nicholas et al., 1985). Shussler and Westgate (1991) concluded that low ovary water potential may induce zygotic abortion directly by altering reproductive sink strength. Increased flower abortion and reduced pod numbers have been reported in cowpea (Hiler et al., 1972) and common bean (Stoker, 1974) under moisture stress, along with decreased individual seed weight . Water limitation can hasten or delay phenological development of plants depending on severity of the water stress ( Turk and Hall, 1980; Lawn, 1982; Rosenthal et al., 1987). In soybean, moisture stress has been reported to decrease the duration of reproductive deveIOpment and consequently yield (Korte et al., 1983). Chickpea (Cicer arietinum) matured early under conditions of limited water (Khanna-Chopra and Sinha, 1987). Turk and Hall (1980) and Lawn (1982) noted that the reproductive activity of cowpea may be hastened or delayed depending on phenological stage of development of the plant and intensity of the moisture stress. Determinate cowpea cultivars had little yield loss when moderate moisture stress was imposed during flowering because the pods matured before the stress became severe (Summerfield et. al., 1985). Thus, sensitive stages can escape midseason drought (Gwathmey and Hall, 1992). Recovery from drought Most leguminous species branch and have stem apices which tend to be protected by older leaves during conditions of moisture stress. The newer leaves have a more negative water potential and water moves fiom the older leaves to the apex. The water status of the apex was thus maintained at the expense of older leaves (Elston and Bunting, 1980). Singh et al. (1995) observed that the cowpea apex remained alive even after the rest of the plant was severely wilted. If the crop was re-watered, the terminal meristem regenerated to form new leaves, flowers and ultimately seed (Elston and Bunting, 1980; Singh et al., 1995). Indetemrinate gowth habit and protection of the apex were useful survival strategies in areas of erratic rainfall. These important survival mechanisms resulted in uneven maturing of the legumes and created difficulties in mechanical harvesting (Elston and Bunting, 1980). Strategies of response to water stress Water stress induced many morphological, phenological, anatomical, and physiological responses in plants (Ludlow, 1989). Often, the responses occurred simultaneously or in combinations. Ludlow (1989) referred to them as ‘strategies.’ He defined a strategy as a combination or gouping of mechanistically-linked responses and characteristics that comprised a particular type of behavior during periods of water stress. mm The drought escape strategy enabled plants to complete their life cycles during a short period of time before drought occurred (Hall, 1993). Seeds germinated quickly after rain, gew and developed rapidly, flowered, and produced seed before the water supply was exhausted (Ludlow, 1989). The time fiom germination to maturity was short and approximated the average length of the gowing season for the particular environment. Cultivars gown by West Afiican farmers had phenologies that shortened as the rainfall decreased from the coast towards the desert (Dancette and Hall, 1979). In the Sahel, newly developed early cultivars of cowpea flowered within 30 days of sowing and produced substantial yield by 55 days, at which time traditional varieties had only begun to flower. The photoperiod sensitivity of these plants permitted flowering to coincide with the average date to the end of the rainy season (Ludlow and Muchow, 1990). This ensured a relatively high gain yield as pests and diseases were avoided and sumcient time was provided to fill gain before soil moisture reserves were exhausted. Drought escape can also be enhanced through phenotypic plasticity and varietal intercropping. It is a conservative survival strategy that occurs at the expense of yield. The benefit is that some seed is obtained to ensure species survival from year to year. Av i Plants that exhibited drought avoidance had tissue that was very sensitive to dehydration. These plants avoided water deficits whenever a water shortage occurred. Processes that aided in geater dehydration avoidance included low stomatal conductance, paraheliotropic leaf orientation, less leaf area, deeper roots that exploited water in deeper soil profiles, higher root/shoot ratio, geater osmotic adjustment, and little photosynthetic adjustment (Hall, 1993; Ludlow, 1989). For example Siratro (Macroptilium atropurpureum), a tropical legume had deep roots for maximum water uptake (Sheriff et al., 1986). It closed its stomates under dry, hot conditions and paraheliotropic movement occurred after stomatal closure (Ludlow et al., 1983). If moisture stress continued, smaller dark geen leaves were produced with a hairy abaxial surface. The smaller leaves had a larger convective heat exchange which moderated the increase of leaf temperature above air temperature when stomata were closed. Under extreme moisture stress, leaves died back progcssively up the stem from the oldest to the youngest, followed by basipetal stem die back leaving only the crowns to survive prolonged droughts (Ludlow, 1989). Cowpea was intolerant of desiccation and its avoidance techniques involved stomatal regulation of water loss (Bates and Hall, 1982). Leaf area was reduced by leaf senescence, abscission, and cessation of new leaf expansion (Turk and Hall, 1980; Akyeampong, 1986). This avoidance technique ensured water conservation by the remaining vegetative tissue and hence plant survival. However, drought avoidance negatively afi'ected photosynthetic capacity and yield potential. In extreme cases, both yield and survival of the plant was threatened by complete defoliation (Gwathmey and Hall, 1992). All the characteristics of drought avoidance did not appear in any one plant. Drggght Tolergge Dehydration tolerance indicates the plant’s ability to maintain vital frmctions as the relative water content decreases (Hall, 1993). These plants exhibited moderate to high osmotic adjustment. Osmotic adjustment assisted in the maintenance of turgor, which in turn assisted maintenance of carbon acquisition by sustaining stomatal opening, photosynthesis and leaf expansion. If carbon acquisition is to continue, water loss becomes inevitable and is often described as ‘the necessary evil.’ This is especially harmful if water uptake cannot match water loss (Ludlow, 1987). In some cases, this results in death of the plant. Osmotic adjustment The exact role of osmotic adjustment in drought resistance is not fully understood and has been questioned (Blum, 1989). Morgan (1984) working with wheat concluded that genotypes selected for a geater capacity for osmotic adjustment under moisture stress yielded more under drought stress than those exhibiting less osmotic adjustment. Grumet et al. (1987) found that barley populations with geater capacity for constitutive osmotic adjustment gew and yielded less under drought stress than those of lower capacity. They suggested that induced osmotic adjustment rather than constitutive osmotic adjustment can be used in the selection for drought resistance. Quick Screening methods for drought tolerance Identifying a quick, reliable and inexpensive method of screening for drought resistance in plants remains a geat challenge to crop physiologists. Several plant physiological responses and genes have been suggested as possible screening tools, but none has been defined as conclusive. Lynch (1995) suggested identifying mechanisms of tolerance and selecting for that mechanism directly or indirectly through molecular markers. Yield has traditionally been used as the main component to evaluate plant performance under drought conditions. The disadvantage is that yield trials are costly to run and results are often variable (Lynch, 1995). Singh et al. (1995) concluded that selecting for drought using physiological parameters is expensive, time consuming, and diflicult to use when screening large number of lines or segegating lines. Screening method for drought tolerance using growth boxes Singh et al. (1995) developed a screening method which determined drought tolerant genotypes during the early vegetative stage. The method used boxes lined with polyethylene sheets containing a 1:1 sand and soil mixture. Plants were watered until partial emergence of the trifoliate leaf, at which time water was withheld and percentage wilting and the number of days to permanent wilting of each cultivar was determined and scored. The surviving plants were re-watercd to check their ability to regow (Singh et al., 1995). Criteria for evaluating the effect of moisture stress on yield Four classes of genotypes can be identified based on the ability of the genotypes to tolerate moisture stress. Group A genotypes yield well under both non-stress and stress environments,. Group B genotypes yield well only under non-stress conditions. Group C genotypes yield relatively well under stress conditions, and goup D genotypes yield poorly under both non-stress and stress conditions (Fernandez, 1993). Various indices have been developed in attempts to assess yield performance under moisture stress. M an tivi Mathematically the mean productivity (MP) can be expressed as MP = (Y. + Yp)/2 where Y. is the yield in stress environment and Yp the potential yield of a given genotype in a non-stress environment. The MP tends to select genotypes for 10 higher yield potential (F emandcz 1993). Genotypes chosen for MP qualities increase yield under both non-stress and stress conditions. However the MP cannot separate genotypes that yield well under both stress and non-stress conditions fi'om those yielding well only under non-stress conditions (Fernandez, 1993) Gegmgtrig meg The geometric mean (GM) separates genotypes that yield well both under stress and non-stress environments from those that yield well only under non- stress, those yielding relatively well under stress, and those yielding poorly under both stress and non-stress conditions (Fernandez, 1993). GM can be expressed as GM = (Y. * Y..)"2 Thedr ts ce tibili inexDI The drought susceptibility index is reported to estimate drought tolerance. A value of one is reported to equal average resistance, values lower than one represent geater than average resistance, and values geater than one indicate susceptibility (Fischer and Maurer, 1978). The DSI of individual genotypes is calculated as DSI = [l-(YJYp)]/DII. The DH is calculated as D1] = 1 - YJY p with Y. representing the average ;yield of all genotypes under stress and Yp representing the average yield of all genotypes under non-stress conditions. Th tr 1e ce in x ST The stress tolerance index (STI) has been developed as an alternative to the DS1. STI is reported to measure both stress tolerance and yield potential. With STI, the 11 higher the value, the geater the stress tolerance and the higher the yield. Genotypes chosen based upon high STI exhibit high yield potential and high yield in stress environments (Fernandez, 1993). Fernandez (1993) expresses the STI as [(Y,)(Y.)]/(Y2)’- Nitrogen and its effect on drought tolerance Nitrogen is an important component of the biochemical constituents that enhance yield producing processes (Sinclair and Horie, 1989). However, it is unclear whether nitrogen deficiency increases or decreases the sensitivity of plants to moisture stress (Bennett et al., 1989). Plants in soils with low ninogen have reduced gowth rates and low shoot to root ratios (Russel, 1977). It has been suggested that this may affect the balance between crop transpiration and nutrient and water absorption (Bennet et al., 1989). Physiological responses of crops have been reported to be altered by nitrogen deficiency (Bennet et al., 1986; Jones et al., 1986). Radin and Parker (1979) suggested that this may result in the alteration of plant characteristics associated with drought resistance. Radin and Parker (1979) observed that cotton (Gossypium hirsutum) gown under low nitrogen levels had a lower water use efficiency. They further suggested that the difference could be used to improve drought resistance. However, Viets (1962) observed that field plants gown under low nitrogen levels had lower abovegound shoots but similar rates of evapotranspiration as plants gown with adequate nitrogen. Bennett et all. (1989), working with maize, inferred that an interaction between moisture 12 stress and nitrogen deficiency reduces total biomass, seed weight accumulation, and nitrogen uptake. Nitrogen contribution of legumes to the subsequent non-legume crops It is generally believed that the advantages of gowing legumes stem mostly from the fact that they fix their own nitrogen and leave some extra nitrogen for the subsequent crop (Bandyopadhyay and De, 1986 ; Senaratrre and Hardarson, 1988). This is particularly true when legumes are gown as geen manure crops (Heichel, 1987). Thus the beneficial residual eflect is to some extent dependent on the abovegound biomass being returned to the soil. For a subsequent crop after a legume to benefit, the quantity of fixed nitrogen returned by the legume to the soil should be more than that of soil nitrogen in the harvested gain (Eaglesham et al., 1982). Zapata et al. (1987) reported that after the removal of pods and the return of straw to a soybean field, there was still a net nitrogen depletion of 54 Kg N ha'1 nitrogen. Senarate and Hardarson (1988) suggested that the nitrogen benefit to the subsequent crop after gain legumes may be a result of a lower uptake of mineral nitrogen by legumes relative to non-legumes and a carry-over of nitrogen from the legume residue. These factors lead to a larger uptake of soil nitrogen by the subsequent crops compared to crops gown after non-legumes. It is further debated whether the beneficial effect of legumes to subsequent crops is because of contribution of nitrogen by fixation or because of an overall rotational efl‘ect, which includes disease control, soil crumb structure improvements, and nitrogen 13 availability (Papastylianou and Puckridge, 1983; Heichel, 1987). Legume/cereal intercropping studies such as maize/common bean, maize/cowpea or maize/ soybean intercropping have shown that the closer the intimacy between the component crops, the more nitrogen the legume fixed (Rweyemamu, 1990). Finlay (1975), Willey (1979), and Rweyemamu (1990) reported transfer of nitrogen fiom the legume to the non-legume such that the depletion of nitrogen by the cereal stimulated the legume to fix more nitrogen. Eflect of moingg stress on nitrogen fixation Moisture stress affects the gowth, physiological activities, and nitrogen fixation capacity of plants (Abd-Alla and Abdel Wahab, 1995; Becana et al., 1986). Leghemoglobin metabolism, respiration, and ATP production are reduced by moisture stress (Becana et al., 1986). Hooda (1986) inferred that the reduction in nitrogenase activity of moisture stressed chickpea may be due to the decline in sucrose translocation to the nodules. Reduced nitrogenase activity may also be a result of leghcmoglobin degadation (Pate et al., 1984). Pate and Atkins emphasized that adequate water is necessary for the maintenance of turgidity in legume nodules and for the influx of fixed carbon and efflux of nitrogen. While it is now generally believed that moisture stress can cause nodules to dehisce and accelerate nodule senescence, it should be noted that nodule functions can be impaired even before stress symptoms are visible on the abovegound foliage (DeVries ct al., 1989; Abd-Alla and Abdel Wahab, 1995). High soil temperatures 14 are thought to reduce the symbiotic performance of common bean more than that of cowpea and soybeans (Piha and Munns, 1987). WWW Summerfield et al. (1976) and Wien et al. (1979) showed that nitrogenase activity in cowpea was depressed by moisture stress. Pararajasingham and Knievel (1980) suggested that nitrogenase activity should recover rapidly to pre-stress levels upon watering in order to maximize dinitrogen fixation. The recovery ability of nitrogenase activity in cowpcas upon re-watering remains unclear. Summerfield (1976) observed that cowpea nitrogenase activity did not recover from drought stress coinciding with the pre-flowering stage, while Wien et al. (1979) reported that nitrogenase activity may be higher in cowpea undergoing moisture stress at the vegetative stage than in control plants. Nitrogen utilization, partitioning, and remobilization Nitrogen is the major limiting nutrient required for plant gowth, especially in agicultural systems (Date, 1973). Legumes are often gown in polycultures, creating a farming system that promotes biodiversity. Cowpeas, Bambara goundnut and soybean usually fix adequate nitrogen and will normally not require N fertilizer (Kurtz, 1976). Peoples et al. (1983) reported that up to 40% of the pod's nitrogen represents nitrogen fixed after flowering. Common bean is considered to be an ineflicient nitrogen fixer and often needs to be fertilized (W estermann et al., 1981). Inefficient nitrogen fixation in common bean is mostly 15 caused by the failure to establish efficient symbioses in the field. Common bean begins to fix nitrogen at a considerably later vegetative stage than other legumes, such that periods of nitrogen stress are observed in common bean before nodules begin to actively fix nitrogen. A starter dose of N is mainly applied to avoid the nitrogen stress potential periods (Sprent and Thomas 1984). Determinate, early maturing bush-type common bean fixes the least nitrogen, while indeterminate climbing genotypes fix more nitrogen (Graham, 1981; Rennie and Kemp, 1983). Generally early maturing varieties are inferior users of photosynthates for biological nitrogen fixation (Piha and Munns, 1987). However it has been suggested that some common bean varieties (most likely type III ) can acquire enough nitrogen, either through fixation or assimilation of mineral nitrogen, for the plant to achieve genetic yield potential under field conditions (W estermann et al., 1981) Deibert et al. ( 1979) estimated that soybeans obtain between 25 and 75% of their nitrogen fiom fixation. The wide variation in the estimated amount of nitrogen fixed by soybean is caused by factors such as the length of time that a cultivar actively conducts nitrogen fixation (Hardy, 1977). W Future improvements in yield may come, in part, from improvements in the partitioning and remobilization of assimilates into harvested components (Loomis et al., 1979). Remobilization may be defined as the net loss of nutrients from 16 living plant parts coincident with their accumulation elsewhere in the plant, mostly though not exclusively, in the reproductive parts (Loberg et al., 1984). The efiect of water stress on nitrogen accumulation, partitioning and remobilization in diflerent legumes is not well documented (DeVries et al., 1989). It is generally believed that moisture stress affects the total accumulation of nitrogen in many species, including cowpea, soybean, geen gam, black gam, and lablab bean (Chapman and Muchow, 1985). Nevertheless, the relationship between the level or timing of water stress and the contribution of remobilized nitrogen to seed nitrogen in soybean was not always consistent. Egli et al. (1983) concluded that the quantity of remobilized nitrogen during the gain-fill stage is more related to the amount of nitrogen accumulated during the whole gowing season than to the ability of the plants to fix nitrogen or to obtain mineral nitrogen during seed filling. Cure et al. (1985) showed a relatively more rapid decline in leaf nitrogen concentration when moisture stress was induced during the mid-seed-fill stage of soybean. In Nigeria, Wien et al. (1979) observed that water-stressed cowpea translocated more nitrogen to the pods than plants supplied with adequate moisture. Foster et al. (1995) reported that a geater proportion of seed nitrogen was obtained from remobilized leaf nitrogen under moderate moisture stress conditions in common bean, but that a severe moisture stress impaired N remobilization. They suggested that nitrogen remobilization helps to maintain yield stability during conditions of moderate moisture stress, but not under severe 17 or prolonged moisture stress. Severe moisture deficits reduced N harvest index and N use eficiency. Foster et al. (1995) concluded that drought susceptible common bean genotypes utilized nitrogen less emciently than resistant genotypes. Peoples et al. (1983) showed that 60% of the nitrogen fixed before flowering is remobilized in cowpea. Selemat and Gardner (1985) inferred that nitrogen was remobilized from leaves to pods during periods of nitrogen stress in non- nodulating peanut cultivars (A rachis hypogaea), but no remobilization occurred in the nodulated plants. Likewise DeVries et al. (1989) and Egli et al. (1983) showed that moisture stress had no effect on nitrogen concentration of leaves and stems of peanuts. Zapata et. a1 (1987) reported that soybean pods and seeds contained up to 73% of the total nitrogen in the plant while they made up less than one third of the total dry matter. Seventy-one to 91% of total N was in the seed of common bean gown under moderate moisture deficits (Foster et al., 1995). Vegetative and reproductive gowth occur simultaneously during flowering and fruit set in indeterminate soybean. During seed-fill stage, the seeds are the main sink and are the recipients of remobilized N (Zeiher et al., 1982). Yield components such as number of fruit and seeds are determined during flowering and fi'uit set, hence the portion of carbon and nitrogen partitioned to reproductive gowth at that stage have direct influence on fi'uit set, seed number, and yield (Egli et al., 1985). Greer and Anderson (1965) suggested that competition between vegetative and 18 reproductive gowth during flower set reduced fi'uit set. Loberg et al. (1984) suggested that determinate cultivars have less competition during the reproductive stage which results in higher yield. Soybean remobilized more nitrogen to the seed than pigeon pea and peanut (Chapman and Muchow, 1985). Zeiher et al. (1982) estimated that contribution of remobilized nitrogen towards seed nitrogen at maturity ranged from 20 to 100% in soybean. Soybean leaf senescence and abscission have been termed as self-destructive (Sinclair and DeWit (1976)). DeVries et al. (1989) showed that peanut and pigeon pea retained a fair amount of leaves with moderate concentration of nitrogen up to harvest maturity. In fact, water stressed peanut leaves were slow to abscise and remained as a nitrogen source when the stress was relieved. Total nitrogen in pigeon pea stems increased throughout the entire season, while the nitrogen in chickpea and soybean stems decreased during the reproductive stages (DeVries et al., 1989). Hooda et al (1986) observed that the nitrogen content of shoots and dry weight in chickpea did not decrease during seed fill, while the undergound plant material showed only a small decrease in dry weight. They inferred that seed dry matter may be derived from current photosynthesis. 19 Moisture stress in Zimbabwe In Zimbabwe, mid-season droughts (intermittent drought) were in an unpredictable fashion. These droughts often coincide with reproduction and reduce yield. To optimize the stability of harvest, farmers practice ‘phased planting.’ With phased planting, farmers distribute the planting of their crops over a long period, preferring to spread the risk instead of maximizing the yields. This technique is wide-spread in Zimbabwe even though there are substantial losses due to late planting. When mid-season drought occurs, the legumes are at various phenological stages of development so farmers are assured of some yield. The late planted crop often matures when the rains have tailed off and suffer fi'om terminal drought. Since these legumes are minor crops and rank behind major crops such as maize, sorghum and goundnut, they are usually planted after the more important crops. Therefore, the gowth period with adequate water is even shorter for legumes. Farmers need early maturing legume varieties. Most of the soils in the communal areas and small scale commercial farms in Zimbabwe are coarse-gained sands derived from ganite. They are generally deficient in available N, phosphorus, sulfur and organic matter. Consequently, they have poor physical structure and low water holding capacity (Mashiringwani, 1983; Mataruka, 1985). Continuous maize farming has further depleted the soil’s fertility. Often farmers cannot afl‘ord to buy fertilizers to replenish the soil. Furthermore, management factors are aggavated by discriminatory land policies 20 that concentrate the population on marginal land (Whitlow, 1988). Most cultivated legumes have the ability to fix N under difi'erent conditions, but eficiency in N fixation differs (Piha and Munns, 1987). Differences occur even within species. Nitrogen-fixing legumes are potentially important for Zimbabwe's inherently low fertile soils and for the N needs of the subsequent non-leguminous crops that are gown in rotation. High yielding germplasm of legumes have been selected under non-stress conditions and for high yielding areas; however, their performance under drought conditions generally has not been evaluated. Determination of the N fixation capacity of these legumes under drought stress conditions is essential. Drought tolerant germplasm is essential for enhanced yield under communal area and small scale farming conditions. With maize and soybean, recommendations have been made for varieties that can be gown in the different natural regions of Zimbabwe. This has not been done for Bambara goundnut, common bean or cowpea. There is a geat need for research that will enable the development of varietal recommendations for Bambara goundnut, common bean and cowpea for the natural regions. Origin and History of Bambara groundnut Bambara goundnut is of Afiican origin but its exact center of origin is debatable. Marcgav De Liebstad's report of 1648 is the oldest known literature where Bambara goundnut is recorded. It was then called ‘Mandubi d'Angola’ 21 implying that it originated in Afiica (Begemann, 1988). In 1763, Linnaeus classified the crop as Glycine subterranea. Du Petut-Thours (1806) found Bambara goundnut in Madagascar and Mauritius where it was called ‘Voandzou. ’ He coined the term Voadzeia subterranea. The name ‘ Voandzou ’ is from a local name ‘Voanjo.’ ‘Voa’ means seed and ‘anjo’ means that which satisfies well (Rassel, 1960). Vigna subterranea is now the scientific name for Bambara goundnut. The word Bambara is the name of an ethnic goup in West Afiica and hence the word is capitalized. Bambara goundnut is gown in West, East and Southern Afiica in countries such as Mali, Burkina Faso, Ghana, Togo, Benin, Chad, Cameroon, Tanzania, Malawi, Zambia, Zimbabwe, Madagascar, South Africa, Zaire, Ivory Coast, Sudan, Ethiopia, Kenya, Uganda, Mozambique, and Angola. It was introduced to Brazil, the Philippines and Indonesia in the seventeenth century. The crop is now also gown in Australia and in many countries in Asia and Latin America (Begemann, 1988). Nutritionfl Value Bambara goundnut is a very balanced food crop with regard to human nutritional needs. The dried seeds have 54.5 to 69.3% carbohydrates, 17 to 24.6% protein, 5.3 to 7.8% fat, and supply 367 to 414 Kcal per 100 g. The protein quality of Bambara goundnut is rich in lysine and methionine, but deficient in isoleucine. The biological value of Bambara goundnut is 56%. It has a digestibility value of 82.6% (Chomchalow, 1993) and is a good complementary 22 diet to cereal. Bambara goundnut is served in a variety of ways in difi‘erent countries. In Zimbabwe, the flesh beans are boiled or served as a soup. Fresh beans are sweet and very tasty. In Nigeria, they are served as stem balls of flour rolled in leaves of ‘akara,’ balls of flour rolled up in oil, or as Bambara goundnut pancakes. Bambara goundnut ranks high for adaptability and for the ability to tolerate harsh environmental conditions. It has demonstrated survivability in challenging arid environments although its yields have always been unpredictable (Anonymous, 1979). As a result myths and taboos have been associated with the crop in some ethnic goups. The crop’s unpredictability has also been reported by researchers. Begemann (1988), working in Zambia, suggested that Bambara goundnut is a short-day plant. Linnemann et al. (1995), working in the Netherlands, concluded that Bambara goundnut genotypes originating fiom ‘higher’ latitudes (IO-15°N) are early maturing and show a weak response to photoperiod while genotypes from ‘lower’ latitudes (5-10°N) are late maturing and show relatively more photosensitive response. The crop gows well in poor sandy soils that are marginal for other crops (Anonymous, 1979; IITA, 1988). According to some researchers, the crop ‘prefers’ poor soils. In nitrogen rich soils, the crop tends to produce too many leaves at the expense of pods and seeds (Anonymous, 1979; Chomchalow, 1993). The optimum daytime temperature for the crop is 20- 28°C. The optimum amount of precipitation for the crop is between 900 mm and 23 1200 mm, but the crop can gow in the precipitation range from 500 mm to 4100 mm. Bambara goundnut can generally withstand water logging except during fruiting and harvesting stages and can tolerate a pH as low as 4.3 (Anonymous, 1979) Pr lms iewi Bamb oun t ution Bambara goundnut yields are generally low. Yields range from 150 - 6000 kg/ha of shelled seed, depending on location (Chomchalow, 1993). Low yields reflect low-densities because farmers mainly intercrop Bambara goundnut with other crop plants (Anonymous, 1979). Late earthing, poor earthing practices such as incomplete covering of developing pods and damage to developing pods, and poor weeding are other problems often encountered in Bambara goundnut production. Earthing is the process of building up the soil around the base of the plant so the developing pods are not exposed to light. Bambara goundnut is repeatedly described as disease and pest resistant (Chomchalow, 1993). It has also been argued that the reason it does not seem to be attacked by pests may be because it has been gown only in isolated fields and intercropped with non-related crops. It can be inferred fiom this theory that Bambara goundnut farmers ensured that the crop did not become susceptible to pests by having multiple crops in isolated fields. This is a sound example of Bambara goundnut farmers having practiced what the rest of the world now realizes as aspects of sustainable cropping system. Bambara goundnut has the 24 potential to become a stable, low cost and profitable food crop, but the crop needs to be promoted because many people even, in tropical Afiica, are unaware of it (IIT A, 1988). The negative aspects such as low yield can be addressed through research (Anonymous, 1979). S f ar oundn t reduction in limb we Bambara goundnut is one of the most neglected legumes in terms of research and development in Zimbabwe. In the past, it has been considered a traditional crop. It is generally thought to be one of the most drought tolerant of all legumes gown in Zimbabwe. Zimbabwe is divided into five natural ecological regions based on the elevation above sea level, temperature and the amount of rainfall. Natural regions one and two have the highest rainfall, the highest elevation, and the lowest temperature. Natural regions ID and IV are generally semi-intense farming regions. Bambara goundnut gows well on the poor and sandy soils, which predominant in natural regions III-IV. Bambara goundnut is suitable for several cropping systems and crop rotations (Chomchalow, 1993). Cowpea Cowpea originated in West Africa and was taken to India by the Sabaen trade route (Smartt and Hymowitz, 1985). In India, the cowpea produced two new distinct forms, ‘cylindrica,’ an erect gowing forage type and ‘sesquipedalis,’ a long podded type (Smartt and Hymowitz, 1985). Cowpea was probably introduced into the United States about the 1700 by the Spanish or Portuguese (Blackhurst 25 and Miller, 1980; Smartt and Hymowitz, 1985). 26 REFERENCES Abd-Alla, M. H., and AM. Abdel Wahab. 1995. Response of nitrogen fixation, nodule activities, and gowth to potassium supply in water- stressed broad bean. Journal of Plant Nutrition 18:1391-1402. Acosta-Gallegos J .A and M.W. Adams, 1991. Plant traits and yield stability of dry bean (Phaseolus vulgaris) cultivars under drought stress. Journal of Agricultural Science, Cambridge 117:213-219. Acosta-Gallegos J. A and J .K. Shibata 1989. Effect of water stress on gowth and yield of indeterminate dry bean (Phaseolus vulgaris) cultivars. Field Crops Research 20:81-93. Anonymous. 1979. Bambara goundnut. p. 47-53. In Tropical legumes: resources for the future. National Academy of Sciences, Washington, DC. Akyeampong, E. 1986. Some responses of cowpea to drought stress. p 141-159. In I. Haque, S Jutzi, and P.J.H. 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(W alp)) during and after drought stress. Canadian Journal of Plant Science 70: 163-171. Papastylianou, I. and D.W. Puckridge. 1983 Stem nitrate nitrogen yield of wheat in a permanent rotation experiment. Australian Journal of Agricultural Research 34:599-606. 32 Pate, J.S., C.A. Atkins, D.B. Layzell, DB, and 8.]. Shelp.1984. Efiects of N2 deficiency on transport and partitioning of C and N in a nodulated legume. Plant Physiology 76:59-64. Peoples M. B., J. S. Pate, and C. A. Atikns. 1983. Mobilization of nitrogen in fruiting plants of a cultivar of cowpea. Journal of Experimental Botany 34:563-578. Piha, MI and UN. Munns. 1987. Nitrogen fixation capacity of field-gown bean compared to other gain legumes. Agonomy Journal 79:690-696. Radin J .W. and LL. Parker. 1979. Water relations of cotton plants under nitrogen deficiency. 1. Dependence upon leaf structure. Plant Physiology 64:495-498. Rassel, A. 1960. Le Voandzou (Voandzeia subterranea) et sa culture au Kwango. Bull. Agic. du Congo Belge 5121-26. Rennie, RJ. and GA. Kemp. 1983. N-fixation in field beans quantified by N isotope dilution. H. Effect of cultivators of beans. Agonomy Journal 75:645-649. Rweyemamu, C. 1990. Evaluation of maize/bean intercrops at Soikoine University of Agiculture, Morogoro, Tanzania. p. 114-118 . In Research Methods for Cereal/Legume Intercropping: Proceedings of a workshop on research methods for cereal/legume intercropping in Eastern and Southern Afiica. S.R Waddington, A.F.E. Palmer, and O.T Edje (ed.) Mexico, CIMMYT. Rosenthal, W.D., G.F. Arkin, P.J. Shouse, and W.R. Jordan. 1987. Water deficits on transpiration and leaf gowth. Agonomy Journal 79: 1019-1026. Russel, RS. 1977. Plant root systems: their ftmctions and interaction with the soil. McGraw-Hill, New York. Schussler J .R. and ME. Westgate. 1991. Maize kernel set at low water potential: I. sensitivity to reduced assimilates during early kernel gowth. Crop Science 31:1189-1195. Selemat, A. and F. P. Gardner. 1985. Nitrogen partitioning and redistribution in non nodulating peanut related to nitrogen stress. Agonomy Journal 77:859-862. Senaratne, R and G. Hardarson. 1988. Estimation of residual N effect of faba 33 bean and pea on two succeeding cereals using N-15 methodology. Plant and Soil: 110281-89. Sherifl’, D.W., M. J. Fisher, G. Rusitzka, and CW. Ford, 1986. Physiological reactions to an imposed drought by two twining pasture legumes: Macroptilium atropwpureum (dessication sensitive) and Galactia striata (dessication insensitive). Australian Journal of Plant Physiology 13:329-341. Shibles, R 1980. Adaptation of soybeans to diflerent seasonal durations. p. 199-286. In R.J. SUMMERFIELD and AH. Bunting (ed.) Advances in legume sciences. Royal Botanic Gardens, New England. Shouse, P., S. Dasberg, W.A. Jury, and L.H. Stolzy. 1981. Water deficit effects on water potential, yield, and water use of cowpeas. Agonomy Journal 73:333- 336. Sinclair, T.R and CT. De Witt. 1976. Analysis of the carbon and nitrogen limitations of soybean yield. Agonomy Journal 68:319-324. Sinclair, TR, and T. Horie. 1989. Crop Physiology and Metabolism: Leaf Nitrogen, Photosynthesis, and Crop radiation use efficiency: A review. Crop Science 29 120-125. Singh, B.B., Y. Mai-kodomi, and T. Terao. 1995. A simple screening method for drought tolerance in cowpea. p. 71-72. In Agonomy abstracts. ASA, Madison, WI. Singh, S. P. 1995 Selection for water stress tolerance in interracial populations of common bean. Crop Science 35:118-124. Smartt J ., T. Hymowitz. 1985. Domestication and evolution of gain legumes. p 37- 72. In RJ. Summerfield and EH. Roberts (ed.) Grain legume crops, London, Collins. Smith, T. L., G.A Peterson,. and DH. Sander. 1983. Nitrogen Distribution in Roots and Tops of Winter Wheat. Agonomy Journal 75:1031-1036. Sprent 1.1., and R. J. Thomas. 1984. Nitrogen nutrition of seedling gain legumes: some taxonomic, morphological and physiological constraints. Plant, Cell and Environment 7 :637-645. Stdker, R 1974. Effect of dwarf beans of water stress at different phases of 34 gowth. N. Z. J. Exp. Agic. 2:13-15. Summerfield, RJ., P.A. Huxley, P.J. Dart, and AP. Hughes. 1976. Some effects of environmental stress on seed yield of cowpea. Plant Soil 44:527-546 Summerfield, R.J., J .J . Pate, E.H. Roberts, H.J. Wein, 1985. The physiology of cowpeas. p. 65-101. In S.R Singh and KO. Rachie (ed.) Cowpea research, production and utilization. John Wiley and Sons. Ltd. New York. Turlc RJ. and AB. Hall. 1980. Drought adaptation of cowpea: 1]]. Influence of drought on plant gowth and relations with seed yield. Agonomy Journal 72:428-433. Viets, RG. 1962. Fertilizers and the efficient use of water. Advances in Agonomy 14:223-264. Viets, F.G., Jr. 1965. The plant's need for and use of nitrogen. p. 503-549. In W.V. Bartholomew and FE. Clark (ed.) Soil nitrogen. Westgate, ME. and TD. Grant. 1989. Water deficits and reproduction in maize: Response of the reproductive tissue to water deficits at anthesis and mid-gain fill. Plant Physiology 91:862-867. Westermann, D T., G.E. Kleinkopf, L.K. Porter, and GE. Leggett. 1981. Nitrogen sources for bean seed production. Agonomy Journal 73:660-664. White, J .W., and SP. Singh, 1991. Breeding for adaptation to drought. p. 501-560. In A. van Schoonhoven and O. Voysest (ed..) Common beans: research for crop improvement. CAB international, Wallingford, UK, and CIAT, Cil, Colombia. Whitlow, R1988. Soil conservation history in Zimbabwe. Journal of Soil and Water Conservation 43:299-303. Wien, H.C., E.J. Littleton, and A. Ayanaba. 1979. Drought stress of cowpea and soybean under tropical conditions. p. 284-301. In H. Mussell, and RC. Staples (ed.) Stress Physiology in Crop Plants. Wiley Inter science, New York. Willey, RW. 1979. Intercropping, its importance and research needs. Part 1. Agonomy and research approaches. Field Crop Abstracts 32: 1-10. Zapata, F., S.K.A. Danso, G. Hardarson, and M. Fried. 1987. Time Course of 35 Nitrogen fixation in field-Grown Soybean Using Nitrogen-15 Methodology. Agonomy Journal 79:172-176. Zeiher, C, DE. Egli, J .E. Leggett, and DA. Reicosky. 1982. Cultivar differences in N redistribution in soybeans. Agonomy Journal 74:375-3 79. 36 CHAPTER 1 MOISTURE STRESS EFFECTS ON YIELD AND YIELD COMPONENTS OF BAMBARA GROUNDNUT, COMMON BEAN, AND COWPEA ABSTRACT Legumes are often gown in semi-arid regions under agiculturally challenging conditions. The objectives of the study were (i) to compare the effects of moisture stress on yield and performance of Bambara goundnut ( Vigna subterranea), common bean (Phaseolus vulgaris), and cowpea (Vigna unguiculata) in the field and (ii) to assess the use of a geenhouse screening procedure as an indication of drought tolerance. The field study included three common bean lines (Carioca, Natal Sugar, and T3147), two cowpea lines (IT82D- 889 and 475/89), three Bambara goundnut treatments (inoculated and uninoculated ZVS 530 and inoculated ZVS 546), and a non-nodulating isoline of the soybean (Glycine max) Harasoy gown under stress and non-stress moisture conditions in a rainshelter in MI in 1995 and 1996. For the geenhouse screening, common bean, cowpea, and Bambara goundnut were planted in 1.5 m square boxes at Michigan State University on June 18 and August 20, 1996. The boxes had a depth of 12 or 20 cm and were lined with plastic and filled with a 1:1 mixture of sandzsoil. Moisture stress reduced the number of pods per plant in 37 cowpea and soybean, but not in common bean. Cowpea was more drought tolerant than common bean, although common bean produced a higher yield than cowpea. STI was a better predictor of yield performance than DSI. Species and genotypes difl‘ered in yield, seed weight, pod and seed number, and the effect of moisture deficit on each yield component. 38 INTRODUCTION Herbaceous legumes have wide adaptability, are gown worldwide, and are of geat economic importance (Adams and Pipoly III, 1980). Their high protein content and amino acid composition make them excellent complements for cereal diets, which are high in starch. Legumes are often gown in dry locations where agiculturally challenging conditions exist (Elston and Bunting, 1980). The extent to which moisture stress reduces yield depends on species, the phenological stage of development when moisture stress occurs, the degee of yield component compensation, and the severity and duration of the moisture stress (Korte et al., 1983) Bambara goundnut (Vigna subterranea) is gown by farmers in Afiica, Asia, South America and Australia, although it is a relatively unknown legume (Anonymous 1979; Chomchalow, 1993). Bambara goundnut is believed to be one of the most drought tolerant legumes, to be very disease and pest resistant, and to thrive on poor soils. It is often gown under conditions that are marginal for other crops. Terminal moisture stress reduces yield components such as the number of pods per plant, number of seeds per pod, and individual seed weight (Kadhem et al., 1985). Water limitation can hasten or delay phenological development of plants, depending on the severity of the limitation (Rosenthal et al, 1987). In soybean, moisture stress has been reported to decrease the duration of reproductive 39 development, the length of the seed-filling period (Korte et al., 1985), and consequently yield. Chickpea is also known to mature early under conditions of limited water (Khanna-Chopra and Sinha, 1987). Turk et al. (1980) and Lawn (1982) observed that the reproductive activity of cowpea may be hastened or delayed depending on the time and intensity of the moisture deficit. Gwathmey and Hall (1992) concluded that the sensitive stages can thus escape the mid-season drought. The reproductive stage is reported to be the most sensitive stage to moisture stress in most legumes. In soybean, moisture stress reduced the effective seed filling period, but did not reduce seed gowth rate (Meckel et al., 1984). Difi‘erences between seed yield in stressed and non-stressed plants, even in the same variety, tend to vary markedly from year to year, depending on the phenological stage at which moisture stress occurs (Huck et al., 1986). There is a need to develop rapid, reliable, and relatively inexpensive methods to screen for drought tolerant lines in legumes. Yield is often used as a parameter to evaluate drought tolerance. However, yield trials are costly to run and results may be highly variable (Lynch, 1995). Other methods such as osmotic adjustment, observations of plant physiological responses, and genes have been suggested as possible screening tools, but these methods have not always produced consistent and reliable results. The objectives of the study were (i) to compare the effect of moisture stress on yield and performance of Bambara goundnut, common bean, and cowpea in 40 the field and (ii) to assess the use of a geenhouse screening procedure as an indication of drought tolerance. MATERIALS AND METHODS Field Study Two cowpea genotypes (IT82D-889 and 475/89), two Bambara goundnut genotypes (ZVS 530 and ZVS 564), three common bean genotypes (Carioca, T3147-2, and Natal Sugar), and a non-nodulating soybean (Harosoy) (Glycine max) were planted on a Spinks sandy soil (Psammentic Hapludalfs, sandy, mixed, mesic) in a rainshelter at the Kellogg Biological Station in Hickory Comets, Michigan in 1995 and 1996. The experimental design was a modified split-plot in a randomized complete block with two moisture treatments (stressed and non- stressed) as the main plots, genotype as the sub-plot and four replications. The four row plots were each 2 m long and 0.5 m wide with intra-row spacings of 8, 15 and 25 cm for common bean, Bambara goundnut and cowpea, respectively. The genotype T 3147-2 was obtained from the breeding progam of Dr. James Kelly in the Department of Crop and Soil Sciences at Michigan State University in East Lansing, MI and the non-nodulating Harosoy from Dr. J. E. Harper at USDA- ARS in Urbana, IL. All other species and cultivars were obtained from the Department of Research and Specialist Services in Zimbabwe. Neutron probe access tubes were installed vertically to a depth of 1 m between the two center 41 rows of each plot prior to planting. Forty kg of N per hectare was broadcast using 19-19-19 fertilizer. Common bean was inoculated with a granular form of Rhizobium phaseoli, cowpea with Rhizobium cowpea miscellany nitrogen EL, and Bambara goundnut with Voandzeia Special 1. The cowpea and Bambara goundnut inoculum were obtained from Nitragin TM Inoculants and were manufactured by Liphatech, Inc. In 1995, three applications of fungicide (Benlate for anthracnose and Sevin for Japanese beetles) at 1.12 kg ha’1 were made at two- week intervals beginning on July 14. In 1996, two applications of Benlate were used. Terminal moisture stress was initiated on all the legumes when common bean reached the R1 stage of development (Singh, 1982) on July 29 in 1995 and July 21 in 1996. Separate Analysis of Bambara Groundnut The yield and yield component data for Bambara goundnut treatments were analyzed separately from the rest of the treatments. None of the Bambara goundnut genotypes reached maturity under the Michigan climatic conditions. All of the Bambara goundnut treatments were at approximately the same stage of maturity at harvest time, hence, it was decided to compare the Bambara goundnut treatments only to each other. Greenhouse Study to Assess Drought Tolerance Common bean, cowpea, and Bambara goundnut were planted in wooden boxes, an adaptation of a procedure by Singh et al. (1995 ) in the geenhouse at 42 Michigan State University at East Lansing, MI on June 18 and August 20, 1996. The square boxes were 1.5 m in length with a depth of either 12 cm or 20 cm. The boxes were lined with plastic and filled with a 1:1 mixture of sandzsoil. The experiment was a split-plot in a randomized block design with box depth as main plot and genotype as sub-plot. Cowpea (IT 82D-889 and 475/89), Bambara groundnut (ZVS 530 and ZVS 564), and common bean (Carioca, Natal Sugar and T3147-2) genotypes were gown in rows 7 cm apart with an intra-row spacing of 5 cm. All genotypes were planted to a depth of 2 cm at 2 plants per station. They were later thinned to one plant per station. All species were watered until the partial appearance of the first trifoliate leaf in common bean. Percent wilting on a daily basis and the number of days it took for the plants to die in each row was recorded. RESULTS AND DISCUSSION Yield The Zimbabwean genotype Natal Sugar did not reach maturity in 1995; hence it was not included in the 1996 study. The yield for common bean and cowpea ranged from 237 to 1437 kg ha’1 (Figures 1 and 2), with higher yields in 1995 than in 1996. Under adequate soil moisture conditions, the common bean genotypes had the highest yields with T3147-2 having yields as high as 1437 kg ha“ in 1995 (Figure 1). The cowpea genotype 475/89 had a significantly higher 43 3059 89.8520 8.9Wt‘gcggg53tm é .4 80.. j. -ooNp .Sv— rgow .33 .5 6033” £9.8qu 330205 32.3. 05 .- 8:235! a :. 2.22.53 2:52: =3 323 new 328.5: 32.: .565 .853395 255. .0333 new 53:. 02:50. coon—>3 .3332; 3382:: case .3583 ac 22> .p 2:2“. (wax) m Semen-93826332385 323820 32.8. .82 .5 £25» 3.835 2: .- 3223.! a :. EOE—Eco 0.53.2: :3 393a use 388.5: .025 :32: tax: 02:50. cal->8 ecu 48-32395 235. e838 Antwan: 3332?: case .3553 he 23> .« 8:2“. .OONF yield than the cowpea IT82D-889 in 1995 but not in 1996, mainly due to reduced yield of 475/89 in 1996. Moisture stress reduced the yield of common bean, cowpea and soybean in both years (Figures 1 and 2), with the exception of Carioca in 1996. Yield reductions due to stress in 1995 were generally higher than in 1996 for all species except soybean (Tables 1 and 2), and the common bean cultivars had a higher yield reduction than the cowpea. The geater yield reduction in 1995 may be explained by the moderate (0.54) drought intensity in 1995 and the mild (0.22) drought intensity in 1996. Thus, the moisture stress was geater in 1995 than in 1996. The cultivar T3147-2 had the highest yield reduction in 1995 and one of the highest in 1996 (Figures 1 and 2). The cowpea genotype IT82D-889 had the lowest yield with adequate soil moisture; however, it had the least yield reduction due to moisture stress in 1995 and the second lowest in 1996 (Figures 1 and 2). Drought Susceptibility Index (DSI), Stress Tolerance Index (STI), and Geometric Mean (GM ) The cowpea genotype IT82D-889 had a D81 of 0.97 and 0.50 in 1995 and 1996, respectively (Tables 1 and 2 ). T3147-2 had the highest DSI of all genotypes and species in 1995 and was higher than the other common bean (Carioca) in 1996. Carioca had the highest STI in 1995 and 1996. The DSI is reported to estimate drought tolerance. A DSI value of one is reported to equal average resistance (Fischer and Maurer, 1978). Values lower than one represent 46 @Nd and Rd 9.6 mmd :m wad 2% 5.. $0 wad m8 mad 2H Rd vow Tu: mm 52: am 252500 .32 E E 50860 boo—oi 5 :038m Emma—2m 333— 05 “a 22:28 BREE: :8 383.5: new $83. Bees 56% mogoeow Son 5888 95 new 8960 95 .«o Chmv 5?: 35:23 3.8% :5 A59 5?: 5553383 Ewart .52: oEoEoow demos—co: 20$ 53:2. .52: 030855 E E. mm 9. w_ :cuoevom 205$ m8 new as at. woo .2 my :82 82.55 085 uSubUV :monxom 3.835: 339335 58m .0 3.833. mfioswesmv 50m .0 3336.335 ESV «3300 ASSSSES 3&6: 8300 860mm >803: Nuv: mu. 32.30 mwkhv mwwrflmwb 25980 ._ sea 47 vmd 3.— 3.— 5.0 wed Fm wad wad Nod wad Omd 5Q vow an» «no 03 own 7w: 3— :82 2.50880 00 mm mm 2 cogs—god 205$ .32 5 :2 52:00 >5on 5 sauna Emma—2m 30:3— 2: S 82:38 2339: :8 383.5: can $.28 325 :3on mambo—Sm :8; .5888 2.3 EB 8393 025 .«o chmv 52: 35.5.8 $0.3m 98 A58 59: 5596383. 295% .508 oEoEOom £2832 20$ «:35; .538 one—:55 8v 0% 33 3 so .2 mg :82 235.5 ORE ufiubg gonzom Antum~§ 338653 58m .0 36m? 383% sum .0 ASSEEMS. 33.5 8&60 ASS§SM§ 3:35 89.30 863m >898: Ng.: mp. 8950 awhhv awmA—Nw: 33050 .N as: 48 greater than average resistance, and values greater than one indicate susceptibility. The stress tolerance index (STI) has been developed as an alternative to DSI. STI is reported to measure both stress tolerance and yield potential. With STI, the higher the value, the greater the stress tolerance and the higher the yield potential. In 1995, both D81 and STI would have selected 475/89 as the more drought tolerant cowpea. In 1996, D81 would have selected IT82D-889 and the STI would have indicated that there was no difference between the two with regard to tolerance and yield potential. The greater yield of 475/89 in 1995 and the lack of difl‘erences in yield between the two cowpeas in 1996 indicate that 475/89 would have been the more desirable genotype. Thus STI was a more accurate indicator of cowpea field performance than was DSI. Both D81 and ST] would have selected Carioca as a more drought tolerant line than T3147-2 in both years and this agrees with the field performance, although T3147 has exhibited drought tolerance in other studies (Schneider et al., 1997; Yabba, 1997). Geometric mean is an indicator of yield potential (Schneider et al. 1997; Yabba, 1997). The larger the GM, the greater the yield potential. In both years, Carioca had the highest GM of all species and genotypes (Tables 1 and 2). Ozone damage and sun scald were observed on common bean, soybean, and cowpea during 1996, and the smnmer of 1996 was generally colder than the summer of 1995. This reduced the rate of maturity in common bean and cowpea and undoubtedly contributed to the lower yields in 1996 in comparison to 1995. 49 i1 om n n fcommonbe co A significant difference was observed in seed weight per 100 seeds among the species in both years (Figures 3 and 4). In both years, T3147-2 had a higher seed weight than Carioca, Harosoy and the two cowpea genotypes and Carioca had the second highest. In 1996, moisture stress only reduced seed weight of the non- nodulating Harosoy, but moisture stress reduced the seed weight of T3147-2 and Harosoy in 1995 (Figures 3 and 4). Singh (1995) observed that water stress reduced seed weight of common bean; however, Acosta-Gallegos and Shibata (1989) saw no significant differences in seed weight between water stressed and non-stressed common bean plants. Flores-Lui (1982) concluded that yield components are only reduced when stress is imposed during pod filling, the type of stress imposed in this study. There were highly significant differences in the number of seeds per pod among the different species (Figures 5 and 6), with cowpea having up to 14 seeds per pod and Harosoy as few as 2 (Figures 5 and 6). Moisture stress did not reduce the number of seeds per pod in either year (data not shown). The cowpea 475/89 produced more seeds per pod than IT82D-889 and the common bean Carioca produced more seeds per pod than T3147-2. A significant species diflerence was observed in the number of pods per plant. In 1996, the non-nodulating Harosoy had the highest number of pods per plant (Figure 7), followed by the cowpea IT82D-89. Moisture stress did not reduce pod number in Carioca or T3147-2, but it did in IT82D-889, 475/89, and Harosoy 50 games-93553833585 89.60 8:300 83:. 838: .0- ~0- 51 gm! 305520 - yon .3: ._s_ 62.8» =9...an 32.8. .5 3 322358 a :. 2.0.22.3 8322: :2. «no...» new 383.5: .32.: :32: C85 059:9 .3233 new 85:93uea 233. .3953 A3393) 3232:: .32. .3553 no 303 2: .2. 222» one» .n 2:2“. Figure 4. Seed weight per 100 seeds of common been (Pheselous vulgaris), cowpea (Vigna ungulculete) and soybean (Glycine max) grown under non-stress and stress soil moisture conditions In a rainshelter at the Kellogg Research Station, MI. 19%. DNonstress use»: - - .'.'. .' . . T31 47-2 C. Ce C. 4175/89 ”820-889 Errorbershdicstesslgniflcsncest?_<_0.06. .36 w. n «I 00:35:03 nee-035 E!- 33m cg ion .0 50m .0 89.60 8960 >88... «4.38. 88.5 8B? 8903.... b h p L o E N [T v [IT I o 1 m H ._. r o. a up a .— I -2. 6:25:30 9.332.. =3 383 can 323.5: .8 3:358 8.. 8.5 .83 ..s. 62.5» .83220 82.3. 2: .- 3222... a 2 :26... ca... 8.2.6. csegoe 5:18-32:23 235. e333 A3393... 33323. geen .3588 3 to: .2. steam .w 2.5.“. 53 .oodwtaugo—zcufigzaagm gm 88 o 58.0 8960 8960 .82... «4.22 823 8a.... 8.3%: n n . . . o E 1 N t v IT, A. I.“ - o . o T 2 ._. H m ,N. , 3 rm. .8: ..s. .2230 .322: 2 :25» .8322m 32.8. e5 3 .8355! e :. 3222.3 8322.. :3 «no.3 23 39.5.5: .82.: 5595 C3... 3350. :eeaaoe 2... Ase-.3232... 235. e833 Ant-.23.. 3.0323 .33 .3553 .o 32. .2. £33 .0 2:2... 54 (Figure 7). The number of pods per plant was not determined in 1995. Acosta- Gallegos and Shibata (1989) concluded that the number of pods per plant is the yield component most reduced by moisture stress, however their finding may have been under a more severe stress than the one experienced in 1996. Generally, cowpea aborted the most seeds under both stress and non-stress moisture conditions (Figures 8 and 9). This probably relates to the fact that cowpeas produced the greatest number of seeds per pod. The common bean genotype Carioca aborted the least number of seeds in 1995 (Figure 8). The soybean Harosoy and the common bean T3147—2 aborted the same mnnber of seeds (Figures 8 and 9), although more seeds were aborted in 1995 than in 1996 in all species (Figures 8 and 9). Moisture stress did not increase the number of seeds aborted in 1995 or 1996 (data not shown). Similarly, Acosta-Gallegos and Shibata (1989) observed no differences between control plants and stressed plants in number of aborted seeds or in number of under-developed ovules and concluded that strong intra-ovary competition occurs under both stress and non-stress conditions. This may be a result of a small source relative to the sink during seed fill or inefficient remobilization. Highly significant differences among species were observed in the shelling percentage in both years (Figures 10 and 11). Under adequate moisture conditions, T3147-2 had a significantly higher shelling percentage than non- nodulating Harosoy (soybean) and both cowpeas in 1996 (Figure 11). In 1995 and 55 :80 .0 NJ? 3... 328520 .3... w .. .- oocaczus 8.8.2.. :3 sum {a wndspodiomu .o. -N— .82 ..s. 52.8» 22882 .8522m 32.3. 2.. s .8355! a :. 2.03.2.3 2:52.. :3 use...» 23 38:13: .e25 .2525 CG... 2:36. Season 23 .. 88:032.: 235. e833 Astana... 3.032.... geen :oEEoo .0 Eu... .2. etc: 3 .3532 .5 2:2“. 56 .33... .- 8583? 38...... a... .25.. 83.3 go 88.0 898 3.2-: «4......» 888 8a.... 83%: _ . + . o no M .IHI T. 12m . a m. mam ,n m L w + ,. m... 62.358 82. 323 0:: 323.52 .3: .=2 £0.35. 5.33: 393220 30:8. .5 an 3:235! a 5 .565 .5... 2.350. coon->3 uca .Agafiauca 235. 3:33 Anton...) 2.3323. :3: .3588 5 no: .2. 98.03 «noon .o .3532 .o 052“. 57 .8..w...-8..8.....u..8.8.2.23.2.m :80 0 Son .0 39.50 .8260 8.2... 80.08.... . IT .3 r 0.. .83 ..s. is...» 323.03 2.2.8. o... .- 3222... a 5 22.2.3 2:52.. :3 32.» 2... 32.2.2. .02.: E59... CS... 0525: 53.3.. 2.- Agnosuca 2.9.). 2.953 ..»..uu.a> 3.032.... 52. .8223 c. 2... .2. 92.2.. 2.03 .o .2252 d 2.5... 58 002$ 002.0 320 .0- .36wm‘gg2aggm 0030 BB? dr- ‘0. You 59 .30.. .5 .385» 3200.05 30:3. 05 «0 3203...! 0 5 03.32.00 230.0... :3 0023 2.0 000.32.... .02... :32: Ca... 059:0. 300.30 2.180.332... 0.55. 00033 20:093. 3300...: p.000 3223 3 03023.3 9.50..» .3 2.5... 82.00 32.. Szn. .3.ewm2§§3§.23§.m 3m .0 «.2. pm... db- ~0- .o_. r8 you .82 .2 62.0.0 320220 2.2.3. .0 .0..0...0...0. 0 0. 2.0.22.3 0.3.0... =00 002.0 2.0 0023.00: .02... :30... CG... 0530. 0000.30 2.0 .32202... 0.35. 000.53 42.09.... 00.00002... :00.— 002200 .0 0002.00.00 05:25 .2. 2.5... 60 1996, the cowpeas 475/89 and IT82D-889 tended to have a higher shelling percentage under stress conditions than under non-stress conditions, while the reverse was true for common bean in 1995. The soybean had a significantly lower shelling percentage than all the other species under both stress and non-stress conditions in 1996 (Figure 11). Bambara Groundnut Bambara groundnut flowered well, but tended to stay in the flowering stage for a relatively long time. Less than half the plants produced pods in both years and frost came before they had completed the seed fill stage. Consequently, yields were low (Figures 12 and 13), less than 300 kg/ha each year. Moisture stress did not affect Bambara groundnut and there were no visible signs of wilting (data not shown). The genotype ZVS 564 had the highest yield in both years (Figures 12 and 13), while the inoculated and non-inoculated Bambara groundnut showed no yield diflerences in either year (Figures 12 and 13). All legumes were fertilized at a rate of 40 kg N ha“, the recommended rate for common bean. This level of fertility was probably excessive for Bambara groundnut and may have helped produce lower yields as indicated by previous researchers (Anonymous, 1979; Chomchalow, 1993). It is highly possible that Bambara groundnut yield was inhibited by the Michigan photoperiod. Day length is almost 16 hours in July and August in Michigan, and Bambara groundnut is normally grown in regions of the world that have much shorter photoperiods than Michigan (Heller et al., 1997). 61 8.. w a .- 803502. 38.00. :3 .2... .3585. .83525. .3088: .8 0>~ 80 m>~ 80 0>~ t J. o . 8 r 8. . 8. m -8. m a a . pa .— H .. ._. , 80 - 8» 000.0003 0.30.00. :00 002.0 2.0 008.0000 .0. 00030.00 0.0 0.00 .000. .=z 02.0.0 00.0003. 30.00.05 000:0: 05 .0 03.00050. 0 0. 0.50.0 .8053 0005. 5000020 0.00.000 .0 0.0; .0. 0.00... 62 3... .v. a .- 8082...- 8020... 2:. .000 3.38.... 2538...... 630.32.. 30 m>~ . 80 0>~ . 80 0>~ o . om . 8. H H .8... .— emu . . 8.. .000...0000 20.0.00. :00 002.0 000 002.0000 .0. 0003.000 20 0.00 .000. .2 .0000.» 00.0003. 30.0205 000:8. 00. .0 0.50.0 .000008000 0005. 5000020 2000.00 .0 22> .2. 2:0... 63 Improper photoperiod is known to reduce Bambara groundnut yield (Begemann 1988). Bambara groundnut yields have been reported to range from 150 to 6000 kg ha'1 (Chomchalow, 1993). Earthing is crucial in Bambara groundnut (Nleya Unpublished data) In 1995, all the treatments were not earthed and all earthing occurred beyond the optimum time. In both years, weed pressure was higher than desirable and could have reduced yield. Bambara groundnut is a small plant and cannot compete with weeds as efl’ectively as other legumes like cowpea, soybean and common bean. No herbicides were used because there was uncertainty about which herbicides were safe to use with Bambara groundnut. Consequently, all weeding was done by hand. Bambara groundnut treatments did not difi‘er in shelling percentage (Figures 14 and 15). In 1995 the un-inoculated Bambara groundnut genotype ZVSS3O had the highest seed weight of the Bambara groundnut treatments (Figure 16), while ZVS 564 had the highest in 1996 (Figure 17). In both years, Bambara groundnut had very low seed weight, suggesting the growing season was not long enough. The original seeds from Zimbabwe had 100 seed weight of 148.7g, while these data show a 100 seed weight of less than 30 g. Greenhouse Smdy The greenhouse temperatures in July when watering was terminated for the first experiment were generally much higher than in September when watering was terminated for the second experiment. As a result all cultivars survived for a 64 2.3038520838523300 083.88.. 20080.00. 6.168.. .0... 0>~ 80 0>N 80 0>~ .000...0000 20.0.00. :00 002.0 000 002.0000 .0. 000.2000 20 0.00 .000. .2 52.0.0 .00.00.0.m 000:8. 00. .0 .0..0:00.0. 0 0. 0.50.0 300000.000 0003. 5000020 0.02000 .0 008000.00 005000 .3 200.... :00 .8 .8 .2 . vs .2. .2 65 .8..w.i§l80008830§83800 .8368: 6.0085... .8368: 3.. 0>~ 80 0>N 80 0>~ 4 L 1 0000.008 20.0.00. :00 002.0 000 002.0000 00030.00 0.5000 0.00 .000. :2 .0000.» 00.00001 30.00.03 000:0: 00. .0 300000.! 0 0. 0.50.0 .000008000 0003. .0000020 2000.00 .0 00300200 005000 .0. 0.00... .Séwmfiscaoscuzsiuzaaeu .8189... 20.085... 8.038.. «00 0>~ 80 0>~ 80 0>~ to (m) rumpus l—-l .000...0000 20.0.0.0 :00 002.0 000 002.0000 .0. 00030.00 20 0.00 .000. :2 .00..0.0 00.00000 .00.00.05 000:3. 0... .0 .0:0..00.0. 0 0. 0.50.0 500000.000 0005. 5000020 2000.05 .0 00000 0... .00 0.0.0.5 0000 .0.. 200... 67 .3... w 0 .- 8035000 8.8.0... 0.3 .000 6.188.. €008.00. 62088.. 30 0>~ 80 0>~ 80 0>~ 5%. u; (”mm-mm I-H i--I 18 |——l .000...0000 20.0.00. =00 002.0 000 002.0..000 .0. 00030.00 20 0.00 .000. ..s. .0000... 00.00001 .00.00.0.m 000:3. 00. .0 3000050. 0 0. 030.0 .30§00 0005 30000020 2000.00 .0 00000 00. .00 20.03 0000 .2. 200.“. 68 longer length of time after watering was terminated in September, since moisture stress under low temperature is less devastating to the plants than moisture stress under high temperatures (Tables 3 and 4). In both experiments, common bean cultivars were the most susceptible to moisture stress (Tables 3 and 4). The cowpea cultivars were the most tolerant to moisture stress in the June planting, but cowpea and Bambara groundnut did not difl‘er in the August planting. In the June planting, cowpea had terminal green leaves well after the common bean and Bambara groundnut were dead. The cowpea cultivars showed a tendency to shed lower leaves once water was stopped. This agrees with the field data which showed that cowpea cultivars had the least yield reductions under moisture stress conditions. In the June planting, the box depth aflected the time it took the plants to die (Table 3), undoubtedly due to the greater soil moisture reserves in the box with the 20 cm depth and the higher temperatures that plants were exposed to during the summer months. Plants dried out more rapidly in the 12-cm than 20—cm box. CONCLUSIONS Moisture stress reduced the number of pods per plant in cowpea and soybean, but not in common bean. Moisture stress reduced seed weight of T 3147. It reduced the number of seeds per pod in cowpea in 1996. Cowpea was more drought tolerant than common bean, although common bean produced a higher 69 a. a .0 30 f; f; f; a: 00. .5 8 0.000 00m wv 0 .N 0cm 0N. 0N. 0N. am. *0 N. Eu N. 0.000 xom 00....3 .00000000 0. 050D .mod 0 n. .0 00020.0... .000....&.. 0.00.00. 0.8.0.... 03.9... 00.2... 0-5. m H 800m .807. 000000 03 m>N 0mm m>N 0030000 0000...? .0 20.05000 30.8305. 9&5. 80300 ASSESS... 9&5. 000300 .0....0&.§ 00.00000... 000m .0 3.830... 00.00035 50m .0 630.... 388.0. a... .0 8000.00.00 3&5. .0.—0000.0 0.00.0.5 A00§§0..00 3&5. 3000020 0.0080m 00.0000 000 00000 .03. .00 .3. o. 03. .0. 000.. .00... 3.0.0303 0.8m 000.000). 0... .0 30000003 0 0. 000 cm x m. x m. 000 N. x m. x m. .. 038. 0.30.0 0. 0.00:. ..00.0000 .H. 0 0. 030.0 3.0.0033... 3&5. 000300 000 .Am...0&.§ 00.00.0005 000.. 000.800 A00§§0300 3&5 . 3000080 0.00005 .0.. 00....3 .00000000 0. 0500 00.50005 000.20 00.00200 00080.0. .0000... 3.00.00 .m 0.00... 70 0. 0 0.. 0 mm 00 mm 0 on 00 X 0 mm 000 0m 0.000 00m. 000.0800 w0.....$ 80008.00 0. 0000. 000.03... 00.3.. «-0... m 0. .0w0m .807. 000.00 00m m>N 0mm m>N 000.0000 8.0 w 0 0 8800.0 080000 28.0.. 0003... 00..0..0> .0 .00.0E000 0.0.0.0333 3&5. 000300 0.0.0.0333 3&5. 000300 .0....0&.0> 00.00033. 000m .0 A0...0&.0> 00.00005... 000m .0 A0...0&.0> 00.000053 0000 .0 000000.000 3&5. .000000.w 0.0000... 0.000.030 3&5. 800000.» 0.0083. 00.0000 000 00000 .000. .00 .3900 3 002 .00 0:03. 80... 3.0.0000... 0.0.m 00000.5. 00. .0 .00000000.& 0 0. A80 om x m. x m. 000 N. x 0.. x m. .. 00.80 0.30% 0. 0.008 0000000 .H. 0 0. 030.0 0.0.0.0303 3&5. 000300 000 0.2030. 00.00000... 0000 008800 .A0000t0300 3&5. .000000.w 0.0080m. .0.. m0....3 80008.00 0. 0000 w0.=00008 000.08 w0.000.00 0000.0.0. .0w00... 3.00.00 .0. 0.00 0. 71 yield than cowpea STI was a better predictor of yield performance than DSI. Natal sugar did not mature in Michigan, but T3147 produced a smaller number of pods than Carioca and had a higher yield reduction under stress. The cowpea genotype 475/89 produced a higher yield and greater number of seeds per pod than IT82D-889. Cowpea produced more seeds per pod than bean or Bambara groundnut and had the highest percentage of seed abortion under both stress and non-stress conditions. Unfortunately, field performance of Bambara groundnut could not be compared to the other three species. Results of both the 12- and 20- cm box depths indicated that cowpea was more drought tolerant than Bambara groundnut and that Bambara groundnut was more drought tolerant than common bean 72 REFERENCES Acosta-Gallegos J. A and J .K. Shibata 1989. Effect of water stress on growth and yield of indeterminate dry bean (Phaseolus vulgaris) cultivars. Field Crops Research 20:81-93. Adams, M.W. and J .J . Pipoly III. 1980. Biological structure, classification and distribution of economic legumes. p. 1-16. In RJ. Summerfield and AH. Bunting (ed.) Advances in legume science. Royal Botanic Gardens, Kew, England Anonymous. 1979. Bambara groundnut. p. 47-53. In Tropical legumes: resources for the future. National Academy of Sciences, Washington, DC. Begemann, F. 1988. Ecogeographic differentiation of Bambarra groundnut (Vigna subterranea) in the collection of the International Institute of Tropical Agriculture (I.I.T.A.). Ph.D. diss. University of Munich. Chomchalow N. 1993. Bambara groundnut. FAO regional office of Asia and the Pacific. Maliwan Mansion, Thailand. Elston J. and AH. Bunting, 1980. Water relations of legume Crops. 1980. p. 37- 42. In RJ. Summerfield and AH. Bunting (ed.) Advances in Legume Science. Royal Botanic Gardens, Kew. Fischer, RA. and R Maurer, 1978. Drought resistance in spring wheat cultivars. 1. Grain yield responses. Australian Journal Agriculture Research 29:277-317. Gwathmey C. 0., A.E. Hall. 1992. Adaptation to mid-season drought of cowpea genotypes with contrasting senescence traits. Crop Science 30:300-305 Heller, J ., F. Begemann, and J. Mushonga. 1997. Bambara groundnut Vigna subterranea (L.) Verdc. International Plant Genetic Resources Institute. Rome, Italy. Kadhem, F.A., J .E.Specht,. and J .H.Williams. 1985. Soybean irrigation serially timed during stages R1 to R6. 11. Yield components responses. Agronomy Journal 77:291-298. Khanna-Chopra, R, and S.K.Sinh. 1987. Chickpea: physiological aspects of growth and yield. p 163-189. In M.C. Saxena and KB. Singh (ed.) The Chickpea CAB. International, Wallingford, great Britain. 73 Korte, L.L., J .E. Specht, J .H. Williams, and RC. Sorensen. 1983. Irrigation of soybean genotypes drning reproductive ontogeny. 11. yield component responses. Crop Science 23:528-533. Lawn, RJ. 1982. Responses of four legumes to water stress in Southern Queensland. 1. Physiological response mechanisms. Australian Journal of Agricultural Research 33 :48 1-496. Lynch, J .P. 1995. Adaptation of beans (Phaseolus vulgaris) to low phosphorus availability. HortScience 30:12-16 Meckel, L., D.B. Egli, RE. Phillips, D. Radchfie, and J .E. Leggett. 1984. Effect of moisture stress on seed growth in soybeans. Agronomy Journal 76:647-650. Nleya, T. 1992. Some aspects of cowpea research in Zimbabwe. Agronomy Institute in Zimbabwe. Unpublished data. Rosenthal, W.D., G.F. Arkin, P.J. Shouse, and W.R Jordan. 1987. Water deficits on transpiration and leaf growth. Agronomy Journal 79:1019-1026. Schneider, K.A., R. R. Rosales-Sema, F. Ibarra-Perez, B.Cazares-Enrique, J .E. Costa-Gallegos, P. Ramirez-Vallejo, N. Wassimi, and J .D. Kelly. 1997. Improving common bean performance under drought stress. Crop Science. 37:43-50. Singh, B.B., Y. Mai-kodomi, and T. Terao. 1995. A simple screening method for drought tolerance in cowpea. p. 71-72. In Agronomy abstracts. ASA, Madison, WI. Singh, S. P. 1995. Selection for Water Stress Tolerance in Interracial Populations of Common Bean. Crop Science 35:118-124. Singh, SP. 1982. A key for identification of different growth habits of Phaseolus vulgaris L. Bean Improvement Cooperative 25:92-95. Turk, K]. and A. E. Hall. 1980. Drought adaptation of cowpea: III. Influence of drought on plant growth and relations with seed yield. Agronomy Journal 72:428-433. Yabba, MD. 1997. Assessment of root morphology as an indicator of drought resistance in common bean (Phaseon vulgaris L.). Master’s thesis. Michigan State University. 74 CHAPTER 2 EFFECT OF MOISTURE STRESS ON NITROGEN PARTITIONING AND REMOBILIZATION IN BAMBARA GROUNDNUT, COWPEA, AND COMMON BEAN ABSTRACT Improvements in N partitioning and remobilization may lead to yield increases. This study was undertaken to study the efi'ects of moisture stress on nitrogen partitioning in Bambara groundnut ( Vigna subterranea), common bean (Phaseolus vulgaris), cowpea (Vigna unguiculata), and a non-nodulating isoline of the soybean (Glycine max) Harosoy. The study included three common bean lines (Carioca, Natal Sugar and T 3147), two cowpea lines (IT82D-889 and 475/89), three Bambara groundnut treatnrents (inoculated and uninoculated ZVS 530 and inoculated ZVS 564), and Harosoy grown under stress and non-stress moisture conditions in a rainshelter at the Kellogg Biological Station in Hickory Corners, MI in 1995 and 1996. Cowpea contained the highest leaf- and stem-N concentration at all stages of development and had the highest reproductive-N concentration at flowering and podfill, with the exception of Bambara groundnut at podfill. Soybean remobilized more N from the leaves than common bean and common bean remobilized more than cowpea and Bambara groundnut. There was 75 a tendency for moisture stress to increase N concentration in common bean. Leaf- N concentration was lower in 1996 than in 1995 in all species and at all growth stages. 76 INTRODUCTION Future improvements in yield may come from improvements in N partitioning and remobilization of assimilates into harvested components (Loomis et al., 1979). Remobilization may be defined as the movement of nutrients from living plant parts to other parts, mostly though not exclusively, to the reproductive parts (Loberg et al., 1984). Difi‘erent legume species have different abilities to remobilize nutrients during the reproductive stages. Zeiher et al. (1982) estimated that remobilized nitrogen contributes 20 to 100% of total nitrogen at maturity in soybean. Moisture stress affected the total accumulation of nitrogen in cowpea, soybean, and lablab bean (Chapman and Muchow, 1985). Cure et al. (1985) showed a relatively rapid decline in leaf nitrogen concentration when moisture stress was induced during the mid seed-fill stage of soybean. In Nigeria, Wien et al. (1979) observed that water-stressed cowpea translocated more nitrogen to the pods than plants supplied with adequate moisture. Foster et al. (1995) observed that a greater proportion of seed nitrogen was obtained from remobilized nitrogen under moderate moisture stress conditions in common bean, but less N remobilization occurred under severe moisture stress. They suggested that nitrogen remobilization might aid yield stability during conditions of moderate moisture stress, but becomes less important under severe or prolonged moisture stress. Selemat and Gardner (1985) inferred that nitrogen was remobilized from 77 leaves to pods during periods of nitrogen stress in non-nodulating peanut (A rachis hypogaea) cultivars, but no remobilization occurred in the nodulated plants. Likewise, DeVries et al. (1989) showed that moisture stress had no effect on nitrogen concentration of leaves and stems of peanuts. This study was undertaken to study the efl‘ects of moisture stress on nitrogen partitioning in Bambara groundnut, common bean, cowpea, and non-nodulating soybean. MATERIALS AND METHODS The experiments were planted in a modified split plot design on a Spinks sandy soil (Psammentic Hapludalfs, sandy, mixed, mesic) in a rainshelter at the Kellogg Biological Research Station in Hickory Comers Michigan in 1995 and 1996. The experimental design was a modified split-plot in a randomized complete block with two moisture treatments (stress and non stress) as the main plots and genotypes as sub-plots. There were four replications and treatments consisted of two cowpea genotypes (IT82D-889, 475/89), two Bambara groundnut genotypes (ZVS 530 inoculated, ZVS uninoculated, and ZVS 564), three common bean genotypes (Carioca, T3147-2, Natal Sugar) and a non-nodulating soybean isoline (Harosoy). All the genotypes were obtained fiom the Department of Research and Specialist Services in Zimbabwe except T3147-2 and Harosoy which were obtained from the breeding programs of Dr. James Kelly at Michigan State University and Dr. J. E. Harper at USDA-ARS in Urbana, IL., respectively. 78 Neutron probe access tubes were installed in each plot to a depth of 1m prior to planting. Forty kg N ha’1 was broadcast using 19-19-19 fertilizer, the normal fertilizer rate for common bean. Common bean was inoculated with a granular form of Rhizobium phaseoli, the cowpeas with Rhizobium cowpea miscellany nitrogen EL, and Bambara groundnuts with Voandzeia Special 1. The cowpea and Bambara groundnut inoculum were obtained from Nitragin T" Inoculants and were manufactured by Liphatech, Inc. The non-nodulating soybean (Harosoy) and a non-inoculated Bambara groundnut ( ZVS 530) treatment were used as controls. It was assumed that the Bambara groundnut rhizobium was not present in the soil since Bambara groundnut had never been grown on that soil. An inoculated ZVS 530 was also grown. The four-row plots were each 2 m. long and 0.5 m wide. The intra-row spacings were 8 cm, 15 cm and 25 cm for the common bean, Bambara groundnut and cowpea respectively. Three applications of frmgicide (Benlate for anthracnose and Sevin for Japanese beetles) of 1.12 kg ha" were made in 1995 at two week intervals starting on July 14. Two applications of Benlate were made in 1996. Terminal moisture stress was initiated on July 29 in 1995 and July 21 in 1996. Sampling for nitrogen partitioning was done at three stages - vegetative, flowering, and podfill. Planting was done on June 20 and June 6 in 1995 and 1996, respectively. Sampling for the vegetative stage was done on August 4, 1995 at 44 days after planting (DAP) and on July 19, 1996 (45 DAP) for all treatments. 79 =3- In 1995, sampling during the flowering stage was done on August 25, (66 DAP) for all treatments. The flowering stage of common bean was used as the reproductive sampling date. In 1996, the treatments were sampled at diflerent dates as each species and genotype reached the flowering stage. Common bean was sampled on August 8 (64 DAP), soybean on August 16, (72 DAP), cowpea on August 23 (79 DAP), and Bambara groundnut on September 15 (102 DAP). In 1995, sampling for the podfill stage was done on September 9 for common bean and cowpea (81 DAP), October 1 for soybean (103 DAP), and October 8 for Bambara groundnut (110 DAP). In 1996, sampling for the podfill stage was done on August 23 (79 DAP) for common bean, September 15 (102 DAP) for cowpea, and October 3 (120 DAP) for soybean and Bambara groundnut. At sampling, three plants per plot were cut at the base of the stem, dipped in water to remove all soil, and separated into leaves, stems and reproductive parts (flowers and/or pods) for subsequent determination of dry weight and total nitrogen. Nitrogen was determined by Kjeldahl digestion and total nitrogen was analyzed using the Latchet procedure. The Fischer and Maurer (197 8) drought intensity index (D11) was used to determine the degree of moisture stress that had been induced. This method uses the average yield of all genotypes under stress and non-stress (Y. and Yp), respectively to determine drought intensity according to the following equation: D1] = 1- Y./Y p. 80 RESULTS AND DISCUSSION Nitrogen Partitioning gem. In 1995, leaf-N concentration for the two cowpea genotypes (IT 8d-889 and 475/89) did not differ during the vegetative, flowering or podfill stages (Tables 1 and 2). During the vegetative stage cowpea had a significantly higher leaf-N concentration than Bambara groundnut (a 5 0.0001), common bean ( a s 0.01), and soybean (a 5 0.10) (Tables 1 and 2 ). Leaf-N concentration remained significantly higher (a 5 0.001) in cowpea leaves than in Bambara groundnut, common bean, and soybean leaves during flowering. By podfill, cowpea had a significantly higher leaf-N concentration than common bean (a _<_ 0.10) and soybean (a s 0.01), but did not difi'er from Bambara groundnut (Tables 1 and 2). In 1995, common bean had a higher (a 5 0.0001) leaf-N concentration than Bambara groundnut during the vegetative stage, but did not differ from soybean (Tables 1 and 2). During flowering, common bean had a higher leaf-N concentration than Bambara groundnut (a 5 0.01) and soybean (a 5 0.05). By podfill, common bean and Bambara groundnut did not differ, and common bean had a higher leaf-N concentration than soybean (a 5 0.001) (Tables 1 and 2). T3147-2 had a lower leaf-N concentration than the Zimbabwean common bean genotypes (Carioca and Natal Sugar) at flowering and podfill. Leaf-N concentration values were lower in 1996 than in 1995 (Table 1), 81 5.958552 45555555» 855=am 585—5855 55 5.555555% 5.85553 .855 95855 5508553— 3 .5 5.358552 588.55 552 555 .5385» 552 55 505 558252 m 555 m2 .md . 3:285 585555 5.5 5.55.: a 55588 3.5 w a 5 8:285 5855.5: 5828: 5:58 a 555, 528. 508555. o 2 3: 5: o 3 :3 can 53. 588:5 588m : on a 2 8 on 8 3 5 an o 3. o 2 8m m>~ 855:5 : I“ : S 5 E o 3 5 3. 8 an 8 3 cm m>N 535:5 : 2 a .2 8 :a 5 3 5 an 8 n: u: on 555% m>~ 5:55:55 5 8 a 3 o 5.” o 2 5 an 5 5m 8 S. 32$ :85 .o 8 .1 a 8 8 on 5 an 5 I“ : N... 5: 3. 8555 :85 .o 5.... a 3“ a 3. 5 am 8 3. 5.55 552 :85 .u : 2 a 3 : n... 5 Z a 3. : S. 5: S. 35:. 8538 : ma : 3 : NM 5 ma : 3. : 3 .5 55 5532.5 8538 5 m2 5.. 332 332 332 332 332 8:558 8:558 8:558 8:558 8:558 .5: @5325 o>_§omo> 5...:— mEbBoE o>5fiowo> cabofib 860% 55:_ moo_ .553 555 32 E .3 .5255 5555858 8&255 $2.3. 55 55 5285555: 5 5 5525558 83595 :8 5855 555 $25 555 50555 535% ASSESES aw: 8538 555 GEE mSobDV 53558 8.25%?» 5538.35 552. . Aumauteaa. 3&5: 55555553 855555m E mow—3:. :5qu 555 555035: 63.3%? on. 55 3% 505555858 Z853 _ 253. 82 5.35858. 58...: 55 .35... .3... .3... .2 .5 m. a 5 8:20.55. 5855.55 59.88: :.:....._..:.. .+ 585:5 2.5.. $838555 .855 95855 555 5555552» EBEam .58oaum m. 55 m5 m5 m5 m5 m5 3m m>N m> cvommm>N :: a: a: a: a: 5: om m>~ 5. 6883 .1 I- l- .. .. 55 55> EN .m> Ng.: a. .1 1. a--- ... m5 m5 swam .852 .m> 82550 55 55 + .. .. .. .. m5 :1 2. .5.» 85.550 + m5 m5 m5 m5 m5 3R? m> awwdwh ............ + .2. 5...... .. 55 585.58 .m> 550m .U 2...... m5 m5 m5 ...... 1...... Susana .m> 58m .U 2...... + r. .. r... + 58.58 .9 5.....8 5.1.... .. ............ + .12.. .1. 50m .0 .m> 509550 m5 ... .....:..... m: 5...... 3...: Ruwngm .m> 509500 585500 :25:— wEbBoE o>5flowo> Econ $532.5 o>=5$wo> owflm 5380 3:0 55555553550 2.0.8..— oofl mam— .oafl 555 32 5. A2 .5058m 8%205 mmo=o¥ 05 55 58—05555: 5 5 532m 085 5.5.8.500 55238 555 A8§h8§5 323.50 50538 _ .3553»... 5.385.230 5505 .355552555 3585 5.555550% «Essen .55 5055555858 2.052 58 385.58 8.85m .N 5355. 83 probably due to leaf bronzing and chlorosis resulting from ozone and smscald, respectively, in 1996. Nevertheless, patterns of leaf-N concentration in 1996 were very similar to those of 1995 (Tables 1 and 2 ). Cowpea retained a higher leaf-N concentration than common bean from the vegetative stage through podfill in 1996, while common bean had a higher leaf-N concentration than soybean at podfill. Leaf-N concentration of Bambara groundnut at podfill equaled that of cowpea in 1996. This research utilized a non-nodulating soybean, but the results are similar to that of DeVries et al. (1986) which found that soybean leaves at harvest contained less N than peanut and pigeonpea leaves at harvest. Results indicated that soybean partitioned the least amolmt of N to the leaves, followed by common bean, with cowpea and Bambara groundnut partitioning the most. It suggests that soybean remobilized more N from the leaves than common bean and that common bean remobilized more than cowpea and Bambara groundnut. The soybean was non-nodulating and the 40 kg N ha'1 is the recommended N fertilizer rate for common bean, but was insufficient to meet the needs of the non- nodulating soybean as indicated by the light green color of the soybean leaf tissue during the growing season. Bambara groundnut did not mature within the Michigan environment and the higher leaf-N concentration may simply reflect that the plant had not completed the process of remobilizing N from leaves to developing seeds. Cowpea reached physiological maturity approximately three weeks after common bean and the higher leaf-N concentration may again simply 84 ”-5. La. reflect that N remobilization from cowpea leaves was less advanced than in common bean and soybean by the sampling date in 1995. However, species comparisons produced the same results in 1996 when each species was sampled when it reached each specific stage of development. The relatively higher N concentration in cowpea is compatible with the statement by Summerficld et al. (1985) indicating that cowpea yields appear to be limited by the crop’s ability to assimilate carbon and N during the reproductive period and its ability to partition large amounts of C and N into fruit production. By podfill, the cowpea 475/89 had a lower (a S 0.10) leaf-N concentration than the cowpea IT82D-889. Values for the nitrogen concentration in the leaves by podfill ranged fi'om a low of 2.0% to a high of 3.4 % in 1995 and a low of 1.1% to a high of 2.5% in 1996 (Tables 1 and 2). These values are consistent with values reported by Dubois and Burris (1986) m In 1995, cowpea had a higher stem-N concentration than Bambara groundnut during the vegetative and reproductive stages (Tables 3 and 4). Bambara groundnut had a higher stem-N concentration than common bean at the vegetative (a 5 0.0001), flowering (a 5 0.05), and reproductive (a 5 0.0001) stages in 1996, but was only higher at flowering in 1995. (Tables 3 and 4). As with leaf-N concentration, no differences were observed between the Bambara groundnut genotypes in stem-N concentration at any stage of development in the 85 303800 mar—030$ on mv 0 0.0 0 0.0 a 0; no N.— a «A a v.— 0 mg 00 N.— 0 m0 00 0.0 on 5.0 0 md a A: an N.— n 0.0 a v; 3305 :02 3305.». :02 0% 3325 a. 33005 303.000 5.000 0m 3 m6 0 N.— 00 ad 30 rd 0 To 0 md 3305 :02 0% 3&0ch 305800 o>080w0> 000 _ 002 .05. 30— 5 dz .0035 :033M 305.05 3030— 05 8 02.0558 0 E «0020000 0560:. =8 80:... 05. $05 :00 30:: 030% A80~=03m§ 0:05 000300 05 08.: 050.000 5000a .ESSE. “$008.30 500 008800 A00§§03§ EMSV Sacczohm 3350mm E $.30 05. .watoBoc .036 023.0%; 05 an 30 003530000 2.8on E £3 3.. £3 a 2 a 2 £3 a 2 e. a... a. o. o\.. 00mmobm :Oz 0% 3325 305800 5:000 32 z 2: 3.. 3... 3.. o 2 an. a 3 an. a. 3 3805... :02 0% 3325 303800 $3305 2 .0 mg a Nd DNN a fin 0 mg 0 EN 0 vd 0 ed *0 ON 330:... :02 a. 3325 303800 0>030m0> .088: v8 m>~ om m>N €33 m>~ 32$ 000.50 396 .802 92me 03.0%: 099030 20380080 .Bcccaocw 838.5 33.0005 05 500.50% 8382— .800 mean?— Eomoaom 3 .0 00:03.50 88550.. 080— ....»8—3. 0. wear—008 no.0 v. 0 3 coachogv Edomfiwmm 0082000 0.33— 0:03me >0 500mg 8380mm 8380mm .uBnEam 03m .0 50m .0 30m .0 000300 30300 8.00% .m 2.3 86 0.2.088. .880 05. .800 .80 .30 .2 .o w a 0. 85.00% 0.80000 0.8202 ._....._......_............. .+ 230...... 2:. .....0>.000%00 .0000 $000.00 .000 3000003 0000000.. 00000000”. 2 2. 2. .. 8 2. 2. $33 a, 628% a. 2. 2. 2. 2. a. omm>m a, Sommi ..-- --- -: 00 3...... 1...... 00> EN .m> $50. m... I E 0.--- m0 m0 m0 00w0m .0002 .m> 000.000 00 m0 00 00 1...... 1.... ”.0. m... .0> 000.000 m0 m0 00 00 00 00 0.2an 0> and”... m: m: m: .. I... :2... 0000000. 0., 0000 .0 1...... I... 1...... m0 3...... m0 0000000m .m> 000m .0 .2... s. a. + 2.: 1.: 52.80 .0, 80.60 3.. 1...... 5.. 00 .. 2...... 000m .0 .m> 000300 3...... m0 m0 m0 3.. 2...... .0000000m .m> 000300 0005000 .5000 @0030... 0>.0000m0> 5.00.. $00.50.... 0>.0000w0> 0m3m £3000 gov 005000000000 2-0—Sm 000. 30. 000. 000 30. 0. d). 00:06 .00.w0.0.m 30:00. 05 00 000.00.00.00 0 0. 20.0.0000 0030.00. :8 00000 .000 000000 000 00.000 030% 083 050.09 0009.00 .000 ASS~§§§ EMS. 000300 .3530: 00.000035 000.. 00.503 A00§h05§0 Shiv 0:000:00w 003.0%. ..0 00000000000 2-00000 00.. 3000000 00.00% .0 0.00... 87 two years, with the exception of the vegetative stage in 1996 (Table 4). Inoculation or lack of inoculation made no difference in ZVS 530, presumably because the 40 kg N ha'1 was suficient to meet the needs of the crop. Soybean had a significantly lower stem-N than common bean genotypes at all stages of growth in 1995, but the two did not difi‘er in 1996 (Table 4). Cowpea had the highest stem-N concentration followed by Bambara m groundnut, although the data for Bambara groundnut must be viewed with suspicion since Bambara groundnut did not reach physiological maturity (Table 3). Chapman and Muchow (1985) observed increased nitrogen partitioning in stems and leaves of cowpea, lablab, black gram and pigeon pea under moisture stress conditions. In the current research, moisture stress did not afl‘ect stem-N concentration and only affected leaf-N during flowering in 1995. Foster et al. (1995) reported higher stem-N under stressed conditions. They concluded that high stem-N concentration could imply inefl'lcient remobilization of stem-N under severe moisture stress. Considering their observation, the lack of increased stem-N under stress in this study may simply be due to the mild moisture deficit, especially in 1996. mm Cowpea had a significantly higher (a _<_ 0.0001) reproductive-N concentration at the flowering stage than did common bean in 1995 and at podfill in 1996 (Tables 5 and 6). Reproductive-N concentration in cowpea was 88 20200096: 4:50:83 aBnEam 5083005 5:: 5:55:03 838.5 .80: @528 0:80:90M 3 4 5320033.. 6030:: 5:: .305: :02 4E 50: 80:050.. m 5:: m2 rm»: 00:20.5: Enomfiwmm 0000— :.500—3. 8 @6300: 3.0 m a :0 00:80:25 Smog—ma 80:050.. :8200 a :22? 3030. 80.0%? 89 : an : a: : a: 5 3 o 2 .8885 8258 5 S o 8.: 5 no 8m m>~ 8:98: 5 3 o no 5 no on: m>~ 23:8 : N: o v: 5: Z 6:9. m>~ 55:8 5: ca 5: M: : S 5 3 o: :m 323 :8: .0 £2 83 53.. 5a.: 2. 2 8:80 :8: .o : f o S .5 325 8:2 :8: .u : 3 8 a: : S : 3H 5: 5 2%: 89:8 : «a t: 2 5: 2 : mm : 0.: 25.33: 8:38 m 0.2 .x. m a mz m 8 m2 m a. 52 8:558 8:558 8:588 . mm @8263 m . m .m gross—m 0:50:00 860nm 82 82 .82 0:: 82 :2 .3 .885 8:88: game—Em wwo=0v~ 05 a: 8:228: a E 0:203:00 0:322: :8 30.5: 5:: $05: :0: 65:: 559% ASSESES 3:35 00:38 5:: $88 059mm: 50:58 .ESMNQ: .5 :00: 58:80 A30§h05§ EMSV S:::=o..w wags—am 8&3... :_ 3:32: Emma—29$: 5:: 85.530: .0>_§0m0> 05 0a 3% 5505:0050 2-038388% .m 0.8.... 25:80.52 .88.: 8: .80.: .8: .3: .20 w a a 8:885 285:»: 582:2 int-f... .+ 22:5: 25 23500000: .305 wing: 5:: 3:55:03 wanedm 0:002:35 t. m: m: :- Smm>N a, Sommm>N m: m: m: 88% 0: €233 -- -- m: 3.. _. 20> EN .m> Ng.:— C. -- -- m: ii... :85 5802 .m> 00050 -- -- m: 3...... «$3 a. .m> 000500 m: a m: m: $ka m> awn-Ow: + m: m: 0 830m .m> 50m .0 _. 2.... I -- 0:00:55 .m> 50m .U m: m: m: .. * _._ 50555 .m> 000300 .. m: m: t...- ::8 .0 as 82:8 _. ... _. ... m:- mfiwnaam .m> 000300 0:80:00 =55om 850303 __550._ 350305 035 5305 £5 8580:0080 2020005053“ ........... 50a _ ------ -------mma _ ------ .502 5:0 m3. :_ dz £0505 8&205 30:03 05 :0 :0:—050:5: a :_ ”0:025:00 00820:: :0:. 30.5: 5:: 0:03: :0: 505:: :BSw CBS 050ARVV 50550: 5:: A80303M§ at: 000300 A220M~§ 0.300035 :85 :08800 4005:2038. 3&5 3:5:00E massam .50 5503:0800 203805050: :0.“ 3:80:00 02003 .5 030,—. 90 significantly ( a _<_ 0.0001) higher than in soybean at the flowering stage in 1995 (Table 6), however no difi‘erences were observed in 1996 between cowpea and soybeans at flowering or podfill. Between the cowpea genotypes, IT82D-889 had a higher (a 5 0.1) reproductive-N concentration than 475/89 in 1996 but not in 1995 (Table 6). The common bean genotype Carioca had a higher reproductive-N concentration than T3147-2 (Tables 5 and 6), in 1995 but not in 1996. The inoculated treatment of ZVS 530 had a higher reproductive-N concentration at podfill than the inoculated ZVS 564 in 1996 (Table 6). The non-nodulating soybean had a surprisingly high reproductive-N concentration in both years (Table 5). When considered along with the low N concentration in soybean leaves and stems, this supports the interpretation that soybean is very efiicient in remobilizing N from vegetative to reproductive structures. While not significant, there was a tendency in common bean for increased N concentration in leaves, stems, and reproductive structures of stressed plants at podfill in 1995 (Table 7) and in leaves and reproductive structures in 1996 (Table 8). In 1995, plants experienced a moderate moisture deficit (0.54) and a mild moisture deficit in 1996 (0.22). The tendency for increased N is consistent with the findings of Foster et al.(l995) which reported a tendency for higher nitrogen concentration in plants under severe moisture stress Foster et al. (1995) suggested that nitrogen remobilization may be severely impaired by greater moisture deficit, while N redistribution during a moderate moisture stress may contribute to yield 91 3.0 006 omd wmd m m2 080% R: 00.0 on: 50.0 0m: 00.: m m2 080% 00. _ 00. _ mod ow. _ m m2 3:0: 0200:0050“: 00: S.— m m: w _ .— SN 3.: m m .2 0:0: 0>00:00::0.m 3: mm.— Nw._ ow: m m2 00>00-H 05.0. 00.0. mod m6~ mm.m _N.m m m2 000,004 .000— 5 H2 £0500 b.0005 :_ :008m 0003205 3300— 05 :0 00:05:00: 0 E 0:020:00 00:50:. :00 Amv 0005.: 0:0 620 00050-5: 000:: 850% 04 0.0.8300: 0:30:35 :00: :0EE00 .00 00:30:30 0300:0800: 0:0 .0880 .0260. .00 000005800 2 .82 s :2 .3058 ESE: 5 :0008 3030—05 30:3— 0.: :0 :0:—0:050: 0 :_ 0:030:00 00:50:. :00 Amv 3000 0:0 Amzv 00050-5: 80:: gew Ai— 005M~§ 0.500030% :00: :08800 .00 00:80:50 0200:0050: 0:0 .0808 .m0>00_ .00 5005:0050 Z .0.-bv— mu. aofio 0:50:00 .w 030.—. N-hv— mp. 000000 :0m:m .0002 0:30:00 .5 030,—. 92 stability. CONCLUSIONS Soybean remobilized more N from the leaves than common bean and common bean remobilized more than cowpea and Bambara groundnut. Similarly, cowpea contained the highest leaf- and stem-N concentration at all stages of development and had the highest reproductive-N concentration at flowering and podfill, with the exception of Bambara groundnut at podfill. There was a tendency for moisture stress to increase N concentration in common bean. Leaf-N concentration was lower in 1996 than in 1995 in all species and at all growth stages. 93 REFERENCES Chapman, A.L., and R.C. Munchow. 1985. Nitrogen accumulated and partitioned at maturity by grain legumes grown under different water regimens in a semi-arid tropical environment. Field Crops Research 11:69-79. Cure, J .D., C.D. Raper, R.P. Patterson, W.P. Robarge. 1985. Dinitrogen fixation in soybean in response to leaf water stress and seed growth rate. Crop Science 25:52-58. DeVries, J .D., J .M Bennett, S.L. Albrech, and K.J. Boote. 1989. Water relations, nitrogenase activity and root development of three grain legumes in response to soil water deficits. Field Crops Research 21:215-226. Dubois, J .D. and RH. Burris. 1986. Comparative study of N uptake and distribution in three lines of common bean (Phaseolus vulgaris L.) at early pod filling stage. Plant Soil 93:79-86. Fischer, R.A. and R Maurer, 197 8. Drought resistance in spring wheat cultivars. 1. Grain yield responses. Australian Journal Agriculture Research 292277-317. Foster, E. F., A. Pajarito, and J. Acosta-Gallegos. 1995. Moisture stress impact on N partitioning, N remobilization and N-use efficiency in beans. (Phaseolus vulgaris). Journal of Agricultural Science, Cambridge 124227-37. Loberg G., R. Shibles, D.E. Green, and J .J . Hanway. 1984. Nutrient mobilization and yield of soybean genotypes. Journal of Plant Nutrition 7: 131 1-1327. Loomis, RS., R. Rabbinge, and E. Ng. 1979. Explanatory models in crop physiology. Ann. Rev. Plant Physiology 30:339-367. Selemat, A. and F.P. Gardner. 1985. Nitrogen partitioning and redistribution in non nodulating peanut related to nitrogen stress. Agronomy Journal 77:859-862. Summerfield, R.J., J .S. Pate, E.H. Roberts, and H.C. Wien. 1985. The physiology of cowpeas. p. 65-101. In S. R Singh and KO. Rachie (ed.) Cowpea: research, production, and utilization. John Wiley & Sons, N.Y. Wien, H.C., E.J. Littleton, and A. Ayanaba. 1979. Drought stress of cowpea and soybean under tropical conditions. p. 284-301 In H. Mussell, and RC. Staples ’ (ed.) Stress Physiology in Crop Plants. Wiley Intersciencc, New York. 94 Zeiher, C., DE. Egli, J .E. Leggett, and DA. Reicosky. 1982. Cultivar differences in N redistribution in soybeans. Agronomy Journal 74375-3 79. 95 CONCLUSIONS Moisture stress reduced the number of pods per plant in cowpea and soybean, but not in common bean. Moisture stress reduced seed weight of T 3147, a common bean, and reduced the number of seeds per pod in cowpea in 1996. Cowpea was more drought tolerant than common bean, although common bean produced a higher yield than cowpea. Among common bean genotypes, Natal Sugar did not mature in Michigan, but T3147 produced a smaller number of pods than Carioca and had a higher yield reduction under stress. Between cowpea genotypes, 475/89 produced a higher yield and greater number of seeds per pod than IT82D-889. Cowpea produced more seeds per pod than bean or Bambara groundnut and had the highest percentage of seed abortion under both stress and non-stress conditions. Species and genotypes differed in yield, seed weight, pod and seed number, and the efiect of moisture deficit on each yield component. STI was a better predictor than DSI of yield performance under moisture stress. Results of both the 12- and 20-cm depth screening boxes indicated that cowpea was more drought tolerant than Bambara groundnut and that Bambara groundnut was more drought tolerant than common bean. Unfortunately, field performance of Bambara groundnut could not be compared to the other two species. The non-nodulating soybean partitioned the least amount of N to the leaves, followed by common bean, with cowpea and Bambara groundnut partitioning the 96 most. This suggests that the non-nodulating soybean isoline remobilized more N from the leaves than common bean and that common bean remobilized more than cowpea and Bambara groundnut. Cowpea contained the highest leaf-, stem-, and reproductive-N values. There was variation for N concentration of leaves, stems, and reproductive structures among genotypes within each species. The relatively mild moisture stress in this study did not afi‘ect N concentration, although there was a tendency for moisture stress to increase N concentration in common bean. 97 TTTTTTTTT . LIBRRRIES \\\\\\\\\\\\\\\\ \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\“ill 78 9762