THESIS m W3 1293 00084 6018 This is to certify that the thesis entitled Effects of water stress imposed at mid-pod filling upon yield and dry matter partitioning in dry beans (Easeseigé zgigezie L-> presented by Catalina Samper has been accepted towards fulfillment of the requirements for __M..S_.__ degree in Wee EZZZ%?::2t:Egjg/i:;%;;;;2§;anzgf-. Major professor Date—mmflmlt 0-7839 MS U 1': an Waive Action/Equal Opportunity Induction MSU filijURNING MATERIALS: Place in book drop to ”33.4.9455 remove this checkout from —c—- your record. FINES will be charged if book is returned after the date stamped below. AUG 3 0 1991 Guava“! F5???" f5 . _ 1. Van J 5" 16'? j 290 #12:!) Q 5 ‘qu .". 1?} ‘ J _ - EFFECTS OF WATER STRESS IMPOSED AT MID-POD FILLING UPON YIELD AND DRY MATTER PARTITIONING IN DRY BEANS (Phaseolus vulgaris L.) BY CATALINA SAMPER 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 Science 198“ ABSTRACT EFFECTS OF WATER STRESS IMPOSED AT MID POD FILLING UPON YIELD AND DRY MATTER PARTITIONING IN DRY BEANS (Phaseolus vulgaris L.) By CATALINA SAMPER Two experiments were conducted to study the genetic potential for differential storage and remobilization of non-structural carbohydrates and its relation to yield performance of cultivars grown under conditions of drought imposed in the mid-pod filling stage, and low soil nitrogen. A close relationship between grain yield and the change in stem and leaf dry weights from anthesis to maturity implicates assimilate remobilization as an important contributor to seed yield under late season water stress. The daily assimilate partitioning to the fruit was found to be determined by genotype and influenced by water treatment. The top yielding cultivars were those which had a long 'vegetative phase and a high fruit growth rate accompanied by a seed filling period that did not differ in length between the water treatments. The geometric mean as opposed to other criteria for selecting drought tolerant cultivars proved to be very advantageous. It is suggested that an understanding of the type of water limitation and a quantification of the drought environment are necessary for designing an ideotype to be used in developing drought tolerant cultivars intended for a particular production system. To Dad, Mom and Ivan for their love, generosity and encouragement of my growth ACKNOWLEDGEMENTS I cannot find the words to express my gratitude to my major professor, Dr. M. Wayne Adams. During the course of my studies he has been not only a major professor, but a friend and a colleague. He was always at my side, sharing moments of joy and sadness, giving me encouragement and unconditional support. The challenging discussions that we had, his encouragement of my independent thinking and his deep honesty, will always be with me as an example to follow. I had the privilege to work with a great scientist and a true teacher , but best of all, with a great human being. I want to express my gratitude to: Dr. Andrew Hanson, a member of my committee, for his encouragement of my development as an independent thinker, his thorough and constructive criticism of my work, his generosity and kind support. His conceptualization of science and his fine example as a continuos learner and actively involved researcher are qualities that I greatly admired. ii Dr. Al Smucker, committee member, for reviewing this manuscript and for his help on the progress of my research project. Dr. Peter Graham, Dr. Rogelio Lepiz, Dr. Ronald Ferrera, Mr. Jorge Acosta and Mr. Abelardo Nunez, for their help and interest in this project. Special thanks to Greg, Nasrat, Sue, Joe, Rhea, Francisco, Earl and to all the graduate students, the professors and technicians of the "bean program", for their intellectual stimulation, the hard work and the good times that we shared #together. Last but not least, to my brothers Juan, Gordo and Bite, my sister Cuca, and my friends Kim, Touran and Regina for their love and unconditional support. iii LIST OF TABLES LIST OF FIGURES INTRODUCTION TABLE OF CONTENTS LITERATURE REVIEW . . . . Yield Con Allocation of Assimilates straints . . Biological Nitrogen Fixation Photosynthate Partitioning Drought Tolerance Mechanisms MATERIALS AND METHODS . . RESULTS . . I. Water A. B. C. D. Effects . . Biological Yield Economic Yield Harvest Index Seed Size . Seed Number . Length of Vegetative Reproductive Stages Leaf Dropping Plant Dry Weight at Physiological Maturity . . Plant Dry Weight Changes: Remobilization . Starch Analysis iv Page vi ix wa ll 19 2a 30 3o 32 3a 37 39 39 41 "9 49 S3 57 TABLE OF CONTENTS (Continued) Page K. 20 Upper and Lower Pods: Seed number and Size . . . . . . . 61 II. Nitrogen Effects . . . . . . . . . . 65 B. Plant Dry Weight . . . . . . . . 67 C. Plant Dry Weight Changes: Remobilization . . . . . . . . . 70 DISCUSSION . . . . . . . . . . . . . . . 76 1. CrOp Growth Rate . . . . . . . . . . 77 2. Partitioning . . . . . . . . . . . 81 3. The Filling Period . . . . .' . . . . 9O YIELD POTENTIAL AND DROUGHT SUSCEPTIBILITY . . . . 96 1. Drought Susceptibility Index . . . . . . 96 2. Relationship between Control and Stress Yields . . . . . . . . . . . 103 3. Geometric Mean of Stress and Control Yields as,a Selection Criterion for Drought Tolerance . . . . . . . . . . 10? SUMMARY AND CONCLUSIONS . . . . . . . . . . . 116 LITERATURE CITED . . . . . . . . . . . . . 119 APPENDIX A : Durango Experiment: Experimental Design and Yield Data . . . . . . . . . 126 APPENDIX B : Starch Analysis . . . . . . . . . 129 TABLE 1. TABLE 2. TABLE 3. TABLE 4. TABLE 5. TABLE 6. TABLE 7. TABLE 8. TABLE 9. TABLE 10. TABLE 11. TABLE 12. LIST OF TABLES Biological Yield (kg/ha) under two water treatflflflufll. Igualéh 1982-300 0 o 0 Economic Yield (kg/ha) under two water treatments. Iguala, 1982-3. . . . . . Harvest Index under two water treatments. Iguala, 1982-30 0 o o o o o o o 0 Weight of 100 seeds (grs) under two water treatments. Iguala, 1982-3. . . . . . Seed number (seeds/mtz) under two water treatments. Iguala, 1982-30 0 o o o 0 Days between flowering and physiological maturity under two water treatments. Iguala, 1982-30 0 o o o o o o o o o o 0 Leaf dropping under two water treatments. Iguala, 1982-30 0 o o o o o o o 0 Stem and Pod 1 of total dry weight at physiological maturity under two water treatments. Iguala, 1982-3. . . . . . Mean values of starch (mgrs/gr dry wt) at three different physiological stages under two water treatments. Iguala, 1982-3. . . Seed number of 20 upper and lower pods under two water treatments. Iguala, 1982-3. Seed weight (mgrs/seed) of 20 upper and lower pods under two water treatments. Iguala, 1982-3. 0 o o o o o o o o Shoot:Root ratio under two Nitrogen treatments at two physiological stages. Iguala, 1982-3. 0 o o o o o o o 0 vi 33 35 38 NO 42 “A 50 52 58 63 6A 73 TABLE TABLE TABLE TABLE TABLE TABLE TABLE TABLE TABLE TABLE TABLE TABLE TABLE 13. l“. 15. 16. l7. 18. 19. 20. 21. 22. 23. 2M. 25. LIST OF TABLES (Continued) Average Crop Growth Rates (kg/ha/day) form planting to flowering. Iguala, 1982-3. Average Crop Growth Rates (kg/ha/day) from flowering to maturity under two water treatments. Iguala, 1982-3. . . . . . Average Fruit Growth Rate from flowering to physiological maturity (kg/ha/day) under two water treatments. Iguala, 1982-3. Partitioning Factor under two water treatments. Iguala, 1982-3. . . . . Comparison between Grain yield, Fruit Growth Rate, Seed number and Effective seed filling period under two water treatments. Iguala, 1982-3. . . . . . Individual cultivar drought susceptibility indices. Iguala 1982-3 and Durango 1983. . Group drought susceptibility indices -S- Iguala 1982-3 and Durango 1983. . . . Group ranking by drought susceptibility index (8). Iguala 1982-3 and Durango 1983 Ranking by drought susceptibility index (S) of the eight cultivars planted in Iguala and Durango . . . . . . . . . . Yield differential, Arithmetic mean and Geometric mean for the Iguala experiment . Yield differential, Arithmetic mean and Geometric mean for the Durango experiment . Cultivar ranking for using four different the Iguala experiment selection criteria . the Durango experiment selection criteria . Cultivar ranking for using four different vii 79 80 83 85 9A 99 100 102 102 108 109 111 112 LIST OF TABLES (Continued) TABLE 26. Mean yields of the selected top 20% cultivars, using two different selection criteria. Iguala experiment. . . . . . . 11M TABLE 27. Mean yields of the selected top 20% cultivars, using two different selection criteria. Durango experiment. . . . . . 115 TABLE A. Economic Yield (kgs/ha) under two water treatments. Durango, 1983. . . . . . . 128 viii FIGURE 1. FIGURE 2. FIGURE 3. FIGURE u. FIGURE 5. FIGURE 6. FIGURE 7. FIGURE 8. FIGURE 9. FIGURE 10. FIGURE 11. LIST OF FIGURES Maximum and minimum daily temperatures. Iguala, 1982’30 o o o o o o o, o o Flowering dates and maximum daily temperatures. Iguala, 1982-3. . . . . Biological yield under irrigation and flowering dates. Iguala, 1982-3. . . . Economid yield under irrigation and flowering dates. Iguala, 1982-3. . . . Stem, R ot, Pod and Leaf dry weights (grs/mt ) over three physiological Stages. Iguala, 1982-30 0 o o o o 0 Changes in Stem-Starch contents (grs/mtz) over three physiological stages under two water treatments. Iguala, 1982-3. . Changes in Pod-Starch contents (grs/mtz) over three physiological stages under two water treatments. Iguala, 1982-3. . Stem S of total plant dry weight at flowering time. Iguala, 1982-3. ., . . Stem, Root, Pod and Leaf weights at flowering and at 15 dap. under two different levels of added Nitrogen. Iguala, 1982-3. . . . . . . . . Proportion of fruit growth that can be accounted for by post-anthesis photosynthesis under irrigated conditions. Iguala, 1982-3. . . . . Proportion of fruit growth that can be accounted for by post-anthesis photosynthesis under stress conditions. Iguala, 1982-3. . . . . . . . . ix 25 A5 A6 in SA ~59 60 69 71 87 88 FIGURE FIGURE FIGURE FIGURE FIGURE LIST OF FIGURES (Continued) Relationship between change in stem and leaf weight from anthesis to maturity and grain yield under irrigated conditions. Iguala, 1982-3. . . 91 Relationship between change in stem and leaf weight from anthesis to maturity and grain yield under stress conditions. Iguala, 1982-3. . . . 92 Relationship between control and Stress yields Iguala, 1982-30 0 o o o o 104 Relationship between control and stress yield. Durango, 1983. . . . . . 105 Calibration curve. Mgs. of starch vs. units of absorbance (F). . . . . . . . . .131 INTRODUCTION Varietal differences in the amount of starch present at flowering time,grain filling and physiological maturity in the dry bean (Phaseolus vulgaris L.) have been previously reported (4,30). The capacity of certain genotypes to store and remobilize starch to the grain may be an advantage when the plants are subjected to stress and their photosynthetic activity is reduced. The general objective of the project of which this thesis is part'of, was to study the relationship between photosynthate partitioning, remobilization, and the seed filling processes in several genotypes of P; vulgaris grown under different stress conditions. Initial objectives were: 1) to determine the effect of drought stress imposed during the latter part of the seed filling period on the yield performance of 22 different bean cultivars and to relate their performance under stress to their ability to accumulate and remobilize non-structural carbohydrates; 2) to compare the effect of nitrogen fertilizer versus biologically fixed nitrogen (BNF) under stress conditions, and subsequently to determine the relationship between total amount of non-structural carbohydrates and their remobilization with the plant's ability to buffer the adverse environmental conditions; 3)to identify bean genotypes having tolerance to drought and high BNF 2 potentials and to relate their performance under stress conditions with the patterns of accumulation and remobilization of starch and soluble sugars; u)to identify specific traits or physiological characteristics that could be associated with better cultivar performance under drought conditions, 5)to use the information and genetic materials obtained during the course of this research as sources of new improved germplasm in the development of varieties with resistance to drought and with the capacity to fix nitrogen under water stressed conditions. For these purposes an experiment was conducted in Iguala,Mexico, from December of 1982 to April of 1983. This experiment was intended to study and exploit the genetic potential for differential storage and remobilization of non-structural carbohydrates and the genetic capacity for higher levels of BNF, and to relate this to the yield performance of cultivars under conditions of drought and low soil nitrogen. A second experiment was conducted in the summer of 1983 in Durango, Mexico to provide further data on varietal performance under stress. LITERATURE REVIEW Yield constraints ‘ Over forty five percent of the world production of dry edible beans (Phaseolus vulgaris) is consumed in Latin America. Nevertheless, low yields of this crop are limiting the traditional role beans play as a staple food in the diets of poor and middle income consumers of this region. Although bean yields of over 11000 kg./ha. have been reported from experimental plots at the Centro Internacional de Agriculture TrOpica1(CIAT) in Colombia, the average bean yield in Latin America remains near 600,kg"/ha. (52). In the dryland production region of Mexico the long-term yields are reported to average less than 300 kg./ha. (1). A significant closing of the gap between current yields and potential yields must be achieved if this crop is to fulfill its role in meeting the nutritional needs of the population. In large areas of Latin America and Africa, where beans constitute a major source of dietary protein, production is limited mainly because beans are a crap of the small farmer and the conditions under which the crop is usually grown are typified by low soil fertility, and minimal technical inputs, such as irrigation, fungicides and insecticides . Approximately 20% of all potentially arable land in the world is in arid and semiarid zones, and about 16% of the world's population lives on these lands (111). Research and development in arid and semi-arid agriculture has, 4 therefore, global significance. Arid and semi-arid lands have been defined in a number of different ways. Their main characteristic is a low and variable seasonal rainfall, a condition which is often directly exacerbated by other variable elements of the climate, such as temperature, sunshine, wind and humidity conditions. Beans, among a few other crops, are dryland staples in many deveIOping countries, providing almajor source of affordable protein and carbohydrate» Bean breeding over the years has focused on improving agronomic adaptation along with disease resistance, with less direct emphasis upon yield itself. It is acknowledged by bean plant breeders that there have been no decisive breakthroughs in yield, excepting increases originating from disease resistance>or favorablelmaturity adjustments (2L.Increasing yield is imperative, but this objective must be integrated with the genetic improvement of adaptation and resistance to stresses brought about by diseases,insects and physical causes. The improvement of both agronomic characters and yield could maximize the responses of the bean plant to available resources characteristic of the site and local production system.‘This is especially important for the Latin American small farmers,because the conditions under which the crop is usually grown are typified by the lack of irrigation systems,little or no use of fungicides and insecticides, and small amounts of fertilizers. In Mexico, where 1.7 million hectares are planted annually with beans, 24 out of the 30 states that produce beans raise them under rainfed conditions. During 1970 to 1975 approximately 1.2 million hectares were planted annually with beans,and the average yield was around 5A5 kg./ha (35). This was enough for the internal demand, but from there on only during 1978 and 1980 was production considered to be at its normal level. As a consequence, during 1980 Mexico had to import more than 250,000 tons of beans to satisfy the internal demand. This production shortfall originated basicallqr because of adverse climatic effects such as drought and early frost. In Mexico, beans are planted twice a year, during the Spring-Summer and the Autumn-Winter cycles. During the Spring-Summer cycle when the majority of the total production is obtained, about 1.4 million ha. are planted and 530,000 tons are harvested. In this cycle typical low yields of 387 kg/ha are caused by adverse environmental factors such as drought -scarce or irregular rainfall-and early frost in the northern part of the country. During the Autumn-Winter cycle about 260,000 ha. are planted and 246,000 tons are harvested; this corresponds to 311 of the total national production and 16% of the total planted area. It is interesting to note that with only 16% of the total planted area almost one third of the total national production is obtained, with average yields being 933 kg./ha. In states such as Nayarit, Sinaloa and Baja California where irrigation is widely practiced, average yields are over 1100 kg./ha., while for the country as a whole 88% of the area that produces beans is rainfed only 6 and the average yields are about 350 kg./ha. Of this, 88% or approximately 1 million ha. are in the states of Aguascalientes, San Luis Potosi, Zacatecas and Chihuahua. These areas are frequently affected by either scarce or badly distributed rain throughout the growing season. In the state of Durango, nearly 30% of the planted beans are lost annually due to insufficient water,and in bad years such as 1979 the losses can reach up to 60% of the total planted area‘(1). In Colombia, in the states of Huila, Narifio and Antioquia where the average farm sizes are 29J5, 9.2 and A.” hectares, respectively, the percentage of farms that use irrigation is 2, 0, and 0 and the average yields are 680, 1467 and 533 kg./ha. (‘45). On the other hand, in the state of Valle del Cauca, where the average farm size isIHLO ha., “51 of the farms use irrigation and the average yield is 906 kg./ha. Among factors other than drought tolerance that could contribute to improved crOp yields , the availability of fixed nitrogen to crops is probably one of the greatest importance. In 1971! , 110 x 106 tons of fertilizer nitrogen with an approximate value of 8 billion dollars were used , as opposed to the 3.5 x 106 tons that were used annually twenty five years ago (28). The scarcity of nitrogen fertilizers and their increased selling price has produced a tremendous interest in the search for alternative technologies. Inoculation of legumes with Rhizobium at the farm level appears to offer promise as a possible substitute for nitrogen fertilizers. Recent reports from farm trials performed in Colombia by CIAT show that in the absence of any nitrogen amendments, inoculation of a local variety with a mixture of Rhizobium strains gave yields that were not significantly different from a: farmers' technology treatment, in which 20 kg./ha. of chemical nitrogen in the form of urea and 2 tons/ha. of chicken manure were applied. Substitution for nitrogen fertilizers by a Rhizobium inoculant would reduce total costs of production by 34%, while the net return per peso invested would rise from 545 to 7.7 pesos. A bean breeder who wants to develop a variety for the small farmers of Latin America should be aware that increased yields must be obtained with very limited cash inputs. Allocation‘g§_Assimilates In recent years breeders have been considering the development of plant ideotypes (1A). In dry beans an ideotype for production under monoculture has been proposed by Adams (2), who suggested that productivity increases in dry beans could be obtained if a more efficient allocation of assimilates into the economic sink is developed by breeding. Two of the principal physiological processes that can be considered for improvement of crop yields are photosynthate production and photosynthate partitioning to the economically important organs. However, the importance of transpiration as a central factor in explaining the 8 influence of water limitation on productivity, as pointed out by Fischer and Turner (20) cannot be overlooked. It depends on the inevitable association between water loss and C02 assimilation. Dry matter production over a given period of time is a function of the total transpiration for the given period and the water use efficiency. The importance of respiration rates in determining the net accumulation of dry matter is commonly overlooked. As Gifford gt; 3;; (22) pointed out, in leaves the fixed carbon is partitioned between its retention in the plant and its photorespiratory release. Over long periods, a full understanding of productivity requires consideration of how each increment of dry weight is allocated to both vegetative and reproductive sinks. The potential for increasing crop productivity by optimizing canOpy structure has been documented by experimental research, modeling, and computer simulation (51). Assimilate partitioning is a dynamic process and varies with the stage of plant development. In the vegetative stage of the dry bean plant, the distribution of assimilates is dominated by the proximity between the source and the sink. After flowering, when the developing pods become major sinks, there is a more complex pattern, although the relationship between leaves and pods in their own axils still predominates (3). Use of 1“C as a tracer, and changes in dry weight of specific organs have been important techniques in helping to 9 understand assimilate distribution. However, many important aspects of this process, like the mechanisms of regulation, accumulation and remobilization of storage assimilates under different conditions, still remain to be studied in order to provide guidelines for the increase of yields by manipulation of photosynthate partitioning. Large varietal differences in the ability to translocate 1“C- assimilates and a clear trend for varieties with the higher translocation rates to have higher photosynthetic rates, were reported by Adams and Reicosky (3). From data obtained on carbohydrate translocation patterns in beans, they suggested that the two facets upon which breeding studies might be focused were rate of translocation and direction of partition to sinks of the assimilate. They also suggested that these characters may be under genetic control and might be used in a plant breeding program. In recent years, attention has been given to carbohydrate production and partitioning in plants as factors related to crap yield; carbohydrate mobilization may be especially important under stress conditions (6). Varietal differences in carbohydrate accumulation or partitioning may be related to maintenance of a high rate of seed filling during periods of temporary environmental stress when photosynthesis is adversely affected. Evans (18) considers that whereas photosynthesis during the storage phase can be an important determinant of yield, IO ptiotosynthesis prior to that contributes to the deetermination of storage capacity and generates reserves tliat may be mobilized during the storage phase. Gifford gt a}; (22), reviewing the partition of {photoassimilates and crop productivity, examined the photosynthetic basis for increasing yield of major field crops in terms of improving the partitioning of photoassimilates to organs of economic interest. Although little is known about the regulation of carbohydrate partitioning between starch storage (for later utilization) and sucrose synthesis (for immediate export), they affirm that sink demand plays a very important role. The Partitioning of photosynthetically fixed carbon is important fkor plant growth not only because the formation of sucrose IDartially determines the carbon export from I>hotosynthesizing leaves, but also because leaf starch is Inobilized to sucrose when current photosynthesis is low relative to sink demand for assimilates. In their discussion, they suggest that photosynhtesis and the mechanism of phloem loading determines the amount of photosynthetic assimilate available fro translocation, while the mechanism and kinetics of unloading into competing sinks determines the partition of loaded materials. Carbohydrates reach a maximum concentration in the plant's vegetative parts around flowering time, after which they start to decrease. Yoshida (59) found that stored carbohydrate could be translocated into the rice grain, thus contributing to grain filling, or it could be consumed as a substrate for respiration. The carbohydrate loss from the vegetative parts during grain filling provides only a maximum estimate of the contribution of the stored carbohydrates to the grain. Evidence that stored carbohydrate can be translocated into the grain has been obtained for rice and wheat by labeling the stored carbohydrate with 1“C. Cock and Yoshida (11) showed that under normal field conditions 60% of the stored carbohydrate was translocated into the grain. When photosynthesis during the ripening period is restricted by shading or defoliation, the stored carbohydrate appears able to support the grain growth of rice and corn at almost the normal rate for some time. Perhaps the stored carbohydrate can serve as a buffer to support normal grain growth despite weather fluctuations (59). Whether the yield capacity or assimilate supply limits the grain yield is not clear. However, defoliation and shading experiments in rice at or after heading clearly demonstrate that impaired photosynthesis during the ripening period can severely limit the grain yield (A9). Assimilate supply may limit grain yield under stress conditions: if photosynthetic activity is limited by shading, or if translocation of assimilates into the grain decreases, a certain portion of the grains may remain unfilled (59). Biological Nitrogen Fixation Beans are a crop of small farmers in much of the third 12 world, and are often produced on marginal soils deficient in nitrogen. In a world of rising fertilizer prices, the need for cultivars with improved ability to fix nitrogen is especially important. The identification of genetic variability for biological nitrogen fixation (BNF) in beans has made selection for enhanced BNF possible (5). Graham (25) suggested that at least three factors could contribute to the variability in N-fixation observed in P.vulgaris : a) supply of carbohydrates to the nodules, b) relative rates of nitrogen uptake from soil, and c) time to flowering. Hardy and Havelka (29) indicated that the amount of photosynthate available to the nodules may be the most significant factor limiting N-fixation. They examined factors that affect photosynthate availability to the nodule such as light intensity, size of photosynthetic source, competitive sinks, 002 enrichment and photosynthate translocation. With respect to the effect of variation of each of these parameters on N-fixation in soybeans, N- fixation correlates directly with the amount of photosynthate available to the nodule. Nodules in general maintain low reserves of readily utilisable carbohydrates relative to their requirements for fixation, so they probably rely for their growth and functioning on photosynthetic products currently translocated from the leaves, or on carbohydrate reserves mobilized from'other regions of the plant (42). Experimental evidence is consistent with this view, since a very close relationship 13 has been observed between photosynthesis, amount of photosynthate , and N-fixation. Reducing light cn' defoliation decreases fixation, while supplemental light increases it (7,26,27,29,42,47,48,50) ; pod removal increases N-fixation (7,27,28) presumably by leaving more photosynthate available for the nodules. Lawn and Brun (33) indicated that the decline in soybean nodule activity was associated with the development of the pods as a competing assimilate sink. The fact that the decline in nodule activity coincided with the time when pod growth rate first exceeded total top growth rate is an indication of mobilization of previously assimilated material into the pods. Factors, both genotypic and environmental, which tend td lessen competitive effects by enhancing the photosynthetic source-sink ratio, may be expected to minimize a decline in N- fixation and should be considered in the future deveIOpment of higher yielding varieties with high BNF potential. In order to understand how varietal differences in N- fixation might relate to carbohydrate supply and availability in the bean nodule, Graham and Halliday (23) planted fourteen commercial varieties, inoculated and sampled at initiation of fixation and at the beginning of decline in fixation rates. Marked varietal differences were found, and a highly active N- fixing variety (P590) showed a higher soluble carbohydrate percentage in all organs and also partitioned more of its total carbohydrate to the nodule as compared to an inactive N-fixing line (P635). In this study, climbing varieties which had been previously reported to be good N-fixers (2A) were found to hold more of their carbohydrate in the soluble form. The ontogenetic development of four dry bean cultivars with reference to the relationships that may exist between symbiotic nitrogen fixation and the energy supply (in the form of carbohydrates ) to the nodules was studied by Martinez.(39L.His.data are consistent with the hypothesis that carbohydrate supply to the nodules limits fixation. He showed that an increase of total photosynthate available to the symbiotic system, achieved through C02 enrichment, resulted in higher rates of nitrogen fixation. The nitrogen in the bean plant is stored temporarily in the leaves, and it is suggested that mobilization of this nitrogen to the seeds results primarily from leaf aging. Martinez (39) showed a similar phenomenon of mobilization of carbohydrates temporarily stored in the stems and leaves. Wilson 23 1;;(57) performed experimentslto study the nonstructural carbohydrates, the nitrogen content of plant tissues and the nitrogenase activity throughout the deve10pment of male sterile and male fertile soybean plants. Male sterile plants set approximately 85% fewer pods than the male fertile plants, and reduced pod set was found to increase carbohydrate accumulation in the leaf and root systems. Although roots of male sterile plants contained 15 greater quantities of carbohydrate, a decline in nitrogenase activity occurred after flowering. The low percentage of soluble carbohydrates in roots of either type (male sterile and male fertile) during the pod filling stage might be one of the many possible explanations for the similar trends observed in male sterile and male fertile nodule activity. In efforts to increase N-fixation it is not necessary to restrict selection only to genetic factors that affect nodulation, increase nitrogenase activity or generate larger amounts of accumulated nitrogen. Certain genotypes may be superior to others in their allocation of assimilatory resources to the various plant parts (27,29,142) . The functional economy of whole plants and the interactions of their organs during growth should be considered in order to determine the plant factors that are responsible for the variation in nodulation and nitrogen fixation (58). Effective photosynthate partitioning The selection of cultivars with more effective partitioning of nitrogen and carbon assimilates to the reproductive organs than older cultivars was thought to be the key factor for the improvement of yield in other crops, namely rice (59), peanuts (16) and cotton (56). Genotypic variation in carbohydrate and nitrogen remobilization during periods of environmental stress, when l6 photosynthesis is adversely affected, may enable maintenance of a high rate of seed filling and may buffer and stabilize yields. Photosynthate partitioning has been shown to be under genetic control in cereals (15), soybeans (32) and sugar beets (A6). In beans, Adams 32; 2;; (A) showed genetic variation for accumulation of starch during reproductive deveIOpment. Izquierdo (31) also showed that differences in sugars and starch. ( total nonstructural carbohydrates ) and nitrogen were associated with cultivars and physiological stages over the entire reproductive growth period. Izquierdo (31) showed genetic variation of seed filling parameters (rate and duration) in this crop and the relationship of these parameters to patterns of assimilate partitioning among genotypes. He concluded that yield differences among cultivars are more associated with the length of the seed filling period than with the rate of seed growth. . Constable and Hearn (12) performed a series of experiments with sorghum and two soybean varieties (Ruse and Bragg) under two different water treatments. Sorghum and Ruse soybean showed a significant (17-25%) loss in stem dry weight during grain filling under both treatments. In Bragg soybeans, only the stressed plants had a loss in stem dry weight during grain filling. One can infer that in sorghum and in Ruse, the significant loss in stem dry weight during grain filling could have been a consequence of relocation of dry matter from the stem to the developing grain. This l7 agrees with Yoshida's conclusion (59) that the weight loss from vegetative parts during grain filling sets an upper limit to the possible contribution of stored carbohydrates to the grain. An apparently large difference between soybean cultivars in the effect of water treatment on the contribution of stem storage to yield was reported by Constable and Hearn (12); in cultivar Ruse an estimated 25% of grain dry weight could have come from the stem, while in Bragg only the stressed plants appeared to use stem reserves. This suggests that Bragg was sink limited and had little requirement for storage carbohydrates, except during stress. Rawson gt a}; (43) substantiate Constable and Hearn's conclusion that when water deficits restrict current photosynthesis during grain development, the plant may buffer yield by drawing heavily on reserves. Also , Egli and Leggett (17) have suggested that soybean seed growth rates are not closely related to rates of photoSynthate production because storage carbohydrate acts as a buffer between seed growth and photosynthesis. Evidence supporting the idea that plant growth rate and seed yield are not directly affected by total photosynthesis was reported recently by Ford 33 _a_l_. (21). They used soybean lines divergently selected for rates of 1“002 uptake per unit leaf area and tested the effect of this divergent selection for leaf total photosynthesis on crop growth rate and seed yield. Their data showed that selection for improved photosynthesis per unit area did not neccessarily enhance seed yield. 18 The effects of drought on nodulation and nitrogen fixation in field grown cowpeas were studied by Zablotowicz gt g}:_(60). The nodulation process was inhibited by drought , and maximum nodulation was observed at mid-pod fill in the drought regime while plants from the well watered regime showed maximum nodulation at early flowering. As the plants matured beyond mid-pod fill,there was no significant difference in nodule mass between water treatments. Droughted plants failed to form nodules of high nitrogenase activity during the early stages of deveIOpment, and at the reproductive stages the N-fixation capacity of the crop decreased, probably because there was insufficient carbohydrate to support high activity at this stage. Field canopies of two semi-dwarf wheat genotypes were subjected to water stress that caused visible wilting during the grain filling stage, and the distribution of photosynthesis within canopies and the patterns of translocation of labeled assimilates following 1”COB uptake were determined (32). In stressed plants 2A hours after labeling, 46% of the ”C was found in the grain compared to 35% in the control plants. Of the total 1"’C recovered from the shoots at maturity, 83% was found in the grain of stressed plants and 69% in control plants. The lower percentage of 1“C in grain of control plants at maturity was due to its accumulation in stem segments, primarily in the form of structural carbohydrates. Fischer and Turner (20) stated that water stress during seed filling has its 19 major effect upon current assimilation through reductions in assimilatory activity and assimilatory surface. They concluded that water stress not only increases the proportion of current assimilate translocated to the seed, but also may increase the contribution from assimilate stored prior to seed filling. In the broad bean , Vicia faba , N-fixation has been found to be severely suppressed once flagging of the lower leaves has commenced (A7). If flagging of the lower leaves takes place, photosynthesis is likely,to be arrested and since these leaves are likely to be the main providers of C to the nodules, it is possible that the first reduction of N-fixation during drought will be caused by reduction in assimilate supply (A2) . Drought tolerance mechanisms Plant responses to water stress can be classified broadly into escape, avoidance or tolerance mechanisms (36,5A). Escape can be achieved through more rapid development and through developmental plasticity, whereby the coincidence of critical developmental stages with periods of drought is avoided (3A). Water stress avoidance involves mechanisms either to reduce water loss or increase water uptake. Water stress tolerance implies the ability to survive large water deficits and may involve mechanisms such as osmotic adjustment. Lawn (3A) evaluated the response of four different LU grain legumes, soybean (Glycine max), black gram (Vigna mungo), green gram (Vigna radiata) and cowpea (ligna unguiculata) to water stress under field conditions. These four legume species responded to the stress in several ways, but the degree of expression varied substantially between species. Each cultivar exhibited some tendency to escape through faster development in response to stress; the effect was small in soybean and large in the 11532 cultivars, particulary in the flowering to maturity period. Each cultivar also exhibited to some degree two mechanisms which served to avoid dehydration by reducing plant water loss. The most important of these was stomatal control of water loss in response to declining leaf water potentials, for which there appeared to be substantial differences in response between cultivars. Finally , under stress , each cultivar showed some paraheliotropic leaf movement ; in these studies there was some suggestion that paraheliotropy helps to lower leaf temperatures under stress and presumably further restrict water loss. Developmental plasticity can be seen as a mechanism that facilitates the matching of crop growth and development to the constraints of the environment, especially in terms of'minimizing theloccurrence of the critical reproductive phase during drought periods. Faster development may allow the successful completion of the plantfls life cycle before the existing water supply is exhausted. Turk 3333;; (53) , growing cowpeas under water stress, observed that drought 21 resulted in earliness when present at moderate levels, but severe drought delayed reproductive activity. This provides the plant with two possible adaptive responSes. Under moderate drought the plant produces early pods which may mature before the soil water is depleted. If there is severe drought at early flowering, the plant remains in a vegetative stage but has the ability to continue reproductive activity if water is supplied. Determinate types flower, whether water levels are optimum or not, while indeterminate types remain in a vegetative stage under adverse conditions. Once rains start, the latter enter into the reproductive phase while the former can start a whole new cycle. It can be speculated that more determinate cultivars may have less capacity for recovery after mid- season drought. Leaf movements which orient the leaf parallel to the sunfls rays, leaf flagging, and rolling are common features of response in dry situations especially once leaf water potential begins to fall (20). It is unknown whether these leaf movements are beneficial to the plant. Shackel and Hall (AA) considered that leaf movements in cowpeas could substantially reduce heat load and water deficits in cowpeas by minimizing transpiration. On the other hand , Lawn (3A) states that paraheliotropic leaf movements act to reduce total light interception by the canOpy, implying a reduction in photosynthesis. Recently, Ludlow and Bjorkman (37) reported that the paraheliotropic movement of water stressed 22 Macroptilium atropurpureum cv. Siratro protected the primary photosynthetic reactions from damage by excess light (photoinhibition), heat, and the interactive effects of excess light and high leaf temperatures. They concluded that even though heat damage is more severe when it occurs, photoinhibition may be a more common phenomenon during drought, unless paraheliotropic leaf movements reduce the amount of solar radiation incident on water stressed Siratro leaves. The importance of root morphology for maintaining a supply of water to the plant should not be overlooked. Under drought conditions, an: extensive root system is a characteristic that enables the plant to exploit a higher proportion of the available soil water without incurring severe plant water deficits (8). Deeper root penetration of soybean was particularly evident in the drought periods (Lawn, 3A). He suggested that perhaps this root system is related to the tendency of soybeans to keep stomata open longer into the drought periods, thus maintaining a supply of photosynthate for continued root growth. No definite conclusions can be reached about the "best" strategy to overcome drought stress. However , one can conclude that there is no absolute character to "drought resistance". Rather, there are several alternative and perhaps inter-related mechanisms, and their relative success depends on the seasonal pattern of water availability, on soil type and depth, and on other factors. The most appropiate strategy forzaparticular environment presumably will be the one that simultaneously maximizes production and minimizes risk in that environment. Identifying the appropriate strategy requires assessment of the probability of particular seasonal patterns of water availability for that particular environment. One effective approach to breeding for higher yield under stress would be to identify physiological and morphological components causing varietal differences in economic yield in the presence and absence of stress, and to gain an understanding of their genetic control. Evidence indicates that genetic variability exists for all such components (55). If physiological genetic data are used in selecting parents, it should be possible to select directly for yield, using standard selection and breeding procedures. Knowledge of the physiological genetics of yield will improve the plant breeder's understanding of desirable plant types and habit, and appropiate selection and breeding methods can then be used. As world food demand increases, production of drought tolerant beans may become increasingly important to make optimal use of water-limited lands. MATERIALS AND METHODS An experiment was conducted at the Campo Agricola Experimental de Iguala-CAEIGUA-, Iguala, Mexico.‘The station is located in the state of Guerrero, at the meridian 99° A5' longitude West and the parallel 18° 30' latitude North. The altitude at the station is 739 meters above sea level. The average minimum temperature is 7°C and the average maximum is A2° C, with an annual average of 2A.5 . The average annual precipitation is 11551nillimeters, and the rainy season starts during the last part of June. Eighty percent of the total annual precipitation occurs between the months of May and October. The experiment was planted in the second week of December, and the final harvest was taken in the last week of March. Precipitation and temperatures were recorded during the course of the experiment, and are shown in Figure 1. The experimental plots were on a silty clay soil, with a high alkaline pH that varied between 8.25 and 8.75. The organic matter content as well as total nitrogen were low , the percentage of organic matter being 1.05 and the total nitrogen 0.112 ppm. The levels of potassium, calcium and magnesium were high, but the phosphorus content was relatively low (10.22 ppm). Before planting, A0 kg. of phosphorus per hectare were applied to all plots and A0 kgs. of nitrogen per ha. (in the form of Urea) were applied to half of the plots. At planting time all plots were 24 25 e lllllllllllll 0 lllllllllllll IIIIIIIIIIII a 3 "Illll llllllllllllllll llllllllll “-1 35 25 15 6 Temp. C 110 00 40 Dave Alter Plentlng Flgure 1. Mexlmum and Minimum Dally Temperatures. Iguala, 1982-3. a=flllllmetere e! reln 26 inoculated with a commercial granular Rhizobium inoculant, NITRAGINl.x.AA1 for dry beans, obtained from the Nitragin Company in Wisconsin ; 1.5 gms. of inoculant per meter of row were appplied. Twenty one dry bean genotypes were selected on the basis of their performance under drought as well as on their nitrogen fixation capabilities. They included: a) three good nitrogen fixing lines from the University of Wisconsin: 23-61, 21-58, and 21-5A. 6) five CIAT lines reported to have some tolerance to drought: BAT 332, BAT 85, BAT A7, A-162, and BAT 798. c) seven Mexican lines with some tolerance to drought: Pinto Nacional 1, Durango 222, Ojo de Cabra, Bayo Madero, C- 5, 1213-2, and LEF-2-RB. d) two Michigan State varieties with good architecture and high yielding potential: Neptune and 61065. e) two Michigan State lines that showed leaf flagging under severely dry conditions and were high yielders: 81017 and 800122. f) two Michigan State lines that showed leaf flagging under severe dry conditions and were poor yielders: 790131 and 800205. A Tepary bean, Phaseolus acutifolius was also planted. Each plot consisted of 6 rows A meters long; the distance between rows was 75 cms. and the distance between plants within a row was 10 cms. Two empty rows were always left between adjacent plots. in order to facilitate water 27 management. The experimental units were arranged in a split plot design with three replications. The combination of nitrogen source and‘water level was the whole plot factor and cultivars were the split plot factor. All plots were flood-irrigated every two weeks starting before the planting day, until flowering time. Individual plots of each‘cultivar were treated as separate units for water management. After flowering, only the so-called "plus" water plots continued to receive water. A commercial micronutrient foliar spray was applied A2 and 50 days after planting. Insects were controlled by spraying once a week with available commercial insecticides. Two center rows of each plot were used for periodic sample collection, two were used for final harvest, and the two outer rows were discarded. Flowering notes were recorded and when 50% flowering was reached, the first sample was taken. Ten of the twenty two planted cultivars were selected for detailed sampling. This selection was based on previous information regarding differences in N-fixation potential and drought tolerance. The 10 cultivars chosen for more . detailed study included 8 drought tolerant lines ( A from Mexico, 2 from CIAT and 2 from MSU ), one good N-fixing line from Wisconsin and one drought susceptible line from MSU. Each sample consisted of five plants that had uniform competition, they were dug up trying to get as much of the roots as possible. Each sample was separated into stems, roots and leaves; this material was placed in an oven at 80° C for one hour and then was left out in the sun for completion of drying. After dry weights were recorded, the tissue from each sample was ground in a Wiley mill and saved for starch and soluble sugars determinations. At the same time a 2-plant sample was taken (plants were kept entire); after drying they were ground and saved for total Kjeldahl nitrogen determinations. The second sample was taken 15 days after flowering, the time when the stress was expected to become effective. The third and last sample was taken at physiological maturity. The sampling procedures for the second and third samples were the same as for the first sample, except that in the last two samples pods were also separated. Additional observations and notes such as occurrence of leaf flagging, leaf drapping and leaf yellowness were recorded. A leaf drOpping scale from 1 to 5 was adapted, where 1 was no defoliation and 5 was complete defoliation. Scores for each plot were taken 85 days after flowering (before physiological maturity was reachedL.At harvest time both economic and biological yield were recorded and the HarvestIndex wascalculated. A random sample of 10 plants was taken at harvest time to observe if there were any differences for seed weight and seed number between the plant's upper and lower pods. For this purpose the two lowest pods as well as the two highest pods of each sampled plant were taken and their seed number and weight recorded. 29 Starch contents were determined with a colorimetric method with perchloric acid, described in Appendix B. RESULTS I. Water Effects The objective of this experiment was to determine the effect.of1drought stress imposed during the latter part of the seed filling period on the yield performance of 22 different cultivars and to relate their performance under stress with the ability to translocate non-structural carbohydrates. To accomplish this objective, the different genotypes were irrigated every two weeks from planting until anthesis. Working under the assumption that with high temperatures and high solar radiation the potential evaporation was high, we expected the irrigation water to be depleted at about two weeks after it was added. Based on these assumptions, withholding the water at anthesis presumably would cause an effective stress in the middle of the seed filling period, defined as 2 weeks after flowering. The control plots were continously irrigated every two weeks throughout the entire growing season.1Different cultivars were treated independently, meaning that each plot was considered as a separate unit for irrigation purposes. The first evident symptom of water deficit was premature defoliation; it started to occur two weeks after the plants were expected to be under stress. A two-week lapse between the time that we had intended to have the 30 JJ. stress and the first visible signs of stress might indicate that we did not actually impose the stress at the physiological stage that we had originally intended. However, we can not assure that the plants were not under stress before this time because measurements that would have indicated that, such as stomatal closure, osmotic adjustment and photosynthesis reduction, were not taken. Another indication of the presence of the water stress in the crop consisted in the reduction of the length of the seed filling period ( days from flowering to physiological maturity ), in the water stressed plots as compared to the irrigated plots. Perhaps a faster development allows the completion of the reproductive stage before soil water is completely exhausted. It is evident that we did have a water stress, but what we can not assure is the degree of the stress or its precise timing. The degree of correlation between control and stress yields has been considered to be an indication of the severity of the stress ( 9,10). A mild drought stress reduces yield, but the grain yield of the stressed plots is highly correlated with the yield potential in the absence of the stress. Severe stress provokes very different responses among genotypes with similar yield potential, and the correlation between grain yield under stress and yield potential is weaker. Since in this case the correlation of control yield vs. stress yield was found to be positive and highly significant ( calculated r: 0.895 ), we can infer that the 32 stress was moderate rather than severe. Since there were not significant effects of N- treatment, the water effects described herein are based on both the plus and minus N treatments. A. Biological Yield A significant cultivar effect as well as a significant water effect were indicated by the Analysis of Variance. Twelve of the twenty two cultivars had a significant reduction of Biological Yield under water stress, while only two cultivars, MSU 800122 and Mexico LEF-2-RB, showed a significant increase for this trait under stress (Table 1). The other eight cultivars didn't show any significant differences between treatments, but except for cultivars MSU 61065 and CIAT BAT 332 , Biological Yield was reduced under water‘stress. In the case of 800122 and LEF-2-RB we have no evidence that will allow a reasonable explanation. The size of the biological yield reduction in some cultivars was unexpectedly high, considering that the stress was not effective until late in the season. In fact, in cultivar Bayo Madero this reduction was more than 50%. Differences in magnitude for Biological Yield were observed; the high values of 81017,0jo de Cabra, and Bayo Madero contrast with the relatively 1x»: values of Durango 222 and Pinto Nacional. It is interesting to note that entry 33 Amowv mo. am am; u as Amway op. um own u * mewm mwmm armada mm a. Ammm mPQm shame me one am mmmm maem mmm omeaeaa om a: opmm pm—m F HanoHomz coca; @— ae mpom msmm was HLacm .mamwmp .mamst .nocoSumoeo Loom: oz» Lone: Am:\mxv oaofiz cwsocoom .m canoe 36 and economic yield for .both cultivars was non-significant under the plus water treatment, while under water stress for both 790131 and Durango 222 there was a significant negative correlation, with values of 0.850 and 0.975 respectively. Even though these are low yielding genotypes, their economic yield was not significantly reduced under stress. This is consistent with the hypothesis that remobilization is enhanced under stress conditions. . Bayo Madero and 800122 incurred significant reductions in economic yield under stress as well as a significant increase in stem dry weight , suggesting either a poor remobilization and a low capacity to huffer adverse environmental effects, or a weak sink that does not have the ability to utilize the stored assimilatesu 800122, a late maturity cultivah, did not flower until late in the season; for this reason , as shown in Figure 2, during the reproductive stage it was subjected to high temperatures. I believe that the high temperatures during this stage of deveIOpment kept this particular variety from remobilizing and senescing normally, and as a consequence yield was significantly affected. ~ .The three Wisconsin cultivars 23-61, 21-58 and 21-5A, as well as Neptune, A-162 , BAT 85 and Ojo de Cabra, had a significant reduction in biological yield under stress, however, their economic yield was not significantly reduced. This is supportive of the hypothesis that in those genotypes that have the ability to remobilize assimilates from stems ,storage photosynthates act as a buffer between 37 seed growth and photosynthesis. However, we can not determine if the contribution to seed yield is coming mainly from assimilates that were produced before the plants were subjected to the water stress,N.O was H=.o m=.o mno m— F=.o o=.o mum—mp pp ea um.o 3:.9 mmlmummq o— mm.o om.o Fmpomu m mz.o No.0 momoow m as 0:.o om.c wpopm w as mm.o mm.o mm_oom c ea w:.o w:.o moopo m .. oa.o mm.o oeeoooz : as p:.o .m.o amupm cow: m oz.o _=.c amt—m new: m a. m=.o mm.o poumm on“: P amoepm noummficea newumofiufiucooH .oz xeucm .mnmmmp .mamsmH .macoEBmoeo Loom: oz» coon: xoocH uno>cmz .m canoe 39 D.Seed Size The AOV for this trait, measured as weight of 100 seeds, reveals a significant effect for cultivars and water treatment. All entries incurred a reduction in single seed weight of about one centigram due to stress (Table A). However, only three out of the twenty two entries had a statistically significant reduction in the weight of 100 seeds under the water stress treatment. These three entries were all Mexican lines (Bayo Madero, Pinto Nacional and Durango 222). Variations in economic yield due to water stress in the cultivars Bayo Madero and Pinto Nacional were due to reduction of seed size as well as seed number. Smaller seeds under a low water regime are the consequence of incomplete filling, indicating lower photosynthesis and/or an inadequate reallocation of carbohydrates during the seed filling process. E. Seed Number The AOV for the number of seeds per square meter indicated a significant cultivar effect as well as a significant cultivar - water interaction, but the water effect itself was not statistically significant. Since the water stress did not become effective until the late part of the growing season, when the number of seeds had already Amw.pv mo.o um omq u a: Amm._o op.o so one u . 40 m=._. em... sesame mm m=.mm mm.mm menmo on Ono Pm .. so.m= mm.om mmm omeaeao em as o_.mm mo.mm _ amcofiomz cacao ma op.mp mm.om was h.cm mm emm mp Pm.mm mo.:m muu m. —>.:m om.mm mumpmp F— mo.:m op.mm mmumummq op po.mm _—.mm .mpom> m o~.mp no.0. momoom w wo.m_ oo.om upopw 5 wo.mp om.cp mm_oom o p~.hp wm.w— moo—o m mm.m_ . m:.o. oeeoooz a op.a— mo.om amupm on“: m wo.om mm.om emu—N on“: m 93.». mm.mp Pcumm on“: F mmoeum ooummficeH cowumo«ufipcooH .oz zcucm .mammmp .mamamH .mucoESmmeo Loom: oz» Loc=:.AmLmvomooom oo— mo games: .: magma 41 been determined, no water treatment effect is to be expected for this trait. Only two of the twenty two entries had a significant reduction in the number of seeds under the water 'stress treatment, while three had a significantly larger number of seeds under stress (Table 5) . The three cultivars that had a significant increment in the number of seeds (Neptune, 61065 and BAT 332) had a reduction of seed weight under stress. This might be an indication of component compensation, in which the reduction of seed weight is caused by the increment in seed number. Although the reductions in seed number for Bayo Madero and Pinto Nacional were not statistically significant, they can be considered large enough to explain the economic yield loss observed under water stress. F. Length of Vegetative and Reproductive Stages The AOV for the length of the seed filling period, measured as the number of days between 50% Flowering and Physiological Maturity, showed a significant cultivar effect as well as a significant water effect. All cultivars, without exceptions, incurred a reduction in the length of the seed filling period under the water stress treatment (Table 6). However, these reductions turned out to be significant only for 15 of the 22 entries. Variability in seed filling duration between cultivars and between treatments within cultivars is shown in the A_m_o mo.o so ems u a. Apopo o..o om emu u . mom. New. shadow mm op. amp meomo on one Pm opm .mm «mm omcmhsa om mom :mm _ Hmcowomz cocoa a. mem 9mm om» h.mo op.o am am; u a o Amm.mo mo.o om omo u as Aoo.9o op.o om nmo u a m ~o.ms me.oe ao.mP m..o_ mmm omeoeoo No.95 om.c> N—.o— mp.mp mo H mm.mo mm.op op.op mmm e~ mo.o> mo.m— o:.=p mum—mp sa mo.=> mm.oo .m.m— mp.op mmumummo as mo.o> cm.oo oz.hp >m.~— —mpom> as Po.Fm mm.om as mm.mm o=.>m mmpooo oo.p> om.Pp =m.u_ mm.>— moopo no.9» mo.ow mm.m_ >N.~F poumm on“: museum teammacsH mmoeom ooommfieLH :oHomoHoHocooH DR 60m NR Bvum .mamom— .mamzmH .nocosomoeo Leon: 03» Leon: zoaczomz Haoamoaoaosea so Basso: are Hoooo oo a ooa sea zoom .m oaoae 53 a sink demand insufficiently strong to require remobilization. The high yielding cultivar LEF-2-RB had a different behavior; under no stress the stem weight corresponded to 18.1 1 of the total dry weight, while under stress it was only 15.3 1. The changes in dry weight induced by the stress, though not large by these figures, may be enough to sustain the seed filling process temporarily and as a consequence economic yield under stress was not significantly reduced. Pod 1 of total plant dry weight showed a significant reduction under‘minus water in the low yielding cultivars 800122 and Bayo Madero, indicating that reduction in economic yield in these two cultivars probably was due not only to the decrease in single seed weight but alsolto the reduction of seed number. I. Plant Dry Weight Changes: Remobilization Figure 5 shows the changes in stem, root, leaf and pod dry weights over the three different sampling times (Flowering, 15 days after Flowering and P.Maturity) for six different cultivars. From Flowering to 15 ddhf. stem weight increased in all cultivars, however, the size of this increment varied among cultivars. One can see fairly large increments in cultivars such as 61065 and BAT 85, while 790131,1213-2 and Bayo Madero showed only a relatively small 54 .mnuamw 6.3.0.623; 3030-0333 00:: .36 Aussies: 3:30? a; see.— oce con— .sooc .Eosm .o 0.53“. .>U «mu 000 no bin 0.23: .m N6 pm — pn pcmh .ooa s\\\\\\m \ i... m Toma .m 1 Own sxmmmmm low low .ooc 52m loo— saezm » I 3.53: 323.21.... .. 0 5.68.2! - D 9:332“. n B 55 increase. The changes from 15 d.a.f. to P.Maturity differed in the sampled cultivars. BAT 85, 61065 and 790131 had a reduction in stem dry weight, while Durango 222, 1213-2 and Bayo Madero had an increase. When comparing the stem dry weight reduction in the water stress versus the non-stress plots, one can observe a general tendency towards a greater reduction in dry weights under the stress treatment. Durango 222 and 1213-2 incurred a reduction of dry weight under the stress treatment, while no reduction occurred under the plus water conditions. Bayo Madero showed an increase in stem 'dry weight at P.Maturity with respect to 15 d.a.f., however, the increment was slightly smaller under stress. BAT 85, as noted before, incurred a reduction in stem dry weight from 15 d.a.f. to P.Maturity, the reduction being greater under stress. 790131 had a small reduction from 15 d.a.f. to P.Maturity but no differences were seen between the stress and the non-stress treatments. The high yielding lines BAT 85 and 61065 had the largest stem weights at 15 d.a.f. Their respective losses from 15 d.a.f. to P.Maturity might indicate that remobilization of stored assimilates had taken place. The low yielding line Bayo Madero, although it had high values for stem weight at 15 dJLfs, apparently did not remobilize its stored carbohydrates to the seeds. In the case of Durango 222 remobilization occurred only under stress. The lack of remobilization under non-stress conditions was probably due to the lack of need to utilize 56 the stored carbohydrates because assimilate demand by the seeds was being satisfied by currently produced photosynthates. Only when photosynthesis is adversely affected would the seed filling process depend upon the stored assimilates and their reallocation . A significant correlation of 0.39A between root weight at flowering time and economic yield points out the importance of the root system in relation to yield. However, one must be careful when interpreting these results, because a low correlation even though statistically significant, still leaves a great deal of yield variance unaccounted for that has to be explained by other factors. The top yielding cultivars BAT 85 and 61065 had the highest values for root dry weight at flowering, while the bottom yielding line Durango 222 had the smallest value. No significant correlations were found between economic yield and root weight at either 15 d.a.f. or P.Maturity. Large values of leaf weight at flowering and at 15 d.a.f. represent a large photosynthetic area and therefore a substantial carbohydrate manufacturing site. The data show that the highest values for leaf weight at these physiological stages were produced by the top yielding lines BAT 85 and 61065. Changes in leaf weight from 15 d.a.f. to P.Maturity show that under stress the reduction of leaf weight is greater as compared to the non-stress values. However, as pointed out before when describing the leaf dropping results, economic yield and defoliation did not show a significant correlation. 57 In general one can observe that the pod dry weight data presented in Fig. 5, as expected, are in broad agreement with the economic yield data given in Table 2. Small discrepancies such as the higher pod weight in BAT 85 which was outyielded by cultivar 61065 (Table 2) might indicate a greater dry weight of the pod walls in BAT 85 which are not included in the economic yield data. Nevertheless, these discrepancies are small and not statistically significant. J. Starch Analysis Significant cultivar differences for the amount of starch present at flowering, 15 dJLf. and physiological maturity in the stems, roots and pods were detected by the AOV. Table 9 shows the starch percentage ( mgrs of starch per gr of dry weight ) for the different plant components at three physiological stages.The estimated values are very low as compared to starch determinations previously reported for dry beans (30,A0). These low values might be the result of the lack of sensitivity of the method used, starch being determined by the colorimetric method already described, or from high respiration rates caused by high temperatures that prevailed during the growing season. Figures 6 and 7 illustrate the changes in starch content in the stems and pods over the 3 sampling times. One can see that the starch content is always lower under the stress treatment as compared to the irrigated plots. The AOV hoaezosa Hooomoaooehsq u xx measaaa cooled: use: Mcqe030au «m s 523 n.~— —.N— m.¢ . ¢ h.mm v.—v 2m m.¢ b.> —.®m mm: m.— o.m_ m «mm cocoesn N.—— o.~— 9.0 o.— m.v n.> rm b.m o.~ m.mv mm: P.N n.0v m mm 9 m.N— rm III III III mm: , m.N b.mn m Nnn a.m n.¢ m.¢~. mm: s.. m.on m Nun.~_ o.v— —.¢— V.— *.N >.n— m.m 1m III III III km: ..N O.mn m mxINImmA m.—— «.m— m.— b.— ¢.> m.ow :m n.—— n.N m.hm mm: b.— m.Nn m .m—omb o... m.—. v.0 N._ ¢.m *.m In III III III mm: m.— b.m. @ NN-Oom «.m— N.np m.o ,v.o ¢.v 0.5 mm v.m n.N o.mm mm: —.N #.—N m moo—o ¢.—— m.Np —.— 6.0 —.> o.m :m Ill III III hm: P.— m.ON m vnI—N camcooqu museum ooaemussn mmouam ooaewsuau museum oouomauua doom osoom oaosm sosasm eoasaoasaseoes .nlwmm. saesmm .oacosueouu Lead: or» soon: commas fiscaononhzm aeououmso seen» as A .u: hue um \ some v seesaw no moaus> coo: .m canoe 59 — 1"190106 -- - 31f... s :1 yrs/mt: _ - 1 ‘ - \ ~e "I-u-I: \ \ l~ — _ — * 1 2 s 1 2 s 1 2 a 1 2 s 1 2 :1 11121-54 noes 200122 790131 LEF-RB ” ~ \ /\ s - \ s‘ ‘ — _ 1 2 a 1 2 s 1 2 3 1 2 a 1 2 a 121:1-2 a-wsduo an 332 an as one 222 1' Flowering 2' HIG-Pod-Flll 3- Physiological Maturity Figure 6. Changes In Stern - Starch Contents ( firs/mt: ) Over Three PhYSiO'Ogica Stages Under Two Water Treatments. Iguala. 1982 - 3. grs/mt2 OTC/1111 60 u — trrlgeted v - - 1 Stress V ’ . I ’ I ’ V / 2 3 1 2 2 1 2 3 1 2 2 1 2 2 '21-54 .1005 200122 720121 LIP-II O . ' ’I ’ I ’ I’ ~ ’ I ’ _ 2 3 1 2 3 1 2 3 1 2 2 1 2 3 I-Iedero IA? 222 BAT 25 000 222 1213—2 "Planning 2" Itd-Ped-Fm J- Phyeloleglcel Ieturlty Flgure 7. Changes In Pod - Starch Contents ( grs/n‘lt2 ) Over Three Physiological Stages Under Two Water Treatments. Iguala, 1982 - 3. revealed significant cultivar and treatment differences for the amount of starch present in the stems at physiological maturity. Figure 6 illustrates the seasonal variation in starch content in the stems. Bayo Madero was the only cultivar that had an increment in the amount of starch in the stem from m.p.f. to PM, and this increment was smaller under the water stress treatment. A greater utilization of assimilates stored in the stems under water stress may constitute a strategy by which the plants cape with adverse‘ environmental effects. A negative and significant correlation between the starch present in the stems at P.M. and seed yield supports this hypothesis. The calculated correlation was -0.5 under water stress, while under irrigation the corresponding value was -0.3. This might indicate that the seed filling process, when photosynthesis is adversely reduced, utilizes the stored carbohydrates, and that the greater the capacity to remobilize them, the higher the seed yield would be. Under irrigation, when photosynthesis is not drastically reduced, there is a continuos supply of assimilates so the plant does not have to drawupon the reserves so heavily. K. Twenty Upper and Lower Pods: Seed Number and Size Significant differences were found among cultivars for seed number in both the upper and lower pods, but no significant water effect was indicated by the AOV. When the number of seeds of the upper pods versus the lower pods was compared, no significant differences.were observed (Table 10). However, for seed weight the AOV revealed a significant cultivar effect as well as a significant water by cultivar interaction. Seed weight in the upper and lower pods was reduced under the minus water treatment (Tables A and 11) , seeds from the upper pods being smaller than those from the lower pods. Since the lower pods are the first ones to be formed during the plant's developmental processes , they were at a more advanced seed filling stage when the stress became effective. This probably implies that either they did not have to rely upon the stored carbohydrates to fill their seeds because they were being filled with currently made photosynthates, or due to closer proximity they were the first ones to use the stored carbohydrates; they had essentially completed filling before the stress became severe. Aopv mo.o om omq Aopv op.o am on; ll 11: .0 Aomv mo.o am am; Ahpv o—.o am am; u a m 63 mm mm m: cm mmm omeaeoe oop m—P so. oop mo H.>Nv o—.o am am; u s m m.mo= m.pm: aam.~N= =.mpm mmm omcmesa aa~.pm— m.ppm o.mom m.mpm om H._>F Nmm hm ~.mo: sap.pmm o.o:= oeocmz oamm _.:mm o.h=m N.Psm o.oom Numpmp m.m:m m.m:m 9.3mm m._mm mmrmummo m.upm —.m_m —.—mm p.omm pmpomp —.mmp m.mop m.mm— m.mo. mmpoom o.mo— N.:>P w.omp m.omp moopo m.mm_ m.ma_ m.mmp >.o—m ponmm ohm: mmoeom coommHLLH anoeom ooomchLH acoomoamaocooH omuoo some: om onooa eozoa om .mnmmmp .mamsz .mocoSomoco Loom: oz» have: moon Lozoa one soon: cm 90 Accom\nemso ozmamz comm .PF magma II.Nitrogen Effects A secondary objective of this experiment was to determine the nitrogen fixation potential of the 22 cultivars, and to relate their potential with the effect of drought stress imposed during the latter part of the seed filling period and with the ability to translocate non- structural carbohydrates. To accomplish this objective, the twenty two cultivars were planted under two contrasting nitrogen levels and under two water regimes. As described in the Materials and Methods section, the«experimental plots were on a Silty Clay soil in which the organic matter and total N contents were low (10f organic matter = 1.05, total N = 0.112 ppm). Before planting the so called plus N plots were fertilized with A0 kgs of N. per hectare, applied in the form of urea, while the minus N plots did not receive any N fertilizer. At the time of planting all plots, except 2 border rows that ran the length the field, were inoculated with a commercial granular Rhizobium inoculant. We expected to see differences due to the N treatment, but we could not observe any visual symptoms of N deficiency in the non- fertilized plots; also, the observed nodulation throughout the season was considered fairly poor for plants grown under the two different N treatments.‘The only clear N deficiency symptoms, such as severe yellowness and reduced growth, were observed in the two border rows that had neither fertilizer nor inoculant. We have no definite 65 explanations for the lack of difference between the plus and minus N treatments. Whether the soil analysis was faulty and the actual content of N in the soil was higher than shown by the analysis is unknown. We can't answer this question now because after harvesting this experiment the soil was plowed and uniformly fertilized for the next crap to be planted. Another possible explanation, though it may be remote, might be found in the levels of N03 present in the irrigation water. If such levels were high enough to provide the plants with sufficient N for their vegetative growth, it is possible that no N treatment differences did in fact exist. The fact that only two border rows, which were at the end of the field and therefore did not receive as much water as the other plants did, supports this assumption. The quality of the applied inoculant turned out to be poor, having only 5.8 x 10“ rhizobia per gram. A good quality inoculum should have at least 108 rhizobia per gram. Nevertheless, this does not imply that there were not enough bacteria in the soil sufficient to have established a symbiotic relationship with the host plantso Countings of the native Rhizobia population existing in the soil before inoculation ranged from 1.8 x 103 to 1.7 x 107 colonies per gram of soil. Since the water stress was not effective until the late pod filling stage and the data herein described refers to earlier physiological stages, the results are based on only one water treatment. 67 AsNon-significant effects The individual AOVs for Biological Yield, Economic Yield, Harvest Index, Weight of 100 seeds, Length of seed filling period, Leaf dropping, Seed number and weight from the 20 upper and lower pods and S of Nitrogen did not show a significant Nitrogen effect. However, some Nitrogen x Cultivar interactions as well as Nitrogen x Water and Nitrogen x Water x Cultivars interactions were significant. These interactions will be referred to in the next section. The effect of added Nitrogen on N-fixation depends on the specific cultivar; different cultivars show different responses to N fertilizer. In the section, Interaction Effects, the differential response of the genotypes used in this study will be discussed and I will attempt to reach some conclusions from this experiment. B. Plant dry weight The AOV for total plant dry weight at the three sampling times (Flowering, 15 dJLf., and Physiological Maturity) did not detect any significant differences due to N effect. However, with respect to the individual components of plant dry weight over the three different samples, a significant Nitrogen effect was given for stem 1 of total 68 plant dry weight at flowering time. Figure 8 illustrates the differential responses of the 10 sampled cultivars over the two different levels of Nitrogen. In genotypes such as BAT 332, 61065, and 800122, the stem constituted over A2 1 of their total plant dry weight, while in Durango 222 the corresponding value was less than 30 1. Even though the correlation between stem 1 of dry weight at flowering and Economic yield was expressed as a significant r value of 0.A08, the data show that in high yielding lines such as BAT 85 the stem 1 of total dry weight was approximately the same as in the low yielding lines Bayo Madero and 790131. Different cultivars showed different responses to N fertilizer. A line previously selected for high BNF potential, Wisconsin 23-61, showed an increase in stem weight when N was not added; BAT 332, also previously reported by CIAT to be a good N-fixer, showed an Opposite-f response. No conclusions can be drawn from these results except that if stem 1 of total dry weight is positively correlated with yield, good N-fixers should have high stem weights at flowering time. The carbohydrates that are stored in the stems can be remobilized and utilized in the later stages of plant deveIOpment when photosynthetic activity is reduced, particulary in the lower (shaded) portion of the canopy where carbohydrates might be needed for supporting N- fixation. In the case of N-fixation, a great amount of photosynthate is required by the nodules in order to 69 «an 093.50 no h0 .2 use... 2:9. as u n . Boos: «an ._.. — _ .mNmm— £25.. .comoEz nouns .o 225. 392.3 oz: cone: int n p on can 55332.... on 9:925 30.. ocn tom .30.... .505 m .9“. mm h— mmm m: Nrmpma m.Pm mom, so mmnmlmmo >.om mom. mo .mpoms p.mm momp ob mm—oom _.om ommp 2o moopo w.mp was, . 2o Po1mm on“: .zoam oo wcfiocman Amn\mxo socm some zozocm .3oam on Lozoam ommao>< coooms zen amooh on name eoaoooaeaoeoeH .mamzmH .mcfieozoam oo mcoocndo scam Ammoxm:\mx omega; sozocm coco ommco>< .m— manna 80 m.mm o.mm oomm Nzom mmm cosmos: o.mm o.~o Noam moo: mo H ommm com: omlmumoo >.o> :.om poem Pmo: pmpomb m.pm ~.oo comm mom: mmpooo _.oo m.=> mpo: oomm moopo >.oo m.oo omom zoo: Foumm ohm: nnocom coomoacaa mnocom topmooceH :2 oo .Ha eoee noose Aoe\mxo so so sozoem mono oomco>< Looome sec Hooch :ofiomowooocooH .mumoo. .oaeomH .mocosoaoco soon: 03» Love: moacsoms co ocaaozoao so: A rookie. o moon; nozoco no.5 oomeo>< .3 magma. 81 RB, 800122 and 61065 had higher growth rates under the minus water treatment as compared to the irrigated plots. The other 6 cultivars had lower crap growth rates under stress. It becomes evident from these data that not only do cultivar differences for crOp growth rate exist but also that different cultivars react differently under water stress. Net photosynthesis is the result of a biological input- output system that has several constraints. Identifying and quantifying the relevant constraints would help the plant breeder achieve a maximization of photosynthetic production. Physiological and morphological components which determine the crops efficiency of light conversion in a particular environment, such as rapid establishment of a closed leaf canopy, (efficient canopy photosynthesis and effective distribution of assimilates to the relevant economic sinks for as long a period as possible, and the genetic variation associated with them, should be the focus of detailed study. 2. Partitioning The most important determinant of economic yield, as Donald and Hamblin (15) stated, is not total crop photosynthesis, but the way in which assimilates are distributed within the plant, either for continued vegetative growth or for accumulation in storage organs, seeds or fruits. However, it is not clear how this allocation is regulated. It can be regulated by the supply of assimilates (source strength), by the ability of the sink to make use of the assimilates (sink strength) or by the rate of translocation. How far sink strength can influence photosynthetic rate is still an unanwered questions The term partitioning, as used here, indicates the allocation of assimilates between reproductive and vegetative plant parts. It is a dynamic day-to-day process, that differs with cultivars and with physiological stages such as early or late pod filling. The partitioninig of assimilates between new vegetative tissue and storage can be very important for plant performance under environmental stresses such as temperature or water stress. Table 15 illustrates the fruit growth rates of the 10 sampled cultivars under irrigated and stress conditions. Differences not only among cultivars but also among treatments were obtained. This indicates that the daily partitioning of assimilates to the fruits was determined by the genotype and the water treatment. When comparing the data shown in Table 1n (Crop gowth rates - can-) with the corresponding values in Table 15, one can see that Fruit growth rates -FGR- exceeded CGR in 7 cultivars under water stress, while under irrigation FGR exceeded CGR in 5 cultivars. One of the basic questions to be answered is whether or not the water stress treatment induces a greater partitioning of stored assimilates to the fruit. The 83 o.oo o.~m mmm omenese =.mo_ c.mmp mo e> oolmnmmo o.oo o.oo pmpcmu =.oo m.:o mm_ooo m.pop o.oo moopo o.oo. o.oo ponmm omfiz mnocom ooomomeeH scoonoHoaocooH .m1momp .mamsoa .mocosomoeo coon: oz» Loos: Ammo\m:\noxo aoaanums HmoHooHonmsn oo ocacozoflm echo mom; zozocm ounce omnco>< .mp manna division of FGR by CGR during a given period of time gives the average fraction of net photosynthate partitioned to fruit growth. If all fruit growth can be explained by current photosynthesis, net accumulation of dry matter should be greater than or equal to fruit growth; if not, one can assume that fruit growth was sustained in part with photosynthates that were fixed in an earlier developmental stage. A calculated partitioning factor, shown in Table 16, indicates that in 7 out of the 10 sampled cultivars under stress, the calculated partitioning ratio exceeded 1001, and under irrigation in 5 entries the ratio exceeded 1001. Whether this can be extrapolated to the extent that we can be sure that water stress induces a greater partition of assimilates to the fruit is not clear, but it is clear that treatment and cultivar differences in partitioning exist. A greater partition of assimilates can be the result of a greater fruit load, or what was called before, namely "sink strength". We have no conclusive evidence to say that this in fact is the case, but the data show a very consistent trend in which the cultivars with a high partitioning factor such as BAT 332 and BAT 85 had between 1A9 and 231 grs of seed/mtz, while in cultivars with a low partitioning factor such as Durango 222 and Bayo Madero sink size varied from 80 to 111 grs of seed/mtz. Considering the change in plant dry matter between anthesis and maturity as an indicator of net plant photosynthesis during this period, and comparing this 85 cop xaooma sozoeo occo\oomc nozoco owscmouu Pa =.oe m.em mmm omeoeso P.cpm ~._o_ mo H mnmpm. o.m—_ o.-o_ om1m1mmo o.opp N.mo .mpomu o.oo o.opp mm—ooo o.om— m.mmF moopo w.mmp =.—m Poamm on“: mnocom ooommwcem :oHomOooHocooH _ a oeoeasoanu .mumomP .naosmH .noeoseooeo moon: oz... Loos: Looomm mcwcoHoHocmm .o. manna increment with the corresponding increment in fruit weight, seems to be a reasonable way of illustrating the proportion of pre-anthesis and post-anthesis assimilates that were utilized for fruit growth under the 2 water treatments. In Figures 10 and‘k1,,plus water and minus water treatments respectively, the X-axis is the net post-anthesis photosynthesis expressed in kgs/ha and the Y-axis is the fruit growth from anthesis to maturity also expressed in kgs/ha. The 1:1 line shows the position where a cultivar would lie if all the assimilate produced after anthesis had gone into the grain. A cultivar that lies further from and below the line is fixing more carbon and it is using it for fruit growth at a slower rate than it is produced. On the other hand in a cultivar that is positioned above the 1:1 line fruit growth exceeds total growth for that period, implying that the pods had to be receiving assimilates produced and stored in an earlier stage of development, which in this case would be pre-anthesis assimilates. If the water stress treatment induces a greater partition of pre- anthesis assimilates to grain growth in some genotypes, their position with respect to the 1:1 line should differ under the plus water and minus water treatments. In fact, when comparing Figures 10 and 11, one can see that cultivars 1 (Wise 23-61), A (790131) and 6 (1213-2) were below the line under the plus water treatment but under the minus water treatment they are positioned above the line. On the other hand, cultivar 7 (Bayo Madero) is below the line under the 2 water treatments, but its position changed, being much 87 .m.«om p .223. 6:25:30 peanut... some: o.oossgmouosoofiofico .30.. .3 so. oescooooo on one «05 532m :3: oo cozsooosn o P .mE .239: 23553393 £355.82. «02 80h 0000 68m 80¢ DOOM OOON l? n _ a a _ . be «an oaono. anions «morgue 28.3.91. «Arias acéimsnm 332.1... 2381." s35 us. 3.2 3.3 n s .2... t p Don P OOON OOmN DOOM comm COO? Dame 80m (cu/36x) Amman: o; sgsaulue ulou qiMOJB 11mg 88 .. .n.wmmp .226. 6:055:00 «35¢ 30:: «3055339.: 335:5 .82. .3 .2 US$508 on can 35 530.6 «:5 .0 coioaoi w p .9“. .239: «3052339... £355.32“ “oz 805 0000 08m COO-V 86m OOON q a d u _ _ NNNOOO a. 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The duration of seed deve10pment is often restricted, but we cannot be sure whether these restrictions are caused by the low availability of assimilates (source limited) or by a low demand for assimilates from the fruits (sink limited). The length of the grain filling period rather than the rate of filling has been repeatedly cited (13,30) as a more important determinant of varietal differences in grain yield. A rapid initial growth and an increased longevity of the photosynthetic tissue capable of maintaining the seed filling process would seem a desirable plant strategy for maximizing seed yield. The data presented in Table 17 arrange the 10 sampled cultivars into three different subgroups according to their grain yield, FGR and seed number. What appears interesting is that none of the cultivars that were included in group I had a significant reduction in the length of the seed filling period due to stress (data presented in Table 6). The calculated means of grain yield, FGR and seed number for irrigated and stress conditions are relatively high in group I, intermediate for group II and low in group III. When the length of the seed filling period was not reduced, as in the case of cultivars included in group I, grain yield under stress did not differ from the irrigated plots. An increment in the FGR under stress can probably explain the lack of yield reduction. In groups II and III, the length of the seed filling period was reduced under water stress. In the case of cultivars included in group II, even though the FGR was higher under water stress,this did not prevent a 94 Table 17. Comparison between Grain yield, Fruit growth rate, Seed number and Effective seed filling period under two water treatments. Iguala, 1982-3. Grain Yield FGR Seed N3. ESFP (kg/ha) (kg/ha/day) (seeds/mt ) (days) Group I BAT 332 Ir' 1779 91.0 1052 30 St 1919 123.2 1181 29 BAT 85 Ir 1966 123.0 999 33 St 1751 109.9 899 33 61065 Ir 1851 99.0 999 35 St 1938 101.5 1108 39 i, 3.0. Ir 1853, 99 102.6, 17.6 998, 52 33, 3 St 1869, 103 111.3, 10.9 1061, 199 32, 3 Group I; LEF-Z-RB Ir 1969 77.5 732 39 St 1775 116.9 735 36 790131 Ir 1225 77.0 539 30 St 106a 88.6 u7u 28 800122 Ir 1571 8u.2 957 3n St 1178 86.9 787 39 wIs 23-61 Ir 1536 80.6 892 37 St 1500 109.8 862 33 i, s.d. Ir 157a, 303 79.8, 3.3 766, 180 35, 9 St 1379. 322 100.0, 10.0 719, 168 33. 3 Group III 000 222 Ir 1102 57.6 221 50 St 985 96.8 216 M7 1213-2 Ir 1519 56.9 021 u2 St 1200 62.5 397 ”0 B.Madero Ir 1183 56.7 269 52 St 792 37.3 178 M8 X, s.d. Ir 1266, 218 57.0, 0.5 309, 109 98. 5 St 976, 229 48.8, 12.7 2u7, 87 as, u * Ir: Irrigated St: Stress 95 reduction in grain yield. In group III, FGR was lower under the stress treatment and a reduction in grain yield under the stress treatment was observed. The data presented here indicate that the length of the seed filling period and the rate of filling are both important determinants of varietal differences in grain yield. A higher FGR accompanied by a filling period that showed no significant differences in length between the water treatments, even though it was not a very long one, resulted in the highest yielding cultivars under both treatments. YIELD POTENTIAL AND DROUGHT SUSCEPTIBILITY Given the lack of reliable information on specific drought resistance mechanisms, plant breeders are still largely guided in their selection for drought resistance by grain yield and its stability under dry conditions. High yields could be the result of drought escape or high yield potential, rather than the possession of specific drought resistance mechanisms that favor yield performance under water stress. The identification and separation of the influence of these mechanisms upon yield under drought would facilitate breeding and selection. Utilizing the data from the Iguala experiment, as well as the data collected in a similar experiment planted in Durango, Mexico in July of 1983, I will concentrate in this section upon the economic yield results, their adjustment for drought escape and the separation of effects due to differences in yield potential. A brief description of the Durango experiment and the data collected are given in Appendix A. 1.Drought Susceptibility Index The relationship between stress yield and control yield is generally positive and strong. A poor yielder in the control treatment cannot give by any means a good yield 96 97 under stres. However, as stated in the CIAT's 1982 Annual Report (10), the degree of correlation between control and stress yield probably depends on the severity of the stress. Differential yield reduction due to stress has been commonly used asaacriterion for selecting cultivars with tolerance to water stress. This strategy can be counterproductive because of the likelihood of selecting generally low yielding cultivars whose yield differential (Yc - Ta) is relatively small. A dimensionless slope termed Drought Susceptibility Index (S) was suggested by Fischer and Maurer (19) as a useful way of. comparing cultivar performances between drought levels and experiments. This sIOpe is calculated from the following formula: Y3 = Yp ( 1 - SD ) where D is defined as the drought intensity and calculated by D = ( 1 - is / 2p ), is being the mean yield of the stress plots and ip the mean yield of the well watered plots. D ranges from 0 to 1. Y8 is the yield under stress and Yp (yield potential) is the yield under well watered conditions. This equation expresses the separate effects of yield potential and drought susceptibility on yields under \ drought, and in these terms lower drought susceptibility is considered synonymous with higher drought resistance. Although S should be independent of drought intensity, its exact value will depend on the cultivars included in calculating the drought intensity index ( D ); for this reason, when comparing a group of cultivars grown under different environments for their drought susceptibility, it is better to base the comparison on their ranking rather. than on the absolute S values. Drought susceptibility indices were calculated for the individual cultivars as well as for the cultivar groups of the Durango and Iguala emperiments. Grouping was done according to cultivar origin. The cultivars planted in the Durango experiment were subdivided into 4 groups: group I - Mexican cultivars, group II - CIAT cultivars, group III - Wisconsin cultivars and group IV - Michigan cultivars previously selected for high yields. The cultivars planted in Iguala were subdivided into 5 groups: groups I, II and III correspond to Mexican, CIAT and Wisconsin cultivars, while group IV includes Michigan cultivars previously selected for high yields and group V includes Michigan lines ‘ previously selected for low yields. Cultivar ‘names and the calculated S values appear in Tables 18 and 19. Variation of the drought susceptibility indices between groups is as great as within groups, so associations between cultivar origin and drought tolerance are not apparent. While the Mexican cultivars appeared to have a lower S value in Durango than in Iguala, the opposite was observed for the CIAT lines. Fischer and Maurer (19) assert that despite differences in drought intensity, S values should be consistent for a given cultivar grown in different eXperiments. Environmental differences between the two experiments, such as temperature, nutrient availability, 99 Table 18. Individual cultivar drought susceptibility indices. Iguala 1982-3 and Durango 1983. Cultivar Iguala Experiment.A Durango Experiment.B LEF-Z-RB 1.20 1213-2 2.59 1.95 C-5 2.66 Bayo Madero 4.65 1.02 Pinto Nacional 1 3.68 Durango 222 1.32. 0.98 311 95.6888 -131. BAT 85 1.36 BAT “7 0.02 ‘ 0.85 A-162 0.60 BAT 798 0.93 1.32 Wisc 23-61 0.29 Wisc 21-58 0.95 0.55 Wisc 21-SM -1.02§ Neptune -0.96. 61065 -0.85. 0.89 800122 3.12 0.80 81017 0.51 800205 2.29 790131 1.6M iA D = 0.08 § negative values because Ys2>Yc 53 D = 0.29 100 O Table 19. Group drought susceptibility indices - S - Iguala 1982-3 and Durango 1983. Group Iguala Experiment Cultivars Durango Experiment Group Cultivars II III IV LEF-2-RB 1213-2 0-5 Bayo Madero Pinto Nacional Durango 222 Ojo de Cabra BAT 332 BAT 85 BAT A7 A-162 BAT 798 Wisc 23-61 ' Wisc 21-58 Wise 21-54 Neptune 61065 800122 81017 800205 790131 2.30 0.39 0.82 2.03 II III IV 1213-2 Bayo Madero Durango 222 BAT H7 BAT 798 Wisc 21-58 61065 800122 0.55 0.87 lOl radiation, etc might affect the expression of Yp, but they should not alter the S values drastically, unless other factors besides water availability play an important role in determining yield. Table 20 illustrates the group ranking by the S value. The consistency of the group ranking contrasts with the differences in ranking obtained for individual cultivarsy (Data shown in Table 21). Drastic changes in ranking for cultivars such as 800122 and BAT 798 illustrate the importance of local adaptation when selecting for drought tolerance. Under the Iguala conditions, 800122 was considered very susceptible to water stress, while under the Durango environment it was drought tolerant. This apparent inconsistency simply says that one must be aware of the importance of other environmental factors in determining the overall plant performance in a given environment. However, if the drought conditions differ cultivar differences in ranking would probably reflect this. On the other hand, in cultivars such as BAT 47,1213-2, Bayo Madero and Durango 222, there was no apparent change in the ranking between the two experiments. One can probably say that these cultivars had a broader adaptation. The lack of correlation between Yp and S (1': -0.03 ) does not agree with the high correlation reported by Fischer and Maurer (19). As far as this experiment has shown, there is no association between yield potential and the drought susceptibility index. The diversity of the bean genotypes Table 20. Group ranking by drought susceptibility index ( S ). Iguala 1982-3 and Durango 1983. Group Iguala Durango Experiment .' Experiment I 5 9 II 2 3 III 1 1 IV 3 2 V u Table 21. Ranking by drought susceptibility index ( S ) of the eight cultivars planted in Iguala and Durango Cultivar Iguala Durango Wisc 21-58 u 1 61065 1 4 800122 7 2 BAT H7 2 3 BAT 798 3 7 1213-2 6 8 Bayo Madero 8 6 Durango 222 5 5 103 used in these experiments, which contrasts with the similarity of the genotypes used by Fischer and Maurer, probably can explain the difference in the results. 2.Relationship between control and stress yields Figures 14 and 15 show the relationship between control and stress economic yields for the Iguala and Durango experiments. In Figure 1‘1, all the cultivars that had a negative value for the To - Ys differential are above the 1:1 yield line ( b=1), while the cultivars that had a yield reduction under stress are below the 1:1 yield line. The distance between each individual point and the regression line is proportional to the yield differential. Points 13 , 6 , 19 and 8 which correspond to Bayo Madero,800122, Pinto Nacional and 800205 are the farthest from the regression line, while 22 (Tepary), 1 (Wisc 23-61), and 18 (BAT 798) are the closest to it. The distances from the regression line of points 18 and 1 are almost the same,.however their yields under both stress and non stress are significantly different. Cultivar 1 (Wisc 23-61) outyielded cultivar 18 (BAT 798) by 415 Ikg./ha. Points 19 (Pinto Nacional) and 8 (800205) are at approximately the same distance from the regression line, however 800205 outyielded Pinto Nacional by more than 500 kg./ha. under stress conditions. When looking at the distance from the regression line of 104 .n.umm — .225. .20; :25 3:0 .2250 c0253 San—3520:. .vw 052.... .259: 0> 000w 000’ 000.. 00.; 00m— 000_. 000 000 — . _ fi _ _ _ . .\ tunabluu \ 0pm .5561 2. up. \ «263 no... \ 3.. 2:... 1.2 2:53 .. o. \\ com «3212 \ 5.2a 1.: a? 8.5:. 1.... \ «85¢ a! u \ 2:8: .u an. \ 000- 6.0“. «v ”F. \ «.231 Z a. \ 9...“.qu no. \ 8526 \ 833.... o. «e. \\ .831» 6 «~88 no 3 \ 00“.. moo—one 252.02 1' \\ Amp-\QUv: 3.32.31." \ 0> 3.3 8.31... \ 8.9.. 8.3... . \ 100a; .1000— 000— 000a 105 .mmm p 69350 .20; 395 new .0580 c0050: 0223520". .m w 059“. Amp—39: 0> 000 _. 000— 00 w w 000 00h 00m _ _ . d . q 000 005 00m .289: Bed 1 m> .e \\ 1 co. . \\ «aw once—5 u o \ Sons! 280 u h \\ a . n8. 1 o o2. Eu .1. m \\ 3. 5m 1 v 1 000 .. «a Son 1 a \\ moo; n a \\ 3.3 8.3 n p \ L \p u a 00m P 106 cultivar 7 (81017) and cultivar 17 (A-162), one can observe that A-162 is closer to the regression line. Nevertheless, the yield of 8101? under stress was over 250 kg./ha. higher than its homologue for A-162. The distances between each individual point and the regression line for the Durango experiment are shown in Figure 15. Points 5 and 6 which correspond to BAT 798 and 1213-2 are the farthest from the regression line, while 8 (Durango 222), 2 (61065) and 7 (Bayo Madero) are the closest to it. The distance from the regression line of points 7 and 2 is almost the same, nevertheless their yields under both stress and non-stress differed by more than 200 kgs/ha. Cultivar 2 (61065) outyielded cultivar 7 (Bayo Madero). From these data it becomes evident that when one examines the To vs Ys graph trying to select for tolerance to water stress, two important factors should be taken into consideration : (1) distance from the origin and (2) distance from the regression line. The distance from the origin is an indication of the yield potential of each individual cultivar ; the farther a particular cultivar is from the origin, the higher its yield potential. The distance from the regression line is an indicator of the reduction in yield under stress conditions. 107 3. Geometric mean of stress and control yield gg‘g selection criterion for drought tolerance The likelihood of selecting generally low yielding cultivars, when differential yield reduction due to drought is used as a criterion for selecting cultivars with tolerance to water stress, suggests the use of an alternative selection criterion. The geometric mean of stress and control yields, is probably a better option since the two critical factors, yield potential and yield differential, are both taken into account. In this section, a comparison between the yield differential (Yc - Is), the arithmetic mean, the geometric mean and the drought susceptibility index will be made. Calculated values f0r the yield differential and the arithmetic and geometric means for the Iguala and the Durango experiments are given in Tables 22 and 23. The negative values under the yield differential column in Table 22 indicate that for these particular cultivars the stress plots outyielded the control plots. However, as already stated (Table 2), these differences were not significant. It is clear that the water stress when imposed late in the seed filling period under Iguala conditions did not affect yield significantly. Only six cultivars of the twenty two that were screened had significant yield reductions under stress (Table 2). The correlation between stress yield and control yield was positive and highly um ee\emx e“ esee 826“» . mom. mom. hm >eeeeh mm one Poo mo1 mcnmu on one Pm «so, ago. A.— mmm emceeso om ooo— chop mum . Hmcofiomz opcam mp moop moo_ um was ~— Ppw— «pm. me u: H:op mmo— mmm momoow w zaom aaom mm FPO—m m Pom. mum, mom mNFoow c ohm? wwwp 3N9: moopo m Npo— mp0. omp1 mczuamz z smmw mwmp mo—u :m1pm on“: m =Fm— opmp m=P mmupm onfi: m m—mp m—mp om Pc1mm on“: F N my x o») + o» 1 o» :owumowufiucmuH .oz >cucm 8.»:oeficoqxo mamsmH may Lou cams cacaosomo .Hegseeeeccfle eHeH» cam :mos caumszuwg< .NN manmh 109 Table 23. Yield differential, Arithmetic mean and Geometric mean for the Durango experiment.s Entry No. Identification Yc - Ys To 4» Ys VYc x Ys A 2 1 Wise 21-58 161 921 ' 917 2 61065 327 1098 1086 3 800122 306 1089 1078 4 BAT 47 363 1289 1276 5 BAT 798 399 836 812 6 1213-2 625 1166 1123 7 Bayo Madero 299 854 840 8 Durango 222 391 1168 1151 .Yield data in kgs/ha 110 significant ( calculated r = 0.895 ). This might indicate, as suggested by the CIAT 1981 Annual Report (9), that the degree of stress was not very high. For the Durango experiment, the correlation between control and stress yield was also positive and significant, but its calculated value ( r: 0.76) was smaller than the one obtained for Iguala. One can then assume that the water stress was more severe in Durango, a result that is confirmed by the calculated drought intensity. Comparing the calculated values under the arithmetic and geometric mean columns shown in Tables 22 and 23, one can see the greater conservativeness of the geometric mean, the calculated values always being smaller than or equal to the arithmetic means. Since the absolute values for yield differential and the calculated means differed in magnitude, a more illustrative comparison is given in Tables 29 and 25 based on the cultivar ranking when using different selection criteria ( Yc - Ys,(Yc + Ys)/2{V7:-;-7; and S ). Ranking based on the arithmetic and geometric means did not differ, except for a one position change in cultivars BAT 798 and Pinto Nacional 1 in the Iguala experiment. 0n the other hand, the results of ranking based on the yield differential are very similar to the results obtained when ranking cultivar performance based on their drought susceptibility index. However, the To - Y3 and S ranking was substantially different from the (Yc + Ys)/2 and m ranking. The advantage of utilizing the geometric mean as a selection criterion rather than the yield differential is illustrated 111 A m_ m. m heeeee _ mm mm m meeeu me one 5. cm om m. mmm omeeesa Fm mp mp om Hmeofioez 60:28 a a. m. A no» sea __ m m P. «82.2 m e A m we Hem m. a a 8. mm Hem m m m _ mmm Hem mm .m .m mm oeeemz exam 3. e. e. a, m-o m. m. m. p. mumpmp m_ m m mp mm1m10mq o. u. >_ a. .m_om~ A. a a a, momoom o. P _ o_ epopm em =. :2 .m mmpoom m m m m moo—e : o. o. m messeez m m. m. a :m-.m on“: m2 8 e m_ mm-_m on“: e __ ._ e _e1mm 6853 x02...“ 33330033 :mos cums 5 35:23.53 semeoeo ofiesesoeo espeseufiee eHeH» ee>susao macmuaco :ofiuomaom acosomuwc snow mean: acmefoqxo mamsmH on» no.“ mcwxcmc Lm>gasu Jam wanna. 112 m m N o mmm omcmgso o w b m ogmomz oxmm w m m m mumpmp w m m p was efladso mfigouago :oHuomem acmgmumfio Lsou magma ucwsfmaxo omcmgzo 9.... new media; Lm>3H3o .mm magma in Tables 26 and 27. When selecting the t0p 20 1 of the cultivars by both criteria and comparing their yields under stress and non-stress conditions, the mean yields of the Yc - Ys selected groups are IOwer than the mean yields of the VYc x Ys group. 114 m:\nmx* mm h9 a gas amnpm on“: ocsaqoz moopc Hmfiucmgomufio map. omo. «mm yam adv“; an a new mmogum cofiummacga ..m>o voucoaom mo 33» :mo: 2.23:5 ozocmcouomamm .ucoeflcoaxo mamzmH .mwcoufigo coauomaom acocouufic oz» mafia: .mcm>3a:o s cm no» nouooaom on» «0 undo; :mo: .om magma. 115 m:\mmx. NNN owcmcso mmo. >_:P u: H9 m ace Hmaucmaoccao mes moo. mm-_~ on“: vats» >9 m ace mnogum cofiummHLLH a.n>o nouooaon mo cam; :32 mgmiuaso asocm nmuooaom .ucosfigmaxo omcmczo .mHgouHLo :owuooaom acogouufiu o3» mean: .ncm>3H:o a om no» oouooaom on» no 2:0: coo: ém “:an SUMMARY AND CONCLUSIONS These experiments were designed to get a better understanding of agronomic and certain physiological responses of the bean crop to water stress. The studies are on-going and it is premature to draw lasting conclusions at this time, but we have obtained some information that allows us to speculate on the importance of certain characters and their relative contribution to the plant's ability to withstand an environmental stress. The major findings of this thesis can be summarized as follows: 1. A relationship between grain yield and the change in stem and leaf dry weights from anthesis to physiological maturity (b=-0.5fl), a relationship that was accentuated under the minus water treatment (Dz-0.70), implicates assimilate remobilization as an important contributor to seed yield, especially under late-season water stress. 2. The daily partition of assimilates to the fruits is determined by genotype and influenced by water treatment. A high partitioning ratio under water stress in 7 of the 10 sampled cultivars shows that treatment and cultivar differences in partitioning exist and that they probably represent a desirable character for plants grown under water stress. 116 117 3. The length and the rate of the seed filling period are important determinants of varietal differences in grain yield. The top yielding cultivars under stress and irrigated conditions were those which had a higher than average fruit growth rate -FGR- accompanied by a seed filling period that was not significantly different in length due to water treatments. 4. The environmental inputs and constraints in a particular environment are critical determinants that must be considered in the design of an appropiate "crop model" or ideotype to be used in developing improved varieties specifically intended for a particular production system. Simple observations and measurements in a given environment, such as dry matter production, flowering date, length of the vegetative and reproductive stages and leaf area index permit the investigator to reach useful conclusions underlying causes of yield differences. An understanding of the type of water limitation, along with a more complete quantification of the drought environment, are essential to the task of producing an appropiate ideotype. 5. Grain yield and its stability are the most widely used selection criteria when selecting for drought resistance. The utilization of the geometric mean of Yc and Y3 as a selection criterion rather than the yield differential (Yc - Ys) or the drought susceptibility index, proved to be very advantageous. The mean yields of the groups selected by the 118 geometric mean.were.higher than the mean yields of the groups selected on the basis of yield differential. 6. The relationship between cultivar yield performance (based on the geometric mean) and remobilization is evident. The two cultivars with the highest partitioning ratios (BAT 85 and 61065) were also in the top 20% of cultivars selected by the geometric mean. 7. Genotypic variation exists for many of the physiological characters that determine the net photosynthesis of the crop canopy and the distribution of assimilates to the grain, such as CGR, FGR, partitioning ratio and length of the vegetative and reproductive stages. It should be possible for the plant breeder to make use of this variation to deve10p improved varieties for water-limited regions. LITERATURE CITED LITERATURE CITED 1. Acosta, J.A., A. Nunez, and J. Carrillo. 1983. Eficiencia del Uso del Agua por el Cultivo del Frfjol (P. vulgaris) en Regiones de Baja Precipitacion. Campo Agricola Experimental Valle del Guadiana. Durango. S. A. R. H. INIA. , 2. Adams, 14.11. 1973. "Plant Architecture and Physiological Efficiency in the Field Bean" in Potential of Field Beans and Other Legumes in Latin America. CIAT Series Seminar #Z-E. Cali, Colombia. 3. Adams, 14.11., and D. Reicosky. 1975. Plant Architecture and Physiological Efficiency in Field Beans. A Progress Report and Renewal Request for 1975-76 to the Rockefeller Foundation. u. Adams, M.W., J. Wiersma, and J. Salazar. 1978. Differences in Starch Accumulation Among Dry Bean Cultivars. Crop Sci. 18:155-157. 5. Bliss, F3A., J.R. McFerson, and J.C. Rosas. 1982. Genetic Analysis of Host Factors Affecting N Fixation in Common Beans. Progress Report SEA/CR- AID. 6. Bouslama, M. 1977. Accumulation and Partitioning of Carbohydrates in Two Cultivars of Navy Beans (P. vulgaris) as influenced by Grafting and Source-Sink ManipulationJ‘d. S. Thesis, Michigan State University. 7.Brun, W.A. 1972. Nodule Activity of Soybeans as Influenced ‘by Photosynthetic Source-Sink Manipulations. 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Press. London. pp. 385-903. 122 27.Ham, G., R.Lawn, and W. Brun. 1976. Influence of Inoculation,N Fertilizers and Photosynthetic Source- Sink Manipulations on Field Grown Soybeans.In:PJL ‘ Nutman (Editor), Symbiotic N-Fixation in Plants. Cambridge Univ. Press. London. pp. 239-253. 28. Hardy, R.W., and U.D. Havelka. 1975. Nitrogen Fixation Research: A Key to World Food ? Science 188:633-6u3. 29. Hardy, R.W., and U.D.Havelka. 1976. Photosynthate as a Major Factor Limiting N-Fixation by Field Grown Legumes with Emphasis on Soybeans. In: PCS. Nutman . (Editor), Symbiotic N-Fixation in Plants. Cambridge Univ. Press. London. pp. 1121-1139. 30. Izquierdo, J.A. 1981. The Effect of Accumulation and Remobilization of Carbon Assimilate and Nitrogen on Abscission, Seed Development and Yield of Common Bean (§;vulgaris) with Differing Architectural Forms. PhJL Thesis, Michigan State University. 31.Jeppson, ILG., R. Johnson, and H. Hadley. 1978. Variation in Mobilization of Plant Nitrogen to the Grain in Nodulating and Non-nodulating Soybean Genotypes. CrOp Science 18:1058-1062. 32. Johnson, R.R” and D.N. Moss. 1976. Effect of Water Stress on 1900 Fixation and Translocation in Wheat During Grain lling. Crop Sci. 16:697-701. 33. Lawn, R. J., and w. A. Brun. 19711. Symbiotic N- Fixation" in Soybeans.2[. Effect of Photosynthetic Source- Sink Manipulations. Crop Sci. 14:11-16. 3H. Lawn, RHL.1982. Response of Four Grain Legumes to Water Stress'in South-Eastern Queensland.ILPhysiological Response Mechanisms. II. Plant Growth and Soil Water Extractions Patterns. III. Dry Matter Production, Yield and Water Use Efficiency. Austr. J. Agric. Res. 33:481- 521. 35. Lépiz, R. 1982. Logros y Aportaciones de la Investigaci6n Agricola en el Cultivo del Frijol.Secretaria de Agricultura y Recursos Hidraulicos.S.AJLH.INIA. Mexico. Publicacion No. 83. 123 36. Ludlow,M.M. 1981. Environmental Factors Affecting Plant Growth. In:D.E. Byth and V.E. Mungomery (Editors), Interpretationof Plant Responseand Adaptation to Agricultural Environment. Aust.Inst. Agric.Sci. Brisbane. 37. Ludlow, M.M., and 0. Bjorkman. 19811. Paraheliotropic Leaf Movementas 3 Protective Mechanism Against Drought Induced Damage to Primary Photosynthetic Reactions: gagage by Excessive Light and Heat. Planta 161: 505- 38. Martinez, L.R., and A. Janowitz. 1978. Determinaci6n de Almidon. Anélisis Bromatolégico de Yuca. M.C. Thesis. Secci6n Quimica Agricola. Unidad Czahutitlén, Izcalli. Universidad Autonoma de M xico. 39.Martinez, R. 1976. Nitrogen Fixation and Carbohydrate Partitioning in P__._ vulgaris. PhD. Thesis, Michigan State University. 40. Mligo, JQK. 1983. Inheritance Study of Starch Accumulation ' in Stems of Dry Beans.M.S.Thesis, Michigan State University. 111. Office of Technology Assesment. OTA. U.S. Congress. 1983. Water Related Technologies for Sustainable Agriculture in Arid/Semiarid Lands. Selected Foreign Experience. Background Paper. 112. 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Nitrogen Fixation by Legumes Subjected to Water and Light Stresses. In: P.S. Nutman (Editor), Symbiotic N-Fixation in Plants. Cambridge Univ. Press. London. pp. 405-420. 49. Stansel, J.W., C.N. Bollich, J. Thysell, and V. Hall. 1965. Rice Journal 68:34-35. 50. Streeter, J.C. 1973. Growth of Two Shoots on a Single Root as a Technique for Studying Physiological FactorsLimiting the Rate of N-Fixation by Nodulated Legumes. Plant Physiology (Supplement) 48:34. 51. Tanaka, A., and K. Fujita. 1979. Growth, Photosynthesis. and Yield Components in Relation to Grain Yield of the Field Bean. J. Fac. Agric. Hokkaido 59:145-237. 52. Temple, SJL, and L.Song. 1980. Cr0p Improvement and Genetic Resources in P; vulgaris for the Tropics. In: R.J. Summerfield and A.H. Bunting (Editors), Advances in Legume Science. Univ. of Reading. England. pp. 365-373. 53. Turk,KuLw AWE. Hall, and C.W. Asbell. 1980. Drought Adaptation of Cowpea. I. Influence of Drought on Seed Yield. II. Influence of Drought on Plant Water Status and Relations with Seed Yield. Agronomy Journal 72:413- 439. 54. 55. 56. 57. 58. 59. 60. 125 Turner, N.C., J.E. Begg, H.M. Rawson, S.D. English, and A.B. Hearn. 1978. Agronomic and Physiological Responses of ‘Soybean and Sorghum Crops to Water Defficits. III. Compone ts of Leaf Water Potential, Leaf 0049110158909: 1 C02 Photosynthesis, and Adaptation to Water Deficits. Aust. J. of Plant Physiol. 5:179-194. Wallace, D.H., J.L. Ozbun, and M.M. Munger. 1972. Physiological Genetics of Crop Yield. Advances in Agronomy 24:97-146. WelIs, R.,and W.Meredith. 1984. Comparative Growth of Obsolete and Modern Cotton Cultivars. II.Reproductive Dry Matter Partitioning. CrOp Science 24: 863-868. Wilson, R.F., J.N. Burton, J.A. Buck, and C.A. Brim. 1978. Studies on Genetic Male Sterile Soybeans. I. Distribution of Plant Carbohydrate and Nitrogen During Development. Plant Physiol. 61:838-841. Wynne, J.C., S. Ball, T. Isleib, and T. Schneeweis. 1982. Host Plant Factors Affecting N-Fixation of the Peanut. In: P.H. Graham and S.C. Harris (Editors), BNF Technolbgy for Tropical Agriculture. pp. 67-75. Yoshida, S. 1972. Physiological Aspects of Grain Yield. Ann. Rev. Plant Physiol. 23:437-467. Zablotowicz, R.M., D.D. Focht, and G.H. Cannell. 1981. Nodulation and N-Fixation of Field Grown Cowpeas as Influenced by Well Ikwigated and Droughted Conditions. Agron. J. 73:9-12. APPENDICES APPENDIX A A field experiment was planted in the second week of July of 1983 at the Campo Agricola Experimental Francisco Madero in the state of Durango, Mexico. The experimental station is at the meridian 104° 20' longitude West and the parallel 24° 20' latitude North. The altitude is 1932 m above sea level. The minimum temperature during the growing season was 4°C and the maximum was 35°C, with a season average of 20°C. The total precipitation between July 6th and October 30th was 402 mm, distributed as follows: 13 5 during July, 63 1 during August, 19 1 during September and 5 : during October. The experimental plots were on a Silty Clay soil, with a pH of 6.5. Eight dry bean cultivars were selected from the Iguala experiment, on the basis of their good adaptation to the Durango conditions. They included: 1. One line from the Univ. of Wisconsin : Wisc 21-58 2. Two CIAT lines : BAT 47 and BAT 798 3.Three Mexican lines : 1213-2, Bayo Madero and Durango 222 4. Two Michigan State lines : 61065 and 800122 The experimental plots were arranged in a split plot design with 3 replications, the water treatment was the whole plot factor and cultivars were the split factor. Before planting, 35 kg./ha. of Phosphorous and 25 kg./ha. of Nitrogen were applied. I 126 All plots were rainfed until flowering time, and thereafter only the so-called plus water plots received rain..A *wooden structure was built around the stress plots, and every time that it rained a clear plastic sheet was placed over the structure to cover the plots and prevent them from getting water. Individual plots of each cultivar were treated as separate units for water management. Each plot consisted of 4 rows 2 meters long; the distance between plants within a row was 10 cms. and the distance between rows was 0.75 cms. Economic yield was taken at harvest time. Two rows of 2 meters each were harvested, grain yield adjusted to 10 1 moisture was recorded. ( Data given in Table A ). 128 Loam: o3» Loos: $2?me .33» ofisocoom .< wanna mum mom, NNN omcmgso m mow moo. ocean: oxmm 5 mm» mp3. mum_~_ o ems ems. mm» Ham m cop. chap h: H33: 0.. OOm 00¢ con OON 00.. GOP DON Don av.¢m _. —. un— 00? can 000; x aoueqaosqv HI GRN STRTE UNIV LIBRRRIE 1111111111111111 3111111111011111 l11111|111|11|11|L1111|