Symbiotic interaction of Rhizobium with roots of legume plants leads to the formation of root nodules that are capable of reducing atmospheric nitrogen. In nodule cells, bacteria are always enclosed inside the peribacteroid membrane (pbm) which is derived from the plant cell plasma membrane. The pbm mediates all the molecular exchanges between the host plant and bacteria. The pbm of soybean (Glycine max) nodules induced by Bradyrhizobium japonicum was characterized for the presence of nodule-specific proteins (nodulins), which may be involved in some of the nodule-specific roles the pbm plays. The pbm was found to contain a number of nodulins, and most of them were shown to be of plant origin. The peribacteroid fluid (pbf) was also purified and shown to contain nodulins. Some of the pbf proteins were highly glycosylated. Immunological localization at the electron microscopic level has shown that pbm nodulins are inserted specifically in the pbm; almost none are detected in the plasma membrane (pm) of infected cells even though the pbm is derived from it. The amino acid sequences of three different pbm nodulins (nodulin-23, -24 and -26) do not share significant primary structure homology, neither do their tentative secondary structures. Our results do not preclude targeting based on pbm-nodulin-specific feature(s) of the proteins; but it is possible that pbm-specific localization is achieved by differential rates of membrane synthesis, or turnover, in pbm as compared to the plasma membrane.

Soybean leaf consumption for the most common semilooper species, Trichoplusia orichalcea (F.) was established in the laboratory using a leaf area meter. The total consumption per larva was 120,85 cm$ sp2$. The yield reduction of our soybean cultivars (Glycine max (L.) Merrill) being Duiker, Gazelle, Roan and SCS1 was measured in relation to different levels of defoliation. The defoliation was induced manually singly or sequentially over three different growth stages. / At soybean maturity, counts of pods per plant, number of seeds per plant, weight per 100 seeds and weight of seeds per plant were obtained. Yields were converted to a percentage of yield and linear regressions fitted to the relationship between percentage yield and defoliation. The percentage yield was influenced by the cultivars, the levels of defoliation, and the timing of defoliation. / The most critical growth stage for defoliation was the seed development stage, but the differences between them were small and not significant. SCS1 was the most resistant cultivar to defoliation, while Duiker was the most susceptible to single defoliation. / The economic thresholds were determined for the soybean cultivars demonstrating significant linear relations between percentage yield and single defoliation. Based on three insecticides and two application methods, the economic thresholds were determined at the flowering stage for Duiker, at the pod development stage for Duiker and Roan and at the seed development stage for Duiker, Gazelle, Roan, and SCS1 cultivars. The numbers of semilooper caterpillars per metre of row required to reach the economic thresholds, are generally higher than the natural levels of infestation.

This research tested the hypotheses that (a) suboptimal root-zone temperatures (RZT) limit the soybean-Bradyrhizobium N$ sb2$-fixing symbiosis primarily through an inhibition of symbiosis establishment and (b) this inhibition is modified by the genotype of micro- or macrosymbiont. Controlled environment and field experiments were conducted utilizing two soybean genotypes and six B. japonicum strains. At 19$ sp circ$C RZT fixed nitrogen levels decreased by 30-40%, predominantly due to a restriction in the latter stages of nodule development. Reductions of 10% and 30% in specific nodule activity rates at 19$ sp circ$C and 15$ sp circ$C RZT respectively, indicated nodule function to be comparatively insensitive to low RZT. Soybean genotypes did not differ in seedling nodulation or N$ sb2$-fixation under cool-soil, field or controlled environment, conditions. At all temperatures, commercial B. japonicum strain 532C was more efficient, but not effective, than strains obtained from the cool-soils of Northern Japan. Under cool-soil field conditions, two of the latter strains increased seedling nodulation and N$ sb2$-fixation.

Soybean is emerging as a very important food, market and oil crop in Ethiopia. However, its productivity in Western Ethiopia is constrained by several production constraints, of which soil acidity is one of the most important ones. On acidic soils the availability of several plant nutrients is limited; among which phosphorus is the least available. Thus, development of high yielding and low P tolerant soybean varieties need to be among the top priorities in areas with such problematic soils. Therefore, the objectives of the study were to: 1) conduct a Participatory Rural Appraisal (PRA) study to assess farmers’ perception on various soil fertility, soybean consumption and marketing issues, 2) evaluate soybean genotypes under low and high P regimes, and 3) conduct genetic analysis of soybean performance under low and high P conditions. The PRA was conducted to assess farmers’ perception on various soil fertility, soybean consumptions and market issues. A total of 186 soybean producing farmers across three locations of Western Ethiopia were interviewed using a semi-structured questionnaire. Results from the study indicated that the use of soybean for crop rotation and soil fertility improvement was more important to the farmers than household consumption and marketing of the crop. The study also revealed poor demand for soybean compared to other crops on the local market. The majority of respondent farmers’ recognized that soil fertility has been declining over time and obtaining inorganic fertilizers on time was difficult; mainly due to high price of fertilizer. Though farmers’ cooperative was identified as the major supplier of fertilizer, farmers rated the quality of its service in supplying fertilizer as poor. With deteriorating soil fertility and limited capacity to use inorganic fertilizers, farmers are producing soybean under low soil fertility conditions. Thus, breeding programs need to develop varieties that perform well under low fertility soil. Screening soybean genotypes for response to different P regimes was performed in a field experiment using a split plot design, where the main plots were three levels of applied P (0, 100 and 200 kg ha-1 P), and the sub plots were 36 soybean genotypes (G) planted across three locations (L) with two replications. The extent of genetic variation of the 36 soybean genotypes was assessed under low (0 kg ha-1) and high P (100 kg ha-1) conditions. The analysis of variance revealed significant differences among genotypes for all the traits, except pod number at low P; while all the traits, except root volume, pod number, and number of seeds per pod showed significant differences at high P. Plant fresh weight, root fresh weight and root volume exhibited high genotypic coefficient of variation (GCV) and phenotypic coefficient of variation (PCV) under both P conditions. Both principal component and cluster analyses revealed variation in the population. The 100-seed weight, plant height, roots and plant fresh weight combined high heritability and genetic advance estimates indicating that the inheritance of such traits is controlled by additive gene action under both P conditions. In general, the study revealed high genetic variation in the population, which can be exploited to improve performance under both high and low P conditions. The analysis of variance revealed significant genotype X phosphorus (GXP) interaction for number of nodules and total nodule weight at Jimma, and Assossa, and for root weight and root volume at Mettu. Though the GXP and GXPXL interactions showed non-significant difference for across locations analysis, the genotypes displayed significant difference for root fresh weight, root volume, tap root length, and weight of effective nodule. Genotypes: Pr-142 (26), AGS-3-1, SCS-1, AGS 234, and H 3 were identified among the best for root and nodulation characteristics. Yield and yield related traits were also assessed separately in the screening program. The results revealed significant GXP interactions for grain yield only at one site; while the genotypes exhibited highly significant differences for most of the traits in all the sites. G and GXL interaction were significantly different for most the traits. Essex 1, IAC 11, and AGS-3-1 were the best performing genotypes at high P; while genotypes IAC 11, AA 7138, G 9945 and AGS-7-1 displayed tolerance to low P. Genotypes AA-7138, PR-142 (26) and H3 exhibited stable performance across the three P levels. These genotypes have paramount significance in breeding soybean for low P tolerance and stable performance in varying P conditions for resource poor subsistence farmers.The genetic control mechanism for the major quantitative traits for performance under high and low P condition was studied in a nine parent half diallel cross. The results revealed that the GCA effects were highly significant for grain yield, pod length, days to maturity and plant height under low-P conditions. GCA effects were highly significant for grain yield, 100-seed weight, days to maturity, plant height, pod number, and pod length under high P. GCA effects were also significant for number of seeds per pod under high P condition. In addition, the relative contribution of GCA was higher than SCA under both P conditions, except for 100-seed weight at low P. Variety Hardee-1 was the best general combiner for most of the quantitative traits under both P conditions, indicating that it can be used in breeding programs to improve soybean for better genetic response to low and high P. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.

Soybean [Glycine max (L.) Merr.] is a tropical to subtropical legume that requires root zone temperatures (RZTs) in the 25 to 30°C range for optimal symbiotic activity. The inability of soybean to adapt to cool soil conditions limits its development and yield in short season areas. In particular, nodulation and nitrogen fixation by this crop species is sensitive to cool RZTs. The isoflavone genistein, which is the most effective plant-to-bacterium signal in the soybean nitrogen fixation symbiosis, has been used to pretreat Bradyrhizobium japonicum inocula. This resulted in increased soybean nodulation and nitrogen fixation in several studies, indicating that genistein preincubated inocula could overcome low RZT inhibition of plant growth and yield. The effectiveness of isoflavones was found to vary among soybean cultivars. Some legume cultivars apparently supply limiting amounts of the flavonoids. The objective of this thesis was to determine how soybean cultivars of different maturity groups would respond to genistein incubation of B. japonicum prior to inoculation. Two field experiments were conducted in 1997 and 1998 involving eleven soybean cultivars of three maturity groups organized in a randomized complete block design. Cells of B. japonicum, treated with genistein or not, were applied onto seeds in the furrow at the time of planting. The results of this study indicated that genistein application increased nodule number and nodule dry matter per plant, increased plant nitrogen content, grain protein and grain yield of all cultivars. There was no interaction between maturity group and genistein application, and there was no correlation between maturity groups and increase in nodulation, total biomass, nitrogen content and yield due to genistein treatment. Thus, responses of soybean cultivars of different maturity groups to genistein treatment are not related to maturity and/or yield potential.

A field experiment was conducted on a homogeneous sandy soil and a layered soil of southern Quebec from 1988 to 1990. This was done in order to evaluate the yield response of indeterminate soybean to subsurface irrigation and to determine the performance of subsurface irrigation in a layered soil. It was found that indeterminate soybean varieties increase their yield by approximately 30% for two out of three years. Soybean are very sensitive to competition between themselves as well as with weeds. This sensitivity is increased during subsurface irrigation. Weeds were more prominent in the irrigated area. It was concluded that the soybean yields are functions of water table depth, percent weed and plant population density. The minimum allowable water table depth for soybean was found to be 45 cm. At a water table depth greater than 95 cm no yield response was observed. / Water table management is not only possible but very functional in the layered soils of southern Quebec. It was found that surplus water did not drain from the irrigated area until the water table anywhere in this area was 10 cm higher than the elevation of the overflow pipe in the control chamber. It was therefore concluded that a water table depth range of 10 cm should be included in the design of the water table control system to allow for the effects of rain.

Genetic improvement of a number of crops including soybean (Glycine max L. [Merr]) has been associated with stay-green. Research on stay green genes has focused primarily on genes involved with photosynthesis and chlorophyll degradation. The current study explores the impact of a group of developmental genes, known as the E gene series, on the rate of soybean leaf senescence. The objective of this experiment was to determine the role of E-genes in the control of leaf senescence in soybean. The experiment was conducted in a split-plot design with three replications. The main plots were two photoperiods imposed following R1; i) natural day length (Amb) and ii) incandescent day length extension of 3 hours (Amb+3). The split plots were five E-gene near-isogenic lines (NILs), planted on different dates to obtain synchronous flowering. Phenology, photosynthesis, normalized difference vegetative index (NDVI) and fluorescence measurements were taken including, dark adapted photosynthetic efficiency (Fv/Fm), electron transport rate (ETR), and leaf chlorophyll concentration (SPAD). Leaf tissues were also analyzed for gene expression patterns among Harosoy isolines. Yield parameters like dry matter accumulation, harvest index and grain yields were recorded. The leaf net photosynthesis was more closely related to ETR than to SPAD values, suggesting that visual observation of stay-green may not be as effective in evaluating functional senescence as measurement of ETR. Cultivars with the dominant E1 allele maintained functional photosynthesis for longer, such that full senescence was delayed by 10-15 days in these cultivars. This phenomenon was observed under both photoperiod treatments and irrespective of the genetic background (Clark and Harosoy) in which the alleles appeared. Maintenance of functional photosynthesis by the E1 dominant allele can be attributed to maintenance of high ETR, and Fv/Fm, as well as delayed decline in leaf chlorophyll concentrations. Expression of senescence related genes were delayed in the isoline which had delayed leaf senescence phenotype. Consistent with the effect on leaf senescence, the dominant alleles also reduced the rate of phenological development, such that R5 occurred later in genotypes with dominant alleles and under the Amb+3 treatment. Cultivars with the dominant E1 allele under extended photoperiod treatment accumulated more biomass and had decreased apparent harvest index which caused no change in grain yields. The dominant E allele may delay leaf senescence directly or indirectly, through its delay of reproductive development.

Corn-based tortillas and wheat-based pizza crust were formulated using soybean presscake (SP) and defatted soy flour (SF); changes in nutritional properties, selected anti-nutritional factors, physical characteristics and consumer acceptance were evaluated as were in vitro and in vivo evaluation of glycemic index (GI) for tortillas at selected SP fortification levels. Protein quality and quantity improved by adding soy products. Fat levels increased with SP but decreased with SF. While levels of trypsin inhibitor and phytic acid generally increased, levels were considered acceptable. Texture of SP tortillas was more like the corn control than SF tortillas, likely because of higher fat content in SP. Flavour, texture and overall consumer acceptability were higher for tortillas containing soy products. In vitro analysis showed lower starch hydrolysis for the soybean tortillas, but in vivo GI values were not significantly different. Thus, incorporation of SP and defatted SF to fortify bakery products has potential.

A concern in transgenic crops is the potential risk posed by unintended effects which could result from genetic transformation. The objective of this work was to develop an untargeted approach that could characterize transgenic crops, as well as conventional crops, at the molecular level. An experimental approach was designed and used to compare conventional and transgenic soybean varieties. Varieties were compared using their metabolite fingerprints obtained by reverse-phase high performance liquid chromatography (HPLC) and both the analytical and biological variability were assessed. Multivariate and univariate statistical analyses were applied to the data to detect significant differences between the varieties. It was found that transgenic variety PS 46 RR was the most different variety analyzed and that it differed most from Mandarin (Ottawa) and AC Dundas. The statistical analyses also determined that PS 46 RR differed more from the conventional varieties tested than 2601R did.

The above-ground part of a plant has an important contribution to plant development and yield production. Physiological activities of a plant canopy highly correlate to morphology of plant vegetation. Obviously, leaf area index is a good indicator for leaf area, but does not provide any information about the spatial architecture of plant canopy. With the development of fractal theory, a quantitative toot is now available for the investigation of complex objects and shapes such as plant structure. Vegetation structure of corn ( Zea mays L.) and soybean (Glycine max. (L.) Merr.] plants might be affected by the plant population density (low, normal, high) of each crop and corn-soybean intercropping. Skeletonized leaf-off images provided acceptable information to estimate the fractal dimension of the soybean plant 2-dimensionally, using the box-counting method. Fractal dimension varied among soybean treatments, with rankings: low > normal > intercrop > high, in the overall mean and normal ≈ intercrop ≈ low > high, in the slope of time plots. An adjustment of field corn plants to treatments, by changing the orientation of the plane of developed leaves with respect to the row, was observed. Thus, the fractal dimension of corn plant skeletal images from each of two sides, side I (parallel to row) and side 2 (perpendicular to row), was analyzed. On the basis of overall means of fractal dimension, treatments were ranked as: high > normal ≈ intercrop ≈ low for side 1 and intercrop > low ≈ normal > high for side 2. In both cases of soybean and corn plants, leaf area index, plant height and number of leaves (only in case of soybean plant) increased over the experiment for all the treatments, indicating a positive correlation with fractal dimension. In contrast, light penetration decreased during crop development, indicating a negative correlation with fractal dimension. Furthermore, a modified version of the Beer-Lambert equation, in which fractal dimension mu