Soybean improvement strategies: Insect-pollinator attraction and genetic resistance to whitefly and to brown stem rot

Soybean [Glycine max (L.) Merr.] is one of the most important plants cultivated worldwide. It is a source of oil and protein and is used for livestock feed, human food, and also for industry. Over the years, yield increases have been accomplished due to genetic improvement and enhancement of agronomic practices. The purpose of this research project was to investigate different strategies for soybean improvement, from genetic resistance to biotic stresses, to surveying perennial wild relatives for insect-pollinator attraction characteristics that could be useful in hybrid seed production in the cultivated species. The first objective of this research was to determine if four plant introductions (PI) from south-central China, identified as resistant to the disease brown stem rot (BSR), represented new sources of BSR resistance genes. Four plant introductions were crossed to a BSR-susceptible cultivar to develop F2 populations. Each segregating population and the parental lines were screened for BSR resistance in growth chamber conditions. The F2:3 individual plants of each population were tested with the simple sequence repeat (SSR) markers that map closely to BSR resistance quantitative trait loci (QTL) on chromosome 16. One population showed non-association with SSR Satt547. This could be indicative of the presence of a new BSR resistance gene in PI 594637. The second objective of this study was to identify QTL for whitefly (Bemisia tabaci) resistance in soybean. Two F2 segregating populations, derived from crosses between whitefly resistant lines `Cajeme\u27 and \u27Corsoy 79\u27 and the susceptible line `Williams 79\u27, were developed to determine inheritance of resistance to B. tabaci. Parental lines were screened with SSR evenly distributed across the soybean genome. Segregating F2 populations and parents were evaluated for whitefly infestation. Results indicate that whitefly resistance is a polygenic trait, controlled by QTL on different chromosomes. The significant QTL detected in this study were located on chromosomes 12, 18, and 19 The third objective of this research was to determine nectar composition (sucrose, glucose, fructose, and total carbohydrates) and flower size of greenhouse-grown wild perennial plants. Genetic variation for nectar sugar composition, and flower size was found across all perennial Glycine species. Sugar proportions varied across species and on average, the nectar was dominated by sucrose (62.5%), followed by fructose (25.1%) and glucose (12.4%). Multivariate analysis was used to detect groups of species with similar nectar sugar characteristics. Two groups were detected, one group was formed by the two species G. falcata and G. canescens, which were similar in nectar sugar concentration and composition. The other 17 species conformed the second group. The information gained from the floral nectar composition of the wild perennial species will guide research for nectar composition-outcrossing associations in the cultivated species