Evaluation and characterization of QTL controlling seed composition in soybean and breeding for resistance to sudden death syndrome of soybean

The first quantitative trait locus (QTL) mapping study in soybean (Glycine max) was published over twenty years ago. Since then numerous QTL mapping studies have been performed for most traits of economic interest within the soybean research community. Though many putative QTL regions have been identified follow up breeding work that is necessary for the practical use of these regions within breeding programs is lacking. In this research, follow up breeding work is performed on QTL controlling seed composition in soybean and QTL conferring resistance to sudden death syndrome of soybean. In chapter 2, a genetic locus conferring pink flowers, the wp locus, and a confirmed seed protein concentration QTL located on chromosome 20 are evaluated in four genetic backgrounds for associations with the traits: protein concentration, oil concentration, yield, plant height, seed size, plant maturity and lodging. The chromosome 20 QTL increased protein concentration and plant height while the QTL decreased oil concentration, yield, seed size, and days to maturity consistently across environments and genetic backgrounds. The wp locus increased protein concentration, seed size, and days to maturity but decreased oil concentration, yield, and plant height variably across genetic backgrounds and environments. Significant associations between the wp locus and the tested traits were most frequently observed in the Loda background. Significant interactions between the wp locus and the chromosome 20 QTL were rarely detected as the two genomic regions generally acted independent of each other for the traits tested. Lines containing high protein alleles at both loci often had the largest increase in protein concentration but also had the largest decreases in oil concentration and seed yield. The wp locus was generally associated with a greater yield decrease and a smaller increase in protein concentration than the chromosome 20 QTL. The wp locus appears to be a poor candidate for use within a marker assisted selection program because of the inconsistent increases in protein concentration and the consistent, large decreases in seed yield associated with it. In chapter 3, the chromosome 20 protein QTL is evaluated in four genetic backgrounds across ten environments for associations with the traits: protein concentration, oil concentration, yield, plant height, seed size, plant maturity and lodging. Protein concentration and oil concentration were significantly associated with the QTL across genetic backgrounds and environments. The size of the QTL effect varied across environments. In the maturity group IV genetic backgrounds, significant increases in the size of the QTL effect were observed when the iii populations were grown in more southern locations. The magnitude differences observed for seed oil concentration were significantly associated with temperature and day length. Seed yield was variably associated with the QTL across genetic backgrounds and environments. This result suggests that environment and genetic background may influence the size and magnitude of the associated decrease in seed yield that is often observed with an increase in seed protein concentration for this QTL. In chapter 5, a previously identified QTL conferring resistance to sudden death syndrome (SDS) from the cultivar Ripley and located on chromosome 19 was tested and confirmed (p