Putative QTLs Affecting Seed Protein Concentration in Two Recurrent Selection Populations in Soybean.

Three cycles of recurrent selection for seed protein concentration were evaluated in two different soybean populations. One population (designated UP2) was developed from seven unadapted plant introductions selected for their high seed protein concentration from the USDA Soybean Germplasm collection.  The second population (designated UP3) was developed using eight high-yield cultivars and experimental lines.  Previous evaluation of the parent lines from each cycle showed significant increases in seed protein concentration of nearly 14 g kg^-1 cycle^-1 in both populations.  The objective of this research was to evaluate allele frequencies for polymorphic SSR markers in the parent lines of the Cycle 0, Cycle 2, and Cycle 3 populations from both UP2 and UP3. Significant directional changes in allele frequencies were detected in both populations over cycles of selection for increased seed protein concentration. Several SSR loci exhibiting significant associations with increased protein content map near previously identified QTL in both populations.  There were 7 putative QTL associated with seed protein content identified on 7 different LGs in the UP3 population, and up to 14 putative QTL on 13 different LGs in the UP2 population.  Significant SSR marker regions on LG B1 and D1b were common between the populations.  The previously identified QTL on LG I was significant only in the UP2 population, but not in the UP3 population which was developed from elite experimental lines and cultivars.  Some new and unique QTL also were identified in both populations.