Utilizing True Breeding Values to Explore Soybean Germplasm for Drought and Agronomic-Related Traits.

Selection of parents is one of the main decisions faced by plant breeders. True breeding values (TBVs) can be a guide in selecting parental genotypes in a breeding programs. True breeding values were calculated using the results from genome wide association studies (GWAS) of drought related traits including canopy temperature (CT), canopy wilting (CW), carbon isotope ratio (δ¹³C), oxygen isotope ratio (δ¹⁸O), and nitrogen derived from atmosphere (NDFA), measured from our research along with several traits from GRIN including seed shattering (SS), height (Ht), lodging (LG), oil (OL), protein (PR), seed weight (SW), stem termination (ST), and yield (Y). Accessions (373) used for GWAS were considered a training set and the rest of the accessions in the germplasm collection were considered a validation set. Over 14,000 accessions from the germplasm collection have phenotypic data for agronomic traits. From phenotyped accessions, two traits, ST and SW, which are not affected greatly by environmental variation and sampling error, were used to check the accuracy by correlating actual phenotype and TBVs. We observed highly significant positive correlations between actual phenotype and TBVs for ST (r = 0.60) and SW (r = 0.56). Based on TBVs, we found that the expected correlations between agronomic traits such as yield were significantly correlated with height (r = 0.50) and oil (r = 0.56), and negatively correlated with protein (r = -0.23), early seed shattering (r = -0.68), late seed shattering (r = -0.48), and seed weight (r = -0.37). Similarly, we observed the expected correlations between drought-related traits including a positive correlation between CW and CT (r = 0.60), and a positive correlation of δ¹³C with CW (r = 0.53) and CT (r = 0.67). Extreme drought-tolerant accessions were identified, which can be used as potential parents in a breeding program.