Genetic and environmental factors regulating soybean reproductive stages and their transitions

The reproductive stage of soybean is influenced by the effect of genotype, environment, and their interactions. While days to flowering and days to full maturity have been studied, a systematic and comprehensive study that investigates the variation in days to each stage and the role of maturity-related genes and environmental variables is lacking. Therefore, we studied 508 unique accessions from the USDA germplasm collection from maturity group 0-IV, and a set of 67 near-isogenic lines differing for maturity-related genes. Field experiments and evaluations were conducted in central Iowa, USA. The days to each of the reproductive stages, R1-R8, were recorded. We report considerable variation in the duration of reproductive growth stages between flowering and maturity, which is largely explainable by known flowering and maturity genes as well as environmental variables, day length, and growing degree days. Besides the known maturity-related genes E1, E2, and Dt1, we identified two novel SNPs, such as Glyma.01G180600 and Glyma.10G221300, as potential targets for genetic regulation of reproductive stages. We also captured two other loci, Glyma.08G216800 and Glyma.04G088100 for day length and growing degree days, respectively, that revealed dynamic regulation of environmental gradients on the reproductive stages. Furthermore, we developed a random forest-based genetic maturity model that can predict genetic and environmental effects across a wide range of genotypes. This study broadens the understanding of the factors that contribute to reproductive development, which will help to develop cultivars that combine the optimal combinations of stage durations for a higher seed yield and enhanced resilience.