Mutant alleles are highly accumulated in early planting-adaptable Japanese summer type soybeans.

To avoid crop failure because of climate change, soybean ( (L.) Merrill) cultivars adaptable to early planting are required in western Japan. Because current Japanese cultivars may not be adaptable, genetic resources with high early-planting adaptability, and their genetic information must be developed. In the present study, summer type (ST) soybeans developed for early planting were used as plant materials. We examined their phenological characteristics and short reproductive period as an indicator of early planting adaptability and performed genetic studies. Biparental quantitative trait loci (QTL) analysis of a representative ST cultivar revealed a principal QTL for the reproductive period duration on chromosome 11. The results of resequencing analysis suggested that circadian clock-related (soybean orthologue of ) is a candidate QTL. Additionally, all 25 early planting-adaptable germplasms evaluated in this study possessed mutant alleles in , whereas 15 conventional cultivars only had wild-type alleles. These results suggest that mutant alleles in are important genetic factors in the high adaptability to early planting of these soybeans, and thus, these alleles were acquired and accumulated in the ST soybean population.