Identification of QTLs for Single Seed Weight and Their Relationships to Other Seed Yield Components in Soybean

Single seed weight (SSW), or seed size of soybean is a determinant of seed quality, and a considerably wide variation of SSW is used for traditional food products in Japan. SSW is also a component of seed yield, and thus small seed cultivar seems to be inferior to large seed cultivar in seed yield. However, the seed yield of small seed cultivar is comparable to that of large seed cultivar. In order to examine how small seed cultivar offsets the impact of decreased SSW on yield, we applied quantitative trait locus (QTL) analysis for SSW and other seed yield components, number of seeds per pod (NSP) and number of pods per plant (NPP), using three recombinant inbred populations derived from crosses between small seed and standard cultivars. SSW of the small seed and the standard cultivars ranged from 128～185 mg and 313～400 mg, respectively. Composite interval mapping detected a total of five stable QTLs associated with SSW in the three populations. Two of them were common in more than one population, and they seemed to be identical to qSw17-1 and Ln. Two QTLs for SSW were located near the QTLs for NSP, while the other three QTLs for SSW were located near the QTLs for NPP. Small seeded allele at each QTL linked to the allele increasing NSP or NPP, suggesting that the decrease of SSW could be complemented with the increase of either NSP or NPP.