Sokichi Shiro

By Sokichi Shiro and Yuichi Saeki

Some soybean varieties harbor the Rj genes, which regulate nodulation by preventing infection and nodulation by specific rhizobial strains. Soybean genotypes carrying several Rj genes may enhance the occupancy of useful bradyrhizobia, which exhibit potent nitrogen fixation ability and exhibit nodulation compatible with the Rj genotype of soybean. Therefore, we bred soybean lines presenting the Rj2Rj3Rj4 genotype by crossing the Japanese cultivars “Bonminori” (Rj2Rj3) and “Fukuyutaka” (Rj4) and studied the effects of Rj gene accumulation on productivity. To investigate yield components, three Rj gene-accumulated soybean lines (B × F − E, B × F − M, and B × F − L) and three soybean cultivars (“Enrei,” “Sachiyutaka,” and “Fukuyutaka”) were cultivated in 2016 and 2017. Pod and seed number and yield were the highest in B × F − M. The occupancy rate of isolates in cluster of Bradyrhizobium diazoefficiens USDA 110T carrying the hydrogen uptake genes tended to be lower in the Rj2Rj3Rj4 soybean lines than in “Sachiyutaka” and “Fukuyutaka.” Additionally, the occupancy rate of this cluster was positively correlated with yield. Therefore, promoting infection by bradyrhizobial strains carrying the hydrogen uptake genes may improve soybean productivity. Moreover, the Rj2Rj3Rj4 genotype of soybean may be inoculated with B. diazoefficiens USDA 110T, which is not restricted by the Rj2 gene, to further enhance soybean productivity.

Part of the book: Soybean