Diversity and field site variation of indigenous populations of soybean bradyrhizobia in Japan by fingerprints with repeated sequences RSα and RSβ

Two hundred and thirteen isolates of soybean bradyrhizobia indigenous to six field sites in Japan were characterized using hybridization probes RSα, RSβ, nifDK and hupSL from Bradyrhizobium japonicum and indole-3-acetic acid production to clarify diversity and endemism of their population structures. Significant diversities and site-dependent variations were observed in terms of Bradyrhizobium species, hup genotype and fingerprints with repeated sequences RSα and RSβ. The fingerprints at one site with no history of soybean cultivation were less diverse than those at other sites. Even within the populations of B. japonicum hup^- isolates, which were commonly indigenous to the six field sites, several RSα copies clustering around nif genes were highly conserved. The results suggest that soybean bradyrhizobia may be diversified in individual fields as associated with host plants and local soil conditions.