Genetic relatedness of Bradyrhizobium japonicum field isolates as revealed by repeated sequences and various other characteristics.

Forty-nine isolates of Bradyrhizobium japonicum indigenous to a field where soybeans were grown for 45 years without inoculation were characterized by using four DNA hybridization probes from B. japonicum. nifDK-specific hybridization clearly divided the isolates into two divergent groups. Diversity in repeated-sequence (RS)-specific hybridization was observed; 44 isolates derived from 41 nodules were divided into 33 different RS fingerprint groups. Cluster analysis showed that the RS fingerprints were correlated with the nif and hup genotypes. We found multiple bands of RS-specific hybridization for two isolates that differed from the patterns of the other isolates. These results suggest that RS fingerprinting is a valuable tool for evaluating the genetic structure of indigenous B. japonicum populations.