Diversity of indigenous Bradyrhizobium strains isolated from three different Rj-soybean cultivars in terms of randomly amplified polymorphic DNA and intrinsic antibiotic resistance

Diversity of indigenous Bradyrhizobium strains isolated from three different Rj-genotypes of soybean (Glycine max L. Merrill) cultivars which was investigated based on randomly amplified polymorphic DNA (RAPD) fingerprinting, intrinsic antibiotic resistance (IAR) and indole-3-acetic acid (IAA) production, was correlated with preference for and compatibility with Rj-genotypes of soybean cultivars for nodulation. Seventeen strains from Akishirome (non-Rj), 22 strains from CNS (Rj(2)Rj(3)) and 19 strains from Fukuyutaka (Rj(4)) were isolated. All of the isolates from Akishirome and Fukuyutaka and 8 isolates from CNS formed effective nodules on each Rj-soybean cultivar, while 14 isolates from CNS did not form effective nodules on Fukuyutaka after inoculation under sterile conditions. The 14 isolates from CNS produced IAA. Cluster analysis based on RAPD fingerprinting using 5 primers revealed the presence of two clusters, A and B. Cluster B contained B. elkanii USDA 61, USDA 76 and indigenous bradyrhizobia of 14 isolates from CNS showing IAA production and cluster A contained B. japonicum USDA 110, A1017 and indigenous bradyrhizobia not showing IAA production. Indigenous bradyrhizobia strains in cluster A were further divided into 3 subclusters, A-1, A-2, and A-3 different from the cluster of B. japonicum USDA 110 and A1017. Identity of subclusters between RAPD fingerprinting and IAR phenotype was not completely obtained. Subclusters A-1, A-2, and A-3 consisted mainly of isolates from Akishirome, CNS, and Fukuyutaka, respectively. Preferences of bradyrhizobia for Rj-soybean cultivars for nodulation may be estimated by genetic diversity at the strain level.