Diversity of a Soybean Bradyrhizobial Population Adapted to an Indian Soil

Soybean (Glycine max) is an introduced crop in India. Over the years it has been regularly inoculated with indigenous rhizobia. In this study genetic diversity has been studied at a site where soybean has been regularly grown with inoculation. Rhizobia were plant trapped using soybean varieties as host, and fingerprinted using BOX-PCR. BOX-PCR genomic fingerprints of 69 isolates from the nodules of 4 soybean varieties Pusa22, Bragg, PK1041 and PK1142 showed a high level of genetic diversity. The population profiles of the 69 isolates clustered them into 10 groups. Root nodule isolates from the four varieties were Bradyrhizobium japonicum types, growing in 4–7 days with typical colonies which were found to be genetically distinct from the USDA and SEMIA strains of B. japonicum and B. elkanii. Also the genotype of the host plant seemed to be one of the factors determining the diversity. The high diversity could be attributed both to lateral transfer of genetic material between inoculant and indigenous strains and to genomic rearrangements during the adaptation to the Indian soils.