Genetic diversity among rhizobial isolates from field-grown Astragalus sinicus of southern China

The genetic diversity among 204 rhizobial isolates from field-grown Astragalus sinicus collected from 52 ecological different sites of seven southern provinces of China was investigated by using rep-PCR fingerprinting with REP primers and 16S rDNA PCR-RFLP and sequence analyses. Most isolates (78.4%) belonged to different 16S rDNA genotypes from that of Mesorhizobium huakuii type strain CCBAU2609(T). Rep-PCR fingerprinting analysis of 136 randomly chosen isolates categorized 27 REP groups at a similarity level of 60%. Genetically diverse rhizobial strains could be detected at single site, and strains with the same genetic type could be found in different geographic locations. Twelve representative strains were selected for identification using 16S and 23S rDNA analyses, which resulted in four 16S and five 23S rDNA PCR-RFLP genotypes. When both 16S and 23S rDNA PCR-RFLP data were combined together, seven different genotypes were detected among the 12 representative strains, and no strain shared a genotype with the M. huakuii type strain. Both 16S and 23S rRNA genes analyses clustered the 12 representative stains within the Mesorhizobium branch. The 16S rRNA results obtained by PCR-RPLP were confirmed by sequencing the first 600 bp of the 16S rRNA genes.