[Genetic diversity and phylogeny of rhizobia isolated from peanut (Arachis hypogaea)]

Forty three rhizobium strains isolated from peanut (Arachis hypogaea) and 15 reference strains from other genus and species were analyzed by the method of 16S rRNA RFLP, 16S rRNA sequencing and 16S-23S IGS PCR RFLP. The results of the 16S rRNA RFLP shown that 43 strains tested were all ascribed to the genus of Bradyrhizobium phylogenetically. Strains tested were adjacent to the B. japonicum and far from B. elkanii 16S rRNA genotype. The genotypes generated by the 4 restriction endonucleases, Mbo I, Dde I, Hae III and Msp I, were same as the representatives of B. japonicum. The dendrogram generated by 16S rRNA sequence and Neighbor-joining method shown that peanut rhizobia clustered into the subcluster represented by B. japonicum and B. liaoningense, were more close to B. liaoningense genetically, and the sequence difference between them was less than 1%. High sequence similarity was also determined between B. liaoningense and B. japonicum. JZ1, representative strain of peanut rhizobia were systematically far from the B. elkanii, and the sequence divergence about 2%. The results from IGS RFLP analysis indicated that although they were phylogenetically close to B. japonicum and B. elkanii, peanut rhizobia forming an independent group at the similarity of 71% could be further divided into four subgroups, A, B, C and D. Subgroup A consisted of strains from different region, subgroup B was composed of strains from Wuchang, Qianjiang and Jingzhou, subgroup C was mainly composed of strains from Jingzhou and starins of subgroup D mainly from Neijiang. Reference strains from B. japonicum and B. elkanii were independently clustered into the subgroup E at the similarity of 71%. The geographical factor effect on genetic diversity of rhizobia was found.