[Genetic diversity of rhizobia isolated from common legumes in the Karst area. Northwest Guangxi].

Legumes, with a strong resistance to the adverse environmental conditions, are pioneer plants in degraded habitats, and play an important role in ecosystem restoration. In this study, the nodulation characteristics of 24 legumes were surveyed in the Karst area of Northwest Guangxi. A total of 39 nodule samples were collected from 15 legumes, the DNA was extracted and the 16S rDNA and nifH gene were amplified. A phylogenetic tree was then constructed to analyze the genetic diversity of rhizobia. The results showed that 15 legumes were nodulated, of which 14 belonged to the Papilionoideae, one to the Mimosaceae, and none to the Caesalpinoideae. No nodules were found on some legumes that were reported as nodulated, which might result from soil water stress in Karst. BLAST result and phylogenetic analyse indicated that most of the legumes were associated with rhizobia that belonged to the genus Bradyrhizobium, with the exception of two samples from Callerya nitida that were associated with the genus Mesorhizobium. In the phylogenetic tree, the sequences obtained from the same plot or the sequences from the same host species clustered together in most cases. This finding suggested that host selection and the ecological environment are the major factors that influence the genotype of rhizobia.