Assessment of molecular diversity in chickpea (Cicer arietinum L.) rhizobia and structural analysis of 16S rDNA sequences from Mesorhizobium ciceri.

Molecular diversity studies of 19 rhizobia isolates from chickpea were conducted using simple sequence repeats (SSR) and 16S rDNA-RFLP markers. Phenotypic characterization with special reference to salinity and pH tolerance was performed. These isolates were identified as different strains of Mesorhizobium, Rhizobium, Bradyrhizobium, and Agrobacterium. Twenty SSR loci of Mesorhizobium ciceri, distributed across the other rhizobial genome, clearly differentiated 19 rhizobial isolates. Analogous clustering supported the results of 16S rDNA sequence-based phylogeny. Analysis of the 16S rDNA sequences from M. ciceri strains revealed that nucleotide variables (signature sites) were located at 20 different positions; most of them were present in the first 820 bp region from 5' terminal. Interestingly, 14 signature sites were located in two main regions, the variable region V1 (nt 527-584), and variable region V2 (nt 754-813). The secondary structure and minimal free energy were determined in these two regions. These results will be useful in characterizing the micro-evolutionary mechanisms of species formation and increase understanding of the symbiotic relationship.