Phenotypic and molecular characterization of microsymbionts associated with Tephrosia strigosa in the central Aravalli region

Legume–rhizobia symbiosis is central to sustainable agriculture due to its role in biological nitrogen fixation. However, rhizobial diversity in ecologically significant regions such as the Aravalli range remains insufficiently explored. This study investigates the microsymbiont diversity associated with Tephrosia strigosa , a legume species for which no prior symbiotic data are available from this region. A total of 83 root nodule bacterial (RNB) strains were isolated from multiple sites across the Central Aravalli range and assessed for their phenotypic and genetic diversity. Based on BOX-PCR fingerprinting, 30 isolates were subjected to 16S rRNA gene sequencing and phylogenetic analysis. Analysis of 16S rRNA gene sequence similarity revealed that 23 RNB isolates were related to rhizobial genera ( Sinorhirobium and Rhizobium ), while 7 belonged to non-rhizobial strains. Phylogenetic analysis indicated that 15 isolates clustered within the genus Sinorhizobium and were closely related to Sinorhizobium aridi , S. mexicanus , S. kostiense , S. adhaerens and S. terangae . Eight isolates clustered with Rhizobium species, including Rhizobium pongamiae , R. bangladeshense , R. pakistanense and R. oryzihabitans , however, among these two isolates (TS3 and TS16) closely related to R. oryzihabitans failed to nodulate their original host in the host authentication test, indicating their non-symbiotic nature. Overall, the phylogenetic structure of RNB isolates associated with T. strigosa demonstrates that nodulation is primarily mediated by Sinorhizobium and Rhizobium species, with a clear dominance of Sinorhizobium . This dominance suggests that Sinorhizobium spp. serve as the primary microsymbionts of native legumes in the Central Aravalli region. These findings contribute to a deeper understanding of rhizobial diversity, biogeography, and host specificity in an ecologically important yet understudied ecosystem.