Molecular and Functional Characterization of Pea-Nodulating Rhizobia Isolated from Southern Rajasthan

Rhizobium species are recognized as efficient nitrogen-fixing bacteria that contribute to sustainable agriculture. A total of nineteen rhizobial strains were obtained from pea nodules collected from Udaipur, Banswara and Dungarpur, southern Rajasthan (India), a geographically under-characterized pea-growing region and were initially identified based on their morphological and biochemical characteristics. In multiple PGPR studies, eleven isolates solubilized phosphate, 14 produced ammonia, 17 produced HCN, 11 produced siderophores, 13 solubilized potassium, 15 solubilized zinc, and 12 solubilized silica, and two strains were found to be the best strains for GA3 production. In controlled nodulation experiments, all inoculated plants formed nodules, the in vitro nodulation test strains reported affirmative results for shoot length, root length, chlorophyll content, and number of nodules in pea plants. The most effective rhizobial strains were identified using 16S rDNA amplification, and their molecular identities were revealed. Among them, R 10.2 and R 12.2 were found to be R. indicum (accession PZ655056) and R. laguerreae (accession PZ655057), respectively. The study identifies native pea-associated rhizobial resources with potential for further bioinoculant development; however, for commercial production, further field-level studies can be helpful to validate their superior nodulation, plant growth promotion, and multiple PGPR activities.