BIOCHEMICAL AND MOLECULAR CHARACTERIZATION OF NATIVE Bradyrhizobium STRAINS ISOLATED FROM PIGEON PEA ROOT NODULES OF EASTERN INDIA

Abstract

Pigeon pea (Cajanus cajan) is a major legume in Eastern India, contributing to the nutritional security and soil fertility through symbiosis with Bradyrhizobium spp. However, the efficiency of native strains under local conditions remains poorly understood. This study aimed to isolate, characterize, and identify native isolates from pigeon pea root nodules, and to evaluate their symbiotic efficiency and plant growth-promoting traits. Fourteen bacterial isolates were obtained, of which 12 belonged to Bradyrhizobium spp., while isolates S5 and S15 were identified as Pseudomonas azotoformans and Paenibacillus amylolyticus, respectively. All Bradyrhizobium isolates tested positive for catalase, oxidase, nitrate reductase, and nitrogenase activity. Isolates S9, S3, S6, S13, and S1 showed significantly higher nitrogenase activity as compared to the other isolates. Plant growth-promoting assays revealed phosphate solubilisation, zinc solubilization, and potassium solubilization in ten, eight and five isolates, respectively. Eleven isolates produced siderophores and all of these synthesized indole-3-acetic acid (IAA). Notably, isolate S6 (Bradyrhizobium yuanmingense) exhibited all PGPR traits and high nitrogenase activity, identifying it as the most promising isolate. Isolates S3, S1, and S9 also demonstrated strong potential. These results demonstrated the value of efficient native isolates as region-specific bioinoculants for pigeon pea, reducing reliance on chemical fertilizers and promoting sustainable agriculture. © 2025, ACS Publisher. All rights reserved.