Abstract

• Rhizobium is an important microorganism for the environment because of its nitrogen-fixing ability when in symbiotic relationship with plants (mainly legumes). The present study was conducted to isolate and characterize the rhizobia from the root nodules of Vigna mungo (L.) Hepper (Black gram) and Vigna unguiculata subsp. unguiculata (L.) Walp. (Cowpea). The experiment was performed at the Microbiology Laboratory, Department of Botany, University of Yangon in 2022. The two isolated bacterial strains were given named as (PVMR from black gram.) and (PVUR from cowpea). Both isolates on YEMA medium showed white, circular, entire margin, convex elevation, produced mucoid and translucent colonies. The microscopic examination revealed that both isolates are gram negative and rod shaped. In two bacterial strains: PVMR was identified as Rhizobium sp. and and PVUR was identified as Bradyrhizobium sp. based on the results of authentication test. Biochemical characterization of both strains showed positive reaction with catalase, methyl red test, nitrate reduction, and urea test, while negative reaction was observed in citrate utilization, gelatin hydrolysis, hydrogen sulphide production, indole, Triple Sugar Iron Agar (TSI), and Vogas Proskauer test. In antibiotic resistance test, PVMR strain resistance to only Penicillin and sensitive to Amoxicillin, Chloramphenicol, Tetracycline, whereas, PVUR strain resistance to Amoxicillin, Chloramphenicol, Penicillin but sensitive to Tetracycline. The plant inoculation assay indicated the improvement of plant growth and nodules formation in the treatments inoculated with two rhizobial isolates compared with noninoculation treatments.