Morpho-physiochemical and genotypic characterization of rhizobia from chickpea (Cicer arietinum) root nodules

Rhizobia can enhance legume crop productivity, reduce nitrogen fertilizer use and promote sustainable agriculture. This study focused on isolating, identifying and characterizing rhizobia strains from chickpea root nodules. Forty strains were isolated from chickpea root nodules collected from nine districts in Bangladesh, which were cultured on Congo red yeast mannitol agar medium to obtain single colonies and study their morpho-physiological and genetic characteristics. Various physicochemical tests, including gram-staining, bromothymol blue test, temperature, salt and pH tolerance, phosphate solubilization and indole-3-acetic acid (IAA) production tests, were conducted using theisolated strains. These strains formed milky white colonies with spherical convex surfaces with 1.77 to 8.33 mm diameters. Physicochemical results indicated that strains were gram-negative, fast-growing and acid producers. Maximum strains thrived at pH levels 6 to 8, temperatures ranging from 28 to 35 ºC and 5 % sodium chloride (NaCl). Seven strains exhibited strong phosphate solubilization capabilities and 30 % performed better in IAA production. In aseptic conditions, the inoculated plants showed higher dry matter percentage and higher nitrogen concentration in shoot than non-inoculated ones. Nodulation-positive strains possess nifH gene, indicating nitrogen-fixing capability of these strains. High genetic diversity was observed among the studied rhizobial strains, as determined by enterobacterial repetitive intergenic consensus sequence-based fingerprinting and they formed two major groups. Two strains, CRB-20 and CRB-28, were more diverse than others. Rhizobia isolated from different regions varied in morpho-physiological, genetic characters and symbiotic performances. These strains can be used for field trials to assess their suitability for efficient biological nitrogen fixation and growth of chickpeas.