The genetic diversity, symbiotic efficiency, and drought resilience of rhizobia associated with mung bean in central and northern regions of Afghanistan.

Rhizobial inoculants are effective tools for maximizing legume productivity and ensuring the sustainability of legume-based systems. The bacterial diversity and symbiotic efficiency of rhizobia associated with mung bean (Vigna radiata L.) root nodules in Afghanistan are unclear. Hence, mung beans were inoculated with soil from Afghanistan, and 50 rhizobial strains were isolated. Based on colony morphology and growth conditions, eight isolates were selected for physiological and genetic characterization, abiotic stress, and plant tests. 16S rRNA and multilocus sequence analysis of multiple housekeeping genes (rpoB, atpD, glnII, and recA) classified the isolates of KM5, KM7, KaM1, and KM12 as taxonomically similar to Bradyrhizobium yuanmingense, BgM3, KaM6, and KaM14 to Ensifer psoraleae and BgM20 to Bradyrhizobium liaoningense. The BgM20 and KaM1 strains of Bradyrhizobium exhibited better responses to abiotic stress (heat and salt) and produced the highest levels of indole-3-acetic acid and biofilm, respectively. In contrast, BgM3 and KaM14 from the Ensifer group tolerated a low pH of 5, with BgM3 showing the highest solubilization of phosphorus and potassium. The KM12 and BgM20 isolates showed more consistent results in terms of Soil–Plant Analysis Development (SPAD) value, shoot and root dry weights, nitrogen fixation, and mung bean growth under drought stress. It was found that Bradyrhizobium and Ensifer are the dominant genera of mung bean root-associated rhizobia in Afghan soil, and promising isolates were screened, which have practical potential for mitigating drought stress, improving nitrogen fixation activity, and enhancing mung bean yield under water scarcity and drought conditions in Afghanistan.