Characterization of rhizobia for beneficial traits that promote nodulation in legumes under abiotically stressed conditions.

This article focuses on the phenotypic and phylogenetic characterization of 40 rhizobia strains isolated from root nodules of indigenous and exotic legumes in South Africa and other countries, with an emphasis on their tolerance to abiotic stresses relevant to sustainable agriculture. Using multilocus sequence analysis of genes including 16S rRNA, recA, nodA, nodC, acdS, and exoR, the isolates were identified as belonging to the genera Sinorhizobium, Bradyrhizobium, Rhizobium, Mesorhizobium, and Aminobacter, exhibiting significant variation in tolerance to temperature, salinity, acidity/alkalinity, and heavy metals. The study highlights that several isolates, particularly those nodulating Vigna unguiculata, showed strong tolerance to multiple abiotic stresses and possessed beneficial genes such as acdS (encoding ACC deaminase) and exoR (involved in exopolysaccharide synthesis), which are linked to stress mitigation and effective nodulation. These findings provide baseline molecular and phenotypic data to support the selection and development of elite rhizobia inoculants for legume production under climate-affected and stress-prone environments, especially in sub-Saharan Africa.