Phylogeny and symbiotic effectiveness of indigenous rhizobial microsymbionts of common bean (Phaseolus vulgaris L.) in Malkerns, Eswatini.

In most legumes, the rhizobial symbionts exhibit diversity across different environments. Although common bean (Phaseolus vulgaris L.) is one of the important legumes in southern Africa, there is no available information on the genetic diversity and N2-fixing effectiveness of its symbionts in Malkerns, Eswatini. In this study, we assessed the phylogenetic positions of rhizobial microsymbionts of common bean from Malkerns in Eswatini. The isolates obtained showed differences in morpho-physiology and N2-fixing efficiency. A dendrogram constructed from the ERIC-PCR banding patterns, grouped a total of 88 tested isolates into 80 ERIC-PCR types if considered at a 70% similarity cut-off point. Multilocus sequence analysis using 16S rRNA, rpoB, dnaK, gyrB, and glnII and symbiotic (nifH and nodC) gene sequences closely aligned the test isolates to the type strains of Rhizobium muluonense, R. paranaense, R. pusense, R. phaseoli and R. etli. Subjecting the isolates in this study to further description can potentially reveal novel species. Most of the isolates tested were efficient in fixing nitrogen and elicited greater stomatal conductance and photosynthetic rates in the common bean. Relative effectiveness (RE) varied from 18 to 433%, with 75 (85%) out of the 88 tested isolates being more effective than the nitrate fed control plants.