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Studies of Phylogeny, Symbiotic Functioning and Ecological Traits of Indigenous Microsymbionts Nodulating Bambara Groundnut (Vigna subterranea L. Verdc) in Eswatini 


Rhizobial microsymbionts of grain legumes are ubiquitous in soils and exhibit a wide range of diversity with respect to colony morphology, genetic variability, biochemical characteristics, and phylogenetic relationships. This study assessed the phylogenetic positions of rhizobial microsymbionts of Bambara groundnut from Eswatini exhibiting variations in morpho-physiology, adaptive characteristics, and N2-fixing efficiency. The isolates’ ERIC-PCR profiles revealed the presence of high genetic variation among them. These test isolates also exhibited differences in pH tolerance and IAA production. Multilocus sequence analysis based on the 16S rRNA, atpD, glnII, gyrB, and recA gene sequences of representative test isolates closely aligned them to the type strains of Bradyrhizobium arachidis, B. manausense, B. guangdongense, B. elkanii, and B. pachyrhizi. However, some isolates showed a high divergence from the known reference type strains, indicating that they may represent species yet to be properly characterized and described. Functional characterization in the glasshouse revealed that most of the isolates from the contrasting Agro-ecologies of Eswatini were efficient in N2 fixation, and therefore elicited greater stomatal conductance and photosynthetic rates in the homologous Bambara groundnut. Of the 75 isolates tested, 51% were more effective than the commercial Bradyrhizobium sp. strain CB756, with relative symbiotic effectiveness ranging from 138 to 308%. The findings of this study indicated that the analysis of housekeeping genes and functional traits of Bambara-nodulating microsymbionts can provide a clear view for understanding and predicting rhizobial community structure across environmental gradients.

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We are grateful to the South African Research Chair in Agrochemurgy and Plant Symbioses, the National Research Foundation, and the Tshwane University of Technology for financial support to FDD’s research, and for a SARCHI Chair master bursary to STD. We also acknowledge Malkerns Research Station, Department of Grain Legumes in Eswatini for providing us seeds and land for the experiment.

Data Accessibility

The nucleotide sequences of all test genes were submitted in the NCBI Genbank database under accession numbers MT522377 - MT522397 (16S rRNA); MT514533 - MT514555 (atpD); MT514556 - MT514581 (glnII); MT514582 - MT514607 (gyrB); MT514634 - MT514658 (recA); and MT514608 - MT514633 (nifH).

Author information




S.K.J and F.D.D conceived the ideas and developed the research questions. S.T.D. executed the research. M.M. recorded gas exchange data. S.K.J and S.T.D. analyzed the data and led the writing of the manuscript. All authors gave their final approval for publication.

Corresponding authors

Correspondence to Sanjay K. Jaiswal or Felix D. Dakora.

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The authors declare that they have no conflict of interest.

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Dlamini, S.T., Jaiswal, S.K., Mohammed, M. et al. Studies of Phylogeny, Symbiotic Functioning and Ecological Traits of Indigenous Microsymbionts Nodulating Bambara Groundnut (Vigna subterranea L. Verdc) in Eswatini . Microb Ecol 82, 688–703 (2021).

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  • Genotypes
  • Agro-ecosystem
  • Housekeeping and symbiotic genes
  • Horizontal gene transfer
  • PCA
  • Correlation