Symbiotic effectiveness and ecologically adaptive traits of native rhizobial symbionts of Bambara groundnut (Vigna subterranea L. Verdc.) in Africa and their relationship with phylogeny

• Published in: Scientific reports 2019-09, Vol.9 (1), p.12666-17, Article 12666
• Main Authors: Ibny, Fadimata Y. I., Jaiswal, Sanjay K., Mohammed, Mustapha, Dakora, Felix D.
• Format: Article
• Language: English
• Subjects: 45/22; 45/23; 45/77; 631/326/171/1818; 631/449/2676/2678; Adaptation, Physiological; Bradyrhizobium; Calcium phosphates; Drought; Drought resistance; Drug Resistance, Microbial; Genes, Bacterial; Genes, Essential; Geography; Humanities and Social Sciences; Indoleacetic acid; Kanamycin; Legumes; multidisciplinary; NifH gene; Phenotype; Phosphates - metabolism; Photosynthesis; Phylogenetics; Phylogeny; Plant Root Nodulation; RecA protein; Regression Analysis; Rhizobium - genetics; Rhizobium - isolation & purification; Rhizobium - physiology; RNA, Ribosomal, 16S - genetics; Root Nodules, Plant - microbiology; rRNA 16S; Salinity; Science; Science (multidisciplinary); Sodium chloride; Soil - chemistry; Soil microorganisms; Solubility; South Africa; Streptomycin; Symbionts; Symbiosis; Tryptophan; Vigna - anatomy & histology; Vigna - growth & development; Vigna - microbiology; Vigna subterranea
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-019-48944-1

Bambara groundnut ( Vigna subterranea L. Verdc.) is an indigenous, drought-tolerant, underutilized African food legume, with the ability to fix atmospheric N 2 in symbiosis with soil bacteria called rhizobia. The aim of this study was to assess the morpho-physiological, symbiotic and phylogenetic characteristics of rhizobia nodulating Bambara groundnut in Ghana, Mali and South Africa. The morpho-physiologically diverse isolates tested were also found to exhibit differences in functional efficiency and phylogenetic positions. Based on Enterobacterial Repetitive Intergenic Consensus (ERIC)-PCR banding patterns, the isolates were grouped into eight major clusters. The concentrations of Ca, Na and K in soils had a significant (p ≤ 0.01) effect on the distribution of rhizobia. Though many isolates were symbiotically very effective, the effectiveness index varied markedly (p ≤ 0.05) among them. Moreover, the isolates also exhibited tolerance to a wide range of NaCl (0.5–7%), streptomycin (50–500 µg.ml −1 ), and kanamycin (25–150 µg.ml −1 ) concentrations. Additionally, these isolates could produce 0.02 to 69.71 µg.ml −1 of indole-3-acetic acid (IAA) in tryptophan-supplemented medium, as well as solubilize tri-calcium phosphate. Phylogenetic analysis of these rhizobial isolates using 16S rRNA, atpD , glnII , gyrB , recA and symbiotic ( nifH and nodC ) gene sequences revealed distinct and novel evolutionary lineages related to the genus Bradyrhizobium , with some of them being very close to Bradyrhizobium vignae , B . kavangense , B . subterraneum , B . elkanii and B . pachyrhizi .