Abstract
Bambara groundnut (Vigna subterranea L. Verdc.) is an indigenous, drought-tolerant, underutilized African food legume, with the ability to fix atmospheric N2 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.
Highlights
IntroductionWith the ability to fix atmospheric N2 in symbiosis with soil bacteria called rhizobia
African food legume, with the ability to fix atmospheric N2 in symbiosis with soil bacteria called rhizobia
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 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
Summary
With the ability to fix atmospheric N2 in symbiosis with soil bacteria called rhizobia. The isolates 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. 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. The crop derived its name from a tribe called “Bambara” in Segou, central Mali It is the third most important food legume in Africa after groundnut and cowpea, both in consumption and land area under cultivation[3]. Bambara groundnut can produce high yields even in low nutrient soils, and where there is drought stress due to low soil moisture
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