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

Abstract

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 .

Biodiversity and Geographic Distribution of Rhizobia Nodulating With Vigna minima

“…IV (1.6%), and B. liaoningense (1.49%) (Figure 3A). The predominance of B. elkanii and B. pachyrhizi was in accordance with the previous reports for rhizobia of other Vigna species such as V. radiata, V. unguiculata, Vigna subterranea, and V. angularis (Zhang et al, 2007;Yang et al, 2008;Han et al, 2009;Ibny et al, 2019;Puozaa et al, 2019). The super dominance and ubiquitous distribution in the 11 sampling sites of B. elkanii, B. pachyrhizi, and B. ferriligni (Figure 3 and Table 1) demonstrated them as the most adapted or affinity symbionts of V. minima in the study area.…”

Molecular and Symbiotic Efficiency Characterization of Rhizobia Nodulating Bambara Groundnut (Vigna subterranea L.) from Agricultural Soils of Daloa Localities in Côte D’ivoire

“…These isolates presented a great genetic diversity and grouped respectively with various reference strains, in This variability in symbiotic efficiency is linked to the genetic diversity of these strains revealed by the phylogenetic tree of the 16S RNA gene. This information is consistent with results reported by Guei et al, (2019) and Ibny et al, (2019) who respectively identified and authenticated the rhizobia associated with Bambara groundnut in Côte d'Ivoire. Indeed, the inoculation of each plant was done with 1 mL of bacterial broth induced the average number and dry matter of nodule per plant varying respectively from 18 to 87 and 21,67 to 289,33 mg. however, Kumari et al, (2010) authenticated the rhizobia isolated from Indigofera species and reported that the average number of nodule varied depending on species.…”

“…On solid YEM medium, these bacterial isolates forming gummy colonies with rapid growth were phenotypically diverse in terms of appearance, shape, size and color of the colonies which evoke the rhizobia. It confirms the results reported by Ibny et al, (2019) who revealed that the rhizobial isolates nodulating the Bambara groundnut in Africa showed a great morpho-physiological diversity, which varied from differences in size, shape and texture of the colonies. Gnangui et al, (2019) also reported that rhizobia isolated from the Bambara groundnut rhizosphere in Côte d'Ivoire had rapid growth.…”

“…These differences in nodulation and dry weight yield of the plants were accompanied by marked variations in the relative symbiotic efficacy of the isolates tested. Various authors have found strong correlations between aboveground biomass, root biomass and the number and mass of nodules (Fausta, 2013;Ibny et al, 2019).…”

“…Rhizobium pusense and an unidentified cluster. However,Ibny et al, (2019) have shown that the Bambara groundnut is generally nodulated in African soils by various species of Bradyrhizobium.…”