Symbiotic interaction of bambara groundnut (Vigna subterranea) landraces with rhizobia spp. from other legume hosts reveals promiscuous nodulation

Bambara groundnut (Vigna subterranea) is one of the most underutilized and neglected legume crop used for human consumption worldwide. Unlike the common food and forage legumes, the symbiotic properties of this legume have not been studied sufficiently. This study is designed to investigate the nodulation compati-bility and symbiotic performance of twelve landraces of V. subterranea with five different Rhizobia species isolated from the nodules of other legumes under glasshouse conditions. Pre-germinated seeds of each land-race planted in sterile river sand medium were inoculated with 108 cfu/ml of each rhizobium inoculum sus-pension and monitored with regular watering using nitrogen free Hoagland's solution for six weeks. The taxonomy and phylogeny of the five rhizobia species was determined using nucleotide sequence analysis of the 16S rRNA and recA (DNA recombination protein) genes. A concatenated multiple sequence alignment was used to construct an MLSA tree to further analyze the phylogeny of the strains. Significant differences were observed among individual bambara genotypes and rhizobia strains in terms of nodule numbers and dry weight, as well as plant biomass. Statistical analysis showed that Rhizobia strains XBD2 and XS34 identi-fied as Bradyrhizobium zhangiangens and B. centrosematis respectively exhibited the highest nodulation com-patibility in terms of nodule number and nodule dry weight with one or more bambara groundnut landraces. This study demonstrated that V. subterannea does not show preference to unique rhizobia, confirming that they are promiscuously nodulated by more than one species of rhizobium belonging mainly to the cowpea miscellany cross inoculation group. The findings of this study also provide insights into the selection and development of appropriate low cost rhizobia inoculants in the sustainable production of this underutilized legume for use by smallholder farmers in South Africa.& COPY; 2023 The Author(s). Published by Elsevier B.V. on behalf of SAAB. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Automated summary

This study aims to investigate the nodulation compatibility and symbiotic performance of twelve landraces of Bambara groundnut with five different Rhizobia species. Significant differences were observed among individual bambara genotypes and rhizobia strains in terms of nodule numbers and dry weight, as well as plant biomass. The findings of this study provide insights into the selection and development of appropriate low-cost rhizobia inoculants for sustainable production.