Insights into the Biodiversity of Native Rhizobia from Africa: Documented Novel Species, Valorization Status and Perspectives—A Review

Rhizobia are a polyphyletic group of Proteobacteria comprising approximately 700 different species. Despite significant advancements in their taxonomy, evolutionary history, and ecological importance, substantial knowledge gaps remain regarding a detailed understanding of rhizobial biodiversity in a geographical context and the interest in studying and valorizing native rhizobial strains. This bibliometric study used data from the last four decades (1985–2025) to review the taxonomic and functional diversity of the documented novel taxa of rhizobia described from African ecosystems, as well as their valorization status as biofertilizers. It aims to discuss the interest in knowing, preserving, and valorizing native rhizobial resources in the global context of climate change and biodiversity erosion. The study revealed that the first African indigenous novel species of rhizobia was published in 1988, although research on rhizobia dates back to the 1950s in Africa. To date, ~63 species (approximately 9% of the total in the world) and two genera of rhizobia have been described using native isolates from 11 African countries, with substantial discoveries from the Succulent Karoo hotspot of biodiversity in South Africa. Approximately 51% of species are affiliated with Bradyrhizobium and Mesorhizobium, with Vachellia karroo and Senegalia spp. (formerly Acacia spp.) as their primary hosts. Most species-type strains (~89%) were found to be infective on legumes and are good candidates for biofertilizer development. However, there is a limited level of commercial valorization of indigenous isolates as inoculants, mainly because the production of biological intrants is still at the experimental stage in Africa. Interestingly, important breaking point discoveries have been made using native rhizobial strains from Africa, including the pioneering demonstration in 2001 that Burkholderia (beta-rhizobia) is a symbiotic genus with legumes. It also includes the discovery of stem-nodulating rhizobia and Nod factor-independent symbiotic processes in some rhizobia. Together, this review highlights the importance of native African rhizobial strains. This underscores the need to accelerate their agronomic valorization to better support the transition to more resilient and sustainable legume-based farming systems in African countries.