Cross-Infectivity of 11 Different Legume Species by 15 Native Rhizobia Isolated from African Soils

Selecting symbiotic rhizobia for use as inoculants in agriculture is a major challenge, though it is necessary for exploiting biological nitrogen fixation as an eco-friendly source of N in contrast to chemical N fertilizers which can pollute the environment. In addition to high symbiotic efficiency, bacterial strain ability to infect and effectively nodulate a wide range of host plants is also desired. Cross-infectivity studies are therefore important for identifying rhizobial strains that are highly effective with a broad host range. The legume/rhizobia symbiosis has the potential to contribute about 80% or more N to agricultural systems, thus providing a sustainable source of N in cropping systems. This study assessed the cross-nodulation, colony morphology, relative symbiotic effectiveness and N₂ fixation of native rhizobial isolates from Africa that nodulate diverse legume species. The results showed that the rhizobial isolates differed significantly in symbiotic performance and relative symbiotic effectiveness. As a result, they differed markedly in nodulation and shoot DM induced in their host plants.