Rhizobial inoculation methods affect the nodulation and plant growth traits of host plant genotypes: A case study of Common bean Phaseolus vulgaris L. germplasms cultivated by smallholder farmers in Eastern Kenya

Rhizobia inoculants are soil bacteria that promote biological nitrogen fixation (BNF). Understanding of rhizobia-host genotype association is a critical step in enhancing legume productivity. Questionnaires were used to identify the common bean varieties cultivated in Eastern Kenya. The native rhizobia were isolated from the root nodules of MAC 13 and MAC 64 bean varieties. Afterwards, a greenhouse bioassay with four inoculation treatments using sterilized soil; 1) mixture of isolated strains, 2) commercial exotic inoculant (Biofix), 3) mixture of isolated strain + commercial inoculant, 4) control without inoculation were set up in a complete randomized design with three replications. Four weeks later, beans were sampled and examined for nodule number (NNO), nodule dry weight (NDW), shoot dry weight (SDW), root dry weight (RDW), shoot nitrogen (%N) and phosphorus (P). Results demonstrated that highest and significant (p<0.05) NDW, SDW and shoot %N content were achieved in a mix of native consortium+ commercial rhizobia, while the highest and significant (p<0.05) P content was realized in a consortium of native rhizobia inoculation. Moreover, there was a significant interaction (p<0.05) between  rhizobia and bean varieties with Kabuu recording the highest NDW, SDW, %N and P contents in a mix of native consortium+ commercial exotic rhizobia. Gacere recorded the highest NDW and SDW when inoculated with commercial rhizobia. Native rhizobia inoculation recorded the highest shoot %N variability in all bean varieties when compared to commercial and a mixture of native+ commercial rhizobia. These results show the mutual preference that exists between rhizobia and bean varieties and the multistrain synergism between native and commercial exotic rhizobia. Further studies should explicate the performance of diverse native rhizobia inoculants used in this study under field conditions.