Indole Acetic Acid Producing And Phosphate Solubilizing Bacteria Native To Kenyan Soils Promote Growth of Common Bean (Phaseolus Vulgaris L.)

Abstract Use of phosphate solubilizing bacteria (PSB) and rhizobia can have a positive effect on the growth of common bean. This study aimed at determining the mechanisms of action of native bacterial strains; and to determine their effect in enhancing growth of common bean. The strains were screened for their ability to solubilize insoluble inorganic phosphates and production of indole acetic acid in vitro. A greenhouse experiment was set up to evaluate the response of common bean to inoculation with selected bacterial strains. Six of the bacterial isolates tested showed a positive result for IAA production. Rhizobium pusense showed the greatest solubilization efficiency of 648 followed by Bacillus megaterium (322.3) and Rhizobium phaseoli (308.7). Inoculation of common bean with Rhizobia and PSB had a significant effect on the number of nodules per plant. The highest shoot biomass was observed when Rhizobium phaseoli was co-inoculated with P. polymyxa (4.3g plant-1) compared to the single Rhizobium phaseoli inoculation (1.14 g plant-1). The shoot tissue nitrogen and phosphorous concentration was increased as a results of co-inoculation up to 32.5% and 75.4% respectively. Therefore, tested bacterial strains have great potential in being formulated and used as biofertilizers that can be evaluated under varying field conditions.