Abundance and Symbiotic Potential of Common Bean (Phaseolus vulgaris) Nodule Associated Bacteria in Western Kenya Soil

Abstract

Plant growth-promoting Rhizobacteria are beneficial native soil bacteria that colonize plant roots and result in increased plant growth. Those that colonise the nodules of legumes are known as nodule associated bacteria. The aim of this study was to determine the effect of chemical soil factors on the abundance of nodule associated bacteria and the symbiotic efficiency of these bacteria when coinoculated with Phaseolus vulgaris in Western Kenya soils. The soil samples were collected from cultivated lands in Kisumu near Lake Victoria, slopes of Mt. Elgon and Kakamega. In each of these regions, the soil samples were collected from four regions. 1ml of soil solution at 10 fold dilution for seven dilution steps (10-1to 10-7) and three replications for each dilution was used to inoculate common bean seedling in the Leonard jars. They were harvested after four weeks to determine abundance of nodule associated bacteria using most probable number plant infection method. Mt. Elgon region had the highest population of nodule associated bacteria (120000 cells per gram of the soil), followed by Kisumu (1290 cells per gram of the soil) and Kakamega region had the lowest (17 cells per gram of the soil). The effect of plant growth-promoting Rhizobacteria on the yield of common beans was significantly higher (p < o.oo1) when co-inoculated with Rhizobia compared to the yield of Rhizobia inoculated alone or negative control (not inoculated) (p < 0.05). This study therefore provides knowledge on the factors that favour the survival of common bean symbiotic bacteria and their symbiotic capability which is necessary for production of plant growth-promoting Rhizobacteria inoculants suitable to the soils of Western Kenya.