Influence of native rhizobacteria co-inoculation and formulation of bacterial inoculants on the growth and yield of common bean (Phaseolus vulgaris L.)

Abstract

Introduction

Incorporation of inoculum in different carrier materials may increase the efficacy of bacterial inocula.

Materials and Methods

Field experiments were conducted using two strains of rhizobium and phosphate-solubilizing bacteria (PSB) and their respective combinations using different carrier materials in common bean-growing regions in three soil types in Kenya. The field experiment was laid out in a split-plot arrangement with the strain inoculations as the main plot while the subplots consisted of the carrier materials (filter mud, peat moss and yeast extract mannitol broth [YEMB]). Each main plot included two controls: uninoculated negative control and uninoculated controls that received N and P fertilizer. The experiment was conducted for two cropping seasons. Data were collected on the nodulation, shoot and root biomass and yield.

Results

Co-inoculation of the common bean with Rhizobium phaseoli + Bacillus aryabhattai strains had significantly higher number of nodules (55 nodules per plant) compared to single R. phaseoli inoculation (38 nodules). The co-inoculation of the rhizobia and the PSB yielded statistically at par with the application of diammonium phosphate (18:46:0) across the soil types and seasons. The use of filter mud as a carrier material led to a higher number of nodules for most of the rhizobia strains inoculation and their respective co-inoculation with the bacillus strains. Significantly higher yield was obtained with the filter mud (1.64 Mg ha⁻¹) while there was no significant difference in the yield of common bean between peat moss and YEMB as carrier materials for the bacterial strains.

Conclusion

The solid carrier material, specifically filter mud, showed potential for use in the formulation of inoculants. Specific co-inoculation of rhizobia (R. phaseoli and Rhizobium pusense strains) and PSB (Paenibacillus polymyxa and B. aryabhattai) increased the growth, nodulation and yield of common bean more efficiently than the control.