EFFECTIVENESS OF RHIZOBIA ISOLATES FROM NJORO SOILS (KENYA) AND COMMERCIAL INOCULANTS IN NODULATION OF COMMON BEANS (PHASEOLUS VULGARIS)

Abstract

Bean production in Kenya barely meets half the demand because of low soil fertility among other factors. While use of rhizobia inoculants can substantially increase bean yields, less than 1% of the farming population is aware of inoculants. The objectives of this study were, one, to isolate and evaluate indigenous rhizobia populations in two agro ecological zones in Njoro, and two, to test the efficacy of the isolates against commercial rhizobia inoculants in relation to nodulation and shoot dry matter of Rose Coco bean cultivar. Rhizobia isolates were collected from field 8 of Egerton University and Kerma farm in Njoro. The isolates were tested against Biofix (market available inoculant) and USDA 9030 (pure culture of Rhizobia tropici) under greenhouse conditions. Rhizobia inoculation had no effect on shoot dry weight (SDW), nodule dry weight (NDW) and shoot N content. However, significant differences were observed among rhizobia strains used, where Biofix produced a higher NDW and Kerma isolate resulted in higher shoot N content than other strains. Symbiotic effectiveness of 111%, 107%, 97% and 92% was observed for Kerma isolate, Field 8 isolate, Biofix and USDA 9030 respectively. Our results indicate that rhizobia isolates from Njoro had comparable symbiotic effectiveness to commercial inoculants and should be tested further using other bean varieties to assess their potential.