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.
