EVALUATION OF BEAN VARIETIES (phaseolus vulgaris L) FOR RESISTANCE TO bean common mosaic virus (BCMV) and bean common mosaic necrotic virus (BCMNV) ACROSS A SOIL FERTILITY GRADIENT IN WESTERN KENYA

Abstract

Bean Common Mosaic and Bean Common Mosaic Necrosis are some of the most devastating diseases of common beans (Phaseolus vulgaris L) in Kenya. These viral diseases cause more than 80% yield losses. Control by chemical method is difficult once they have set in. Use of resistant varieties offers a sustainable and economical solution. In this study, observational survey was carried out in 20 farms in Nandi South. A field study was conducted for one season in four sites across soil fertility gradient in Nandi south. Alphar lattice design was adapted for the experiment. The bean genotypes screened for BCMV and BCMNV included twenty three bean lines developed for resistance to bean root rot (BRR) and three phosphorus efficient bean lines selected from an earlier field screening of fifty Phosphorus efficiency lines. Two control varieties, RWR 719 resistance to BCMV and GLP-585 a commercial variety were included in the trial as control lines. Parameters scored were BCMV and BCMNV incidence, Aphid counts, stand counts and yield. The data was subjected to ANOVA using SAS 8.2 Statistical software and LSD at 5% level of significance was used to compare the means of the genotypes for all variables. Further twelve genotypes that did not show the viral symptoms in the field were selected and artificially inoculate in the screen house to confirm this resistance. This was done in a Completely Randomised Design. The highest incidences of BCMV (61.5%) and BCMNV (8.2%) were in Koibem. The bean root rot resistant lines showed significant differences in resistance to both BCMV and BCMNV. Six lines were resistance to BCMV while 14 were resistant to BCMNV. The genotype BCO-05/18 and BCO-05/07 were particularly resistant to both viruses. The P efficient lines were completely susceptible to BCMNV, but resistant to BCMV. These results indicate that both BRR and P efficient lines can be good sources of resistance to transfer BCMV and BCMNV resistance to popular but susceptible bean varieties.