Effect of Soil Fertility and Intercropping on the Incidence and Severity of Root Rot Diseases of Common Bean (Phaseolus vulgaris L.)

Abstract

High occurrence of root rots is attributed to continuous and inappropriate cropping systems, low soil fertility levels, low moisture in soil, use of farm saved seeds and use of root rot susceptible bean (Phaseolus vulgaris L.) varieties. This study evaluated the effect of soil fertility and intercropping on the incidence and severity of root rot diseases of common bean. Soil samples were collected at the start of the 2016 short rain cropping season to determine the soil nutrients status, and the incidence and population of soil borne fungal pathogens. The soil samples were analyzed for total nutrient status and pH levels. Soil borne fungal pathogens were isolated from the soil and stem bases by pour plate technique. Farm saved seeds of bean varieties KK8 and GLP2 were planted in field experiments at three sites in pure stand, intercropped with maize, applied with and without fertilizer. Data collected included seedling emergence, stand count, bean fly incidence, root rot distribution, incidence and severity, and yield. The pathogens isolated from soil and stem bases included F. oxysporum, F. solani, Pythium spp, Macrophomina and Rhizoctonia spp, with Fusarium spp. being the most predominant at 40% incidence and mean population of 3000 CFU/g of soil. Bean intercropped with maize had 22% lower intensity of root rot compared to the sole crop. The findings of this study demonstrate that low soil fertility, use of farm saved seeds and high inoculum levels of soil borne pathogens in the soil contributed to the high incidence of root rots in the study sites. In addition bean varieties intercropped with maize had a 17% lower incidence of root rot pathogens compared to bean varieties from sole crop. It was observed that intercropping system reduces pests and diseases. However, root rot pathogens isolated from bean intercropped with maize had a significantly lower incidence than the sole crops.