Common bean (Phaseolus vulgaris L.) root rot in humid lowland: Occurrence, and assessment of biotic and agronomic factors for mitigation prospects

Abstract

Biotic and abiotic constraints jeopardize the expansion of common bean (Phaseolus vulgaris L.) cultivation to the Cameroon warmer lowlands. The crop is traditionally perceived as a cooler region crop unsuited for the humid tropical areas. We surveyed 78 farmer's fields during the 2015 and 2016 growing seasons, across 7 sub-divisions in the lowland agro-ecological zone of the Centre Region of Cameroon, to document the occurrence of the common bean root rot (BRR) epidemic, the identification of causal pathogens, as well as related agro-ecological variables. We found that BRR occurred in all the surveyed farmer's fields, with disease incidence ranging from 7.4% to 92.4% and disease severity from 3.7 to 9 (On the 1–9 disease rating scale). The disease distribution was closely related to tillage, cropping systems, plant age and variety and physiological status in both seasons. The simple linear regression model and the Pearson correlation revealed significantly negative correlations between the soil pH and phosphorus content, and the disease incidence and severity. Five causative fungal genera were identifies, with varying occurrence: Fusarium spp. (65.4%), Pythium spp. (4.2%), Sclerotium spp. (5.1%), and Macrophomina spp. (8.2%), with Fusarium being the most represented and widespread pathogen irrespective of sampling field and season. Fusarium occurred singly, or in complex with the other pathogenic fungal genera. This study provides clear evidence of high prevalence of BRR disease in the humid lowlands of Cameroon, and suggests deep ploughing and phosphoric fertilizer amendment with basic soil for managing BRR in lowland agro-ecosystems.