Evaluation of Selected French Bean (Phaseolus vulgaris L.) Genotypes for Resistance to Angular Leaf Spot (Pseudocercospora griseola) in Western Kenya

Abstract

French bean, a sub-group of the common bean (Phaseolus vulgaris L.), is grown for its tender green pods. It is a major export crop in Kenya but production levels are constrained by both biotic and abiotic stresses. Angular leaf spot (ALS) disease, caused by Pseudocercospora griseola, can cause major reductions in yield. The pathogen is highly variable and endemic in various agro-ecological zones. Genetic resistance against ALS is a high breeding priority, as effective cultural control is difficult. The main objective of this study was to evaluate French bean germplasm for ALS resistance in western Kenya. A set of 26 commercial varieties, three breeding lines, three landraces and two checks (resistant and susceptible dry bean cultivars) were planted in a randomized complete block design with three replicates at three sites in Kenya (Eldoret, Kisii and Kakamega) in 2014. Disease assessment was done using a 1-9 CIAT scale. There were significant (P ≤ 0.05) differences in disease severity between the three sites: the Kakamega site experienced the greatest disease pressure (mean severity of 6.2), followed by the Kisii site (5.7) and the Eldoret site (5.3). Only one out of the 34 entries (not a French bean variety) showed field resistance to ALS. Most exhibited either an intermediate or a susceptible reaction at all three sites. The resistant control Mexico 54 (a dry bean variety) remained clear of ALS infection, so could represent a useful donor of resistance in a French bean breeding program. There remains a need to identify further donors of resistance, preferably within the French bean genepool.