Reaction of selected common bean genotypes to physiological races of Phaeoisariopsis griseola occurring in Kenya

Abstract

The wide pathogenic variability occurring in Phaeoisariopsis griseola , the causal agent of angular leaf spot of common bean ( Phaseolus vulgaris L.), dictates that new sources of resistance be continuously identified. This study was undertaken to determine the reaction of selected bean genotypes to different races of P. griseola in order to identify potential sources of resistance to angular leaf spot. Selected bean genotypes from Eastern and Central Africa Bean Research Network (ECABREN) and National Dryland Farming Research Centre (NDFRC), Katumani in Kenya were separately inoculated with forty-four races of P. griseola and evaluated for disease development under greenhouse conditions. The genotypes included small- and large-seeded types. None of the genotypes was resistant to all the races, indicating a high complexity of the pathogen population. Thirteen genotypes were resistant (disease score 1 to 3) or moderately resistant (score 4 to 6) to at least 40 of the races. Small-seeded bean genotypes ECAB 0754 and ECAB 0617 were resistant or moderately resistant to all races except Mesoamerican race 33-39 and Afro-Andean race 58-18, respectively. Genotype ECAB 0754 exhibited the highest level of resistance, with an average disease severity of 1.1%. All the resistant or moderately resistant genotypes were of the small-seeded bean types which are commercially less popular. The commonly grown large-seeded genotypes were generally susceptible. Among the bean genotypes evaluated, the small-seeded pintos and browns/yellows possessed high levels of resistance. The results of this study indicate that different bean genotypes have varying levels of resistance to angular leaf spot that can be pyramided into appropriate background to provide durable resistance.Une large variabilit\ue9 pathog\ue9nique du Phaeoisariopsis griseola , l\u2019agent causal de la t\ue2che angulaire de feuilles du haricot commun ( Phaseolus vulgaris L.), sugg\ue8re qu\u2019il y\u2019ait une identification continue de nouvelles sources de r\ue9sistance. Cette \ue9tude \ue9tait entreprise pour d\ue9terminer la r\ue9action des g\ue9notypes de haricot s\ue9lectionn\ue9s aux diff\ue9rentes races de P. griseola afin d\u2019identifier de sources potentielles de r\ue9sistance \ue0 la maladie de t\ue2che angulaire de la feuille. Les g\ue9notypes de haricot fournis par l\u2019Eastern and Central Africa Bean Research Network (ECABREN) et le National Dryland Farming Research Centre (NDFRC), Katumani au Kenya \ue9taient s\ue9par\ue9ment inocul\ue9s avec quarante-quatre races de P. griseola pour l\u2019\ue9valuation en serre du d\ue9veloppement de maladies. Les g\ue9notypes comprenaient de petits et gros grains de semences. Aucune des g\ue9notypes n\u2019\ue9tait r\ue9sistant \ue0 toutes les races de maladies, indicant ainsi une complexit\ue9 \ue9lev\ue9e de la population des pathog\ue8nes. Treize g\ue9notypes \ue9taient r\ue9sistants (\ue9chelle de cotation: 1 \ue0 3) ou mod\ue9r\ue9ment r\ue9sistants (\ue9chelle de cotation: 4 \ue0 6) sur au moins quarante de toutes les races. Les g\ue9notypes de haricot \ue0 petits grains ECAB 0754 et ECAB 0617 \ue9taient r\ue9sistants ou mod\ue9r\ue9ment r\ue9sistants \ue0 toutes les races \ue0 l\u2019exception de Mesoamerican race 33-39 et Afro-Andean race 58-18, respectivement. Le G\ue9notype ECAB 0754 avait manifest\ue9 un niveau \ue9lev\ue9 de r\ue9sistance, avec un taux moyen de s\ue9verit\ue9 de 1.1%. Tous les g\ue9notypes r\ue9sistants ou mod\ue9r\ue9ment r\ue9sistants \ue9taient de ceux \ue0 petits grains commercialement moins populaires. Les g\ue9notypes \ue0 gros grains commun\ue9ment cultiv\ue9s \ue9taient g\ue9n\ue9ralement susceptibles. Parmi les g\ue9notypes \ue9valu\ue9s, ceux \ue0 petits grains "pintos" et bruns/jaunes \ue9taient dot\ue9s des niveaux \ue9lev\ue9s de r\ue9sistance. Les r\ue9sultats de cette \ue9tude montrent que diff\ue9rents g\ue9notypes de haricot poss\ue8dent de niveaux diff\ue9rents de r\ue9sistance \ue0 la maladie de t\ue2che angulaire de la feuille pouvant \ueatre combin\ue9s par pyramidage pour d\ue9velopper une vari\ue9t\ue9 de haricot \ue0 r\ue9sistance durable