Pathogenic variability in Phaeoisariopsis griseola and response of bean germplasm to different races of the pathogen

Abstract

The wide pathogenic variability occurring in phaeoisariopsis griseola, the causal agent of angular leaf spot of common bean (phaseolus vulgaris l.), is the greatest set-back to development and deployment of resistant bean varieties. The high pathogen variability dictates that new sources of resistance be continuously identified. This study was undertaken to evaluate reactions of selected bean germplasm to different races of p. griseola in an effort to identify potential sources of resistance to als. Selected bean lines/varieties from ecabren were separately inoculated with forty-four races of p. griseola and evaluated for disease development under greenhouse conditions. Isolates of p. griseola used in this study were collected from diverse bean growing areas in kenya and characterised into races based on the reactions of 12 differential bean cultivars. None of the varieties was resistant to all the races, indicating a high complexity of the pathogen population. eight varieties were resistant (disease grade 1 to 3) or moderately resistant (grade 4 to 6) to at least 40 (91%) of the races. bean lines ecab 0754 and ecab 0617 exhibited the highest level of resistance and were each susceptible to one race of p. griseola. all the resistant or intermediate resistant varieties were of the small- or medium-seeded bean types, whereas the commonly-grown large seeded varieties were generally susceptible. these results indicate that a number of bean varieties have varying levels of resistance that could be pyramided to provide durable resistance to angular leaf spot.