Pathogenic variability within race 65 of Colletotrichum lindemuthianum and its implications for common bean breeding

Abstract

The wide pathogenic variability among and within races of Colletotrichum lindemuthianum has complicated the process of obtaining cultivars of Phaseolus vulgaris that are resistant to anthracnose. Six isolates were inoculated into twelve differential cultivars and seven commercial cultivars of the common bean at concentrations in the range 102 to 106 spores mL-1 . Information concerning the vertical and horizontal resistance of hosts and the virulence of isolates was obtained from diallel analysis. It was clear that the set of differential cultivars recommended for the determination of races of C. lindemuthianum is inefficient in detecting differences within race 65, and it is suggested that new sources of resistance should be identified and added to the cultivar set. There were significant differences in the virulence of isolates from race 65, with isolates CL 837 and CL 844 being the most virulence. No horizontal resistance was detected in the C. lindemuthianum-common bean system.