Virulence and genetic variability among Colletotrichum lindemuthianum (Sacc. & Magnus) Briosi & Cavara isolates from common bean (Phaseolus vulgaris L.)

Colletotrichum lindemuthianum is a fungus that causes bean anthracnose. This study analyzed the virulence and genetic variability among and within C. lindemuthianum isolates occurring in bean-growing areas of southern Ethiopia. Symptomatic common bean leaves and pods were collected from southern Ethiopia. Forty single-spore isolates obtained from the bean leaves and pods were used for this study. The isolates were grouped into 31 physiological races based on their responses to a differential set of common beans. Five of the physiological races (2047, 4031, 2052, 2064, 2174 and 2176) were extremely virulent, causing susceptible reactions on 10 to 11 different cultivars. Rep-polymerase chain reaction revealed high polymorphism, with an average of 87.5% polymorphic loci. The mean Na, Ne, He and I were 1.83, 1.465, 0.278 and 0.427, respectively, within C. lindemuthianum races. Analysis of molecular variance (AMOVA) partitioned a larger part of the total genetic variation within populations (80%). Our collection includes highly virulent races that infected the differential cultivars G2333, Perry marrow and Pi207262 as a possible source of resistance. The differential cultivar G2333 showed strong resistance and can be a potential source of resistance, while the differential cultivars Perry marrow and Pi207262 would be alternative donor parents as sources of resistance in breeding programs for the development of varieties with broader resistance. This study could be a scientific basis for disease prevention and for development of common bean cultivars resistant to bean anthracnose. Identification of a wider range of isolates must be carried out, collecting common bean in different seasons.