Variation Among Isolates of Colletotrichum dematium var. truncata from Soybean and Three Colletotrichum spp. to Benomyl

Abstract

Three isolates of the fungal pathogen Colletotrichum dematium var. truncata were obtained from soybean (Glycine max) during the 1975 growing season in central and southern Illinois and labeled Cd-1, Cd-2 and Cd-3. The three isolates produced curved conidia measuring between 17.8 to 23.3 µ long and 3.2 to 5.1 µ wide. Growth rate and spore production were variable among the three isolates with Cd-3 producing the most spores per cm² of colony growth and Cd-2 producing the largest colony growth at 25° C. Isolate Cd-1, found to be tolerant to benomyl in vitro, showed a uniform radial-growth pattern on potato-dextrose agar amended with 1 to 350 µg/ml commercial benomyl, while isolates Cd-2 and Cd-3 showed a bimodal-type growth curve. Colletotrichum glycine and Coltetotrichum musae were sensitive to benomyl.