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Colletotrichum acutatum Overwinters on Sweet Cherry Buds

Either naturally infected or artificially inoculated sweet cherry (Prunus avium) buds on fruit spurs (mainly containing generative buds) and on 1-year-old shoots (mainly containing vegetative buds) were examined for presence of Colletotrichum acutatum prior to the beginning of spring growth in each of 4 years. Artificial inoculations were made during the growing seasons preceding the bud sampling. The plant material was incubated moist for either 14 (fruit spurs) or 21 (1-year-old shoots) days at 20°C. Following moist incubation at 20°C, C. acutatum frequently sporulated on buds of fruit spurs and shoots. The fungus sporulated in orange, short-thread or hornlike structures, mainly on distal parts of the buds, and was usually easily visible with the unaided eye. The incidence of infected buds on naturally infected and inoculated fruit spurs was 2 to 80% and 38 to 79%, respectively. Incidence on naturally infected and inoculated shoots was 0 to 53% and 4 to 45%, respectively. On buds within fruit spurs, the incidence of C. acutatum was significantly higher on generative than on vegetative buds. This investigation shows that buds can host C. acutatum and thus are likely to be an important source of primary inoculum for anthracnose of sweet cherry.