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First Report of Colletotrichum acutatum on Strawberry in Bulgaria

Recently, there has been increasing interest in growing strawberries (Fragaria × ananassa) in Bulgaria. During the spring seasons of 2001 and 2002, progressive fruit damage in some producers' plots was observed in the Plovdiv Region. Appearance and development of symptoms were typical of anthracnose on aboveground plant structures. On immature fruits, lesions were single or in groups of two or three, circular, small (1 to 3 mm), sunken, and dark brown to black. Lesions on ripe fruits were similar in shape and color, larger (10 to 15 mm), and when coalesced, they covered most or the entire surface. Elliptical, sunken lesions with lighter centers were also found on petioles and stolons, and blighted flowers and infected immature fruits became dark in color. Under wet conditions, salmon-colored masses of conidia were produced mainly on mature but also on unripe fruits, and on petioles and stolons. Conidia were hyaline, cylindrical, and attenuated at both ends measuring 11.5 (9.2 to 13.3) × 4.5 (4.2 to 5.0) μm (2). Colonies of the isolated fungus growing on potato dextrose agar were white with mycelium becoming gray and aerial. Symptoms were reproduced by artificial inoculation of healthy, ripe strawberry fruits. Fruits were wounded with a sterile scalpel, and 5-mm plugs of agar cultures of two isolates were placed on each wound (12 fruits per isolate). An equal number of wounded and noninoculated fruits were used as a control. Fruits were kept in a humidity chamber at 25°C, and 3 to 5 days later, necrotic sunken zones containing acervuli were observed around the wounds of inoculated fruits, and the pathogen was subsequently reisolated. Identical symptoms were obtained after inoculation of raspberry fruits. Intact strawberry stolons and stalks were also successfully inoculated in the lab with two additional isolates using the same technique and tightly covering wounds with adhesive tape. No symptoms were found in the controls of all tests. On the basis of symptoms and pathogen characteristics, the disease was confirmed as anthracnose (black spot) caused by Colletotrichum acutatum. Additionally, the identity of six isolates was confirmed as C. acutatum by species-specific polymerase chain reaction amplification resulting in a single fragment of 490 bp using primers ITS4 and CaInt2 (1). To our knowledge this is the first report of C. acutatum on strawberry in Bulgaria.

References: (1) S. Freeman et al. Pathogenic and non-pathogenic lifestyles in Colletotrichum acutatum from strawberry and other plants. Phytopathology 91:986, 2001. (2) P. S. Gunnell, and W. D. Gubler. Taxonomy and morphology of Colletotrichum species pathogenic to strawberry. Mycologia 84:157, 1992.