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Tissue Necrosis of Sour Cherry Fruits, An Unusual Disease Occurrence Caused by a Phoma sp. in Serbia

Following frequent rains during May and June of 1999, a high incidence of an unknown disease on sour cherry (Prunus cerasus) fruits was observed in western Serbia (Šabac). Initially, small, water-soaked, dark green spots appeared on the fruit tissue similar to infections caused by Pseudomonas syringae or a Colletotrichum sp. (1,2). Later, spots enlarged, coalesced, and became necrotic and covered most of the fruit surface. The diseased tissue was slightly depressed and fruit shriveled and dried. Approximately 60 to 80% of the total yield was affected. Numerous hyaline, unicellular, and ellipsoidal conidia were observed with a microscope. Orange spore masses often occurred on the necrotic tissue following rain. Symptoms of the disease were not expressed during the dry spring of 2000, but were observed in rainy 2001. The most susceptible cultivar was Haiman's Rubin. Disease symptoms were absent on the domestic cultivar Oblačinska. Placing small necrotic fragments on potato dextrose agar (PDA) resulted in grayish fungal colonies that produced black, globose pycnidia with hyaline, unicellular, and ellipsoidal conidia under daylight conditions that were similar to those formed on necrotic sour cherry fruit in the orchard. At 25°C, colonies covered the entire 9-cm diameter surface of PDA after 5 to 6 days. No teleomorph was observed. Bacterial isolations on nutrient agar were unsuccessful. Unripe sour cherry fruits were punctured with a sterile needle and small colony fragments of the fungus were placed over the wound. Symptoms typical of those on fruit found in orchards were observed after 7 days of incubation at 25°C. No symptoms developed on control fruits punctured with a sterile needle. The fungus was reisolated from the inoculated fruits and shown to be identical to the original strains. On the basis of pathogenicity and morphological characteristics of the strains investigated, the fungus was determined to be a Phoma sp. (3), also known as sour cherry necrosis in other fruit-tree-growing regions. To our knowledge, this is the first report of the fungus on sour cherry fruit in Serbia.

References: (1) J. Balaž and M. Arsenijević. Proc.Int. Conf. Plant. Path. Bact. 7:515, 1990. (2) M. Ivanović and D. Ivanović. Zašt. Bilja 201:211, 1992. (3) B. C. Sutton. Pages 379--391 in: Coelomycetes. CMI, Kew, Surrey, England, 1980.