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First Report of Strawberry Fruit Rot Caused by Alternaria tenuissima in Korea

A strawberry (Fragaria × ananassa Duch.) fruit rot disease has been observed in several vinyl-house fields at Nonsan and Taejon, Chungnam district, Korea, especially following moist and cool conditions in the spring and again in September. Over the past 7 years, incidence of the disease has ranged from 0.2 to 2.0%. Early symptoms on fruits were characterized by small, irregular lesions, which were slightly sunken and appeared light green to black in color as sporulation began. Conidia were 25 to 55 μm long by 10 to 17 μm wide; beaks, when present, were 2 to 3 μm wide and up to 40 μm long; and conidiophores were 20 to 110 μm long by 3 to 5 μm wide. Older lesions were circular, largely sunken, firm, and dark-green to almost black because of abundant sporulation. The fungus isolated from infected fruit tissues was identified as Alternaria tenuissima (Fries) Wiltshire, based on the morphological characteristics of the conidia and conidiophores. Pathogenicity tests were conducted by inoculating slightly wounded, ripe (red) and immature (green) fruits with a conidial suspension (1 × 10⁶ conidia/ml). Twenty-four ripe and immature fruits were inoculated with each of six isolates in duplicate and placed in a moist chamber for 48 h at 25°C and then transferred to vinyl-house field. After 7 to 10 days fruit rot symptoms were visible on the inoculated fruits and appeared nearly identical to lesions observed in the field, although there were differences in aggressiveness among isolates. Control fruits sprayed with distilled water did not develop any symptoms. Green fruits were generally more resistant to infection than ripe ones. The causal fungus was easily reisolated from lesions on inoculated strawberries. Alternaria fruit rot of strawberries has been reported from the USA, UK, and West Germany (2). Howard and Albregts (1) first reported a strawberry fruit rot caused by A. tenuissima in Florida, but the disease is generally not considered important. However, occasionally losses from this disease have been extensive in Korea. To the authors' knowledge, this is the first report of strawberry fruit rot caused by Alternaria tenuissima in Korea.

References: (1) C. M. Howard and E. E. Albregts. Phytopathology 63:638--639, 1973. (2) A. L. Snowdon. Pages 250--252 in: A Color Atlas of Post-Harvest Diseases and Disorders of Fruits and Vegetables. Vol. 1. 1990. Wolfe Scientific, London.