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First Report of Anthracnose Fruit Rot Caused by Colletotrichum acutatum on Strawberry in Sweden

Strawberries (Fragaria × ananassa) are the most important soft fruit crop in Sweden and most commonly grown as a perennial crop. Colletotrichum acutatum J.H. Simmond was detected on strawberries in Sweden for the first time in the autumn of 2003. Anthracnose caused by C. acutatum has previously been found on rhododendron in Sweden (2). The infected strawberry plants, cv. Kimberly, were found in a field in the northeastern part of Skåne in southern Sweden. The first plant sample was collected during September 2003, and a second sample was collected during the end of June 2004. Symptoms were seen on stolons as elliptical, black, sunken lesions and irregular black leaf spots originating from the tip. No symptoms were seen on immature green fruits. However, the farmer had observed black spots on the fruits the previous year. Immature fruits were collected in the field, surface sterilized with 70% ethanol, dipped for 1 min in 1.25% NaOCl, and thereafter rinsed in distilled water. Fruits were incubated in a moist chamber at 23°C. The first symptoms were seen as black spots after 3 days; later, salmon-colored conidial masses were produced from acervuli in the center of the lesions. The fungus was isolated on potato dextrose agar (PDA) as single-conidia cultures. Colonies were white-to-pale gray with abundant salmon-colored masses of conidia in the center of the culture. Mycelial growth rate on PDA was 7.5 to 7.9 mm per day at 21 ± 1°C. Conidia (11.0 to 16.5 × 3.9 to 5.7 μm) were cylindrical and hyaline with pointed ends, which is consistent with previous reports for C. acutatum (1). Symptoms were reproduced by artificial inoculation on ripe strawberries (cv. Elsanta). A conidia suspension was prepared from single-conidia cultures and each strawberry was sprayed with 0.5 ml of suspension (2.2 × 10⁷ conidia per ml). The strawberries were incubated in a moist chamber at 22°C. The first typical symptoms were seen after 3 days. Single conidia were isolated from infected fruits and plated on PDA. Stolons and leaves of cv. Alice were inoculated with mycelial plugs of C. acutatum, sealed in a plastic bag for 2 days, and then placed in a greenhouse environment at 70% relative humidity and 21°C. Black, sunken lesions were found on stolons after 7 days. A sample of 300 petioles from the infected field was sent to the Central Science Laboratory, York, England that identified the pathogen as C. acutatum using enzyme-linked immunosorbent assay and plating rinse water from petioles onto selective media. With this report, anthracnose caused by C. acutatum on strawberry has now been reported from all the Nordic countries.

References: (1) B. J. Smith. Plant Dis. 74:69, 1990. (2) O. Vinnere et al. Mycol. Res. 106:60, 2002.