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First Report of Anthracnose of Salal Caused by Colletotrichum acutatum in British Columbia

Gaultheria shallon Pursh (salal) is a native, Pacific Northwest forest understory plant produced by numerous commercial nurseries as a garden and landscape ground cover. Seed is sown in soilless media in greenhouse plug flats, and seedlings are transplanted into larger pots at 24 to 36 weeks. In October 2005, approximately 30% of 16-week-old G. shallon Pursh (salal) seedlings in a commercial greenhouse in coastal British Columbia, Canada were observed to be dying back. Black, water-soaked, cankers girdled the stems and petioles resulting in seedling necrosis. Cankers extended into the base of affected leaves, and irregular, black leaf spots with concentric rings were observed. A Colletotrichum sp. was isolated on potato dextrose agar (PDA) + 0.005% streptomycin. In May 2006, 160 20-week-old salal seedlings (two- to five-leaf stage) in four plug cell flats of 40 seedlings each were inoculated with a hand atomizer with a mycelial and spore suspension of approximately 1 × 10⁸ CFU/ml (dilution plating) in 100 mL sterile dH₂O; 120 seedlings (four flats of 30 seedlings each) were sprayed with water alone. Flats were covered with black plastic for 48 h and then placed randomly in a shaded greenhouse at 14 to 22°C with overhead watering. The percentage of necrotic seedlings with black, water-soaked cankers and leaf spots in the inoculated flats at 1 to 8 weeks was 3.8, 7.6, 8.2, 16.4, 44.9, 62.0, 79.7, and 81.6, consecutively; versus 2.5% at 8 weeks in the noninoculated flats. Infection of the noninoculated seedlings was presumably due to spore splash from irrigation. Both the original isolate used as inoculum and colonies reisolated on PDA from inoculated, surface-sterilized, symptomatic tissues were identified as Colletotrichum acutatum J.H. Simmonds based on morphology (2) and PCR using a species-specific primer (1). Hyaline, aseptate, fusiform conidia, measuring 8 to 16 × 2.5 to 4 μm, were produced in acervuli without setae on plants and in culture. The teleomorph (Glomerella) stage was not observed. To our knowledge, this is the first report of an anthracnose disease of salal.

References: (1) S. Freeman et al. Plant Dis. 82:596, 1998. (2) J. E. M. Mordue. No. 315 in: Descriptions of Pathogenic Fungi and Bacteria. CMI, Kew, Surrey, UK, 1971.