Systematic Botany and Mycology Laboratory, USDA-ARS, Beltsville, MD 20705
Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331
Anthracnose on ash trees has been observed on landscape trees in western Oregon, yet there has been no formal report of the disease or its causal fungus. Anthracnose symptoms are observed annually in May and become severe by July when defoliation starts to occur. From 1989 to now, samples have been received from Benton, Josephine, and Marion counties, suggesting that ash anthracnose has been present throughout western Oregon for some time. To identify the causal agent, a fungus was isolated from acervuli on necrotic lesions on leaves of cultivated white ash (Fraxinus americana L.) trees in Benton County in July 2003. The acervuli produced hyaline, nonseptate, ellipsoid conidia 5 to 11 × 3.5 to 6 µm in diameter. The fungus was identified as Discula fraxinea (Peck) Redlin & Stack (teleomorph Gnomoniella fraxini Redlin & Stack) (2). The sequences of the internal transcribed spacer (ITS) region (GenBank Accession No. AY455814) and large subunit (GenBank Accession No. AY455818) nrDNA agreed with those of D. fraxinea from Maryland, except for three single-base substitutions and three insertions/deletions in ITS1. Ash anthracnose has been reported from the central and eastern United States and California, the prairie provinces in Canada, and recently, from British Columbia (1). A specimen (U.S. National Fungus Collections BPI 843391) and culture (Centraal Bureau voor Schimmelcultures CBS 114053) of D. fraxinea from Oregon were deposited.
References: (1) D. F. Farr et al. Fungal Databases. Systematic Botany and Mycology Laboratory. On-line publication. ARS USDA, 2003. (2) S. C. Redlin and R. W. Stack. Mycotaxon 32:175, 1988.