First Report of Verticillium Wilt Caused by Verticillium dahliae of Ash Trees in Pacific Northwest Nurseries. V. J. Heffer, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331. R. P. Regan, North Willamette Research and Extension Center, 15210 N.E. Miley Road, Aurora, OR 97002. Plant Dis. 80:342. Accepted for publication 9 January 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0342B.
For several years, ash trees in northwestern Oregon nurseries have shown symptoms resembling those of Verticillium will. Occurrence of disease was rare and isolated; however, one nursery reported 20 to 30% losses of marketable trees. Typical symptoms were marginal scorch and necrosis of older leaves on interior branches, with premature defoliation and some branch dieback. Examination of the vascular tissue did not reveal the characteristic discoloration associated with Verticillium wilt. In August and September, 1994, several scorched leaves, both attached and abscised, were collected from each of 31 symptomatic trees in four nurseries. Petioles were surface disinfested, cut into 2 to 3 mm sections, and placed on streptomycin-amended potato dextrose agar and on water agar; some samples were also placed on ethanol-streptomycin-amended water agar. Verticillium dahliae Kleb. was recovered from 18 of the sampled trees; identification was based on production of typical verticillate con-idiophores, the presence of microsclerotia embedded in the agar, and colony morphology. Overall, V. dahliae was recovered from green ash (Fraxinus pennsylvanica Marsh.) cvs. Patmore, Marshall, and Summit, white ash (F. americana L.) cv. Autumn Purple, and F. oxycarpa Willd. (F. angustifolia Vahl) cv. Raywood. To test for pathogenicity, three V. dahliae isolates were inoculated individually into the stems of green ash seedlings. Sterile distilled water served as the control. After 6 to 7 weeks, seedlings inoculated with isolates from Autumn Purple or Raywood ash trees or strawberry showed symptoms of leaf necrosis. Petiole cultures of symptomatic plants yielded V. dahliae. Trees injected with water were symptom-free and culture-negative. This is the first report of V. dahliae recovered from green and white ash in the Pacific Northwest, and the first report of V. dahliae causing leaf scorch on F. oxycarpa cv. Raywood.References: (I) C. L. Ash and D. W. French. Phytopathology 82:1097, 1992. (2) A J. M. Rijkers el al. Neth. J. Plant Pathol 98:261, 1992.