Pacific Yew as a Host for Phytophthora ramorum in California Forests

J.C. Bienapfl, J.W. Zanzot, and D.M. Rizzo, Department of Plant Pathology, University of California, Davis 95616; jbienapfl@ucdavis.edu

English yew (Taxus baccata) has been reported as a host of Phytophthora ramorum in nurseries in Great Britain. In 2004, branch dieback was observed on Pacific yew (T. brevifolia) in a Mendocino County, CA forest and P. ramorum was recovered. Symptoms on Pacific yew, similar to those reported for English yew, included discolored needles and shoot dieback. The Pacific yews were found in the understory of a Douglas-fir/tanoak forest associated with P. ramorum infected bay (Umbellularia californica) and tanoak (Lithocarpus densiflorus). Other P. ramorum hosts (e.g., Vaccinium ovatum, Lonicera hispidula) were present and yielded cultures of the pathogen. A survey of the area resulted in the detection of three P. ramorum infected yew shrubs. Disease progression resulted in branch dieback, but death of individuals was not observed.

Pacific yew is the only plant species known as a natural host for P. ramorum and P. lateralis. Phytophthora lateralis is the closest known relative to P. ramorum. It causes Port-Orford cedar root disease and has been reported as a root pathogen of Pacific yew. Pacific yew twigs and seedlings were inoculated with both Phytophthora species to investigate symptom expression, potential interactions between these two pathogens, and to demonstrate Koch’s postulates.

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