Disease Note

First Report of Phytophthora lateralis on Pacific Yew. G. A. DeNitto, USDA Forest Service, Shasta-Trinity National Forests, Redding, CA 96001, and J. T. Kliejunas, USDA Forest Service, Forest Pest Management, San Francisco, CA 94111. Plant Dis. 75:968. Accepted for publication 25 April 1991. DOI: 10.1094/PD-75-0968C.

Phytophthora lateralis Tucker & Milbrath, which causes a damaging root disease of Port-Orford-cedar (Chamaecyparis lawsoniana (Andr. Murray) Parl.), was isolated from a dying Pacific yew (Taxus brevifolia Nutt.) in northwestern California (Six Rivers National Forest). The moribund tree showed characteristic symptoms of Port-Orford-cedar root disease, including rapid wilting of the crown and a brown discoloration of inner bark and cambium at the root collar. Isolations from the margins of discoloration yielded pure cultures of P. lateralis on Difco cornmeal medium amended with 10 µg/ml of pima ricin. Koch's postulates were completed using the new Pacific yew isolate, inoculating both rooted yew cuttings and 1-yr-old Port-Orford-cedar seedlings. This is the first report of P. lateralis on a host other than Chamaecyparis. The presence of the fungus on Pacific yew, an understory component in most Port-Orford-cedar forest communities, may have implications for management of Port-Orford-cedar root disease. Its presence on a taxonomically distant host may help clarify the origin of P. lateralis, which has eluded investigators since its discovery.