Identity and Pathogenicity of Species of Phytophthora Causing Root Rot of Douglas-fir in the Pacific Northwest

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Abstract
Three species of Phytophthora previously unreported from Douglas-fir were isolated along with P. cinnamomi from diseased trees from forest nurseries, forest outplanting sites and seedling storage facilities in western Oregon and Washington [USA]. Two species were identified as P. cryptogea and P. drechsleri on the basis of sporangial and colony morphology, temperature-growth relations and by comparisons with isolates of known identity. A 3rd species, designated Phytophthora sp. 1, did not correspond to any previously described species. P. cinnamomi and P. cryptogea were highly virulent on dormant and growing Douglas-fir seedlings in greenhouse tests. P. drechsleri and Phytophthora sp. 1 appeared to be less virulent. P. cryptogea, P. drechsleri and Phytophthora sp. 1 are similar to P. lateralis, a destructive pathogen of Port-Orford-cedar, in growth at low temperatures and should be regarded as potentially dangerous forest pathogens in cool, moist sites.

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