Identity and pathogenicity of species of Phytophthora causing root rot of Douglas-fir in the Pacific Northwest

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. 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 third species, designated Phytophthora sp. 1, did not correspond to any previously described species. Phytophthora cinnamomi and P. cryptogea were highly virulent on dormant and growing Douglas-fir seedlings in greenhouse tests. Phytophthora drechsleri and Phytophthora sp. 1 appeared to be less virulent. Phytophthora 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 therefore be regarded as potentially dangerous forest pathogens in cool, moist sites.

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