Distribution and Pathogenicity of P. nemorosa and P. pseudosyringae in California’s Coastal Forests

Camille E. Jensen, Allison C. Wickland and David M. Rizzo; Department of Plant Pathology, One Shields Ave., University of California, Davis, CA 95616; 530-754-9894; cjensen@ucdavis.edu

Phytophthora nemorosa and P. pseudosyringae are two recently described species that have been recovered during studies of P. ramorum (cause of sudden oak death). The distribution of P. nemorosa and P. pseudosyringae was compiled from a number of surveys of coastal California and Oregon. P. nemorosa was isolated from Umbellularia californica, Sequoia sempervirens and Lithocarpus densiflorus in redwood and mixed evergreen forests from Monterey Co., CA to Coos Co., OR. P. pseudosyringae was isolated from U. californica and Quercus agrifolia in mixed-evergreen forests and coast live oak woodlands from San Luis Obispo Co. to Humboldt Co. CA. Inoculation experiments were conducted to satisfy Koch’s postulates and verify pathogenicity of P. nemorosa and P. pseudosyringae on these tree species. Based on re-isolation of the pathogen and lesion lengths significantly different than controls (P<0.05), S. sempervirens, Q. agrifolia, L. densiflorus, and U. californica were confirmed as hosts of P. nemorosa and Q. agrifolia and U. californica as hosts of P. pseudosyringae. The ecology of P. nemorosa and P. pseudosyringae is very similar to P. ramorum, however, these species do not cause landscape level tree mortality.

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