Geographic distribution, disease symptoms and pathogenicity of Phytophthora nemorosa and Phytophthora pseudosyringae in California, USA

Abstract

SummaryDuring the course of surveys for Phytophthora ramorum in coastal forests of California and Oregon, P. nemorosa and P. pseudosyringae were frequently isolated from foliage and stems of the same hosts as P. ramorum. Both species ranged from central California to Oregon within 50 km of the Pacific Ocean. Both were also found in the Sierra Nevada Mountains. Phytophthora nemorosa was primarily found infecting trees in coast redwood forests and was most often isolated from bay laurel leaves (Umbellularia californica), bleeding cankers on the main bole of tanoak (Lithocarpus densiflorus), and leaf and small stem tissue of redwood (Sequoia sempervirens). Phytophthora pseudosyringae was primarily isolated from hosts found in coast live oak woodlands. Bay laurel was the most common host while infection of coast live oak (Quercus agrifolia) stems was less frequent. Inoculation studies confirmed the pathogenicity of P. nemorosa and P. pseudosyringae on their most common hosts.