Japanese white oak seedlings killed by Phytophthora castaneae: a potential source of chestnut trunk rot

Necrotic lesions were found on the leaves and stems of Japanese white oak (Quercus myrsinifolia) seedlings on a nature trail in Japan. A species of Phytophthora was isolated from the necrotic lesions and adjacent soil. Molecular phylogenetic analysis and morphological examination revealed it to be Phytophthora castaneae, known as a causal pathogen of trunk rot on chestnuts. Pathogenicity testing showed that P. castaneae caused leaf blight on previously healthy Japanese white oak seedlings. In addition, using a soil infestation method, we confirmed that it was also pathogenic to chestnut seedlings, but the roots of Japanese white oak were not infected. This is the first report of P. castaneae causing disease in a natural ecosystem in Japan.