Abstract
In autumn, 1997, a powdery mildew on platanus occurred throughout the area of Tokyo, Japan. The fungus formed single conidia and multi-lobed appressoria on hyphae. Therefore, the fungus was identified as an Oidium sp. of the Erysiphe polygoni type. The pathogenicity of the fungus to three species of platanus was confirmed by replicating the disease symptoms in an inoculation experiment. Therefore, three species of platanus were added to the list of host plants of powdery mildew fungus. This report is the first record of platanus powdery mildew in Japan.
