First report of powdery mildew caused by Erysiphe platani on sycamore (Platanus occidentalis) in South Korea.
In early July 2012, after a rainy spell in summer, an outbreak of powdery mildew on sycamore (Platanus occidentalis) was first observed on roadside trees in Gwangju, a southern province of South Korea. A more extensive nationwide survey revealed no powdery mildew in northern or central regions of South Korea. The disease had spread rapidly within Gwangju, although fungicide applications were carried out after the rainy spell. Major symptoms included white, superficial mycelia, grey to brown lesions on the surface of the leaves due to the presence of a hyperparasite, a slight chlorosis, and severe leaf distortion followed by defoliation. Conidiophores were produced singly, straight, and unbranched. Conidia were ellipsoid or doliiform. Primary conidia had a truncate base and rounded apex; secondary conidia had both a truncate base and apex. The conidial outer surface had a reticulated wrinkling. These characteristics and the host species corresponded to those of Microsphaera platani (syn. E. platani). BLASTn searches of GenBank revealed high sequence identity to E. platani (99.5-99.3%). This is thought to be the first report of powdery mildew caused by E. platani on sycamore in South Korea.