Powdery Mildew on Mulberry in Yunnan,China is Distinct from Other Phyllactinia spp. on Morus

The occurrence of an epidemic outbreak of a powdery mildew disease on mulberry in Yunnan province, China, is reported. Its symptoms are characteristic for powdery mildews and visible as white pathches covering the abaxial surfaces of leaves leading to chlorosis and necrosis. The pathogen is morphologically barely distinguishable from Phyllactinia moricola. However, it exhibits several new morphological characteristics which 2–3 conidia could be formed in short chains at the apex of the conidiophores and the conidia could produce two germ tubes in any position. Phylogenetic analyses of ITS sequences show that the pathogen has a close genetic relationship with P. moricola and Ph. broussonetiae‐kaempferi, two species on hosts belonging to family Moraceae. However, the ITS differences between Japanese sequences and the Chinese sequence derived from mulberry are greater than expected for a single species and suggest a cryptic species in China, but the present data are not sufficient for a final conclusion. Therefore, the Morus powdery mildew in Yunnan can currently only be classified as Phyllactinia sp. Morphological features, including conidial germination pattern of this powdery mildew are described in detail, and the local climatic conditions of the disease are analysed, which will provide the base for finding an effective method, including bio‐control, to control the disease under local conditions.