First Report of Powdery Mildew Caused by Erysiphe euonymi-japonici on Euonymus japonicus in Central China.

Abstract

Euonymus japonicus Thunb. is a popular, woody, ornamental plant in China. From June to September 2010, severe outbreaks of powdery mildew occurred on all investigated E. japonicus plants used for hedges in Zhoukou and Shangqiu cities of Henan province in central China, which is the second largest province in terms of ornamental plant cultivation. A large amount of fungicide was used to prevent the fungal disease, which caused serious environmental pollution and was estimated to result in a 40 to 60% increase in preservation cost of E. japonicus hedges. Gray-white colonies of powdery mildew fungi occurred mainly on the leaves of E. japonicus, on average approximately 50% of the leaves of an individual plant were infected by the fungi. On severely infected leaves, mycelia were amphigenous, thick, forming irregular white patches, and effused to cover the whole surface. Subsequently, these leaves became chlorotic, curled, and withered. The fungus was identified as Erysiphe euonymi-japonici (Vienn.-Bourg.) U. Braun & S. Takam on the basis of the following data of microscopic morphology with scanning electron microscopy and molecular phylogenetic analysis of the internal transcribed spacer (ITS) region. The fungus had unbranched conidiophores with an average length of 57.3 μm and width of 8.8 μm, which was composed of a cylindrical foot cell, 15 to 40 × 6 to 10 μm and one to three shorter cells or cells of about the same length. Conidia were borne singly, cylindrical, or ellipsoid-cylindrical, with an average length of 27.7 μm and width of 10.4 μm. Chasmothecia were not observed in the collected samples during the whole outbreak period. PCR amplification and sequencing of the ITS region was amplified using the universal primers ITS1 and ITS4 (4). The obtained ITS sequence was assigned Accession No. HQ012432 in GenBank, which had a 99 and 98% nt similarity with the ITS sequences (ITS region including the 5.8S rDNA) of two Erysiphe euonymi-japonici isolates from Japan and Argentina in GenBank (Accession Nos. AB250228 and AB250229 (3), respectively). To our knowledge, Erysiphe euonymi-japonici has not been reported previously from central China, although synonymous species, Oidium euonymi-japonici and Microsphaera euonymi-japonici, were reported in southwestern (Sichuan Province) (1) and eastern (Shandong Province) (2) regions. Herbarium specimens are available at the Key Laboratory of Plant Genetics and Molecular Breeding, Zhoukou Normal University, Zhoukou, China.