First Report of Powdery Mildew Caused by Erysiphe quercicola on Quercus mongolica in Korea

Mongolian oak (Quercus mongolica Fisch. ex Ledeb.), belonging to family Fagaceae, is mainly distributed in Asian countries, including China, Japan, Korea, and Mongolia. From August to November 2016, a powdery mildew was observed on Q. mongolica on Chilgap Mountain in Chungcheongnam-do and in a garden of Chonnam National University, Gwangju, Korea. Diseased leaves showed irregular chlorotic lesions on both sides. Two voucher specimens were deposited at the Environmental Microbiology Laboratory Fungarium, Chonnam National University, Gwangju, Korea (EML-QMPW1, EML-QMPW2). Conidiophores were erect, 55.5 to 108.5 μm long and composed of 1 to 2 cells. Foot-cells of conidiophores were cylindrical, and straight or curved at the base. Conidia were formed singly, obovoid to ellipsoid, ends subtruncate, and 28.0 to 38.5 μm × 15.5 to 23.0 μm with a length/width ratio of 1.5 to 2.2. The morphological characteristics were consistent with Erysiphe quercicola S. Takam. & U. Braun (†;†). To confirm the morphological identification, genomic DNA was extracted directly from conidia, conidiophores, and mycelium using the Higen Genomic DNA Prep Kit for fungi (Biopact Corp., Daejeon, Korea). The internal transcribed spacer (ITS) region of the ribosomal DNA (rDNA) from isolates EML-QMPW1 and EML-QMPW2 was amplified with primers ITS5 and PM6, as described by†, with a minor modification of the forwarding sequence of ITS5 (5’-GGAAGTAAAAGTCGTAACAA-3’). The ITS sequences of the two isolates, EML-QMPW1 and EML-QMPW2, were deposited as GenBank Accession Nos. KY744237 and KY744238, respectively. A BLASTn search matched the rDNA ITS sequences to E. quercicola at 99.8% (509/510 bp) and 99.8% (508/509 bp) (AB237796 and AB193588), respectively. On the basis of the morphological and molecular analyses, the fungus was identified as E. quercicola. This fungus was reported as a pathogen isolated from tropical plants under the anamorph name of Pseudoidium anacardii, which was later assigned as E. quercicola (†;†). The pathogenicity was confirmed by gently pressing the infected leaves onto 10 healthy leaves of Q. mongolica plants maintained at 23°C ± 2°C. Ten uninoculated leaves served as controls. Nine to 10 days after the inoculation, the symptoms of the inoculated plants and the morphological characteristics of the reisolated pathogen were similar to those observed in the original diseased plants. No symptoms developed on the control plants. So far, E. alphitoides sensu lato has been found in Q. mongolica collected from Korea and Japan (†). In Korea, E. quercicola was previously found on Q. phillyraeoides (†). To our knowledge, this is the first record of powdery mildew caused by E. quercicola on Q. mongolica in Korea. © 2017, American Phytopathological Society. All rights reserved.