First Report of Powdery Mildew Caused by Erysiphe alphitoides on Euonymus japonica in Korea

Abstract

HomePlant DiseaseVol. 101, No. 2First Report of Powdery Mildew Caused by Erysiphe alphitoides on Euonymus japonica in Korea PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of Powdery Mildew Caused by Erysiphe alphitoides on Euonymus japonica in KoreaH. B. Lee and T. T. T. NguyenH. B. LeeSearch for more papers by this author and T. T. T. NguyenSearch for more papers by this authorAffiliationsAuthors and Affiliations H. B. Lee T. T. T. Nguyen , Division of Food Technology, Biotechnology & Agrochemistry, College of Agriculture & Life Sciences, Chonnam National University, Gwangju 61186, Korea. Published Online:16 Nov 2016https://doi.org/10.1094/PDIS-08-16-1128-PDNAboutSectionsSupplemental ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat Euonymus japonica, family Celastraceae, is an evergreen shrub native to Korea, China, and Japan that is often used as an ornamental hedge plant. In October 2014, powdery mildew symptoms and signs were observed amphigenously on the leaves of E. japonica in a park in Seoul, Korea. Also, in June 2016, the same symptoms were found on E. japonica plants in a garden in Gwangju (35°10′N, 126°55′E), Korea, showing higher incidence and severity. Diseased leaves showed white colonies, associated with brown spots on the surface due to the presence of a hyperparasite, Ampelomyces quisqualis, and heavily infected young leaves. Voucher specimens were deposited at Environmental Microbiology Laboratory Fungarium, Chonnam National University, Gwangju, Korea, as EML-EJP1, EML-EJP2, and EML-EJP3. Appressoria of the fungus were lobed, and solitary or in opposite pairs. Measurements were made of 20 conidiophores and 50 conidia. Conidiophores were cylindrical, 45.0 to 77.0 × 6.5 to 10.5 μm. Foot cells of the conidiophores were straight to substraight to cylindrical, and followed by 1 to 3 shorter cells. Conidia were formed singly, cylindrical or ellipsoid-cylindrical, and measured 26.5 (–36.5) to 45 × 12 to 18.5 μm with a L/W ratio of 1.8 to 3.3. Short to moderately long germ tubes were produced terminating in lobed appressoria. The teleomorph was not found. Morphological characters were consistent with anamorphic Erysiphe species. To identify the fungus at the species level, mycelia and conidia of four samples from Euonymus japonica were collected with a sterile needle under a stereomicroscope. rDNA was extracted from mycelia and conidia using the Higene Genomic DNA Prep Kit for fungi (Biopact Corp., Korea). The internal transcribed spacers (ITS1 and ITS2) and 5.8S gene was amplified using primers ITS1F (5′-CTTGGTCATTTAGAGGAAGT-3′) and LR5F (5′-GCTATCCTGAGGGAAAC-3′) as by Lee (2013). A BLASTn search of the rDNA ITS sequences in GenBank indicated that EML-EJP1 (KP325487), EJP2 (KX495611), and EJP3 (KX495610) matched 100% (608/608 bp), 99.6% (766/769 bp), and 99.8% (497/498 bp) with Erysiphe alphitoides (Griffon & Maubl.) Braun & Takam (EF672350, AB257430, and AB292700, respectively). Phylogenetic analysis showed that our strains, EML-EJP1, EJP2, and EJP3, were placed within Alphitoides clade comprising E. alphitoides, E. akebiae, E. menispermi var. dahurica, E. wallrothii, E. sinomenii, and E. euonymicola. Interestingly, when the ITS sequences of our strain and some E. alphitoides were compared with E. euonymicola as a subclade within the Alphitoides clade, there was one base difference between them. The morphological characteristics of our strain completely matched E. alphitoides described by Takamatsu et al. (2007), except for a slight difference in width. The pathogenicity was confirmed by gently pressing the infected leaves onto five leaves of 5-year-old E. japonica plants. Five leaves were inoculated on each plant. The inoculated and noninoculated plants were maintained at 23 ± 2°C with a 12-h photoperiod and 80 to 85% RH. Ten days after inoculation, the symptoms were similar to those observed in the original diseased plants and the fungus on inoculated leaves was morphologically identical to that detected on their leaves, fulfilling Koch’s postulates. No disease developed on the controls. So far, E. euonymicola (formerly Oidium euonymi-japonici) has been found in only Euonymus spp. (Farr and Rossman 2016). In addition, Quercus spp. has been reported as the host of E. alphitoides. Recently, Sorbaria sorbifolia, Wisteria brachybotrys, and W. frutescens have been determined as additional hosts for E. alphitoides (Denton et al. 2016). This information indicates that E. alphitoides is able to infect a wide range of hosts and may pose a threat to multiple woody ornamental plant species. Further studies on the host and geographical ranges of E. alphitoides species are needed. To our knowledge, this is the first report of powdery mildew caused by E. alphitoides on E. japonica in Korea and in the world.