First Report of Powdery Mildew Caused by Erysiphe heraclei on Hedera helix in Mexico

English ivy (Hedera helix L.) is an ornamental plant grown widely in parks and yards. During the falls of 2013 and 2014, typical symptoms of powdery mildew were detected on English ivy plants in parks and yards throughout Estado de México and Distrito Federal, Mexico. Symptoms appeared as irregular white patches on both sides of the leaves. Distortion of leaves was observed when plants were severely infected. The preliminary identification of the fungus was performed by microscopically examining the morphological characters. Mycelium was amphigenous, effuse or in patches; hyphal appressoria were lobed, solitary, 5 to 7 μm diameter; the conidiophores were erect from the top of the mother cell, 102 to 143 μm long, with cylindrical foot cells that were straight, 34 to 59 × 8 to 10 μm, followed by 1 to 3 shorter cells. Hyaline conidia formed singly and were cylindrical, 31 to 47 × 12 to 18 μm, without fibrosin bodies; the germ tube arose from one end of the conidia; and the conidial appressoria were lobed. Chasmothecia were not observed. On the basis of these morphological characteristics, the fungus was identified as Erysiphe heraclei (Braun and Cook 2012). In order to confirm the identification, the complete internal transcribed spacer (ITS) region of rDNA was amplified with primers ITS5 and ITS4 (White et al. 1990), and sequenced directly. The resulting 660-bp sequence was deposited in GenBank (Accession No. KT211366) and was compared with other ITS sequences. BLASTn analysis of the sequence showed a 99% nt identity with those of E. heraclei from English ivy from Italy (EU010381) and chervil (Anthriscus cerefolium L.) from Korea (KF111807). Pathogenicity was confirmed by gently dusting conidia from infected leaves onto 30 healthy leaves of English ivy plants. Ten noninoculated leaves served as controls. Inoculated leaves developed powdery mildew symptoms 10 days after inoculation, whereas no symptoms were observed on the control plants. The fungus present on inoculated plants was morphologically identical to that originally observed on diseased plants. The fungus examined was identified as Erysiphe heraclei through the combination of morphological characterization and amplification of the ITS region of rDNA. Powdery mildew of H. helix caused by E. heraclei has been reported in Italy, South Africa, and China (Liu et al. 2015); but to our knowledge, this is the first report in Mexico. © 2016, American Phytopathological Society. All rights reserved.