First Report of Powdery Mildew Caused by Erysiphe heraclei on Ammi majus in Mexico

Ammi majus L. (family Apiaceae), known as bishop's weed, is a medicinal and ornamental plant widely distributed in parts of Europe, the Mediterranean, and western Asia. During July to September 2013, typical symptoms of powdery mildew were observed on bishop's weed cultivated in gardens throughout Estado de Mexico, Mexico. Diseased plants exhibited patches with white, powdery appearance on leaves, stems, and inflorescences. An examination of infected tissues using light microscopy and scanning electron microscopy showed that the mycelium was amphigenous, effuse, or in patches; hyphal appressoria were lobed, solitary, 4 to 7 [mu]m diameter; conidiophores were erect from top of the mother cell, 110 to 135 [mu]m long, with cylindrical foot cells that were straight, 27 to 55 x 8 to 10 [mu]m, followed by 1 to 2 shorter cells. Hyaline conidia formed singly were cylindrical, 28 to 43 x 14 to 19 [mu]m, without fibrosin bodies; the germ tube arose from one end of the conidia; and the conidial appressoria were lobed. Chasmothecia were not observed. These morphological characteristics were consistent with Erysiphe heraclei(Braun and Cook 2012). The internal transcribed spacer (ITS) region of the rDNA was amplified with primers ITS4 and ITS5 and sequenced directly. The resulting 732-bp sequence was deposited in GenBank (Accession No. KR269918). BLASTn analysis showed 100% nt identity to two sequences (Accession Nos. KM491178 and GU173850) of E. heraclei reported from Peucedanum japonicum and Pleurospermum kamtschaticum in Korea, respectively. Based on its morphological features and ITS sequence, the fungus on bishop's weed was identified as E. heraclei. Pathogenicity was confirmed by gently dusting conidia from infected leaves onto leaves of 10 healthy bishop's weed plants. Five noninoculated plants served as controls. All inoculated plants developed similar symptoms to the original observation after 12 days, whereas no symptoms were observed on control plants. Microscopic examination of the fungus on inoculated plants showed that it was identical morphologically to that originally observed. Erysiphe heraclei has a relatively wide host range among plants in the Apiaceae, including carrot, celery, dill, parsley, and parsnip (Koike et al. 2007), and has been reported causing symptoms of powdery mildew on A. majus in Europe (France, Greece, Italy, Portugal, Spain, and Switzerland), Asia (Israel, Iran, Iraq, and Jordan), and Africa (Morocco and Egypt). To the best of our