Archivio Journal of Plant Pathology

Abstract:

During September to November of 2013 and 2014, typical symptoms of powdery mildew were detected on the leaves of netleaf oak (Quercus rugosa) trees growing in the Distrito Federal (Mexico). Symptoms appeared as irregular necrotic lesions with greyish powdery masses on both sides of the leaves. The preliminary identification of fungus was done based on of morphological characters. Mycelium was amphigenous, persistent, greyish, in dense patches or effuse. Hyphal appressoria were lobed and solitary. Conidiophores were hyaline, erect, straight, length up to about 86 μm. Foot cells were cylindrical, straight, followed by 1-3 shorter cells, and forming conidia singly. Conidia were hyaline, obovoid-doliiform, 27-37x16-24 μm, with germ tubes terminal to subterminal. Conidial appressoria were lobed. Chasmothecia were not observed. The morphological characters were consistent with those of the anamorphic state of Erysiphe alphitoides (Braun and Cook, 2012). To confirm the identification, the complete internal transcribed spacer (ITS) region of rDNA was amplified using primers ITS4 and ITS5, and sequenced directly. The resulting 647 bp sequence was deposited in GenBank (accession No. KR269919). A GenBank BLASTn search of this sequence revealed 99% similarity with three ITS sequences of E. alphitoides (AB292699, AB292702 and AB292704). Based on the morphological data and ITS sequence analysis, the fungus was identified as E. alphitoides. To our knowledge, this is the first report of E. alphitoides causing powdery mildew on netleaf oak in Mexico.