Morphological and molecular identification of new records and new host plants of powdery mildews (Erysiphaceae) from Mexico

Powdery mildew is one of the most severe diseases affecting Cucurbitaceae. We identify the members of Erysiphaceae infecting cucurbits in three producing regions in Mexico. We determined that Golovinomyces ambrosiae (Schwein.) U. Braun & R.T.A. Cook, Neoerysiphe sechii R. Gregorio-Cipriano & D. González, and Podosphaera xanthii (Castagne) U. Braun & Shishkoff infected cultivated and wild cucurbits species or subspecies. Leaf samples showing symptoms and signs of powdery mildew were collected from the northwestern, central western, and eastern regions of Mexico between 2017 and 2020. Species associated with the disease were identified based on morphology and internal transcribed spacer rDNA sequences. All powdery mildew specimens presented only the anamorph. Podosphaera xanthii was the predominant species; it was found in 84.76% of the samples and in 13 out of 14 species or subspecies of cucurbits. Neoerysiphe sechii was found in 15.24% of the samples and in only four cucurbit species from the central western and eastern regions of Mexico. Golovinomyces ambrosiae was documented for the first time in a Cucurbitaceae species (Sicyos deppei G.Don) from central west Mexico. Three new hosts were registered for N. sechii (Cucurbita ficifolia Bouché, Echinopepon milleflorus Naudin, and Sicyos laciniatus L.) and eight for P. xanthii (Cucurbita argyrosperma C.Huber, Cucurbita argyrosperma subsp. sororia (L.H.Bailey) Merrick & D.M.Bates, C. ficifolia, Cucurbita okeechobeensis subsp. martinezii (L.H.Bailey) T.C.Andres & G.P.Nabhan ex T.W.Walte, Cucurbita radicans Naudin, Sechium edule (Jacq.) Sw., S. laciniatus, and S. deppei).