Powdery mildew (Erysiphe cruciferarum) on Brassicaceae in Brazil: Morphological and phylogenetic identification of Erysiphe cruciferarum as the powdery mildew agent of six Brassicaceae species in Brazil

A fungal complex belonging to the order Helotiales (including Erysiphaceae ) has been reported inducing powdery mildew (PM) on members of the Brassicaceae family worldwide. However, no formal report is available employing comprehensive taxonomic analyses of the PM-inducing fungi on these hosts in Brazil. Herein, PM isolates from six Brassicaceae vegetables (viz. broccoli, cauliflower, kale, Chinese cabbage, Indian mustard, and wild mustard) were collected in five geographic areas in the Brazilian Cerrado biome. Morphological aspects of hyphae, conidiophores, and conidia of these isolates were employed in combination with phylogenetic analyses of the sequences of the internal transcribed spacer (ITS) region of rDNA obtained with the pair of Erysiphaceae -specific primers (PMITS1 and PMITS2). Erysiphe cruciferarum was identified as the sole causal PM agent in all six Brassicaceae vegetables. Pathogenicity of the isolates was evaluated by spraying conidial suspension on Brassicaceae seedlings under greenhouse conditions. All isolates were pathogenic to their original hosts. PM has become an emergent foliar disease of Brassicaceae in Brazil especially in dry areas under dripping irrigation systems. This disease has been a limiting factor in the Cerrado region where a long and well-defined dry season favours disease onset and progression.