First report of powdery mildew caused by Golovinomyces monardae on peppermint in Italy
KeywordsMedicinal plants Foliar pathogens Disease symptoms
Peppermint (Mentha × piperita) is widespread in cultivation in many regions of the world as a medicinal plants. During the summer of 2017, in a garden near Biella (northern Italy), 6-month-old peppermint plants exhibited a white powdery mildew growth on the adaxial surfaces of leaves, stems and petioles at temperature range from 15 to 28 °C. Infected leaves turned yellow and dropped. Conidia were hyaline, elliptical to doliform, without fibrosin bodies, and measured 25.2 to 39.8 × 15.7 to 28.9 (31.3 × 22.6 average) μm. Chasmothecia were not observed. Based on morphology, the causal agent was determined as Golovonomyces spp. (Scholler et al. 2016). The internal transcribed spacer region of rDNA of the pathogen was amplified using the primers ITS1/ITS4 and sequenced (GenBank Accession MG205583). BLASTn analysis (Altschul et al. 1997) of the 436 bp obtained showed 99% similarity with Golovinomyces monardae (G.S. Nagy) M. Scholler, U. Brawn & Anke Schmidt) (LC076842, voucher KR:M-43413). Pathogenicity was confirmed in a greenhouse at 18 to 25 °C by spraying leaves of healthy peppermint plants with the pathogen at 1 × 105 conidia/ml. Twenty plants were inoculated, and the same number of non-inoculated plants served as control. Typical spots of powdery mildew developed on inoculated plants 15 to 17 days after inoculation. Non-inoculated plants did not show symptoms. To our knowledge, this is the first report of powdery mildew caused by Golovinomyces monardae on peppermint in Italy. According to taxonomic and phylogenetic studies of the Golovinomyces biocellatus complex (Scholler et al. 2016) the same pathogen has been reported on peppermint in Germany, on Mentha spicata in Italy and on other hosts belonging to Lamiaceae and Verbenaceae (Garibaldi et al. 2010; Scholler et al. 2016).