Occurrence of powdery mildew caused by Erysiphe betae on chard [Beta vulgaris L. subsp. cicla (L.) Koch] in Greece

Chard [Beta vulgaris L. subsp. cicla (L.) Koch] is a tall leafy green vegetable with a thick, crunchy stalk, which is one of the most popular vegetables in the Mediterranean region. In late September 2016, a severe outbreak of powdery mildew on the chard cultivar Verde a Costa' Argentata 2 occurred in an isolated 0.1 ha field in the Heraklio area, Crete, Greece, at an incidence of approximately 90%. Initial disease symptoms included small, scattered, circular, white, dust-like colonies of powdery mildew mainly on adaxial surfaces of older leaves. As the disease progressed, white mycelia covered the whole of the foliar parts, and the plant took on a dusty white appearance. No chasmothecia were found on collected samples. Based on morphological characteristics of the imperfect stage, pathogenicity and internal transcribed spacer (ITS) analysis, the pathogen was identified as Erysiphe betae (Vaňha) Weltzien. To our knowledge, this is the first report of E. betae infections on chard in Greece.