First Report of Powdery Mildew Caused by Erysiphe hyperici on Hypericum ascyron in Korea

Abstract

Hypericum ascyron L., also called giant St. John’s wort, is an attractive wild plant and has become a popular flowering plant in gardens and parks in Korea. Extracts from the plant have antioxidant properties and antidiabetic activity (Kang et al. 2011). In September 2016, about 200 plants in a flower bed exhibited symptoms of powdery mildew with 30% disease incidence in Jinan, Korea (35°46'13N; 127°22'42E). Powdery mildew colonies were circular to irregular, forming white patches on both sides of the leaves, stems, and inflorescence. Severe infections caused malformation and premature senescence of the leaves and markedly decreased the aesthetic value of green leaves and yellow-colored petals. No chasmothecia were observed until the leaves senesced and died. A voucher specimen was deposited in the Korea University Herbarium (KUS-F29495). Hyphal appressoria were well-developed and lobed. Conidiophores were straight, 85 to 140 × 8 to 10 µm, and composed of 3 to 4 cells. Foot-cells of conidiophores were s...