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First Report of Powdery Mildew Caused by Neoerysiphe galeopsidis on Stachys japonica in China

Zhang, Q. C., Li, C. W., Xu, W. G., Pei, D. L.
Plant disease 2018 v.102 no.5 pp. 1027
Acanthaceae, Catalpa bignonioides, DNA primers, Erysiphe, Galeopsis, Lamium album, Lamium purpureum, Lycopus, Stachys, antibiotics, appressoria, calyx, conidia, conidiophores, disease control, germ tube, internal transcribed spacers, medicinal plants, necrosis, new genus, pathogenicity, petioles, polymerase chain reaction, powdery mildew, ribosomal DNA, roots, stems, wilting, China, Japan, United Kingdom
Stachys japonica is a traditional Chinese medicinal plant in the Lamiaceae. The roots are antipyretic, cough-suppressing, antibiotic, antiphlogistic, and have detoxifying effects (Wu and Li 1977). From April to July 2015 and again in 2016, a powdery mildew was observed on 60% of S. japonica plants in a nursery facility in Shangqiu, Henan Province, China. Symptoms first appeared as white colonies, which developed into abundant hyphal growth on both sides of the leaves, petioles, stems, and calyces. The yellow, spotty discolorations of infected leaves resulted in wilting and necrosis. Microscopically, the conidiophores were 102 to 220 × 9 to 11 μm and produced 2 to 7 immature catenescent conidia. Foot cells of conidiophores were straight, cylindrical, and 26 to 50 μm long, followed by 1 to 3 shorter cells. Conidia were hyaline, cylindrical oval to ellipsoidal, measuring 22 to 32 × 12 to 18 μm (length/width ratio = 1.6 to 2.3), and lacked distinct fibrosin bodies. Hyphal appressoria were lobed to multilobed. Germ tubes were produced in perihilar or lateral position of conidia. No chasmothecia were observed. The microscopic features were consistent with those of Neoerysiphe galeopsidis (DC.) U. Braun (Braun and Cook 2012). To confirm the identification, the internal transcribed spacer (ITS) regions of ribosomal DNA (rDNA) were amplified using primers ITS1 and ITS4 and sequenced. The resulting 630-bp sequence was deposited in GenBank (accession no. MF688993), and showed 99.4% similarity with ITS sequences of N. galeopsidis retrieved from plants of Lamium purpureum (KP642000) and Catalpa bignonioides (KP641989) in United Kingdom. Pathogenicity was confirmed by rubbing infected leaves onto leaves of five healthy plants. Five noninoculated plants served as controls. Powdery mildew developed on all inoculated leaves after 5 to 7 days. Noninoculated plants remained healthy. Braun (1999) introduced the new genus Neoerysiphe with Erysiphe galeopsidis as the type species. This species is known primarily on plants in the Acanthaceae, Bignoniaceae, and Lamiaceae (Farr and Rossman 2017). Zheng and Yu (1987) reported E. galeopsidis on Galeopsis bifida, Galeopsis spp., Lagopsis supina, Lamium album, L. barbatum, Lycopus spp., and S. baicalensis. Two records of powdery mildews of E. galeopsidis on S. japonica var. intermedia and S. japonica var. villosa have been reported from Japan (Farr and Rossman 2017). However, this is the first report of N. galeopsidis on S. japonica from China. An effective management program is needed to control this disease that may affect the yield of this medicinal plant in China.