First report of powdery mildew caused by Erysiphe limonii on perennial hybrid statice in Korea

Perennial hybrid statice (Limonium latifolium x bellidifolium, Plumbaginaceae) is cultivated worldwide and grown as a commercial cutflower crop in plastic greenhouses in Korea. During the winter of the 2012 to 2013, perennial hybrid statice cv. Yellow Cream was found to be damaged by a powdery mildew with approximately 10 to 90% disease incidence in 30 greenhouses surveyed in about 10 ha of Gochang (35°26′08.96″ N; 126°42′07.49″ E), Korea. Symptoms first appeared as thin white patches, which progressed to abundant hyphal growth on both side of the leaves and stems. Infected plants were generally not harvested by the farmers, mainly due to signs of discoloration and yellowing. A voucher specimen was deposited in the Korea University Herbarium (KUS). No chasmothecia were found. Hyphal appressoria were well developed, lobed, and solitary or in opposite pairs. Conidiophores were cylindrical, 82 to 142 × 7.5 to 9.0 µm, and composed of 3 to 4 cells. Foot-cells of conidiophores were straight, cylindric, and 25 to 40 µm long. Singly produced conidia were cylindric-oval to oblong, 30 to 49 × 14 to 22 µm with a length/width ratio of 1.6 to 2.9, with angular/rectangular wrinkling of outer walls, and devoid of distinct fibrosin bodies. Germ tubes were produced in the perihilar position of conidia. These structures are typical of Pseudoidium anamorph of the genus Erysiphe. The measurements and host range match with those of E. limonii L. Junell (Braun and Cook 2012). The internal transcribed spacer (ITS) region of rDNA of KUS-F27301 was amplified with primers ITS5/P3 and sequenced (Takamatsu et al. 2009). The resulting 679-bp sequence was deposited in GenBank (Accession No. KF318724). The ITS sequence showed >99% similarity with the sequences of E. limonii on Limonium spp. (LC009897, LC010038, and LC010039). Pathogenicity was confirmed through inoculation by dusting conidia onto leaves of five healthy potted perennial hybrid statice cv. Yellow Cream. Five noninoculated plants served as controls. Inoculated plants were isolated from noninoculated plants in separate rooms in a greenhouse maintained at 16 to 20°C. Inoculated plants developed symptoms after 7 days, whereas the controls remained symptomless. The fungus presented on the inoculated plants was identical morphologically to that originally observed on diseased plants, fulfilling Koch’s postulates. Previously, E. limonii was reported in Europe, Asia, and Canary Islands (Braun and Cook 2012). Powdery mildew disease associated with an Oidium sp. was recorded on L. latifolium x bellidifolium in Japan (Hagiwara et al. 1998) and on L. sinuatum in Korea (Kwon et al. 2001). The Japanese and Korean records were nearly identical to each other and also are close to morphological characteristics of E. limonii. Nevertheless, this is the first report of powdery mildew caused by E. limonii on perennial hybrid statice in Korea. Since perennial hybrid statice is cultivated mostly during the winter season in plastic greenhouses with poor ventilation and low light intensity, the occurrence of powdery mildew disease poses a serious threat to the cutflower production in Korea.