First report of powdery mildew caused by erysiphe hedwigii on viburnum awabuki in Korea

S. E. Cho, S. H. Lee, S. Y. Lee, C. K. Lee, Hyeon-Dong Shin

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Abstract

Viburnum awabuki K. Koch (syn. V. odoratissimum var. awakubi (K. Koch) Zabel ex Rümpler), known as Japanese viburnum, is a broadleaf evergreen in the family Caprifoliaceae. This shrub is native to Japan, Taiwan, and the southern part of Korea, but is now planted worldwide for ornamental purposes (Choi et al. 2012). During summer to autumn of 2013, dozens of V. awabuki shrubs compactly planted for clipped hedge were observed to be infected with a powdery mildew in a public garden (33°28′07.1″ N, 126°29′28.9″ E) of Jeju, Korea. The powdery mildew colonies were circular to irregular, forming thin white patches on both sides of the leaves, detracting from their beauty. The voucher specimens were deposited in the Korea University Herbarium (KUS-F27310, F27319, and F27665). Hyphal appressoria were well-developed, lobed, and solitary or in opposite pairs. Conidiophores were cylindrical, 75 to 130 × 7.0 to 9.0 µm, and composed of 3 to 4 cells. Foot-cells of conidiophores were straight to substraight, cylindrical, and 22 to 40 µm long. Singly produced conidia were oblong-elliptical to ovate, 30 to 45 × 15 to 20 µm with a length/width ratio of 1.7 to 2.7, with angular/rectangular wrinkling of outer walls, and devoid of distinct fibrosin bodies. Germ tubes were produced on the perihilar position of conidia. No chasmothecia were found. These structures are typical of the powdery mildew Pseudoidium anamorph of the genus Erysiphe. The morphological characteristics were consistent with those of E. hedwigii (Lév.) U. Braun & S. Takam. (Braun and Cook 2012). The internal transcribed spacer (ITS) regions from KUS-F27310 were amplified with primers ITS1/ITS4 and sequenced (Takamatsu et al. 2009). The resulting 623 bp sequence was deposited in GenBank (accession no. KX375809). The obtained ITS sequence shared >99% similarity with those of E. hedwigii on V. dilatatum from China (KR048064) and V. lantana from Switzerland (AF298539). Pathogenicity was confirmed through inoculation by gently dusting conidia onto leaves of five healthy potted plants. Five noninoculated plants served as controls. Inoculated plants developed symptoms after 8 days, whereas the control plants remained symptomless. The fungus present on the inoculated plants was identical in morphology to those observed in the field. E. hedwigii has been recorded on some species of Viburnum (Farr and Rossman 2016), but not on V. awabuki. Therefore, this is the first report of powdery mildew caused by E. hedwigii on V. awabuki globally as well as in Korea. Interestingly, E. hedwigii has been known on some species of Viburnum in many countries of Europe, and was recently found on V. dilatatum in Shaanxi of northwest China (not published, but submitted in 2015 and currently available in NCBI database). Therefore, our finding suggests that E. hedwigii is expanding from Europe to Asia. Our field observations suggest that the disease would be a serious threat to the widespread ornamental plantings of Japanese viburnum in East Asia, especially in the case where the shrubs are growing in the shade.

Original languageEnglish
Pages (from-to)2533
Number of pages1
JournalPlant Disease
Volume100
Issue number12
DOIs
Publication statusPublished - 2016 Dec 1

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ASJC Scopus subject areas

  • Agronomy and Crop Science
  • Plant Science

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