First Report of Leaf Spot Caused by Cladosporium cladosporioides on Dendrobium officinale in China

Abstract

HomePlant DiseaseVol. 101, No. 6First Report of Leaf Spot Caused by Cladosporium cladosporioides on Dendrobium officinale in China PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of Leaf Spot Caused by Cladosporium cladosporioides on Dendrobium officinale in ChinaC. Sun, T. Wang, X. L. Shen, G. R. Wang, Q. K. Gao, B. G. Lou, and Y. Q. ShaoC. SunSearch for more papers by this author, T. WangSearch for more papers by this author, X. L. ShenSearch for more papers by this author, G. R. WangSearch for more papers by this author, Q. K. GaoSearch for more papers by this author, B. G. LouSearch for more papers by this author, and Y. Q. ShaoSearch for more papers by this authorAffiliationsAuthors and Affiliations C. Sun , Analysis Center of Agrobiology and Environmental Sciences, Zhejiang University, 310058 Hangzhou, China T. Wang , Institute of Insect Sciences, College of Agriculture & Biotechnology, Zhejiang University, 310058 Hangzhou, China X. L. Shen , Institute of Biotechnology, Zhejiang University, 310058 Hangzhou, China G. R. Wang , Center of Agricultural Technology Extension, 311203 Xiaoshan, China Q. K. Gao , Analysis Center of Agrobiology and Environmental Sciences, Zhejiang University, 310058 Hangzhou, China B. G. Lou , Institute of Biotechnology, Zhejiang University, 310058 Hangzhou, China Y. Q. Shao , College of Animal Sciences, Zhejiang University, 310058 Hangzhou, China. Published Online:4 Apr 2017https://doi.org/10.1094/PDIS-12-16-1857-PDNAboutSectionsSupplemental ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat Dendrobium officinale, an endangered orchid plant native to South and Southeast Asia, is widely used as a traditional herbal medicine in eastern China (Nie et al. 2012). Several bioactive components from D. officinale, such as polysaccharides, dendrobine, and stillnoids, have been demonstrated to exhibit antitumor, antimutagenic, and immunomodulatory activities (Nie et al. 2012). In the summer of 2016, heavy symptoms of an unknown leaf spot disease were seen on greenhouse-grown D. officinale in Xiaoshan of Hangzhou, Zhejiang Province, China, the major production area of this orchid plant. Thirty percent of 10,000 surveyed plants showed typical infection symptoms. Early symptoms observed were yellow or black round spots on leaves that averaged about 2 mm. Later on, spotted areas turned black or dark brown in color, increased to a diameter of about 6 mm and the surface became sunken. Infection always started from basal senescent leaves and went slowly up to the young leaves. Severely infected leaves became chlorotic or dark purple and fell off of the plants shortly after. A total of 20 symptomatic leaves were surface sterilized with 70% ethanol for 1 min, rinsed in 1% NaClO for 4 min and rinsed in sterile water five times. Small pieces (5 to 10 mm2) of disinfected tissue were cut, transferred onto potato dextrose agar (PDA), and incubated at 25°C. Three morphologically different fungi (DOS1 to DOS3) were isolated 5 days later. Pathogenicity of the isolated fungi was tested by spraying a 1 × 106 conidial suspension per ml of each isolate on 30 leaves collected from five healthy D. officinale plants. Another set of 30 leaves were sprayed with sterile water as noninoculated controls. All plants were covered by polyethylene film for 48 h and incubated under 25°C, 12/12 h (light/dark). After 5 to 8 days, only the leaves inoculated with the isolate DOS2 showed leaf spot resembling those observed on naturally infected D. officinale leaves. Pathogenicity tests with DOS2 isolate were repeated three times and results were consistent. The colony reisolated from DOS2, after 18 days of incubation at 25°C on PDA, appeared gray in color, with salient points, short dense fluffiness, clear water exudates on top, and yellow pigment released into the media. The backside of the colony appeared dark brown, identical to the original DOS2 isolate, thereby confirming Koch’s postulates. Microscopically, conidia were round to fusiform, growing singly or in clusters, 3.63 to 19.05 μm long × 3.75 to 8.85 μm wide (n = 100). Septa were observed in some conidia. The rDNA internal transcribed spacer (ITS) region of the DOS2 isolate was amplified using the primer sets ITS1 and ITS4. In addition, the elongation factor (EF) region of the same isolate was amplified using the primer sets EFf and EFr (Mahadevakumar et al. 2016; Yildiz et al. 2014). The ITS sequence of the isolate DOS2 deposited in GenBank (accession no. KX960912) showed 99% identity with that of a Cladosporium cladosporioides isolate (KP689176). Similarly, the EF sequence was also identical to C. cladosporioides reference strain (KP701818). To our knowledge, this is the first report of leaf spot on D. officinale caused by C. cladosporioides in China.