First Report of Powdery Mildew Caused by Leveillula clavata on Wild Poinsettia (Euphorbia heterophylla) in China

Abstract

HomePlant DiseaseVol. 103, No. 5First Report of Powdery Mildew Caused by Leveillula clavata on Wild Poinsettia (Euphorbia heterophylla) in China PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of Powdery Mildew Caused by Leveillula clavata on Wild Poinsettia (Euphorbia heterophylla) in ChinaH. Wu, W. Miao, Y. Pan, R. Di, Q. He, and W. LiuH. WuCollege of Environment and Plant Protection, Hainan Key Laboratory for Sustainable Utilization of Tropical Bioresource, Hainan University, Haikou 570228, China; and , W. Miao†Corresponding author: W. Miao; E-mail Address: weiguomiao1105@126.comhttp://orcid.org/0000-0001-8991-5511College of Environment and Plant Protection, Hainan Key Laboratory for Sustainable Utilization of Tropical Bioresource, Hainan University, Haikou 570228, China; and , Y. PanCollege of Environment and Plant Protection, Hainan Key Laboratory for Sustainable Utilization of Tropical Bioresource, Hainan University, Haikou 570228, China; and , R. DiCollege of Environment and Plant Protection, Hainan Key Laboratory for Sustainable Utilization of Tropical Bioresource, Hainan University, Haikou 570228, China; and Department of Plant Biology, Rutgers, the State University of New Jersey, New Brunswick, NJ 08901, U.S.A., Q. HeCollege of Environment and Plant Protection, Hainan Key Laboratory for Sustainable Utilization of Tropical Bioresource, Hainan University, Haikou 570228, China; and , and W. LiuCollege of Environment and Plant Protection, Hainan Key Laboratory for Sustainable Utilization of Tropical Bioresource, Hainan University, Haikou 570228, China; and AffiliationsAuthors and Affiliations H. Wu1 W. Miao1 † Y. Pan1 R. Di1 2 Q. He1 W. Liu1 1College of Environment and Plant Protection, Hainan Key Laboratory for Sustainable Utilization of Tropical Bioresource, Hainan University, Haikou 570228, China; and 2Department of Plant Biology, Rutgers, the State University of New Jersey, New Brunswick, NJ 08901, U.S.A. Published Online:11 Mar 2019https://doi.org/10.1094/PDIS-09-18-1656-PDNAboutSectionsSupplemental ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat Wild poinsettia (Euphorbia heterophylla L.) is a species in the genus Euphorbia (family Euphorbiaceae), which is a serious weed problem in agricultural and pasture land worldwide (Chachalis 2015). In China, this invasive alien plant is widely distributed throughout the tropical and subtropical regions and is commonly used as an ornamental and in Chinese herbal medicine. In December 2017, typical symptoms of powdery mildew were observed on 60% of E. heterophylla plants in a nursery of Sanya Science and Technology Academy for Crop Winter Multiplication (18°18′10″ N; 109°24′44″ E) in the city of Sanya in Hainan Province, China. White, superficial masses of mycelia and conidia covered the leaf surfaces of affected plants, which caused them to discolor and become necrotic. Mycelium was partly internal and partly external. Conidiophores that developed from internal mycelium and emerged through the stomata were hyaline, single, erect, 117 to 248 × 7 to 11 µm, with cylindrical foot cells, followed by two to three shorter cells. Conidia were formed singly, spathulate or clavate, 47 to 70 × 14 to 24 µm (length/width ratio = 2.8 to 3.6), without fibrosin bodies, showed angular/rectangular wrinkling and verrucose appearance of outer walls, and produced germ tubes at the terminal position. Indistinct appressoria arose from germ tubes. Based on these morphological characteristics, this pathogen resembled Leveillula clavata (Braun and Cook 2012). The teleomorph was not found. A specimen was deposited in the Hainan University Plant Pathology Herbarium as HUEH-17. To confirm the identification, genomic DNA was extracted from mycelium, conidiophores, and conidia with single leaves using a Fungal DNA kit (Omega Bio-Tek, U.S.A.); the rDNA internal transcribed spacer (ITS) region was amplified with the primers ITS1/ITS4 (White et al. 1990) and sequenced directly. The resulting 620-bp sequence was deposited in GenBank (accession no. MH921994). A BLASTn search in GenBank of this sequence revealed >99% similarity with the ITS se-quences of Cf. L. clavata on plants of E. pulcherrima (LC108845) from Japan. To confirm pathogenicity, five healthy potted wild poinsettia plants were inoculated by gently pressing a powdery mildew-infected leaf onto 15 young leaves. Five noninoculated plants served as controls. All the plants were maintained in a greenhouse at 24 to 30°C, 70% relative humidity, and a 16-h photoperiod. After 7 days, inoculated leaves showed powdery mildew symptoms, whereas no symptoms were observed on control plants. The fungus observed on inoculated plants was morphologically identical to that on the original infected leaves, fulfilling Koch's postulates. There are reports of the Oidiopsis state of a powdery mildew on poinsettia in other countries. In Australia, L. taurica was identified as the cause of powdery mildew on wild poinsettia based on the presence of an Oidiopsis anamorph state (Liberato et al. 2005). In Italy, L. clavata was identified as the causal agent on poinsettia based on Oidiopsis anamorph characteristics (Garibaldi et al. 2006). However, morphological characteristics and sequence data of the fungus are more consistent with L. clavata than L. taurica. To our knowledge, this is the first record of L. clavata infecting E. heterophylla in China. It is not yet clear how the pathogen arrived in China. According to our field observations, we are concerned that powdery mildew may reduce the importance of this plant as an ornamental and medicinal plant.References:Braun, U., and Cook, R. T. A. 2012. Taxonomic Manual of the Erysiphales (Powdery Mildews). CBS Biodiversity Series No. 11. CBS, Utrecht, the Netherlands. Google ScholarChachalis, D. 2015. Hell. Plant Prot. J. 8:27. Google ScholarGaribaldi, A., et al. 2006. Plant Dis. 90:827. https://doi.org/10.1094/PD-90-0827C Link, ISI, Google ScholarLiberato, J. R., et al. 2005. Australas. Plant Pathol. 34:409. https://doi.org/10.1071/AP05043 Crossref, ISI, Google ScholarWhite, T. J., et al. 1990. Page 315 in: PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, CA. Crossref, Google ScholarThe author(s) declare no conflict of interest.Funding: This study was supported by Innovative Research Team Project of Hainan Natural Science Foundation number 2016CXTD002, Hainan Key Research and Development Project number ZDYF2016208, China Agriculture Research System number CARS-34-BC1, and National Natural Science Foundation of China number 31660033.DetailsFiguresLiterature CitedRelated Vol. 103, No. 5 May 2019SubscribeISSN:0191-2917e-ISSN:1943-7692 DownloadCaptionTomato leaves infected with Tomato chlorotic dwarf viroid (Olmedo-Velarde, Roy, Belanger, Watanabe, Hamasaki, Mavrodieva, Nakhla, and Melzer). Photo credit: M. J. Melzer. Spinach plants with downy mildew symptoms caused by Peronospora effusa (Kandel, Mou, Shishkoff, Shi, Subbarao, and Klosterman). Photo credit: S. L. Kandel. Metrics Article History Issue Date: 8 May 2019Published: 11 Mar 2019First Look: 27 Dec 2018Accepted: 18 Dec 2018 Pages: 1034-1034 Information© 2019 The American Phytopathological SocietyFundingInnovative Research Team Project of Hainan Natural Science FoundationGrant/Award Number: 2016CXTD002Hainan Key Research and Development ProjectGrant/Award Number: ZDYF2016208China Agriculture Research SystemGrant/Award Number: CARS-34-BC1National Natural Science Foundation of ChinaGrant/Award Number: 31660033

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