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First Report of Powdery Mildew Caused by Erysiphe polygoni on Buckwheat in Yunnan, China

    Authors and Affiliations
    • W. J. Lu
    • L. H. Wang
    • Y. Q. Wang
    • C. H. Li , Biotechnology and Germplasm Resources Institute, Yunnan Academy of Agricultural Sciences, Yunnan Provincial Key Lab of Agricultural Biotechnology, Key Lab of Southwestern Crop Gene Resources and Germplasm Innovation, Ministry of Agriculture, Kunming, 650223, China.

      Buckwheat (Fagopyrum esculentum Moench) is an annual herb, mainly used in China for as food and as a nectar source for pollinators. Since 2012, powdery mildew has been consistently observed on buckwheat in its growing regions in Yunnan, China. Initially, irregular white, dust-like colonies occurred mainly on the adaxial surface of infected leaves. As the disease progressed, colonies became abundant, covering the entire adaxial surface, and white patches then developed on the abaxial leaf surface and on stems. Foot cells of the conidiophores were cylindrical, straight, relatively short, measured 36 to 40 × 6 to 10 μm, and were followed by two cells. Conidia were produced singly, hyaline, cylindrical to ovoid, and measured 30 to 45 × 13 to 19 μm. No fibrosin bodies were observed in the conidia. Germ tubes were produced from the ends of the conidia. Cleistothecia were not detected with a microscopic on collected powdery mildew-infected samples. Based on morphological features, the fungus was identified as Erysiphe polygoni DC. (Bradley et al. 2007; Gaetán et al. 2004). To confirm the identification, the internal transcribed spacer (ITS) region of rDNA of the pathogen was amplified with the universal primers ITS1/ITS4 (Takamatsu et al. 2009), and sequenced. The length of the ITS fragment was 621 bp and the ITS sequence (GenBank Accession No. KP076437) showed 99% homogeneity with those of E. polygoni on Rumes crispus in the United States (AF011308) and on Polygonum arenastrum in the United States (AF011307). To confirm pathogenicity, inoculation was done by gently pressing the adaxial surface of an infected leaf with abundant sporulation onto the adaxial surface of a healthy leaf of a 5-week-old buckwheat plant. Five plants were inoculated. They were grown in a chamber at 20 to 25°C, 80% relative humidity, with 16-h photoperiod. Five noninoculated control plants were grown in another growth chamber under the same conditions as the inoculated plants. Inoculated and control plants were covered with polyethylene bags for 48 h after inoculation. Symptoms consistent with the infected field plants were observed on the inoculated plants, while no symptoms were observed on the control plants. Microscopic observation revealed that the pathogen growing on the inoculated plants was consistent with the morphology of the original fungus. Powdery mildew on buckwheat infected by E. polygoni has been reported in California, China, Germany, India, Japan, Korea, Romania, Russia, Taiwan, Turkey, and USSR (Farr and Rossman 2015). To our knowledge, this is the first report of powdery mildew caused by E. polygoni DC. on buckwheat in Yunnan, China.