First Report of Powdery Mildew Caused by Podosphaera fuliginea on Veronica spicata in China.

Abstract

Veronica spicata L. (syn. Pseudolysimachion spicatum Opiz), Plantaginaceae, is a perennial herb and frequently cultivated in gardens as an ornamental plant in China. In June 2017, powdery mildew infections were observed on V. spicata in Jingyuetan National Forest Park (43.80°N, 125.46°E), Changchun, China. A voucher specimen was deposited in the Herbarium of Mycology of Jilin Agricultural University under the accession no. HMJAU-PM91763. The incidence of the disease on leaves and stems was about 30 to 50%. The disease initially appeared as thin white colonies, which subsequently developed into dense effuse white colonies on the plant. Hyphae were flexuous to straight, septate, 3.0 to 8.0 μm wide. Hyphal appressoria were indistinct or nipple-shaped, solitary. Conidiophores (n=30) arise from the upper surface of hyphal mother cells, erect to straight, 133.4 to 176.2 × 7.8 to 10.7 μm. Foot-cells (n=40) were cylindrical, straight or slightly flexuous, 39.1 to 78.5 × 7.4 to 9.7 μm, and followed by 1 to 3 short cells. Conidia (n=45) were catenescent, ellipsoid, oval, or doliiform, with fibrosin bodies, 17.8 to 27.8 × 12.2 to 17.4 μm, length/width ratio 1.3 to 2.1. Germ tubes were produced at the subterminal to lateral part of conidia, straight or sinuous, without a distinct terminal appressorium. The sexual morph was not observed in the collected samples. The morphological characteristics of the asexual morph were consistent with Podosphaera fuliginea (Schltdl.) U. Braun & S. Takam. (Braun and Cook 2012). To confirm the identification, the complete internal transcribed spacer (ITS) region and partial 28S rRNA gene sequences of the pathogen were amplified by semi-nested PCR with the primers ITS5/P3 followed by ITS5/ITS4, and LSU1/TW14 followed by LSU1/LSU2, respectively. The sequences of 566 bp ITS (MF543026) and 609 bp 28S rDNA (MF543027) were obtained and showed 100% identity with P. fuliginea (AB046986, ON073893) on V. spicata from USA (Hirata et al. 2000). Based on the morphological and molecular characteristics, the fungus was identified as P. fuliginea. To perform pathogenicity assays, three healthy annual plants of P. spicatum were inoculated by gently pressing a diseased leaf onto the leaves, with three non-inoculated plants as controls. All plants were placed in a greenhouse at 21 to 29 °C, 60% relative humidity, with 16 h/8 h light/dark cycle. Nine days after inoculation, typical powdery mildew colonies started to appear on the inoculated plants, while the control plants remained symptomless. The morphology of the fungus on the inoculated leaves was identical to that observed on the originally diseased leaves. Powdery mildews on V. spicata (P. spicatum) were previously referred to as Erysiphe (Golovinomyces) orontii in Italy (Garibaldi et al. 2006) and Sphaerotheca (Podosphaera) fuliginea in many countries, such as Poland, Russia, Switzerland, Wisconsin, Ukraine, etc. (Amano 1986; Braun and Cook 2012; Farr and Rossman 2022; Heluta et al. 2011). To our knowledge, this is the first record of P. fuliginea on V. spicata from China and the first report of this species at all. The results of this study provide important information for horticultural management and plant protection in China. Acknowledgements This work was supported by the National Natural Science Foundation of China (31970019, 31670022).