Powdery Mildew of Veronica persica Caused by Golovinomyces cichoracearum in Guizhou Province of China

Abstract

Veronica persica Poir. is an annual or winter annual herb that reproduces from seed and belongs to Plantaginaceae. V. persica plants are grown in regions of the Guizhou province of China, being widely used in different kinds of traditional Chinese medicine. In September 2017, severe powdery mildew symptoms were observed on V. persica under field conditions in Bijie, Guizhou province, China. Powdery mildew colonies were circular to irregular, forming white patches on the adaxial surface of the leaves. The infection caused premature senescence of the leaves. Chasmothecia were observed after the leaves senesced and died. A voucher specimen (ALB-2) was deposited in Guizhou Academy of Tobacco Science. Conidiophores were erect, 105 to 220 × 10 to 14 μm, and composed of a cylindrical foot cell followed by two to three short cells. Nipple-shaped appressoria were formed on ectophytic mycelia. Conidia were hyaline and cylindrical, without distinct fibrosin bodies, and ranging from 28 to 44 × 18 to 24 μm. Long, unbranched germ tubes were formed from the ends of the conidia. These morphological characteristics suggested that the powdery mildew fungus is the anamorph of Golovinomyces cichoracearum (Braun 1987). To confirm the identification, the ITS1-5.8s-ITS2 region (ITS) of rDNA of ALB-2 was amplified with ITS1 (5′-TCCGTAGGTGAACCTGCGG-3′) and ITS4 (5′-TCCTCCGCTTATTGATATGC-3′) primers and sequenced (White et al. 1990). The ITS sequence obtained was assigned accession number MG657005 in GenBank and was similar to the sequences of several G. cichoracearum accessions (99% similarity) (e.g., HM449077.1 and AY739111.1). Pathogenicity was confirmed through inoculation by gently dusting conidia onto leaves of four healthy plants. Four noninoculated plants were employed as the controls. The inoculated plants developed powdery mildew symptoms after 9 days, whereas control plants remained symptomless. G. cichoracearum (synonym Erysiphe cichoracearum) is a cosmopolitan powdery mildew fungus, parasitic on numerous plant species. It has also been reported infecting Sonchus asper, Melothria indica, and Nicotiana tabacum in China (Pei et al. 2012; Wang et al. 2012). To the best of our knowledge, this is the first report of G. cichoracearum causing powdery mildew on V. persica in Guizhou province of China. Owing to the amount of conidia produced by the pathogen and rapid spread of the powdery mildew, it could cause significant economic losses and become a limiting factor for V. persica production.