Glechoma longituba (Nakai) Kuprian. (syn. Glechoma hederacea var. longituba Nakai) of the Lamiaceae family, known as long tube ground ivy, is native to Vietnam, China, Korea, and the Russian Far East (https:// powo.science.kew.org/). This plant has been used for medicinal purposes in Asia since long [1,2]. In Korea, these plants are dried and marketed as herbal tea [3].

Powdery mildew infections of Glechoma L. species are known to be associated with Golovinomyces biocellatus (Ehrenb.) V. P. Heluta [4]. In Korea, this pathogen is associated with Agastache rugosa Kuntza, Meehania urticifolia Makino, Mentha suaveolens Ehrh., Monarda citriodora Cerv. ex Lag., M. didyma L., and Rosmarinus officinalis L. from the Lamiaceae family [5-10]. Powdery mildew from the Golovinomyces genus associated with host plants of the Lamiaceae family are known to be a part of the G. biocellatus complex [11]. Recent molecular phylogenetic analyses have resolved the taxonomic composition of this complex by categorizing it into several new combinations, including Golovinomyces monardae (G.S. Nagy) M. Scholler, U. Braun & Anke Schmidt, G. neosalviae M. Scholler, U. Braun & Anke Schmidt, and G. salviae (Jacz.) M. Scholler, U. Braun & Anke Schmidt [12]. Currently, Golovinomyces bicellatus sensu stricto is considered to be a pathogen of Glechoma and Lycopus L. species.

During routine plant disease surveys in 2022, G. longituba plants were found to be infected with powdery mildew in Jeongeup, Jeonju, Buan, Jinan, and Wanju, Korea. Subsequently, six samples were deposited in the Mycological Herbarium of Korea University, namely KUS-F32257 (June 15, 2021, Hongcheon), F32837 (May 20, 2022, Jeongeup), F32916 (June 7, 2022, Jeonju), F32934 (June 10, 2022, Wanju), F32977 (June 20, 2022, Buan), and F33540 (November 13, 2022, Jinan).

For morphological examination, a small piece of the fungal colony was scraped off the infected leaves and mounted on a drop of distilled water on a glass slide. Subsequently, they were examined under an optical microscope using bright-field and differential interference contrast (DIC). At least 30 measurements of each structure were taken using an Olympus BX51 microscope (Olympus, Tokyo, Japan) at 40× and 100× magnifications, and a Zeiss AX10 microscope equipped with an AxioCam MRc5 (Carl Zeiss, Göttingen, Germany) was used for capturing the photographs.

Powdery mildew colonies first appeared as circular to irregular white patches but soon progressed to abundant hyphal growth on both sides of the leaves and young stems (Fig. 1A and B). Severe infection caused the withering and premature senescence of leaves in plants, reducing their vigor. In powdery mildew, the hyphae were septate, branched, and 4-9 µm wide, and the hyphal appressoria were nipple-shaped. Conidiophores measured 120-200×10-12 μm and produced 1-4 immature conidia in chains with a sinuate outline, followed by 2-3 cells (Fig. 1C-E). The foot-cells of conidiophores were straight, cylindrical, and 3555 μm long. Conidia were hyaline, were ellipsoid to barrel-shaped, measured 22-30×19-23 μm (length/ width ratio 1.1-1.6), lacked distinct fibrosin bodies, and produced germ tubes at the subterminal position (Fig. 1F). Chasmothecia were not observed. Short conidiophores and a low length/width ratio of conidia are typical characteristics indicating the asexual state of Golovinomyces salviae [12].

MATERIALS AND METHODS

RESULTS AND DISCUSSION