Taxonomy, Phylogeny, and Host Expansion of Powdery Mildew Fungi Parasitic to Veronica Species

Powdery mildew is a prevalent fungal disease that affects various Veronica spp. (Plantaginaceae), caused by species in the genera Podosphaera and Golovinomyces (Erysiphales). There have been recent taxonomic changes in these groups and ongoing disease occurrence on a range of Veronica species previously unrecognized as hosts; however, the pathogen found in Korea remains unidentified. This study aimed to identify the causative agent of powdery mildew on Veronica spp. in Korea through molecular phylogenetic analysis of internal transcribed spacer (ITS) and large subunit (LSU) sequences of rDNA and morphological examination. Our study identified Golovinomyces bolayi as the sole pathogen affecting all nine Veronica species in Korea and confirmed that G. cichoracearum s. str., which was previously identified as the pathogen, was not the causal agent. These results expand the known host range of G. bolayi, including the addition of five Veronica species in Korea: V. hederifolia, V. kiusiana var. glabrifolia, V. longifolia, V. polita, and V. serpyllifolia. Notably, V. kiusiana has been added as a new global host of powdery mildew. These findings substantially enhance our understanding of the taxonomy of powdery mildew pathogens on Veronica species and provide valuable insights into their evolutionary host expansion.