Morphology and Phylogeny of Erysiphe actinostemmatis Affecting Actinostemma lobatum in Korea

Erysiphe actinostemmatis is the only known powdery mildew fungus affecting Actinostemma lobatum (Cucurbitaceae) in Japan and China. Anamorph morphology was insufficiently described, and the phylogenetic placement of this species is unknown. To characterize E. actinostemmatis, eight Korean samples collected between 2007 and 2022 were morphologically examined, and the nucleotide sequences of the large subunit (LSU or 28S) gene and internal transcribed spacer (ITS) regions of rDNA were determined using three voucher specimens. Phylogenetic analyses revealed that E. actinostemmatis formed a distinct clade that diverged from the E. aquilegiae clade. In this study, the detailed morphological characterization of the anamorph, including conidial germination patterns and hyphal appressoria, and molecular phylogeny were discussed for the first time, and the sequences of the ITS and LSU genes were provided.