Morphology, Molecular Phylogeny, and Pathogenicity of Neofusicoccum parvum, Associated with Leaf Spot Disease of a New Host, the Japanese Bay Tree (Machilus thunbergii)

During a survey of diseased plants on Wando Island, Korea from May to June 2020, severe leaf spot disease was observed in the upper leaves Japanese bay tree (Machilus thunbergii). Early symptoms were light blackish spots surface and enlargement older spots. Dry surrounded with deep black margins common throughout plants. Symptomatic samples collected, causal pathogen isolated potato dextrose agar (PDA). Three fungal isolates (CMML20-1, CMML20-3, CMML20-4) cultured PDA for morphological characterization at 25 °C darkness. Fungal colonies circular, fast-growing, olivaceous dark grey, abundant aerial mycelium. Sporulation induced 14 h-10 h light-dark conditions, conidia single-celled, thin-walled smooth surface, ellipsoid round apices, measuring 17.5–20.5 (avg. 17.5) μm × 7.5–10.0 (7.9) μm. The characteristics resembled those typical Neofusicoccum parvum. Molecular identification confirmed by partially sequencing internal transcribed spacer (ITS) region translation elongation factor 1-α (EF1-α) genes. Pathogenicity tests conducted detached whole M. thunbergii. High prevalence observed, Koch postulates fulfilled. This is first worldwide report N. parvum causing Machilus