Colletotrichum siamense Prihast., L. Cai & K.D. Hyde

Classification – Glomerellaceae, Glomerellales, Hypocreomycetidae, Sordariomycetes, Ascomycota

Index Fungorum number – IF515410; Facesoffungi number – FoF 03599

Other useful webpages – outlineoffungi.org; fungalgenera.org; Sordariomycetes.org; coelomycetes.org

Description – Associated with leaf spot of Thalia dealbata. Sexual morph: undetermined. Asexual morph: Vegetative hyphae hyaline, smooth-walled, septate, branched. Setae not observed. Conidiomata dark brown, scattered. Conidiogenous cells 5–9(–10) × 3–4 μm (av. 8 × 3 μm, n = 30), hyaline, cylindrical. Conidia 15–18 × 5–6 μm (av. 17 × 5 μm, n = 50), hyaline, aseptate, smooth-walled, straight, cylindrical with rounded ends. Appressoria 8–10 × 6–8 μm (av. 9 × 7 μm, n = 50), ellipsoidal to ovoid or clavate with entire margin.

Culture characteristics – Colonies on PDA reaching 40 mm diam. after 7 days, white, circular, regular at the margin, mycelium dense and raised, villous, felt, reverse white, conidial masses orange.

Material examined – China, Guangdong Province, Guangzhou City, on leaf spot of Thalia dealbata Fraser (Marantaceae), June 2022, Jingwen Chen (living culture ZHKUCC 23-0835, new host record).

Additional materials – China, Guangdong Province, Guangzhou City, on leaf spot of Alpinia zerumbet (Pers.) Burtt & Sm. (Zingiberaceae), February 2022, Jiachun Wang (living culture ZHKUCC 23-0832, new host record); China, Guangdong Province, Guangzhou City, on leaf spot of Epipremnum aureum (Linden & André) G. S. Bunting (Araceae), June 2022, Jingwen Chen (living culture ZHKUCC 23-0833, new host record). China, Hunan Province, Changsha City, on leaf spot of Hydrangea macrophylla (Thunb.) Ser. (Hydrangeaceae), August 2022, Chao Chen (living culture ZHKUCC 23-0834, new host record).

GenBank accession numbers – gapdh: OR493860; act: OR493804; chs-1: OR493832; ITS: OR272068; tub2: OR453347. For additional GenBank accession numbers, please refer to Zhang et al. (2023) on page 301.

Notes – See Zhang et al. (2023).

Colletotrichum siamense (ZHKUCC 23-0835, new host record). a, b Upper and reverse view on PDA (7 d). c, d Conidial masses. e, f Conidiogenous cells. g–i Conidia. j, k Appressoria. Scale bars: e–k = 10 µm.

Maximum likelihood tree inferred from the combined ITS, gapdh, chs-1, act, and tub2 sequence data for Colletotrichum siamense. The tree is rooted to C. boninense (CBS 123755) and C. brasiliense (CBS 128501). Maximum likelihood bootstrap support values equal to or greater than 70% and Bayesian posterior probabilities equal to or greater than 0.95 are given at the nodes and branches (ML/BYPP). Ex-type isolates are marked with “T”. The new isolates from South China region are indicated in red.

Continued.