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

Colletotrichum siamense Prihast., L. Cai & K. D. Hyde, Fungal Diversity 39: 98 (2009) Fig. 5 Description. Pathogenic to black pepper (Piper nigrum) and causes brown leaf spots on leaves. Sexual morph not observed. Conidiophores hyaline, branched, or unbranched. Conidiogenous cells hyaline, cylindrical 7–20 × 1–2 μm (mean = 14 × 1.5 μm, n = 15). Conidia hyaline, fusiform, obtuse to slightly rounded at the ends, and sometimes oblong, single-celled, smooth-walled, guttulate, 8–18.3 × 3–5 μm (mean = 15 × 4.3 μm, n = 40). Appressoria frequently form from mycelia in slide cultures, brown, ovoid, sometimes clavate, and turn complex with age, 5–10 × 4.5–6.5 μm (mean = 8 × 5.5 μm, n = 20). Chlamydospores and Setae are absent. Culture characteristics. Colonies on PDA reach 70 mm in diameter after 7 days of growth at 25 ° C in the dark, cottony, with medium density. The colony’s surface is covered with numerous small acervuli, with orange conidial ooze. The upper view is white to light grey, and the reverse is greyish to pale yellowish. Material examined. Thailand • Chiang Rai Province, Phan District, Sai Khao. On a leaf of black pepper (Piper nigrum), December 2022, Maryam Fallahi, dried culture MF 21-4 (MFLU 24-0240), living culture, MFLUCC 24-0235 • Chiang Rai Province, Phan District, Sai Khao, on Brazil cherry (Eugenia brasiliensis), December 2022, Maryam Fallahi, dried culture MF 17-4 (MFLU 24-0239), living culture, MFLUCC 24-0234. Notes. On the phylogenetic tree, strains MFLUCC 24-0235 and MFLUCC 24-0234 were placed close to Colletotrichum siamense (ICMP 18578, ex-type) (Fig. 1). The base pair differences between C. siamense strains ICMP 18578 and MFLUCC 24-0235 revealed 0.9 % (2 / 222 bp) differences in chs- 1, 0.97 % (2 / 206 bp) differences in act, 1.3 % (5 / 366 bp) differences in tub 2, and no difference in gapdh and ITS. Strain MFLUCC 24-0235 is similar to C. siamense (MFLU 090230, holotype) (Prihastuti et al. 2009). However, it produced slightly larger conidia with an L / W ratio = 3.5 (8–18.3 × 3–5 μm in C. siamense (MFLUCC 24-0235) vs. 7–18.3 × 3–4.3 μm (L / W ratio = 5) in C. siamense (MFLU 090230, holotype)) and larger appressoria (5–10 × 4.5–6.5 μm (L / W ratio = 1.4) in C. siamense (MFLUCC 24-0235) vs. 4.7–8.3 × 3.5–5 μm (L / W ratio = 1.6) in C. siamense (MFLU 090230)) (Prihastuti et al. 2009). Phylogenetically, C. siamense is closely related to C. asianum; however, morphologically, they are different (Prihastuti et al. 2009). Colletotrichum siamense has been reported as a pathogen on many host plants (Than et al. 2008; Talhinhas and Baroncelli 2021, 2023). It was isolated from anthracnose leaf spot on black pepper in northeast India (Verma et al. 2023). To our knowledge, this is the first report of C. siamense on black pepper in Thailand.