Colletotrichum siamense
Colletotrichum siamense Prihast., L. Cai & K.D. Hyde, Fungal Diversity 39: 98 (2009)
Index Fungorum number: IF 515410 Facesoffungi number: FoF 03599
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 MF21-4 (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 MF17-4 (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). 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 tub2, 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.
Figure 1. Phylogenetic tree of the Colletotrichum gloeosporioides species complex generated by maximum likelihood of combined ITS, gapdh, chs-1, act, and tub2 sequence data. The ultrafast maximum likelihood (ML) and maximum parsimony (MP) bootstrap support values ≥50% (BT) as well as bayesian posterior probabilities ≥0.90 (BYPP) are shown, respectively, near the nodes. The ex-type strains are marked with an asterisk. The tree is rooted in Colletotrichum acidae (MFLUCC 17 2659) and Colletotrichum truncatum (CBS 151 35).
Figure 1. Continued.
Figure 2. Colletotrichum siamense (MFLUCC 24-0235) a leaf of black pepper b front, and c back view of the colony on PDA after five days d acervuli on CLA e, f conidiophores and conidiogenous cells g–i conidia j–l appressoria. Scale bars: 20 μm (e–j); 10 μm (k–l).
- Fallahi M, Armand A, AI-Otibi F, Hyde KD. Pathogenic fungi (Sordariomycetes) associated with annual and perennial crops in Northern Thailand. MycoKeys 117, 191–265. https://doi.org/10.3897/mycokeys.117.137112
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