Colletotrichum dendrobii Gomdola, K. D. Hyde & Jayaward., 2025

Gomdola, Deecksha, Jeewon, Rajesh, McKenzie, Eric H. C., Jayawardena, Ruvishika S., Al-Otibi, Fatimah, Tang, Xia, Wang, Yong, Hyde, Kevin D. & Fu, Li, 2025, Phylogenetic diversity of Colletotrichum species (Sordariomycetes, Glomerellales, Glomerellaceae) associated with plant diseases in Thailand, MycoKeys 119, pp. 137-195 : 137-195

Colletotrichum dendrobii Gomdola, K. D. Hyde & Jayaward. sp. nov.

Figs 3 , 11

Holotype.

MFLU 25-0018 .

Etymology.

The epithet refers to the host genus, Dendrobium , from which the species was isolated.

Description.

Associated with pod blight of Dendrobium sp. Pod blight elongated, pale brown to brown, surrounded with a dark brown margin. Sexual morph: Not observed. Asexual morph on substrate: Conidiomata 200–300 × 180–200 µm (x ̄ = 240 × 190 µm, n = 5), acervular, semi-immersed, scattered or gregarious, dark brown to black. Setae 30–200 µm long (x ̄ = 103 µm, n = 30), scattered or aggregated, straight or flexuous, smooth-walled, 1–5 - septate, brown to dark brown, base darker and apex paler, base 3.5–12.5 µm wide (x ̄ = 7.1 µm, n = 30), cylindrical or ampulliform, tapering to 1.5–5.5 µm (x ̄ = 3.1 µm, n = 30) at the apex. Asexual morph on PDA: Conidiomata 200–1000 µm diam. (x ̄ = 450 µm, n = 10), semi-immersed, scattered or aggregated, globose to subglobose, black, exuding orange conidial mass. Setae not observed. Conidiophores 13–30 µm long (x ̄ = 19.7 µm, n = 10), hyaline, branched or unbranched, smooth-walled. Conidiogenous cells 6–14 (– 20) × 2.5–4.5 µm (x ̄ = 8.3 × 3.5 µm, n = 10), hyaline, cylindrical to ampulliform, sometimes elongated, straight or flexuous. Conidia 11–19 × 4–6 µm (x ̄ = 16.7 × 4.8 µm, n = 30; L / W ratio = 3.5), hyaline, falcate or fusiform, sometimes cylindrical or irregular in shape, smooth-walled, guttulate, aseptate, tapering towards both ends, base conical or rounded, apex acute. Appressoria 15–17 × 17–19 µm (x ̄ = 15.6 × 17.8 µm, n = 5), hyaline, single-celled, globose to subglobose, smooth-walled or verruculose.

Culture characteristics.

Colonies on PDA reaching approximately 70 mm diam. after 7 d of incubation at 25 ° C; mycelium initially greyish white, becoming dark grey to olivaceous brown with age; elevation flat, with an entire or undulate margin.

Specimen examined.

Thailand • Chiang Mai Province, Omkoi District, Yiang Piang Subdistrict , associated with pod blight of Dendrobium sp. ( Orchidaceae ), 16 Oct 2019, D. Gomdola DG 386 ( MFLU 25-0018 , holotype), ex-type MFLUCC 25-0019 .

Additional specimen examined.

Thailand • Chiang Mai Province, Omkoi District, Yiang Piang Subdistrict , associated with pod blight of Dendrobium sp. ( Orchidaceae ), 17 Oct 2019, D. Gomdola DG 387 ( MFLU 25-0019 ), living culture MFLUCC 25-0020 .

GenBank accession numbers.

MFLUCC 25-0019 ; ITS = PV 263306; GAPDH = PV 290911; CHS 1 = PV 274262; ACT = PV 297887; H 3 = PV 400150; and CAM = PV 299292; MFLUCC 25-0020 ; ITS = PV 263307; and GAPDH = PV 290912.

Known hosts, distributions, and lifestyles.

Associated with pod blight of Dendrobium sp. in Thailand (this study).

Notes.

Our isolates ( MFLUCC 25-0019 and MFLUCC 25-0020 ) grouped with 100 % ML and 1.00 PP support. This sub-clade forms a sister clade to Colletotrichum verruculosum ( IMI 45525 ) with strong support (100 % ML and 1.00 PP), indicating a close phylogenetic relationship (Fig. 3 ). In the phylogenetic analyses, our isolates are positioned within the C. spaethianum species complex (Figs 1 , 3 ). The interspecies nucleotide sequence comparison between our isolates ( MFLUCC 25-0019 and MFLUCC 25-0020 ) and C. verruculosum ( IMI 45525 ) revealed the following divergence pattern: 1.3 % in ITS (7 / 519 bp), 3.1 % in GAPDH (6 / 196 bp), 1.9 % in ACT (4 / 211 bp), and 2.4 % in H 3 (9 / 371 bp) regions, but no nucleotide differences in CHS 1 (251 bp) between MFLUCC 25-0019 and C. verruculosum .

Morphologically, the conidiophores and conidiogenous cells of our isolates are hyaline, while those of C. verruculosum ( IMI 45525 ) are pale brown. Additionally, conidiophores of our isolates are shorter than those of C. verruculosum (up to 30 µm vs. 110 µm long). Conidiogenous cells of our isolates are also smaller compared to those of C. verruculosum (6–14 (– 20) × 2.5–4.5 µm vs. 10–25 × 3–5 µm). Setae of our isolates are 1–5 - septate and 30–200 µm long, while those of C. verruculosum are 2–4 - septate and 70–160 µm long. The conidial L / W ratio of our isolates differs from that of C. verruculosum (L / W ratio = 3.5 vs. 4.6) ( Damm et al. 2009).

Based on phylogenetic analyses and morphological data following recommendations proposed by Chethana et al. (2021) and Jayawardena et al. (2021 b), we establish our isolates as a new species, Colletotrichum dendrobii , associated with pod blight of Dendrobium sp. in Thailand.

The primary feature distinguishing Colletotrichum dendrobii from C. verruculosum ( IMI 45525 ) is its variable and irregular conidial shape, along with their distinct phylogenetic lineages.

Figures

Figure 1. Maximum likelihood analysis (IQ-tree) based on a combined dataset of ITS, GAPDH, CHS 1, ACT, TUB 2, H 3, and CAM sequences from dataset 1, which includes all Colletotrichum species. Bootstrap support values (ML ≥ 80 %) and Bayesian posterior probabilities (PP ≥ 0.95) are given above the branches or near the nodes as ML / PP. Hyphens (--) indicate bootstrap support values below 80 % for ML and posterior probabilities below 0.95. The tree is rooted with Monilochaetes infuscans (CBS 869.96) and M. melastomae (CBS 145059). Type, ex-type, and reference species are denoted with T. Our isolates are in bold red font, while our new species are in bold blue font. Different color blocks represent distinct species complexes, with a single color used to denote singleton species.

Figure 3. Maximum likelihood analysis (IQ-tree) based on a combined dataset of ITS, GAPDH, CHS 1, ACT, TUB 2, H 3, and CAM sequences from dataset 3, which includes all species in the C. spaethianum species complex. Bootstrap support values (ML ≥ 80 %) and Bayesian posterior probabilities (PP ≥ 0.95) are given above the branches or near the nodes as ML / PP. Hyphens (--) indicate bootstrap support values below 80 % for ML and posterior probabilities below 0.95. The tree is rooted with C. luanense (CNUCC 157 A- 4-4 and CNUCC 157 A- 4-4 - 2), belonging to the C. destructivum species complex. Type, ex-type, and reference species are denoted with T. Our new species are in bold blue font. Different color blocks represent distinct species complexes.

Figure 11. Colletotrichum dendrobii (MFLU 25-0018, holotype); a, b. Pod blight (Dendrobium sp.); c. Conidiomata with setae on substrate; d. Setae; e. Top and reverse of colony on PDA after 30 d; f. Conidiogenesis and developing conidia; g – m. Conidia; n, o. Appressoria. Scale bars: 200 μm (c); 10 μm (d, f – o).