Colletotrichum orchidis
Colletotrichum orchidis Jayaward., Camporesi & K.D. Hyde, in Hyde et al., Mycosphere 11(1): 595 (2020)
Index Fungorum number: IF556214
Holotype – MFLU 16-2551
Saprobic on aerial stem of Orchis sp. Sexual morph: Undetermined. Asexual morph: Coelomycetous. Conidiomata 55–135 μm (x̅ = 95 μm, n = 10) diam., black, acervulus, oval, solitary or gregarious, comprising dark brown, roundish cells from which setae and conidiophores develop. Setae straight or ± bent, abundant, dark brown to light brown, becoming paler towards the apex, smooth-walled, 3–5-septate, 105 μm long, base cylindrical, slightly inflated, 5. 6 μm diam, apex acute to round. Chlamydospores not observed. Conidiophores simple, up to 65 μm long, hyaline to pale brown, smooth-walled. Conidiogenous cells 8–11 × 3.1–4.4 μm (x̅= 10.5 ± 1.8 × 3.6 ± 0.4 μm, n = 20), hyaline, smooth-walled, cylindrical to slighty inflated, opening 0.5–1 μm wide, collarette or periclinal thickening not observed. Conidia 15.9–20.3 × 1.9–3.2 μm (x̅ = 18.2 ± 1.5 × 2.5 ± 0.6 μm, n = 40), L/W ratio 7.3, hyaline, smooth or verruculose, aseptate, very variable in size and shape, some strongly curved towards the often broadly rounded apex than towards the truncate base, some small conidia almost straight, guttulate. Appressoria 8.2–13.1 × 4.5–8.2 μm (x̅ = 11.5 ± 3.2 × 4.9 ± 1.4 μm, n = 10), L/W ratio 2.3, solitary or in loose groups, single-celled, olivaceous brown to dark brown, irregularly-shaped, but often globose or clavate, smooth-walled (Hyde et al. 2020).
Culture characteristics: Colonies on PDA flat with entire margin, aerial mycelium sparse, short, pale olivaceous-grey, iron-grey acervuli can be observed mainly on the edge of the colony after 7 days; reverse olivaceous green, reaching 60–75 mm in 7 d at 18 °C.
GenBank numbers: ITS: MK502144, gapdh: MK496857, CHS: MK496855, act: MK496853, tub2: MK496859 (MFLUCC 17-1302), ITS: MK502143, gapdh: MK496858, CHS: MK496856, act: MK496854, tub2: MK496860 (JZB330118).
Notes: Colletotrichum orchidis is only known from aerial stem of Orchis in Italy. The conidia of this species resemble those of several species complexes in Colletotrichum (e.g. dematium species complex, graminicola species complex, spaethianum species complex and truncatum species complex) (Jayawardena et al. 2016). Based on DNA sequences, C. orchidis falls within the C. dematium species complex clade and forms a separate branch as a sister taxon of C. dematium (Hyde et al. 2020). A BLASTn search of NCBI GenBank with the ITS sequence of the new species, showed 96% similarity to several Colletotrichum species with curved conidia. The closest match in a BLASTn search in GenBank with the gapdh sequence of the new species showed 99% similarity to C. dematium (2bp differences) and C. lineola (4bp differences). CHS sequence showed a 98% similarity to C. dematium (6 bp differences) and C. insertae (7 bp differences) and act sequences also showed a 98% similarity to C. dematium (4 bp differences). tub2 sequence showed 99% similarity to C. dematium (1bp differences) and C. lineola (1 bp difference). Colletotrichum orchidis differs from C. dematium by smaller conidia and a lower L/W value (C. dematium 21.3 × 3.5, L/W = 6.0) (Hyde et al. 2020).
Colletotrichum orchidis (Material examined – ITALY, Province of Forlì-Cesena, near Premilcuore, on dead aerial stem of Orchis sp. (Orchidaceae), 5 October 2016, E. Camporesi, IT3118, MFLU 16-2551, holotype). a-c Appearance of conidiomata on host. d Setae. e Base of seta. f, h Conidiophores. g Conidiogenous cell. i-k Conidia. l-n Appressoria. o 3 day old culture on PDA. p 10 day old culture on PDA. Scale bars: b, c = 200 μm, d, f, h = 20 μm, e, g, i-k, l-n = 10 μm.
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