Colletotrichum: complex species or species ... - CBS - KNAW

The Colletotrichum acutatum species complex
Fig. 2. Colletotrichum acerbum (from ex-holotype strain CBS 128530). A–B. Conidiomata. C. Tip of a seta. D. Basis of a seta. E–J. Conidiophores. K–O. Appressoria. P–Q.
Conidia. A, C–G, P. from Anthriscus stem. B, H–O, Q. from SNA. A–B. DM, C–Q. DIC, Scale bars: A = 100 µm, E = 10 µm. Scale bar of A applies to A–B. Scale bar of E applies
to C–Q.
is only distantly related to the C. acutatum complex and is therefore
not included in the phylogeny, while C. orchidophilum was found to
be more closely related and was therefore used as outgroup. The
phylogenetic position of these and all other species included here is
exhibited in fig. 1 and 2 of Cannon et al. (2012, this issue).
The individual alignments and maximum parsimony analyses
of the six single genes were compared with respect to their
performance in species recognition. With ITS and CHS-1, only 11
and 13 species, respectively, can be recognised. All subclades are
recognised with TUB2 and GAPDH. TUB2 performs better than
GAPDH due to higher numbers of base pair differences, but even
with TUB2 there are clades with differerences of only 1 bp, which
suggests that both genes should be used for identification. The
performance of the other two genes is intermediate between ITS
and TUB2/GAPDH.
Taxonomy
Based on DNA sequence data and morphology, the 331 strains
studied (Table 1) are assigned to 31 species, of which 29 species
are within the C. acutatum species complex and two outside this
group, including 21 species that proved to be new to science. Two
species formed sexual morphs in vitro. All species studied in culture
are characterised below.
Colletotrichum acerbum Damm, P.F. Cannon & Crous, sp.
nov. MycoBank MB800494. Fig. 2.
Etymology: acerbus = Latin for bitter; referring to bitter rot, the
vernacular name for Colletotrichum disease of apple.
Sexual morph not observed. Asexual morph on SNA. Vegetative
hyphae 1–6 µm diam, hyaline, smooth-walled, septate,
branched. Chlamydospores not observed. Conidiomata absent,
conidiophores formed directly on hyphae. Setae not observed.
Conidiophores hyaline, smooth-walled, septate, branched, to 30
µm long. Conidiogenous cells hyaline, smooth-walled, cylindrical to
ampulliform, sometimes lacking a basal septum and continuous with
the conidiophore, sometimes extending to form new conidiogenous
loci, polyphialides sometimes observed, discrete phialides measure
7–18 × 3–4.5 µm, opening 1.5–2 µm diam, collarette 0.5–1.5 µm
long, periclinal thickening distinct. Conidia hyaline, smooth-walled,
aseptate, straight, cylindrical to clavate with one end round and
one end slightly acute or both ends round, 15.5–20.5(–29) × (4–)
4.5–5 µm, mean ± SD = 17.9 ± 2.4 × 4.7 ± 0.2 µm, L/W ratio =
3.8. Appressoria single or in loose groups, medium to dark brown,
smooth-walled, clavate, ovate or irregular outline, the edge entire
or undulate, sometimes lobate, (8–)9–14(–16.5) × (4–)5–7.5(–9.5)
µm, mean ± SD = 11.3 ± 2.4 × 6.2 ± 1.2 µm, L/W ratio = 1.8.
Asexual morph on Anthriscus stem. Conidiomata acervular,
conidiophores formed on a cushion of pale brown angular cells,
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