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

The Colletotrichum acutatum species complex
Fig. 20. Colletotrichum nymphaea (from ex-epitype strain CBS 515.78). A–B. Conidiomata. C–G. Conidiophores. H–M. Appressoria. N–O. Conidia. A, C–D, N. from Anthriscus
stem. B, E–M, O. from SNA. A–B. DM, C–O. DIC, Scale bars: A = 100 µm, C = 10 µm. Scale bar of A applies to A–B. Scale bar of C applies to C–O.
polyphialidic, 10–20 × 3–4.5 µm, opening 1–2 µm diam, collarette
0.5–1(–1.5) µm long, periclinal thickening visible, sometimes
distinct. Conidia hyaline, smooth-walled, aseptate, straight,
cylindrical with one end round and one end slightly acute to round,
(9–)12–17(–20) × (3.5–)4–4.5(–5) µm, mean ± SD = 14.5 ± 2.3 ×
4.2 ± 0.3 µm, L/W ratio = 3.5.
Culture characteristics: Colonies on SNA flat with entire margin,
hyaline to pale honey, on filter paper and Anthriscus stem partly
covered with floccose-felty white aerial mycelium, reverse same
colours; growth 20.5–21.5 mm in 7 d (27.5–32 mm in 10 d). Colonies
on OA flat with entire margin; surface buff, honey to saffron, partly
covered with floccose-felty white aerial mycelium and saffron to
isabelline acervuli, reverse buff, honey to rosy buff; growth 22–24
mm in 7 d (34–34.5 mm in 10 d). Conidia in mass saffron.
Material examined: Brazil, from peel of fruit of Cucumis melo, unknown collector
and collection date (isolated by H.A. van der Aa, No. 9014 and deposited in CBS
collection 1 Mar. 1984), (CBS H-20785 holotype, culture ex-type CBS 159.84).
Notes: Colletotrichum melonis belongs to clade 1 of the C.
acutatum species complex but occupies a distinct subclade that
is supported by multiple genes. The sole strain that we are aware
of has appressoria with a significantly larger length/width ratio than
those of C. lupini (mean L/W = 1.5 versus 1.2), the most frequently
encountered species of clade 1. These appressoria form singly
rather than in clusters.
The pathogenicity of C. melonis is not known. This appears to
be the first report of a Colletotrichum species from the C. acutatum
species complex as an associate of cucurbits. There are various
reports of disease caused by members of the C. boninense and
C. gloeosporioides clades, but the principal cucurbit pathogens
appear to be Glomerella magna and C. orbiculare (von Arx & van
der Velden 1961, Jenkins & Winstead 1964, Du et al. 2005, Hyde
et al. 2009, Cannon et al. 2012, this issue).
Colletotrichum melonis is separated from other species by
GAPDH, ACT and HIS3 sequences, with GAPDH performing best as a
differential gene, while the TUB2 sequence is the same as that of strain
IMI 384185 (unnamed strain in clade 1). Closest matches in blastn
search with the GAPDH sequence of strain CBS 159.84 (with 97 %
identity, 6 bp differences) were EU168905, EU647318 and EU647319
from sweet orange (Peres et al. 2008, MacKenzie et al. 2009), while
the closest published matches with the TUB2 sequence (with 99 %
identity, 4 bp differences) were FN611029 and FN611028 from Citrus
aurantifolia and Citrus sinensis from USA, Florida (Ramos et al. 2006).
The ITS sequence matched 100 % with EU008864–EU008866 from
Malus domestica in Brazil (Giaretta et al. 2010).
Colletotrichum nymphaeae (Pass.) Aa, Netherlands J. Pl.
Pathol., Supplement 1 84: 110. 1978. Fig. 20.
Basionym: Ascochyta nymphaeae Pass., in Rabenh., Fungi
Europaei edn 2: 2251 (1876, in sched.); Hedwigia 16: 120.
1877.
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