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

Damm et al.
Notes: Von Arx (in litt.) identified the strain CBS 330.75 as C.
acutatum but with the remark “deviating by lack of pigment and
less fusiform conidia”. While the main causal agent of coffee berry
disease (CBD) is C. kahawae (Waller et al. 1993) that belongs
to the C. gloeosporioides species complex (Weir et al. 2012, this
issue), strains from the C. acutatum aggregate are not frequently
encountered associated with coffee. Hindorf (1973) studied
Colletotrichum populations from Coffea arabica in Kenya and
illustrated conidia or ascospores of some strains diverging from
each other in morphology and culture appearance, including a
strain identified as C. acutatum and another as C. gloeosporioides
with conidia some of which are ellipsoidal and acute-ended. One
of the two strains from western Kenya that are assigned to C.
acutatum s. str. is derived from a suspected disease symptom
on a coffee berry from Kenya that did not cause CBD (Gielink
& Vermeulen, 1983). One of the endophytic strains from Coffea
robusta in Brazil studied by Sette et al. (2006) showing antimicrobial
activity against Staphylococcus aureus belongs to the C. acutatum
species complex; since only a short ITS sequence of this strain
was generated (DQ123614), the species cannot be identified.
Colletotrichum walleri (clade 2) is known from a single strain from
coffee, from Vietnam. Colletotrichum costaricense is quite distinct
from either of these taxa based on molecular sequence data.
Two Colletotrichum species have previously been described
from leaves of Coffea sp. in Costa Rica, C. brachysporum and
C. coffeophilum. Conidia of the first are smaller than those of C.
costaricense and have a different shape; they are subgloboseovoid
and measure 7–8 × 4–6 µm (Saccardo et al. 1931), while
those of C. costaricense measure on average 14.6 × 3.7 µm or 14.8
× 3.8 µm depending on the medium. Conidia of C. coffeophilum are
wider than those of C. costaricense, being ellipsoidal and straight
or slightly curved (navicular), and measuring 13–15 × 6–8 µm
(Saccardo et al. 1931).
Colletotrichum costaricense may be differentiated from the other
species accepted here by TUB2, GAPDH and ACT sequences,
and most effectively with TUB2. The ACT sequences of the two
strains differ by 2 bp, but have only 1 bp in common to separate
them from C. lupini and some of the unnamed single strains. The
closest match in a blastn search with the TUB2 sequence of strain
CBS 330.75 with 99 % identity (3 bp differences) was FN611028
from a Citrus sinensis isolate (Ramos et al. 2006), while the
closest matches with the GAPDH sequence with 99 % identity (2
differences) were EU647322 and EU647324 from leatherleaf fern
isolates (MacKenzie et al. 2009). All isolates were from Florida,
USA. The closest matches with the ITS sequence with 100 %
identity were FN566877 from isolate DPI from Citrus aurantifolia in
Florida, USA (Ramos et al. 2006) and isolate c2 from Citrus sp. in
Brazil (Giaretta et al. 2010).
Colletotrichum cuscutae Damm, P.F. Cannon & Crous, sp.
nov. MycoBank MB800500. Fig. 9.
Etymology: Named after the host plant, Cuscuta.
Sexual morph not observed. Asexual morph on SNA. Vegetative
hyphae 1–5.5 µm diam, hyaline, smooth-walled, septate, branched.
Chlamydospores not observed. Conidiomata not developed,
conidiophores formed directly on hyphae. Setae not observed.
Conidiophores hyaline, smooth-walled, simple or septate and
branched, to 35 µm long. Conidiogenous cells hyaline, smoothwalled,
cylindrical to ampulliform, often integrated, polyphialides
occasionally observed, discrete phialides measuring 4–14.5 ×
2.5–4.5 µm, opening 1.5–2 µm diam, collarette 0.5–1.5 µm long,
periclinal thickening conspicuous. Conidia hyaline, smooth-walled,
aseptate, straight, cylindrical with both ends acute, (15.5–)17.5–
21(–27) × (3–)3.5–4.5 µm, mean ± SD = 19.2 ± 1.7 × 4.0 ± 0.3
µm, L/W ratio = 4.8. Appressoria single or in loose clusters, pale
brown, smooth-walled, elliptical to clavate, entire edge (3.5–)5.5–
11.5(–15.5) × (2–)3.5–5.5(–6.5) µm, mean ± SD = 8.5 ± 3.2 × 4.6
± 0.9 µm, L/W ratio = 1.8.
Asexual morph on Anthriscus stem. Conidiomata acervular,
conidiophores formed on pale brown angular basal cells, 3–8 µm
diam. Setae not observed. Conidiophores hyaline to pale brown,
smooth-walled, septate, branched, to 40 µm long. Conidiogenous
cells hyaline, smooth-walled, cylindrical to fusiform with both
ends acute, 8–21 × 2–3.5 µm, opening 1–2 µm diam, collarette
0.5–1 µm long, periclinal thickening conspicuous. Conidia hyaline,
smooth-walled, aseptate, straight, cylindrical with both ends acute,
(15–)17–20(–21) × (3.5–)4–4.5 µm, mean ± SD = 18.6 ± 1.5 × 4.2
± 0.2 µm, L/W ratio = 4.5.
Culture characteristics: Colonies on SNA flat with entire margin,
hyaline to buff, on filter paper and Anthriscus stem partly covered
with woolly to felty white to pale grey aerial mycelium and orange
acervuli, reverse hyaline to buff, under filter paper pale olivaceous
grey; growth 20 mm in 7 d (30 mm in 10 d). Colonies on OA flat to
raised with entire margin; surface partly covered with woolly white
to pale olivaceous grey aerial mycelium and olivaceous grey to
orange acervuli appearing in rings, reverse buff, pale olivaceous
grey to olivaceous grey with orange sectors; growth 19–21 mm in 7
d (27.5–31 mm in 10 d). Conidia in mass orange.
Material examined: Dominica, Castle Comfort, from Cuscuta sp., 1986, C. Prior (IMI
304802 holotype, CBS H-20784 isotype, culture ex-type IMI 304802).
Notes: Colletotrichum cuscutae is known from a single strain,
reported from Dominica. The multigene analysis indicates that
it occupies a single subclade within clade 1, quite distinct from
the principal subclade of C. lupini. Its conidia are substantially
longer than is typical for C. lupini (mean length 18.6 µm as
opposed to 12 µm for C. lupini), though the length range for the
latter species is considerable. The appressoria of C. cuscutae
are narrower than those of C. lupini and also greater in length/
width ratio.
Colletotrichum species have been reported previously
as parasitising Cuscuta species, which are themselves nonphotosynthetic
parasites of other plants. Colletotrichum
destructivum was found to affect Cuscuta campestris parasitising
alfalfa crops in NW USA (Leach 1958). A strain identified as C.
gloeosporioides f. sp. cuscutae was apparently used widely as a
biological control agent “Lu Bao no. 1” of Cuscuta in China after
its adoption in the 1960s (Zhang 1985, Gao & Gan 1992), but its
current commercial status is unknown and it may no longer be in
production (Watson et al. 2000). According to Watson et al. (2000)
and Dinoor et al. (2009) the Lu Bao strain belongs to C. acutatum
rather than C. gloeosporioides. However, no detailed morphological
data are available and the identification as C. acutatum was made
by means of primers that at that time were considered to be
species-specific for the two species that are both now recognised
as species complexes.
Guerber et al. (2003) studied isolates from Cuscuta in the USA
and China that belong to two different species, neither of which
is conspecific with C. cuscutae. Based on GAPDH sequences
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