Introduction to Fungi, Third Edition

340 HYMENOASCOMYCETES: PYRENOMYCETES
Fig12.15 Hypocrea pulvinata.(a)L.S.
lower part of fruit body of Piptoporus
betulinus showing perithecial stromata
of Hypocrea in section (see also
Plate 5c). (b) Acremonium-like conidia
produced from upright phialides.
(c) Asci and ascospores. Note how
the two-celled ascospores may
break up into unicellular part-spores.
spore masses. Detailed descriptions of Hypocrea
Trichoderma connections have been given by
Chaverri and Samuels (2003). Hypocrea rufa
forms conidia referable to T. viride (Fig. 12.16d),
a species with globose, warty conidia. Conidia of
the Gliocladium type, in which conidia derived
from individual phialides coalesce in a single
slimy mass, are found in cultures of H. gelatinosa
(Figs. 12.16a,b; Webster, 1964). The distinction
between Trichoderma and Gliocladium anamorphic
states can be difficult and some species, e.g. G.
virens, have been transferred to Trichoderma as T.
virens (Fig. 12.17a), the anamorph of H. virens
(Chaverri et al., 2001).
The biology and taxonomy of Trichoderma
have been reviewed by Samuels (1996, 2006),
ecological aspects by Klein and Eveleigh (1998),
and keys to identification have been given by
Gams and Bissett (1998). It is a large genus and
species identification is difficult using morphological
criteria. DNA-based and biochemical
techniques are now widely used to support
identification. Such studies indicate that
genus is a monophyletic group within the
Hypocreaceae which evolved about 110 million
years ago (Kullnig-Gradinger et al., 2002).
Trichoderma spp. are cosmopolitan in soil and
on decaying woody substrata. On soil isolation
plates, Trichoderma spp. are often the most
rapidly growing and dominant fungi, smothering
the plates and forming clusters of sticky
green phialoconidia within a few days. Certain
species, especially T. harzianum and T. virens, have
been used in the biological control of soil-borne
fungal plant pathogens such as Rhizoctonia solani
and Pythium ultimum (Papavizas, 1985; Chet, 1987;
Lumsden, 1992; Tang et al., 2001). Antagonism to
the fungal pathogen may be associated with
coiling of Trichoderma around the host hypha,
followed by penetration and parasitism
(Figs. 12.17b d). Volatile and non-volatile
antifungal antibiotics may also be produced.
Several species of Trichoderma are troublesome
contaminants and parasites of mycelia and
basidiocarps of cultivated mushrooms in
Europe and North America (Castle et al., 1998;
Samuels et al., 2002).
Trichoderma reesei is used commercially for
cellulase production, secreting 20 g or more of
cellulase l 1 culture fluid (Durand et al., 1988;
Kubicek et al., 1990). Until recently, this interesting
species had been isolated only once, during
the Second World War on the Solomon Islands
from canvas in contact with soil. Molecular
studies have revealed that T. reesei is the
anamorph of Hypocrea jecorina, an uncommon
tropical species (Kuhls et al., 1996; Lieckfeldt
et al., 2000).