Introduction to Fungi, Third Edition

MICROASCALES
371
Fig12.40 Trichurus sp. on agar. (a) Macronematous
fructification. Note the melanized curved setae typical of the
form-genus.Conidia are produced from annellides arising
from the tips of the parallel hyphae making up the synnema.
(b) Micronematous fructification with annellidic
conidiogenesis.
infections which merely stain the wood. This
so-called sap-stain can none the less be of
economic importance as it reduces the market
value of the infected wood.
The asci of the Ceratocystidaceae (Fig. 12.42c)
deliquesce early in the development of the
perithecium. The perithecium has a very long
neck (Fig. 12.42a) through which the ascospores
are exuded single file, accumulating in a sticky
drop at the tip of the perithecial neck
(Fig. 12.42b). This is thought to be an adaptation
to dispersal by insects which may pick up the
slime containing ascospores upon browsing,
or by feeding directly on it. Many Ceratocystis
spp. produce fruity smells (pineapple, banana,
pear) which attract insects. The substances responsible
are complex mixtures of alcohols, esters
and other volatile substances (Soares et al., 2000),
and industrial processes are being developed to
produce them under fermentation conditions
(Bluemke & Schrader, 2001). The conidial forms
of Ceratocystis are phialidic, and the conidia
are typically barrel-shaped or cylindrical and
are produced deep inside the phialide (Figs. 8.8,
12.42e). This anamorph used to be called Chalara
but has now been renamed Thielaviopsis (Paulin-
Mahady et al., 2002). Additionally, dark melanized
chlamydospores may be present.
In addition to Ceratocystis spp., which are
mainly associated with trees, other members of
this group are soil-borne saprotrophs or weak
pathogens attacking the roots of herbaceous
plants. Examples are Thielaviopsis basicola and
T. thielavioides (Fig. 12.42e), which can cause
significant post-harvest rots in stored carrots
(Punja et al., 1992). The genus Sphaeronaemella
probably also belongs to the Ceratocystidaceae.
Its perithecium is typical of the family in being
long-necked and topped by a frill of hyphae
which hold the ascospore drop in place
(Figs. 12.42a,b). Sphaeronaemella fimicola grows
on dung, and its distinctive perithecia are
commonly found in association with the fructifications
of other coprophilous fungi. Although
S. fimicola can be a weak hyphal parasite, it
also seems to require diffusible metabolites and,
in turn, supplies other metabolites to fellow
coprophilous fungi (Weber & Webster, 1998b).
There is also an interaction of S. fimicola with
animals because its ascospore drop appears
to stick to mites brushing past the perithecial
neck, and the mites in turn hijack rides on
flies (Malloch & Blackwell, 1993). In contrast,
S. helvellae is a mycoparasite infecting the fruit
bodies of Helvella spp. The conidial state of
Sphaeronaemella is called Gabarnaudia and
differs from Thielaviopsis mainly in that the
conidia are formed at the tip of the phialide
(Fig. 12.42d), not inside.