Introduction to Fungi, Third Edition

562 HOMOBASIDIOMYCETES
logs, they may be appressed to the surface of the
wood and are then described as resupinate.
The hyphal construction (hyphal analysis)
of polypore basidiocarps varies (see p. 517 519)
and is useful in identification. In some,
e.g. Bjerkandera adusta, construction is monomitic;
the basidiocarps are composed entirely of
generative hyphae. The basidiocarps of Laetiporus
sulphureus (chicken of the woods; Plate 10b) are
dimitic, whereas Trametes versicolor has trimitic
basidiocarps. The distinction between the different
kinds of construction is best appreciated
by attempting to tear the fruit bodies of these
fungi apart. Trametes versicolor basidiocarps tear
with difficulty, in contrast to the cheese-like
consistency of L. sulphureus. Various modifications
to the different hyphal systems may
occur with age. For example, in L. sulphureus
the generative hyphae may become inflated.
In Polyporus squamosus the binding hyphae arise
relatively late following inflation of the generative
hyphae, converting the sappy flesh of the
fully grown fruit body to a drier and firmer
texture. In Piptoporus betulinus, too, binding
hyphae arise very late but ultimately replace
the generative hyphae. The dissepiments (tissues
between the pores) show a different construction,
being dimitic with skeletal hyphae.
The polyporoid clade is a large group,
probably containing about 70 genera and over
600 species. There is a very extensive literature.
Notes on interesting features of some common
polypores are given below.
Trametes
Trametes (Coriolus) versicolor (Plate 10a), colloquially
called ‘turkey tail’, is a common saprotroph
on various hardwood stumps and logs, causing
white-rot. Both the mycelium and the fruit
bodies are tolerant of desiccation. The annual
fruit bodies have a zoned, multicoloured, velvety
upper surface which readily absorbs rain. Details
of the anatomy of the fruit body are shown in
Fig. 19.24.
Basidiocarps of T. versicolor may come in a
range of colours and shapes, and if such
variations in fruit body appearance occur on a
single log, they can be traced to distinct columns
of decayed wood when the log is serially
sectioned. Dark brown ‘zone lines’ separate the
columns. All isolations from within a column
yield an identical dikaryon, and the zone lines
mark intraspecific antagonism between distinct
dikaryons (see Fig. 18.20a). Therefore, within a
log of wood the fungus does not behave as
a single ‘unit mycelium’ but as a series of
discrete individuals (Rayner & Todd, 1977,
1979). When monokaryons are inoculated experimentally
into logs in the field, they quickly
become converted into dikaryons by anastomosis
with compatible monokaryotic colonies derived
from air-borne basidiospores (Williams et al.,
1981). The individual dikaryotic colonies, once
established, may persist and retain their integrity
over several years, continuing to produce
fresh crops of basidiocarps of the same genetic
constitution each year. Antagonism, i.e. vegetative
incompatibility between different dikaryons,
can also be readily demonstrated in pure culture
as shown in Fig. 18.20c. Monokaryotic mycelia
form arthroconidia. This species is tetrapolar
with multiple alleles.
Because of its prolific production of
peroxidase-type enzymes, T. versicolor is used
industrially in such processes as the bioremediation
of textile dyes or the wood preservative
pentachlorophenol (PCP), and in delignification
and decolorization of Kraft woodpulp. Some
T. versicolor strains used in industry are thermotolerant.
In addition to enzymes, T. versicolor also
produces polysaccharopeptides, and these are
of commercial interest in anti-cancer therapy
(reviewed by Cui & Chisti, 2003). A range of these
substances are produced by different strains of
the fungus. Their exact chemical composition
is variable, with a branched sugar backbone
consisting of b-(1,3) and a-(1,4) linkages and a
protein content of about 30%. Polysaccharopeptides
are extracted from mycelium grown in
fermenters, purified, and administered orally.
Although it is unclear how these large molecules
can be taken up intact by the gut and how
exactly they act to achieve the claimed results,
several effects on the human body are suspected,
with a general enhancement of the immune
system being the most common. They are therefore
considered useful as a complemention of
other, more aggressive anti-cancer treatments.