Introduction to Fungi, Third Edition

602 HETEROBASIDIOMYCETES
Fig 21.6 Auricularia auricula-judae.
(a) Section of fruit body.The
hymenium is on the lower side.
(b) Squash preparation of the
hymenium showing basidia. Note the
transverse segmentation and the
long epibasidia.The basidia are
associated with branched hyphae.
(c) Basidiospores.Two are
ungerminated; one has developed
a septum and is germinating directly
by means of a germ tube; and
two basidiospores have become
three-septate and are producing
lunate conidia from short
conidiophores (denticles).
(d) A basidiospore which had fallen
back onto the hymenial surface and is
germinating repetitiously to form a
ballistoconidium. (b d) to same scale.
backwards from the protoplast-containing
germ tube towards the empty basidiospore.
Such septa are interpreted as retraction septa
(Ingold, 1982a). A richly branched monokaryotic
mycelium of very fine hyphae develops, and after
a while these hyphae form lateral or terminal
denticles which produce clusters of lunate
microconidia.
The lunate conidia are a feature found in
many species of Auriculariales, but their significance
in the life cycle is uncertain. Like basidiospores
and the repetitious ballistoconidia
produced from them, they are capable of germination
to form monokaryotic hyphae, but they
might also function directly as spermatia. The
putative life cycle of A. auricula-judae is shown in
Fig. 21.7.
Another common species is A. mesenterica,
which forms thicker, hairy, fan-shaped fruit
bodies on old stumps and logs of elm (Ulmus)
and other trees. It, too, causes active wood
decay and may occasionally be weakly
pathogenic.
Auricularia as a cultivated mushroom
Although devoid of any distinctive taste, the
fruit bodies of Auricularia are highly nutritious
and possess a chewy, rubbery texture which
renders them attractive ingredients for Far
Eastern soups and stir fries. The main species
cultivated for food is A. polytricha (‘Mu-Erh’).
The history of cultivation dates back to AD 600
in China (Cheng & Tu, 1978; Chang & Miles,
2004), making Auricularia the first cultivated
mushroom for which we have historical
records. Some 465 000 t of fresh fruit bodies are
currently produced per annum (Pegler, 2001).
Very conveniently, the fruit bodies can be
stored dry for several months, and rehydrated
when needed. Cultivation is traditionally performed
by inoculating logs of suitable broadleaved
trees with mycelial spawn. Infected logs
can produce good crops for several years. The
fungus is now also often cultivated in plastic
bags filled with a mixture of sawdust and rice
bran, allowing the fruit bodies to emerge
through holes in the plastic.