damage to the fruit surface during processing and
packing can create portals for entry of decay fungi
(Botrytis cinerea, Penicilliumspp., Mucorspp., etc). To coun-
teract this, biocontrol strains can be applied to fruit
surfaces and are reported to give significant protection
by colonizing minor wounds. Like the ice−strains of
P. syringae, they act by competing for nutrients.
Currently, at least two companies market these prod-
ucts in the USA, using different protectant strains. The
products based on strains of P. syringaeare marketed
for control of postharvest decay of apples and pears,
under the tradename Biosave 110, whileBiosave 100
is marketed to control decay of citrus fruits. A product
based on a strain of Candida oleophilais marketed
under the tradename Aspire, to control Penicillium
spp. on citrus fruit, and B. cinereaand some Penicillium
spp. on apples. Fruit treated with these naturally occur-
ring strains is exempt from the normal “tolerance” levels
that conventional fungicides are subject to.
Commensalism and mutualism
If we exclude lichens as organisms in their own right
(Chapter 13), there are few well-established examples
of fungi that live in association with other fungi, to
their mutual benefit (mutualism) or to the benefit of
one and not to the detriment of the other (commen-
salism). These types of association might be common,
but they are not well documented. Here we consider
one example, from laboratory experiments on the
interaction between Thermomyces lanuginosus (a non-
cellulolytic fungus of composts) and the cellulose-
degrading fungus, Chaetomium thermophile. It extends
the example discussed earlier (see Fig. 11.13).
Both T. lanuginosus(T.l.) and C. thermophile(C.t.)
grow during the prolonged high temperature phase
of composts, when much of the cellulose is degraded
(Chapter 11). It is assumed that T.l. grows in these
conditions by using sugars made available by C.t. or
other cellulolytic fungi. But this is difficult to demon-
strate in the complex environment of a compost, so
most of the evidence has come from in vitrostudies.
The methods used are similar to those described in
Chapter 11. Flasks containing sterile filter paper with
nitrate and other mineral nutrients were inoculated
with C.t. alone, T.l. alone, or C.t. +T.l. The flasks
were incubated for up to 7 weeks at 45°, and the loss
of dry weight of the flask contents was determined
(Fig. 12.19).
Thermomyces could not grow alone, because it can-
not degrade cellulose and it cannot use nitrate as a
nitrogen source. By contrast, Chaetomiumgrew well
when inoculated alone, degrading about 1000 mg of cel-
lulose after 4 weeks, and about 1200 mg after 7 weeks.
But the combination of Chaetomiumand Thermomyces
gave an even larger weight loss – nearly 1500 mg after
4 weeks and over 1600 mg after 7 weeks. All these dif-
ferences were statistically significant.
In addition to using a “standard” level of nitrogen
(giving a C : N ratio of 174 : 1), this experiment
included a double level of nitrogen (C : N of 88 : 1).
The effect of this was to allow the rate of decomposi-
tion to continue for longer, so that after 7 weeks
Chaetomiumalone had degraded 2000 mg (of the ori-
ginal 7000 mg) of filter paper, while the combinationFUNGAL INTERACTIONS 253
Fig. 12.18Colonization of cereal or grass roots by Phialophora graminicola, a nonpathogenic parasite of roots that can
effectively suppress invasion by the aggressive take-all fungus. (a) Dark runner hyphae of Phialophorain a grass root
cortex. (b) Clusters of darkly pigmented cells of Phialophorawithin the root cortex. (c) Heavy invasion of the cortex of
a cereal root by Phialophora, but the vascular tissues are not invaded. (d) At higher magnification, Phialophorahyphae
have colonized the root cortex, but the endodermis (e) prevents invasion of the vascular tissues.