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Chapter 17

Principles and practice of

controlling fungal growth

In this chapter we deal with the major practical methods

of controlling fungi, under the following headings:

• control by management of environmental and
  biological factors


• biological and integrated control


• chemical control of fungi


• the principal cellular targets of antifungal agents


• the use of fungicides for plant disease control


• antifungal antibiotics used for plant disease control


• control of fungal infections of humans

Control through the management of

environmental and biological factors

We have seen many good examples of how fungi can
be controlled through the management of physical and
environmental factors. For example, the management
of water potential is essential for grain storage, and
the combination of temperature and water potential
can be used to predict the safe limits for preventing
growth of mycotoxin-producing fungi in stored food
products (see Fig. 8.10). The storage and shipment of
fresh produce, including many fruits, is often achieved
by controlled atmosphere storage– a combination of
cool temperature and elevated levels of carbon dioxide.
This delays ripening and the onset of senescence, and
can be cheaper than either of the single treatments
alone. Similarly, bananas are routinely shipped from
Central America to the European market as unripe, green
fruits and are then ripened artificially by exposure to
ethylene-generating chemicals. The green fruits survive

long-distance shipping (2–3 weeks), and while they are

green the fruits will not develop lesions of banana

anthracnose (Colletotrichum musae) which is present as

latent infections on the skin (see Fig. 5.3).

Wounding of fruits leads to the release of ethylene,

a wound hormone, and can lead to premature ripen-

ing and invasion by fruit-rotting fungi. To counteract

this, several types of fruit are treated with fungicides

or with wax coatings, and held in cool storage. We

saw in Chapter 12 that several bacteria and yeasts are

now marketed commercially as fruit protectants, as

an alternative to the use of fungicides. It may not be

necessary to use living organisms at all, because the cell

wall fractions of many yeasts, including S. cerevisiae, can

act as powerful elicitors of plant defense mechanisms.

Similarly, there is increasing interest in the use of

chitosanto protect plants from pathogenic attack. At

present, chitosan is obtained commercially by chem-

ical deacetylation of crab shells. It disrupts the growth

of several fungi in vitro, causing excessive branching,

wall alteration, and cytoplasmic disorganization. Chitin

is a characteristic wall component of fungi, and some

fungi – especially Zygomycota – naturally deacetylate

chitin by the enzyme chitin deacetylase. They could

be used as an alternative, renewable source of chitosan

for triggering plant defense reactions.

Sanitation, quarantine, and similar

biologically based strategies

Crop rotationis a traditional, highly effective method

of controlling many plant diseases if the pathogen

does not survive for long in the absence of a host crop.

This is true of the take-all fungus Gaeumannomyces