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while the plant was still alive. Classic examples of this
are the stem base fungi such as the take-all fungus
(Gaeumannomyces graminis, Chapter 12) and the eyespot
fungus (Tapesia yallundae) of cereal crops. The inocu-
lum surviving from the previous growing season can
then initiate infection of a subsequent cereal crop.

Pioneer saprotrophic fungi

Several species of Mucor, Rhizopus and other

Zygomycota are commonly found in soils or fecal-

enriched materials, and also in the rhizosphere (root

zone) of plants, where they utilize sugars and other

simple soluble nutrients. Several Pythiumspecies also

fall into this category because they colonize fresh

plant residues in soil, although they are best known

as pathogens of living root tips and other fleshy plant

tissues (Chapter 12).

The spores of these and similar fungi germinate and

grow rapidly in response to soluble nutrients, and

within a few days they produce a further batch of asex-

ual dispersal spores or sexual resting spores (see Fig. 2.8).

They usually cannot degrade the more complex struc-

tural polymers (cellulose, etc.). In laboratory culture they

are found to be intolerant of the antibiotics or growth

metabolites of other fungi, and they do not themselves

produce antibiotics. So, these pioneer fungi typically

have a short exploitative phase and a high competit-

ive ability.

The sapstain fungi that rapidly colonize newly

felled trees are typical pioneer saprotrophs. They grow

in the nonwoody (parenchymatous) medullary rays

and they discolor the wood by their darkly pigmented

hyphae (Fig. 11.8). Although they cause no structural

damage to the timber, they can seriously reduce its

marketable value. These staining fungi include sev-

eral species of Ophiostoma(related to Ophiostoma ulmi

which causes Dutch elm disease; Chapter 10).

Vanneste et al. (2002) describe how natural products

and biological control agents are being developed to

control the sapstain fungi in New Zealand. However,

similar “bluestain” fungi such as Chlorosplenium aerug-

inascens (Ascomycota) cause an attractive turquoise

pigmentation of wood. This used to be highly valued

for producing inlaid veneers in decorative objects, termed

Tunbridge Ware because the industry was based in the

Kentish town of Tunbridge Wells.

Polymer-degrading fungi

Several fungi have an extended phase of growth on the

major structural polymers such as cellulose, hemicellu-

loses, or chitin. Once established, these fungi tend to

defend the resource against potential invaders, either

by sequestering a critically limiting nutrient such

as nitrogen or by producing inhibitory metabolites

(Chapter 6).

The large number of fungi in this category differ

in the types of substrate they utilize, their different

environmental requirements, and their growth in

different phases of a decomposition sequence. The

following examples illustrate this diversity.

When cereal straw and other cellulose-rich materials

are buried in soil they are colonized by fungi such

as Fusarium, Chaetomium, Stachybotrys, Humicola, or

Trichodermaspp. The Fusariumspp. tend to be favored

220 CHAPTER 11

Fig. 11.8(a,b) Darkly pigmented sapstain fungi growing in the medullary rays of felled trees.

(a) (b)