Antibiotics and disease control by
TrichodermaspeciesTrichodermaspecies (Fig. 12.5) are well-known for their
ability to antagonize other fungi. They were among
the first fungi to be shown to produce antibiotics in
soil (Weindling 1934). In fact, they produce several
antibiotics, including both volatile and nonvolatile
compounds, active against fungi, bacteria or both
(Fig. 12.6).
Many Trichoderma species, such as T. viride, T.
harzianum, and T. hamatum, produce 6-pentyl-αα-
pyrone(6-PAP) as the major volatile antibiotic, while
the major nonvolatile antibiotics include trichodermin,
suzukacillin, and alamethicine. But Trichoderma
virens (as distinct from T. viride) produces a different
spectrum of antibiotics: some strains produce viridin,
viridiol(a reduction product of viridin), gliovirin,
and heptelidic acid, whereas other strains of this
fungus produce viridinand gliotoxin.
The differences in antibiotic production between
strains of Trichoderma seem to be important, and
have led to the widespread use of Trichodermaspeciesas commercial biological control agents against plant-
pathogenic fungi (see later). For example, 6-PAP is
produced by some (but not all) strains of T. viride,
T. harzianum, and T.hamatum, and these 6-PAP pro-
ducers are more antagonistic than are nonproducing
strains when tested against plant pathogens in vitroor
in seedling bioassays. The strains of T. virensthat pro-
duce gliovirin inhibit the growth of Pythium ultimum
but notRhizoctonia solani in vitro, and when applied
experimentally to cotton seeds only the gliovirin-
producing strains controlled seedling diseases caused
by P. ultimum. Conversely, gliotoxin is more active
against Rhizoctonia than against Pythium in vitro,and
gliotoxin-producing strains are better at controlling
Rhizoctoniaon seedlings (Howell et al. 1993).
Antibiotics are not the only factors in the antagonistic
repertoire of Trichoderma. Many strains grow rapidly in
culture – up to 25 mm 24 h−^1 at room temperature. They
secrete chitinase and β-1,3-glucanase when grown in the
presence of other fungi or on fungal wall components.
The hyphae of Trichodermaalso coil round the hyphae
of other fungi (Fig. 12.5) and eventually penetrate the
hyphae from these coils. Few other fungi have such a
formidable arsenal of antagonistic mechanisms.240 CHAPTER 12
Fig. 12.5 (a) Aerial spore-bearing structures of Trichoderma harzianum: the condiophores branch at right angles
and produce conidia at the tips of flask-shaped phialides. (b) Trichodermaspecies frequently coil round the hyphae of
other fungi (in this case, Rhizoctonia solani) and penetrate or disrupt the host hyphae. ( (a) Courtesy of Samuels, G.J,
Chaverri, P., Farr, D.F. & McCray, E.B. Trichoderma Online, Systematic Botany and Mycology Laboratory, ARS, USDA;
from http://nt.ars-grin.gov/taxadescriptions/keys/TrichodermaIndex.cfm)(a) (b)