The strains of Trichoderma used as biocontrol agents
show different mechanisms of action in their antagonistic
interactions with fungal pathogens. These include antibiosis,
through the production of a variety of compounds
with antibiotic activity (Ghisalberti and Sivasithamparam
1991), mycoparasitism or hyperparasitism (Ayers and
Adams 1981), competition for nutrients (Chet 1987), cell
wall-lytic enzyme activity (Lorito et al. 1996; Lorito 1998)
and induction of systemic resistance to pathogens
in planta (Harman et al. 2004). Of these, antibiotic production
is considered to play an important role during biocontrol events, although the interactions in soil and plants are not yet fully elucidated. Different volatile and nonvolatile secondary metabolites have been characterized from Trichoderma spp. by antibiotic assay-guided isolation and the production of antibiotic molecules by certain strains is often well correlated with their biocontrol ability
(Howell 1998). The effectiveness of certain Trichoderma
harzianum isolates to act against Gaeumannomyces graminis
var. tritici has been related to the production of
pyrone-like antibiotics (Ghisalberti et al. 1990). On the
other hand, studies on the mechanisms of action used by
Trichoderma virens indicate that the stimulation of plant
defence responses seems to be a major contributor to successful
biocontrol (Howell et al. 2000).
The strains of Trichoderma used as biocontrol agentsshow different mechanisms of action in their antagonisticinteractions with fungal pathogens. These include antibiosis,through the production of a variety of compoundswith antibiotic activity (Ghisalberti and Sivasithamparam1991), mycoparasitism or hyperparasitism (Ayers andAdams 1981), competition for nutrients (Chet 1987), cellwall-lytic enzyme activity (Lorito et al. 1996; Lorito 1998)and induction of systemic resistance to pathogensin planta (Harman et al. 2004). Of these, antibiotic productionis considered to play an important role during biocontrol events, although the interactions in soil and plants are not yet fully elucidated. Different volatile and nonvolatile secondary metabolites have been characterized from Trichoderma spp. by antibiotic assay-guided isolation and the production of antibiotic molecules by certain strains is often well correlated with their biocontrol ability(Howell 1998). The effectiveness of certain Trichodermaharzianum isolates to act against Gaeumannomyces graminisvar. tritici has been related to the production ofpyrone-like antibiotics (Ghisalberti et al. 1990). On theother hand, studies on the mechanisms of action used byTrichoderma virens indicate that the stimulation of plantdefence responses seems to be a major contributor to successfulbiocontrol (Howell et al. 2000).
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