Discussion
The biocontrol mechanism of T. harzianum is a complex
process mediated by the secretion of extracellular
enzymes, such as chitinases (de la Cruz et al. 1992),
b-glucanases (Lorito et al. 1994) and proteinases (Geremia
et al. 1993), as well as secondary metabolites (Sivasithamparam
and Ghisalberti 1998). The role of
Trichoderma antibiotics in biocontrol is still a matter of
discussion. Although some antibiotics may be the major
factor for the biocontrol activity of a certain strain, this
may not be the case for others (Harman 2000). In addition,
there is still no clear evidence on the production of antibiotic compounds by Trichoderma spp. in the rhizosphere
and spermosphere (Whipps 2001).