Biocontrol of foliar diseases is an alternative means of management of foliar pathogens. One of the most studied commercial
biocontrol agents is isolate T39 of Trichoderma harzianum which can be regarded as a model to demonstrate biocontrol under
commercial conditions and the mechanisms involved. This biocontrol agent (BCA) controls the foliar pathogens, Botrytis cinerea,
Pseuperonospora cubensis, Sclerotinia sclerotiorum and Sphaerotheca fusca (syn. S. fuliginea) in cucumber under commercial greenhouse
conditions. Control e$cacy was similar for three di!erent rates (covering a fourfold range). Involvement of locally and
systemically induced resistance has been demonstrated. Cells of the BCA applied to the roots, and dead cells applied to the leaves of
cucumber plants induced control of powdery mildew. The BCA suppressed enzymes of B. cinerea, such as pectinases, cutinase,
glucanase and chitinase, through the action of protease secreted on plant surfaces. A combination of several modes of action is
responsible for biocontrol. However, biocontrol is not achieved by means of antibiotics or by mycoparasitism, in spite of the fact that
BCA has the potential to degrade cell-wall polymers, such as chitin. ( 2000 Elsevier Science Ltd. All rights reserved