Biological control of foliar pathogens by means of Trichoderma harzianum and potential modes of action

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 efficacy was similar for three different 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. (C) 2000 Elsevier Science Ltd. All rights reserved.