Crop Protection 19 (2000) 709}714 Biological control of foliar pathogens by means of Trichoderma harzianum and potential modes of action Y. Elad* Department of Plant Pathology, ARO, The Volcani Center, Bet Dagan 50250, Israel Abstract 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 green- house 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. Keywords: Botrytis cinerea; Pseuperonospora cubensis; Sclerotinia sclerotiorum; Sphaerotheca fuliginea; Sphaerotheca fusca; ¹richoderma harzianum 1. Biological control under commercial conditions Biocontrol products can serve as an alternative to some chemical fungicides, especially in case of fungicide failure, if they o!er acceptable levels of disease control. Only a few micro-organisms have been fully commercial- ized for the control of foliar plant pathogens (Fravel et al., 1999). One of the most studied commercial biocon- trol agents is isolate T39 of Trichoderma harzianum (TRICHODEX 20SP, Makhteshim Chemical Works) which can be regarded as a model to demonstrate control under commercial conditions and mechanisms of biocon- trol. The use of this biocontrol agent for the control of Botrytis cinerea in vineyards around the world has been described previously (Elad, 1994; O'Neill et al., 1996). This biocontrol agent has also been used for the control of tomato and cucumber diseases in commercial green- houses (Elad, 2000; Elad and Shtienberg, 2000). The present paper describes the attempted parallel control of * Corresponding author. Tel.: #972-3-9683580; fax: #972-3- 9683688. E-mail address: elady@netvision.net.il (Y. Elad). several pathogens, biotrophs and necrotrophs of cucum- ber by T. harzianum T39 under commercial conditions. The pathogens involved were Botrytis cinerea Pers.; Fr.; Pseuperonospora cubensis (B.&C.) Rostow.; Sclero- tinia sclerotiorum (Lib.) de Bary and Sphaerotheca fusca (Fr.) Blummer. [syn. S. fuliginea (Schlecht.; Fr.)]. Two experiments were carried out during the 1998 winter season, in unheated, polyethylene-covered cucumber (Cucumis sativus L. cv. Muhasan) greenhouses located in the cen- tral Coastal Plain of Israel. Natural epidemics had de- veloped in these greenhouses during the fall and winter, and spraying was initiated when the "rst symptoms were observed. The experiments were managed as described previously for other experiments under commercial con- ditions (Elad, 2000; Elad and Shtienberg, 2000; Elad et al., 1993). The e!ects of three doses of TRICHODEX were compared (unpublished results). B. cinerea, S. sclerotiorum and S. fusca caused the diseases observed in experiment 1 (Table 1). T39 at rates of 0.2}0.8 g/l resulted in 35}44% reduction of fruit grey mould and in 43}64% reduction of stem grey mould; the chemical standard achieved similar grey mould sup- pression to that by T39. White mould on fruit and stems was reduced by 64 and 30}35%, respectively, by T39, and 0261-2194/00/$ - see front matter  2000 Elsevier Science Ltd. All rights reserved. PII: S 0 2 6 1 - 2 1 9 4 ( 0 0 ) 0 0 0 9 4 - 6