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Applied and Environmental Microbiology, March 1999, p. 1061-1070, Vol. 65, No. 3
0099-2240/99

Induction of Defense Responses in Cucumber Plants (Cucumis sativus L.) by the Biocontrol Agent Trichoderma harzianum

I. Yedidia,1 N. Benhamou,2 and I. Chet1,*

Department of Plant Pathology and Microbiology, Faculty of Agriculture, The Hebrew University of Jerusalem, Rehovot 76100, Israel,1 and Recherche en Sciences de la Vie et de la Sante, Laval University, University City, Quebec G1K 7P4, Canada2

Received 12 August 1998/Accepted 14 December 1998

The potential of the biocontrol agent Trichoderma harzianum T-203 to trigger plant defense responses was investigated by inoculating roots of cucumber seedlings with Trichoderma in an aseptic, hydroponic system. Trichoderma-treated plants were more developed than nontreated plants throughout the experiment. Electron microscopy of ultrathin sections from Trichoderma-treated roots revealed penetration of Trichoderma into the roots, restricted mainly to the epidermis and outer cortex. Strengthening of the epidermal and cortical cell walls was observed, as was the deposition of newly formed barriers. These typical host reactions were found beyond the sites of potential fungal penetration. Wall appositions contained large amounts of callose and infiltrations of cellulose. The wall-bound chitin in Trichoderma hyphae was preserved, even when the hyphae had undergone substantial disorganization. Biochemical analyses revealed that inoculation with Trichoderma initiated increased peroxidase and chitinase activities within 48 and 72 h, respectively. These results were observed for both the roots and the leaves of treated seedlings, providing evidence that T. harzianum may induce systemic resistance mechanisms in cucumber plants.

* Corresponding author. Mailing address: Department of Plant Pathology and Microbiology, Faculty of Agriculture, The Hebrew University of Jerusalem, Rehovot 76100, Israel. Phone: 972-8-9481315. Fax: 972-8-9468785. E-mail: chet{at}agri.huji.ac.il.

Applied and Environmental Microbiology, March 1999, p. 1061-1070, Vol. 65, No. 3
0099-2240/99


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