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Molecular Plant Pathology

Antifungal, Synergistic Interaction Between Chitinolytic Enzymes from Trichoderma harzianum and Enterobacter cloacae. M. Lorito, Departments of Horticultural Sciences and Plant Pathology, Cornell University, Geneva, NY 14456, Permanent address: Istituto di Patologia Vegetale, Università degli Studi di Napoli, and Istituendo Centro CNR di Studio delle Tecniche di Lotta Biologica, 80055 Portici (Napoli), Italy; A. Di Pietro(2), C. K. Hayes(3), S. L. Woo(4), and G. E. Harman(5). (2)(3)(4)(5)Departments of Horticultural Sciences and Plant Pathology, Cornell University, Geneva, NY 14456; (2)Current address: Cátedra de Patologia Vegetal/ETSIAM, Universidad de Córdoba, Córdoba, Spain. Phytopathology 83:721-728. Accepted for publication 9 March 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/Phyto-83-721.

Biocontrol strains from the genera Enterobacter and Pseudomonas and two chitinolytic enzymes from Trichoderma harzianum isolate P1 were combined and tested for antifungal activity in bioassays. Inhibitory effects on spore germination and germ tube elongation of Botrytis cinerea, Fusarium solani, and Uncinula necator were synergistically increased by mixing fungal enzymes and cells of Enterobacter cloacae but not of Pseudomonas spp. Culture filtrate of E. cloacae contained antifungal compounds and produced moderate levels of inhibition, either in plate assays or in bioassays conducted in potato-dextrose broth. However, the combination of bacterial culture filtrate with fungal chitinolytic enzymes generated only an additive response, indicating that the presence of bacterial cells was required for a synergistic effect. Chitinolytic enzyme activity in the presence of chitinous substrates enhanced the growth of E. cloacae and readily restored the ability of bacterial cells to bind to hyphae of the pathogens despite high concentrations of d-glucose or sucrose in the medium. The results of this study suggest that transgenic bacteria, capable of binding to fungal cell walls and expressing fungal genes encoding cell wall-degrading enzymes, may be powerful biocontrol agents.

Additional keywords: bacterial adhesion, fungitoxic compounds.