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Physiology and Biochemistry

Suppressive Influence of Laccaria laccata on Fusarium oxysporum and on Douglas-fir Seedlings. D. M. Sylvia, Former graduate research assistant, Department of Plant Pathology, Cornell University, Ithaca, NY 14853-0331, Present address of senior author: Department of Plant Pathology, University of Florida, Gainesville 32611; W. A. Sinclair, professor, Department of Plant Pathology, Cornell University, Ithaca, NY 14853-0331. Phytopathology 73:384-389. Accepted for publication 23 August 1982. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-384.

Some strains of the ectomycorrhizal fungus Laccaria laccata can invade primary roots of seedlings of Douglas-fir (Pseudotsuga menziesii) and protect them from lethal attack by Fusarium oxysporum. We appraised the potential of L. laccata to inhibit F. oxysporum and to influence the development of young seedlings. In dual cultures on agar media with pH relatively less favorable for growth of F. oxysporum than L. laccata, diffusible metabolites of a mycorrhizal strain of L. laccata inhibited growth and caused distortion of hyphae of the pathogen. Cell-free fluid from cultures of this strain of L. laccata delayed germination of microconidia and chlamydospores of F. oxysporum. Only slight suppression occurred under conditions that favored rapid growth of F. oxysporum. A nonmycorrhizal strain of L. laccata inhibited growth of F. oxysporum over a wide range of conditions on agar media, but culture filtrates did not affect spore germination. Antibiosis may be a partial basis for root protection by the mycorrhizal strain of L. laccata. On agar plates and in gnotobiotic systems without soil, L. laccata or its cell-free metabolites suppressed root growth of Douglas-fir. In sterile or pasteurized soil, however, no suppression occurred.