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Resistance

Influence of Temperature and Pathogen Aggressiveness on Biological Control of Fusarium Root Rot by Laccaria bicolor in Douglas-fir. N. E. Strobel, Department of Plant Pathology, Cornell University, Ithaca, NY 14853-5908, Present address: Department of Plant Pathology, University of Kentucky, Lexington 40546-0091; W. A. Sinclair, Department of Plant Pathology, Cornell University, Ithaca, NY 14853-5908. Phytopathology 81:415-420. Accepted for publication 6 November 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/Phyto-81-415.

The biological control of Fusarium root rot of Douglas-fir seedlings by Laccaria bicolor was studied in vitro. Primary roots of Douglas-fir seedlings were exposed to L. bicolor for 1 wk and then inoculated with Fusarium oxysporum. Resistance sufficient to prevent lethal infection was expressed to a nonaggressive strain of F. oxysporum at 17 but not at 22 C. Resistance was not expressed against two aggressive strains of F. oxysporum at either temperature. The pathogen entered all inoculated roots but was restricted to cortical intercellular spaces in which effective resistance had been induced. Cortical cell walls with effective induced resistance contained tan-to-brown pigmentation, which darkened during challenge with F. oxysporum. The modest degree and conditional nature of the resistance induced by L. bicolor may preclude the practical application of this fungus as a biological control for Fusarium root rot in forest nurseries.