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Effect of Phosphorus Concentration and Glomus intraradices on Fusarium Crown and Root Rot of Tomatoes. Michel Caron, Research plant pathologist, Agriculture Canada Experimental Farm, P. O. Box 1070, L'Assomption, Québec J0K 1G0; J. André Fortin(2), and Claude Richard(3). (2)Professor and research scientist, Centre de Recherches en Biologie Forestière, Université Laval, Québec G1K 7P4; (3)Research plant pathologist, Agriculture Canada Research Station, 2560, boul. Hochelaga, Sainte-Foy, Québec G1V 2J3. Phytopathology 76:942-946. Accepted for publication 4 February 1986. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/Phyto-76-942.

The effect of colonization of tomato roots by Glomus intraradices on population of Fusarium oxysporum f. sp. radicis-lycopersici and on crown and root rot development in relation to increasing P concentrations in the substrate was investigated. An increase of available P in the substrate as well as in the P content of roots and leaves had no effect on the population of F. o. f. sp. radicis-lycopersici and root necrosis but resulted in a decrease of the root colonization by G. intraradices. Only the presence of G. intraradices resulted in a significant decrease in the population of F. o. f. sp. radicis-lycopersici and root necrosis at all P concentrations. At all P concentrations, the presence of G. intraradices had no significant effect on the mean dry mass of plants, whereas a significant decrease in plant dry mass was observed for plants inoculated with F. o. f. sp. radicis-lycopersici. It is concluded that the improved P nutrition from the endomycorrhizal fungus cannot explain the observed limitation in disease and pathogen development.

Additional keywords: biological control, Lycopersicon esculentum, mycorrhizae.