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Effects of Fungal Communities on the Pathogenic and Saprophytic Activities of Fusarium oxysporum f. sp. radicis-lycopersici. J. J. Marois, Graduate research assistant, Department of Plant Pathology, University of Florida, Gainesville 32611, Present address of senior author: Soilborne Diseases Laboratory, Plant Protection Institute, Agricultural Research, Science and Education Administration, U. S. Department of Agriculture, Beltsville, MD 20705; D. J. Mitchell, professor, Department of Plant Pathology, University of Florida, Gainesville 32611. Phytopathology 71:1251-1256. Accepted for publication 10 April 1981. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-1251.

The pathogenic and saprophytic activities of Fusarium oxysporum f. sp. radicis-lycopersici, as determined by the incidence of infection of tomato and by saprophytic proliferation in soil, respectively, were quantified during exposure of the pathogen to different fungal communities. Chlamydospores of the pathogen were added to soil that had been fumigated with methyl bromide-chloropicrin, and either recolonized by naturally occurring microflora or augmented with conidia of Trichoderma harzianum, Aspergillus ochraceus, and Penicillium funiculosum. In freshly fumigated, nonaugmented soil, 90% of cultivar Bonnie Best tomato seedlings were infected after 2 wk at 20 C, while only 25% were infected in freshly fumigated, augmented soil. In soils infested with the pathogen 46 days after fumigation, 1% of the plants were infected in both augmented and nonaugmented soils. When the pathogen was added to soil samples obtained at 7-day intervals after fumigation, the saprophytic proliferation of the pathogen and the incidence of host infection were correlated inversely (r = 0.89 to 0.94) with the natural logarithm of the total number of saprophytic fungal propagules detected in the augmented or nonaugmented soils. Mechanisms of succession and community ecology were invoked to explain the decrease in the saprophytic and pathogenic activities of the pathogen in soils during recolonization.

Additional keywords: r-selected species, biological control, Fusarium crown rot of tomato.