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United States Department of Agriculture

Agricultural Research Service

Title: Mechanisms of Action and Dose-Response Relationships Governing Biological Control of Fusarium Wilt of Tomato by Nonpathogenic Fusarium Spp

Authors
item Larkin, Robert
item Fravel, Deborah

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 20, 1998
Publication Date: N/A

Interpretive Summary: Knowledge of the mechanisms of action and antagonist-pathogen dose-response relationships of biocontrol agents is essential for effective implementation of biocontrol of plant diseases. In this study, three biocontrol isolates of nonpathogenic Fusarium spp. (CS-1, CS-20, and Fo47) previously shown to reduce the incidence of Fusarium wilt diseases of multiple crops were evaluated. Competition for nutrients between the antagonist and pathogen was involved in biocontrol provided by isolate Fo47, but not isolates CS-1 and CS-20. All three isolates demonstrated evidence of induced systemic resistance (ISR) in tomato and watermelon plants. However, there was variability among the isolates regarding the efficacy of the ISR, with CS-20 being most effective and Fo47 least effective in split-root tests. In dose-response tests, isolate CS-20 significantly reduced Fusarium wilt incidence at low antagonist doses (100 chlamydospores/g soil(cgs))and at all pathogen densities tested (10**2 to 10**5 cgs). Isolate CS-1 was effective in reducing disease at low to moderate doses (100-5000 cgs) as long as pathogen densities were <10**4 cgs. Isolate Fo47 was only effective at reducing disease at very high antagonist densities (10**4-10**5 cgs), regardless of pathogen density. The use of epidemiological dose-response models fit to the observed data clarified these differences among biocontrol isolates and established their biocontrol characteristics. Differences in dose-response relationships were apparently related to differences in the mechanisms of action among the isolates. This research benefits scientists, private industry, and growers interested in commercial development and use of biological agents for the control of plant diseases.

Technical Abstract: Three biocontrol isolates of nonpathogenic Fusarium spp. (CS-1, CS-20, and Fo47), previously shown to reduce the incidence of Fusarium wilt diseases of multiple crops, were evaluated to determine their mechanisms of action and antagonist-pathogen inoculum density relationships. Competition for nutrients between the antagonist and pathogen was involved in biocontrol provided by isolate Fo47, but not isolates CS-1 and CS-20, according to chlamydospore germination and saprophytic growth tests. All three isolates demonstrated evidence of induced systemic resistance (ISR) in tomato and watermelon plants. However, there was variability among the isolates regarding the efficacy of the ISR, with CS-20 being most effective (39-53% disease reduction) and Fo47 least effective (23-25% reduction) in split-root tests. The isolates also differed in their dose-response relationships. CS-20 was effective at antagonist doses as low as 100 chlamydospores/g soil (cgs) throughout all pathogen densities tested (up t 10**5 cgs). Biocontrol with CS-20 was not density dependent, with low antagonist densities providing comparable control as higher densities. Isolate CS-1 was effective at low to moderate doses (100-5000 cgs) as long as pathogen densities were below 10**4 cgs, but did not control disease when pathogen densities were 10**4 or higher. Isolate Fo47 was only effective at reducing disease at very high antagonist densities (10**4-10**5 cgs), regardless of pathogen density. The use of epidemiological dose-response models (described by linear, negative exponential, hyperbolic saturation, and logistic functions) fit to the observed data clarified these differences among biocontrol isolates and established biocontrol characteristics for the isolates.

Last Modified: 10/22/2014
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