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United States Department of Agriculture

Agricultural Research Service

Title: A Quantitative in Vitro Bioassay for Antagonistic Activity of Metabolites Produced by Filamentous Fungi

Author
item Mischke, Barbara

Submitted to: Mycopathologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 7, 1997
Publication Date: N/A

Interpretive Summary: Laboratory tests are needed that measure and predict the potential of microorganisms to function as biological control agents. Microbial biocontrol organisms often suppress disease- causing fungi by secreting antibiotic-like substances that interfere with the growth of the pathogen. A rapid test was developed that measures the ability of one microorganism to inhibit the growth of another microorganism. The results of this test can be quantified and analyzed statistically. The test was applied to the biocontrol strains of Trichoderma that antagonize a pathogenic fungus that causes diseases of potatoes and other vegetable crops. The test accurately measured the antagonistic activity of the strains of Trichoderma. This test provides a means of rapidly screening microorganisms for biocontrol activity and will be useful to those scientist in academia and industry working to discover and develop effective microorganisms as biological control agents.

Technical Abstract: A bioassay and an empirically derived formula were developed to quantify fungitoxic effects. This bioassay can be easily performed and objectively read. In addition, it is suitable for low-volume samples originating from aqueous or organic solvents. The formula defines the Inhibition Index (I), a single value that incorporates both the response to concentrations of the inhibitory compound and the persistence of inhibition. Antagonistic efficacy of metabolites produced by biocontrol strains of Trichoderma spp. were measured based on inhibition of growth of Rhizoctonia solani. Although the bioassay itself was not influenced by pH or light conditions, these factors affect metabolite production or activity. Aqueous extracts from light-grown germlings of Trichoderma virens inhibited R. solani more than extracts from germlings grown in the dark. Low pH increased the inhibitory activity of extracts from T. virens. Tests of fungal strains developed for biocontrol demonstrated that the bioassay reflected their activity both in the field and in other in vitro tests. The bioassay and formula are readily adapted for use with other fungi.

Last Modified: 10/24/2014
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