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A Microcalorimetric Technique for Rapid Assessment of Fungicide Activity. E. B. Lawrence, Monsanto Company, 800 N. Lindbergh Blvd., St. Louis, Missouri 63167 . H. K. Yuen, Monsanto Company, 800 N. Lindbergh Blvd., St. Louis, Missouri 63167. Plant Dis. 79:605-608. Accepted for publication 3 February 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-0605.

Screening for antifungal metabolites from microbial fermentation broths or extracted plant samples is used to identify compounds with potential novel modes of action. The isolation of fungicidal secondary metabolites from these samples relies on the use of a sensitive detection method that can be evaluated in a timely fashion. This paper describes the use of isothermal microcalorimetry to rapidly assess fungicide activity. An in vivo screening test can require from 1 to 4 weeks and milligram quantities of material. Many in vitro tests require only micro-gram quantities, with test durations of from 2 to 5 days. Microcalorimetry, with its ability to detect microwatt changes in metabolic heat, extends this range of sensitivity. By this method, fungicidal activities can be assessed in 4 to 8 hours with only nanogram quantities of material. Techniques for the use of isothermal microcalorimetry were developed for the filamentous fungi Pythium aphanidermatum and Pyricularia oryzae