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Effect of Methyl Bromide or Carbon Disulfide on Armillaria and Trichoderma Growing on Agar Medium and Relation to Survival of Armillaria in Soil Following Fumigation. Donald E. Munnecke, Professor of Plant Pathology, Department of Plant Pathology, Univ. of Calif., Riverside 92502; M. J. Kolbezen(2), and W. D. Wilbur(3). (2)(3)Chemist, and Staff Research Associate IV, respectively, Department of Plant Pathology, Univ. of Calif., Riverside 92502. Phytopathology 63:1352-1357. Accepted for publication 20 April 1973. DOI: 10.1094/Phyto-63-1352.

The in vitro responses of Armillaria mellea and Trichoderma viride to methyl bromide or carbon disulfide were studied by determining the effects on linear growth of the fungi on an agar medium. Visible growth of A. mellea ceased almost immediately upon exposure to methyl bromide at 600, 1,200, or 2,400 ppm (v/v) for periods up to 24 days, and did not resume again for varying periods after the gas was removed. For treatments above 1,000 ppm, and exposures of 1 to 12 days, the lag period (which includes duration of exposure to the toxicant plus the period after treatment before growth resumed) was approximately 20 days with few exceptions. T. viride was more resistant than A. mellea to methyl bromide, and was capable of growing during treatment with concns of 600 and 1,200 ppm of methyl bromide. At 2,400 ppm growth ceased, but resumed almost immediately upon removal of the gas. The responses of the two fungi to treatment with carbon disulfide were similar to those observed with the methyl bromide treatments. Both fungi were more tolerant of carbon disulfide than of methyl bromide. In postulating how T. viride may become antagonistic to A. mellea after fumigation, the supposition is made that A. mellea must be weakened in some way. The lag period observed for A. mellea following fungicide application may be an indication of such weakening. It is feasible that T. viride is able to exploit this period and to exert its antagonistic action toward A. mellea at that time.

Additional keywords: antagonism in relation to fumigation, growth lag following fumigation.