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Physiology and Biochemistry

Fungistatic Activity of Propyl-N-(γ-dimethylaminopropyl) carbamate on Pythium spp. and its Reversal by Sterols. G. C. Papavizas, Research plant pathologist, Soilborne Diseases Laboratory, Plant Protection Institute, Federal Research, Science and Education Administration, U.S. Department of Agriculture, Beltsville, MD 20705; N. R. O’Neill(2), and J. A. Lewis(3). (2)(3)Research plant pathologist and soil scientist, Soilborne Diseases Laboratory, Plant Protection Institute, Federal Research, Science and Education Administration, U.S. Department of Agriculture, Beltsville, MD 20705. Phytopathology 68:1667-1671. Accepted for publication 16 June 1978. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1667.

In vitro fungistatic activity of the new systemic fungicide propyl-N-(γ-dimethylaminopropyl) carbamate HCl [PDAC, SN66752, propamocarb (proposed)] was studied in solid and liquid synthetic medium (BM-1) against eight Pythium spp. The PDAC at concentrations up to 5 μg active ingredient (a.i.)/ml was less fungistatic to Pythium spp. than was its S-analog, N-(3-dimethylaminopropyl) thiocarbamic acid Shylester HCl [DTEH, SN41703, prothiocarb (proposed)]. The dosage-response curves for PDAC were linear from 0.5 to 10 μg a.i./ml, with ED₅₀ values ranging from 2.5 to 5 μg/ml for all species except P. myriotylum which had an ED₅₀ value of about 0.1 μg a.i./ml or less. Four Pythium spp. (not including P. myriotylum) were more sensitive to PDAC at pH of 7.4 than at 6.4 or 5.3. Cholesterol added to BM-1 at 5-30 μg/ml reversed the fungistatic activity of PDAC, but the magnitude of reversal depended on PDAC concentration in BM-1 and on the Pythium sp. used. Cholestanol and sitosterol, but not lanosterol, also reversed activity. With P. myriotylum, even 30 μg/ml of cholesterol did not reverse activity. Greater amounts of cellular constituents (proteins, carbohydrates, amino acids, and soluble salts) leaked from mycelia of Pythium grown in liquid BM-1 supplemented with 0.5 μg a.i./ml PDAC than from mycelia grown in PDAC-free medium. In general, the rate of leakage was constant over a 7-hr period for most cell constituents except soluble salts. Cholesterol added to BM-1 reduced leakage of cell constituents. When added with PDAC, cholesterol reversed the effects of the fungicide on mycelium cell membrane permeability.