VIEW ARTICLE

Ecology and Epidemiology

Effects of Inorganic Salts, Carbonate-Bicarbonate Anions, Ammonia, and the Modifying Influence of pH on Sclerotial Germination of Sclerotium rolfsii. Z. K. Punja, Graduate research assistant, Department of Plant Pathology, University of California, Davis 95616; R. G. Grogan, professor, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 72:635-639. Accepted for publication 28 August 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-635.

Eruptive and hyphal germination on 1% Noble water agar and on 1% Bacto water agar, respectively, of dried sclerotia of two isolates of Sclerotium rolfsii were totally inhibited in buffered systems above pH 7.0, but sclerotia remained viable even at pH values as high as 9.7. Maximum germination of sclerotia was observed on agar adjusted to pHs ranging from 2.0 to 5.0. Of 33 inorganic salts (primarily anions of calcium, ammonium, potassium, sodium, and lithium) tested for ability to inhibit sclerotial germination at 10, 30, and 50 mM concentrations; 18 salts reduced germination at the 50 mM concentration to <10% of that in plates not receiving salts. Of the cations tested, Ca²⁺, K⁺, and Na⁺ were less inhibitory than Li⁺ and NH₄⁺. The anions acetate, formate, and phosphate reduced germination, whereas nitrate, sulfate, and chloride had no significant effect. Calcium propionate, ammonium acetate, ammonium molybdate, potassium sorbate, sodium formate, lithium chloride, tris ((hydroxymethyl) aminomethane), and the carbonate and bicarbonate salts of ammonium, potassium, sodium, and lithium prevented germination, but only the carbonate and bicarbonate salts were fungicidal. The hydrogen-ion concentration of the agar had a profound influence on toxicity of the salts to sclerotia; at high pH (about 8.6), but not at low pH (about 6.0), ammonium salts and carbonate and bicarbonate salts were fungicidal to sclerotia, apparently due to the prevalence of free NH₃ and CO₃^2– -HCO₃^–, respectively, at the high pH.