The Adaptation of Fungi to Fungicides: Adaptation to Copper and Mercury Salts

The susceptibility of Botrytis cinerea to copper sulphate in liquid media increased when the volume, and therefore the depth, of the medium in culture bottles exceeded certain values; when the volume was 40 ml. the maximum concentration allowing growth was 300 p.p.m. By growing mycelium in media containing progressively higher concentrations of copper sulphate a strain was produced which grew at a concentration of 750 p.p.m. In high concentrations of copper sulphate growth always started at the edge of the liquid, and inocula grew only if they were placed in this position. In germination tests spores from the resistant strain were more resistant to copper sulphate than were spores of the parent strain. The resistance of mycelium, and to a lesser extent of spores, was retained after growth of the resistant strain for six months in fungicide‐free media. Spore and mycelial inocula grew in much higher concentrations of copper sulphate when nutrient media were solidified with agar. The strain resistant in liquid media was no more resistant than the parent strain on agar media. The resistance of the fungus was not increased after growth for long periods on agar containing high concentrations of copper sulphate. The resistance of the strain resistant in liquid media was not lost after growth on agar media for 3 months. Attempts to produce strains more resistant than the parent to mercuric chloride were unsuccessful. The results obtained with phenyl‐mercuric acetate were essentially similar to those obtained with copper sulphate, but relatively much more resistant strains were produced.