Influence of copper and zinc ions on toxicity of sodium N-methyldithiocarbamate to Fusarium oxysporum f. sp. lycopersici

Summary

The interactions between the fungicide, sodium N-methyldithiocarbamate (NaMDC), and fungitoxic or non-toxic levels of copper or zinc ions were reevaluated. It was shown that non-toxic levels of MaMDC generally reduce the fungitoxicity of copper sulfate solutions, while copper sulfate solutions of low toxicity, when combined with NaMDC solutions of low toxicity, yielded a highly toxic mixture with an UV spectrum similar to that of dimethylthiuram disulfide, a fungicide which is about 100 times more toxic to the test organism, Fusarium oxysporum f. sp. Lycopersici, as is the compound NaMDC. Fungi with a high sensitivity to copper ions are not suitable for demonstrating a toxic 1:1 complex between copper ions and the dithiocarbamate.

In high concentrations NaMDC proved to be stable even in the presence of copper ions. In these cases, the significantly increased NaMDC toxicity, when combined with copper or zine sulfate, was attributed to the synergistic action of the metal ions on the semipermeability of cytoplasmatic membranes. Since bimodal dosage response curves were obtained for NaMDC in the absence of copper or zine ions in the test medium, the “inversion phenomenon” is probably limited to reactions inside the cell.