Behaviour of Thiuram Sulphides, etc., in Spore Germination Tests

Abstract

SOME seven years ago, in the course of sorting tests of potential organic fungicides, it was noticed that tetramethylthiuram monosulphide sometimes gave irregular results. In certain tests an 'inversion' of toxicity occurred, that is, within a limited range of concentration, toxicity to fungus spores (Venturia inæqualis) decreased as the concentration of fungicide increased. When this effect was first observed it was ascribed to some experimental mishap, but it was repeated with sufficient frequency, though not invariably, to convince us that the phenomenon was authentic. It was later seen in the case of tetramethylthiuram disulphide, though not before several tests had been completed without any indication of it, and has been investigated most fully in relation to this compound. Confirmation of the effect has since been provided by the independent observations on the latter substance reported by Dimond et al.¹, using spores of Macrosporium sarcinæforme.