Inhibitory action of elemental sulphur (S°) on fungal spores

Abstract

The fungitoxic effect of increasing concentrations of elemental sulphur (S°) was studied during the pregermination period of spores of Phomopsis viticola and conidia of Neurospora crassa. High concentrations of S° (> 10 μM final concentration) inhibited respiratory activities strongly and decreased the ATP content of spores and conidia. S° at low concentrations (1 and 3 μM final concentration) did not inhibit the respiratory activities or ATP content of spores and conidia. In spores of P. viticola, low concentrations of S° were reduced by the cells with the production of hydrogen sulphide (H2S), principally at the level of the respiratory chain. However, in the presence of a high concentration of S°, the capacity to reduce S° increased, and was then most probably independent of the respiratory activities. Proteic and nonproteic sulphydryl groups important in cellular metabolism were probably responsible for almost all the reduction of S°. In fact, the addition of increasing concentrations of S° to spores of P. viticola resulted in a dramatic increase in oxidized glutathione, suggesting the participation of reduced glutathione in S° reduction. In conclusion, we suggest that the fungicidal action of S° is probably related to the oxidation of important sulphydryl groups and not to the competitive interaction between S° and oxygen at the level of the respiratory chain.Key words: elemental sulphur, fungicide, fungi, Neurospora crassa, Phomospis viticola.