THE UPTAKE OF A HOMOLOGOUS SERIES OF FUNGICIDES BY PLANT TISSUE AND FUNGAL SPORES

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Abstract
The uptake of 2,5-dimercapto-1,3,4-thiadiazole (DMTD) and its n-alkyl thioethers, ranging from methyl to octyl, by potato disks and fungal cells has been studied. The mineral oil/water partition coefficients of the compounds increased with increasing chain length to the amyl homologue and decreased for the higher members, an effect more marked when the compounds were almost completely unionized at low pH. At equimolar concentrations the uptake of the DMTD homologues by potato tissue was not dependent on alkyl chain length; maximum uptake was given with the amyl member. Experimental evidence indicates that the uptake by potato disks is, at least partially, a cell metabolic process.The uptake of the fungicide series by conidia of Aspergillus niger, Helminthosporium sativum, Monolinia fructicola, and Stemphylium sarcinaeforme increased with increasing length of alkyl side chain to a maximum with the amyl homologue and decreased for the hexyl, heptyl, and octyl members. Experiments with M. fructicola again indicated that the uptake was dependent on cell metabolism. No evidence was found that the compounds were structurally non-specific toxicants and it is suggested that their toxicity is due to chemical interaction in or through a lipophilic biophase of the fungal cell and that this process is dependent on cell metabolic activity. It appears likely that fungal spores are able to detoxify an appreciable portion of the fungicides either in the cell wall or within the protoplasm.

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