EFFECT OF PH, AMINO-ACIDS AND VARIOUS ORGANIC-COMPOUNDS ON THE FUNGITOXICITY OF PYRIMETHANIL, GLUFOSINATE, CAPTAFOL, CYMOXANIL AND FENPICLONIL IN BOTRYTIS-CINEREA

The inhibition of germ-tube elongation by pyrimethanil, fenpiclonil, captafol, glufosinate and cymoxanil was studied in Botrytis cinerea cultivated on various media. The activity of fenpiclonil was not influenced by pH (between 3.6 and 7.3) whereas that of the other pesticides was reduced either in acidic conditions (eg, pyrimethanil) or at pH values greater than 6 (eg, glufosinate, captafol, cymoxanil). The addition of yeast extract, peptone or casein-hydrolysate relieved pyrimethanil, glufosinate, cymoxanil and captafol inhibition but not that of fenpiclonil. A detailed study conducted with amino acids indicated that those containing sulphur were antagonistic towards pyrimethanil, cymoxanil, glufosinate and captafol. For the first 3 pesticides, this reversal could be related to an inhibition in the biosynthesis of sulphur-containing amino acids whereas for captafol it was probably due to its reaction with thiols. Among the other amino acids that exhibit alleviatory effects we can mention glutamine for glufosinate, valine and leucine for pyrimethanil or glycine, and serine for cymoxanil. The relationship between the antagonistic effects of amino acids and the biochemical mode of action of the tested pesticides in B cinerea are evoked. The consequences of the results upon the development of suitable methods for fungicide-resistance monitoring are also discussed.