STEROL COMPOSITION OF ISOLATES OF ERYSIPHE-GRAMINIS F-SP TRITICI DIFFERING IN SENSITIVITY TO FENPROPIMORPH

Isolates of Erysiphe graminis f.sp. tritici with wild-type or reduced sensitivity to fenpropimorph were similar in sterol composition, viz, ergosta-5, 24(28)-dienol(+/-90%) and episterol(+/-10%). Following trea tment with fenpropimorph, the relative content of episterol increased in conidia of all isolates tested, while that of ergosta-5,24(28)-dien ol decreased. These results suggest that fenpropimorph, under the test conditions used, does not inhibit activity of sterol Delta(14)-reduct ase or Delta(8) --> Delta(7)-isomerase but probably interferes with th e final part of the demethyl sterol synthesis. However, modifications in this part of the pathway are probably not responsible for the decre ased sensitivity of the pathogen to the fungicide. (C) 1998 SCI.