FUNGICIDE RESISTANCE IN BOTRYTIS CINEREA, THE RESULT OF SELECTIVE PRESSURE ON RESISTANT STRAINS ALREADY PRESENT IN NATURE

Abstract

Spores of Botrytis cinerea Pers. were obtained from snapdragon plants never exposed to fungicides. A few spores produced sporulating colonies on first exposure to benomyl, dicloran, and the experimental fungicide Bay Meb 6447 (triadimefon). Spores resistant to one fungicide were susceptible to the other two. Succeeding generations from the resistant colonies produced increasing numbers of resistant spores due to selective pressure exerted by the particular fungicide. Spores isolated from plants of fuchsia, geranium, and tuberous begonia that had been exposed to benomyl were completely resistant to this fungicide, but not to dicloran or triadimefon. Isolates from zinnia, marigold, and viola were susceptible to benomyl and exhibited some resistance to dicloran and triadimefon. No differences in pathogenicity were observed among susceptible and resistant strains.