Similarities between the systemic fungicides triforine and triarimol

The fungicides triforine and triarimol, though structurally unrelated have a similar antifungal spectrum. Neither fungicide inhibited germination of conidia of Cladosporium cucumerinum, but both inhibited subsequent mycelial growth. Triforine, like triarimol, proved to be an effective inhibitor of ergosterol biosynthesis. Two mutants of C. cucumerinum selected for resistance to triarimol also exhibited resistance to triforine and to the triarimol analogues ancymidol and bis(4‐chlorophenyl)‐3‐pyrimidinemethanol. Resistance of these mutants, however, did not extend to the sterol inhibitors triparanol and trans‐clomiphene or to sodium o‐phenylphenate and 2,6‐dichloro‐4‐nitroaniline, two compounds usually tolerated by fungi exhibiting general hydrocarbon resistance. Toxicity of either triforine or triarimol to C. cucumerinum was annuled by β‐carotene, vitamin A, progesterone, testosterone and farnesol. The various similarities between triforine and triarimol suggest a common mode of action for the two compounds.