1992 Volume 58 Issue 5 Pages 691-698
The (R)-(-)-isomer of diniconazole showed strong antifungal activity against Gibberella fujikuroi in a liquid medium at more than 10-5M, whereas another isomer, (S)-(+) exhibited no effect on fungal growth even at 10-4M. Gas-liquid chromatographic analysis of sterols revealed that the (R)-(-)-isomer potently inhibited C-14 demethylation during ergosterol biosynthesis in G. fujikuroi at more than 10-6M. The (S)-(+)-isomer showed slight inhibition on it at more than 10-5M. Bioassay of gibberellins extracted from culture filtrates of G. fujikuroi with or without the fungicide revealed that the (R)-(-)-isomer almost completely inhibited a biosynthesis of gibberellins of the fungus at 10-5M and it was much stronger than that of the (S)-(+). Incorporation of 14C-mevalonic acid into fractions of gibberellin precursors revealed that the (R)-(-)-isomer inhibited the oxidation of ent-kaurene to ent-kaurenol during the gibberellin biosynthetic pathway of the fungus. These results indicated that the (R)-(-)-isomer of diniconazole is a strong inhibitor of both biosyntheses of ergosterol and gibberellins of G. fujikuroi compared with the (S)-(+).