INHIBITION OF ABSCISIC-ACID BIOSYNTHESIS IN CERCOSPORA-ROSICOLA BY TRIARIMOL

The fungicide triarimol was tested for its effect on abscisic acid (ABA) accumulation in growing cultures of Cercospora rosicola. ABA accumulation was reduced by approximately 50% with 10-8 M triarimol. Growth of C. rosicola, as measured by dry weight accumulation, was inhibited by triarimol concentrations at or greater than 10-7 M. These results are compared with those obtained with clomazone, ancymidol, and paclobutrazol, which inhibit ABA accumulation by 50% at concentrations of 5 × 10-5, 5 × 10-6, and 5 × 10-7 M, respectively. Triarimol, therefore, is among the most potent inhibitors of ABA biosynthesis reported to date. Feeding studies with [14C]mevalonic acid confirmed the inhibition of ABA biosynthesis by 5 × 10-8 M triarimol. These results support previous suggestions that one or more of the steps in the ABA biosynthetic pathway from mevalonic acid is catalyzed by cytochrome P-450. Feeding studies with 1′-deoxy-[2H]-ABA in resuspended cultures of C. rosicola show that the conversion of this substrate is not inhibited by triarimol. © 1990 Springer-Verlag New York Inc.