Metabolism of the phenylurea fungicide, pencycuron, in sensitive and tolerant strains of Rhizoctonia solani

14C-Labeled pencycuron was applied to four strains of Rhizoctonia solani different in the sensitivity to this fungicide. Of the four strains two were sensitive (S1=C-423, AG***-1, and S2=R-C, AG-4) and the other two tolerant (T1=Rh-131, AG-4 and T2=SH-1, AG-5) to pencycuron. Strain S1 metabolized 85% of the pencycuron in a 0.5 ppm liquid medium. While strains S2, T1 and T2 slowly metabolized only 10-20% of the pencycuron 24 hr after incubation. Main metabolites were cis and trans-3-hydroxycyclopentyl pencycuron (P-1 and P-2, respectively), whose fungicidal activity was weaker than pencycuron. This suggested that pencycuron itself is an ultimate active substance, and that metabolic activation or detoxification is less important to explain the difference among the strains in the sensitivity to pencycuron

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