Abstract
Two populations ofLolium rigidum(R1and R2) from a monoculture of winter wheat were treated with diclofop-methyl, whereas another population ofL. rigidum(R3) was treated with diclofop-methyl plus chlorotoluron or diclofop-methyl plus isoproturon. The R1biotype is resistant to chlorotoluron and isoproturon (ED50R1/ED50Svalues of 6.5 and 4.2, respectively), while the R3also exhibits resistance to chlorotoluron and isoproturon (ED50R3/ED50Svalues of 9.26 and 5.53, respectively). The diclofop-methyl-resistant R2biotype was similarly sensitive to both substituted ureas, as was the susceptible (S) biotype. The resistance mechanism in the R1and R3biotypes is not due to reduced target site affinity for herbicides. There was no difference in the absorption and translocation of [14C]chlorotoluron in the resistant and susceptible biotypes. Fast fluorescence induction curves showed that substituted ureas inhibited whole-leaf photosynthesis in all biotypes. The R1and R3biotypes later recovered fluorescence activity at a slightly slower rate in the R1biotype than in the R3biotype. The R3population was also tolerant to benzthiazuron, buturon, fenuron, methabenzthiazuron, metobromuron, metoxuron, and monolinuron, with tolerance at a lower level to chloroxuron, diuron, and linuron. This biotype was susceptible to chlorobromuron. The R1biotype was tolerant to benzthiazuron and metoxuron and was less tolerant to buturon, fenuron, methabenzthiazuron, and metobromuron, while this biotype was susceptible to chlorobromuron, chloroxuron, diuron, linuron, and monolinuron.L. rigidumbiotypes produced the same pattern of metabolites, but the R1and R3resistant biotypes detoxified the chlorotoluron to conjugated chlorotoluron at a higher rate than the R2and S susceptible biotypes. In all biotypes treated with 1-aminobenzotriazole, a cytochrome P450 inhibitor, N-dealkylation was not affected, while ring methyl hydroxylation was strongly inhibited. These data suggested that the resistance mechanism in both biotypes is due to chlorotoluron metabolism via alkyl oxidation, and this is greater in R3than R1. The cytochrome P450 enzyme could be involved in this oxidation reaction.
Published Version
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