Abstract
The mechanism of diclofop resistance was investigated in two biotypes of wild oat ( Avena fatua L.) that show approximately 12-fold resistance to diclofop compared to a typical susceptible biotype. Absorption and translocation of 14C following application of [ 14C]diclofop-methyl did not differ among the three biotypes; approximately 95% of the applied diclofop-methyl was absorbed into the foliage 48 hr after application, and most of this (>80%) was retained in the treated area in all biotypes. Metabolism of diclofop-methyl, examined by TLC and HPLC, did not differ among the three biotypes. Although results of the TLC and HPLC analyses differed slightly, the amount of free diclofop (acid) was generally consistent among the three biotypes. There were no apparent differences in the nature of the polar metabolites formed in the susceptible and tolerant biotypes. Wheat, which is tolerant of diclofop-methyl, metabolized the herbicide considerably faster than the three wild oat biotypes. Acetyl-coenzyme A carboxylase extracted from the resistance and susceptible biotypes was equally sensitive to diclofop in the range 10 −7 to 10 −4 M, indicating that diclofop resistance is not due to differences at the herbicide target site. Further research is required to explain diclofop resistance in these wild oat biotypes.
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