Abstract: To clarify the resistance mechanism of Alopecurus japonicus to fenoxaprop-P-ethyl and mesosulfuron-methyl, fragments encoding acetyl-CoA carboxylase (ACCase) and acetolactate synthase (ALS) were amplified, cloned and sequenced from resistant (R) and susceptible (S) populations of A. japonicus, respectively. Activity differences of glutathione S-transferases in R and S populations were studied. Dose-response experiments were conducted to evaluate the resistance levels of resistant A. japonicus population to different ACCase-and ALS-inhibiting herbicides. The nucleotide sequence analysis showed that a substitution of tryptophan acid (Trp) 2027 by cysteine acid (Cys) existed in the CT domain of ACCase gene, and a substitution of tryptophan acid (Trp) 574 by arginine acid (Arg) of ALS gene existed in AFT population. The level of metabolic response mediated by GSTs metabolizing enzymes in plants was increased after herbicide treatment, the metabolic detoxification response of plants to herbicides was accelerated, the GSTs activity of R was obviously higher than that of S population. A. japonicus AFT population confered high resistance to clodinafop-propargyl, clethodim, flucarbazone-Na with resistance index of 27.90, 34.43 and 10.30, respectively. Moderate resistance to pinoxaden, imazapic, bispyribac-sodium with resistance index of 5.49, 6.42 and 5.01. This study indicated that the substitutions of tryptophan acid at position 2027 in the ACCase gene, tryptophan acid at position 574 in the ALS gene and the significantly increased of GSTs activity might be linked to resistance to fenoxaprop-P-ethyl and mesosulfuron-methyl in AFT populations.

Key words: Alopecurus japonicus, acetyl-CoA carboxylase, acetolactate synthase, glutathione S-transferases