Impact of a Novel W2027L Mutation And Non-Target Site Resistance On Acetyl-CoA Carboxylase Herbicides In a French Lolium Multiflorum Population

Herbicides that inhibit acetyl-CoA carboxylase (ACCase) are among the few remaining options for the post-emergence control of Lolium species in small grain cereal crops. Here we have determined the mechanism of resistance to ACCase herbicides in a Lolium multiflorum population (HGR) from France. A combined biological and molecular approach detected a novel W2027L ACCase mutation that affects aryloxyphenoxypropionate (FOP) but not cyclohexanedione (DIM) or phenylpyraxoline (DEN) subclasses of ACCase herbicides. Both the wild type tryptophan and mutant leucine 2027-ACCase alleles could be positively detected in a single DNA-based derived Polymorphic amplified cleaved sequence (dPACS) assay that contained the targeted PCR product and a cocktail of two discriminating restriction enzymes. Additionally, we have identified three well-characterised I1781L, I2041T and D2078G target site resistance mutations as well as non-target site resistance in HGR. The non-target site component endowed high levels of resistance to FOP herbicides whilst partially impacting on the efficacy of pinoxaden and cycloxydim. This study adequately assessed the contribution of the W2027L mutation and non-target site mechanism in conferring resistance to ACCase herbicides in HGR. It also highlights the versatility and robustness of the dPACS method to simultaneously identify different resistance-causing alleles at a single ACCase codon.