Abstract
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 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 identified three well-characterised I1781L, I2041T, and D2078G ACCase 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.
Highlights
Italian rye grass, Lolium multiflorum Lam., is an annual or biennial winter weed native to temperate Europe, north-west Africa, and south-west Asia [1]
13 plants did not have any known acetyl-CoA carboxylase (ACCase) mutations, suggesting that the HGR was characterised by non-target site resistance to clodinafop-propargyl
As the impact of the I1781L, I2041T, and D2028G mutations in L. multiflorum or other grass weeds is well documented, this study focused on the novel W2027L variant and non-target site resistance contained in HGR [21,31]
Summary
Lolium multiflorum Lam., is an annual or biennial winter weed native to temperate Europe, north-west Africa, and south-west Asia [1] It is a diploid (2x = 2n = 14) species and obligate outbreeder grown widely within and outside its native range as cover crop, forage, and turf [2,3]. L. multiflorum is characterised by a high genetic diversity and phenotypic plasticity [5] It is a very adaptable species and prolific seed producer that can invade natural grassland and other plant communities that are subject to frequent disturbance [6]. It is an important weed of arable crops and can cause significant yield loss if not properly managed [7]. L. multiflorum can be effectively controlled by different herbicide modes of action including inhibitors of acetolactate synthase (ALS), acetyl-CoA carboxylase (ACCase), photosystem I/II, 5-enolpyruvylshikimate 3-phosphate (EPSP) synthase, very long chain fatty acid, and microtubule assembly [9]
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