A novel mutation Asp-2078-Glu in ACCase confers resistance to ACCase herbicides in barnyardgrass (Echinochloa crus-galli)

Multiple-herbicide resistance (MHR) in barnyardgrass (Echinochloa crus-galli) is a threat to rice production. The Ala-205-Val mutation in acetolactate synthase (ALS) conferred resistance to several ALS inhibitors in the E. crusgalli population AXXZ-2; consequently, ALS-inhibitors were unable to control this noxious weed species. In the present study, the sensitivity to acetyl-coenzyme A carboxylase (ACCase) herbicides and other herbicides having different modes of action was evaluated to determine an effective strategy for chemical weed control. Compared with that of the reportedly sensitive population JLGY-3, the AXXZ-2 population showed differential resistance to three ACCase-inhibitors (cyhalofop-butyl, fenoxaprop-P-ethyl, and pinoxaden), in addition to quinclorac and pretilachlor. A novel substitution (Asp-2078-Glu) in ACCase was detected as the main target-site resistance mechanisms in the AXXZ-2 population. Structural modeling of the mutant ACCase protein predicted that Asp-2078-Glu confers resistance to three ACCase inhibitors by reducing the binding affinity between them and the ACCase protein. To the best of our knowledge, this is the first study to report that the novel Asp-2078-Glu mutation confers resistance to several ACCase inhibitors. Target-site mutations in ALS and ACCase were detected in this MHR population. Except for quinclorac, pretilachlor, ALS inhibitors, and the three ACCase inhibitors, a number of herbicides remain effective in controlling this MHR E. crus-galli population.