Large crabgrass is a major grass weed widely distributed across China. This weed infests maize fields and has evolved resistance to the acetolactate synthase (ALS)-inhibiting herbicide nicosulfuron due to continuous and intensive use. In this study, a total of 25 out of 26 large crabgrass populations collected from maize field demonstrated resistance to nicosulfuron. Amino acid modifications in ALS known to confer resistance to ALS-inhibiting herbicides in other weeds, were not found in the 9 tested resistant populations. The P450 inhibitor malathion significantly reversed resistance to nicosulfuron in 3 tested populations, indicating one or more P450s may be involved. Nicosulfuron was metabolized more rapidly in one resistant large crabgrass population than in a susceptible biotype. This demonstrates that the metabolic resistance mechanisms involving one or more P450s may be responsible for large crabgrass resistance to nicosulfuron in this biotype.
Keywords: Acetolactate synthase; Large crabgrass; Nicosulfuron; Non-target-site based resistance.
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