Mechanism of Resistance to Pyroxsulam in Multiple-Resistant Alopecurus myosuroides from China

Abstract

Black grass (<i>Alopecurus myosuroides</i> Huds.) is a highly competitive weed in winter wheat fields of China. Due to repeated use of acetolactate synthase (ALS) inhibitors, many <i>A. myosuroides</i> populations have evolved resistance to pyroxsulam in some wheat fields. Research was conducted to determine the molecular basis of herbicide resistance in the AH93 <i>A. myosuroides</i> population. Whole-plant dose-response assay confirmed that the AH93 population was resistant to pyroxsulam with a resistance index of 4.2. Cross- and multiple-resistance assays indicated that the AH93 population was cross-resistant to mesosulfuron-methyl and multiple-resistant to pinoxaden. Sequencing of the <i>ALS</i> and <i>ACCase</i> gene revealed that there was no target-site mutation in ALS, but Trp-2027-Cys and Cys-2088-Arg amino acid mutations in ACCase in the AH93 population. A malathion pretreatment study indicated that the AH93 population might have cytochrome P450-mediated herbicide metabolic resistance. This is the first report of pyroxsulam resistance in a multiple-resistant <i>A. myosuroides</i> population in China, and the Cys-2088-Arg mutation is the first reported case of an ACCase mutant conferring herbicide resistance in <i>A. myosuroides</i>.