Mechanism of Resistance to Pyroxsulam in Multiple-Resistant from China.

Black grass ( Huds.) is a highly competitive weed in winter wheat fields of China. Due to repeated use of acetolactate synthase (ALS) inhibitors, many populations have evolved resistance to pyroxsulam in some wheat fields. Research was conducted to determine the molecular basis of herbicide resistance in the AH93 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 and 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 population in China, and the Cys-2088-Arg mutation is the first reported case of an ACCase mutant conferring herbicide resistance in .