Metabolism-Based Nontarget-Site Mechanism Is the Main Cause of a Four-Way Resistance in Shortawn Foxtail ( Sobol.).

Sobol. is a predominant grass weed in Chinese winter wheat fields, posing a substantial threat to crop production owing to its escalating herbicide resistance. This study documented the initial instance of an population (AHFT-3) manifesting resistance to multiple herbicides targeting four distinct sites: acetyl-CoA carboxylase (ACCase), acetolactate synthase, photosystem II, and 1-deoxy--xylulose-5-phosphate synthase. AHFT-3 carried an Asp-to-Gly mutation at codon 2078 of , with no mutations in the remaining three herbicide target genes, and exhibited no overexpression of any target gene. Compared with the susceptible population AHFY-3, AHFT-3 metabolized mesosulfuron-methyl, isoproturon, and bixlozone faster. The inhibition and comparison of herbicide-detoxifying enzyme activities indicated the participation of cytochrome P450s in the resistance to all four herbicides, with glutathione S-transferases specifically linked to mesosulfuron-methyl. Three CYP72As and a Tau class glutathione S-transferase, markedly upregulated in resistant plants, potentially played pivotal roles in the multiple-herbicide-resistance phenotype.