Italian ryegrass has invaded wheat fields in China and is becoming a predominant, troublesome weed. Fenoxaprop-P-ethyl has been widely used for weed control on Chinese farms since the 1990s. However, overuse has led to fenoxaprop-P-ethyl resistance in Italian ryegrass in Chinese wheat fields. In this study, we identified a putative fenoxaprop-P-ethyl—resistant population of Italian ryegrass, HZYC-6, from Henan province, China. Mutations involving Asp-2078-Gly and Ile-1781-Leu substitutions were identified in the carboxyl-transferase domain of acetyl-coenzyme A carboxylase in this population, and these mutations are the likely cause of the target site—based resistance to fenoxaprop-P-ethyl. In addition, we identified cytochrome P450—mediated metabolism of herbicides (non—target site based resistance) in the HZYC-6 population, indicating that multiple mechanisms of resistance may be segregating in this population. Furthermore, HZYC-6 was also highly resistant to haloxyfop-P-methyl and quizalofop-P-ethyl, moderately resistant to clodinafop-propargyl and sethoxydim, and had low resistance to clethodim and pinoxaden.

Nomenclature: Clethodim; clodinafop-propargyl; fenoxaprop-P-ethyl; haloxyfop-P-methyl; pinoxaden; quizalofop-P-ethyl; sethoxydim; Italian ryegrass, Lolium perenne ssp. multiflorum (Lam.) Husnot; wheat, Triticum aestivum L.