Molecular Basis for Resistance to Fenoxaprop in Shortawn Foxtail (Alopecurus aequalis) from China

Shortawn foxtail is a competitive annual grass weed widely spread in east, south-central, and southwest China and parts of the Yellow River basin. One shortawn foxtail population (JSQT-1) resistant to fenoxaprop was identified in Jiangyan, Jiangsu province. Whole-plant experiments determined that the resistant population conferred high-level resistance to fenoxaprop (93-fold), clodinafop (21-fold), sethoxydim (107-fold), mesosulfuron (41-fold), and pyroxsulam (12-fold); moderate-level resistance to haloxyfop (8-fold), clethodim (9-fold), and pinoxaden (8-fold), and no resistance to isoproturon. Molecular analyses confirmed that the Ile-1781-Leu mutation was present in the resistant population. A dCAPS marker was used to detect the Ile-1781-Leu mutation. All 97 plants of the resistant population analyzed were homozygous mutants at the 1781 position. Our study established the first case of fenoxaprop resistance in shortawn foxtail, determined cross resistance to other herbicides, and elucidated that the molecular basis of resistance resulted from, at least partly, an Ile to Leu mutation at amino acid position 1781 in the plastid ACCase.