Cross-Resistance of Japanese Foxtail (Alopecurus japonicus) to ACCase Inhibitors in China

Abstract

The increasing use of ACCase-inhibiting herbicides has resulted in evolved resistance in key grass weeds infesting cereal cropping systems worldwide. Japanese foxtail is one of the most important grass weed species in wheat in China. Most populations have evolved resistance to fenoxaprop-p-ethyl, which is one of the most common ACCase-inhibiting herbicides in wheat. The seeds of two Japanese foxtail populations were collected from wheat fields where farmers complained that control could not be effectively obtained with fenoxaprop-p-ethyl. Seeds from one susceptible population were collected from an area along a roadside where ACCase inhibitors had not been used to be used for validating cross-resistance and elucidating the mechanism of resistance. The experimental results showed that the two populations, Aloja-JS10-R1 and Aloja-JS10-R2, expressed high resistance to fenoxaprop-p-ethyl, with resistance indexes (RIs) of 29.2 and 27.9. These populations also expressed high cross-resistance to clodinafop-propargyl with RIs of 12.8 and 14.7, and moderate cross-resistance to clethodim and pinoxaden with RIs ranging from 2.6 to 11.4. Comparison of the ACCase carboxyl-transferase (CT) domain sequences of the susceptible and resistant populations with blackgrass revealed that tryptophan at position 2027 of the ACCase gene was substituted by cysteine in population Aloja-JS10-R1, and isoleucine at position 1781 of the ACCase gene was substituted by leucine in populations Aloja-JS10-R2. The study confirmed Japanese foxtail resistance to the ACCase inhibitor fenoxafop-p-ethyl, cross-resistance to other ACCase inhibitors, and the resistance mechanism being conferred by specific ACCase point mutations at amino acid position 1781 and 2027.