Resistance status of Leptochloa chinensis to three acetyl-CoA carboxylase (ACCase) inhibitors in rice fields in Shanghai and involved ACCase gene mutations

In order to determine the resistance level and the potential resistance mechanism of Leptochloa chinensis to acetyl-CoA carboxylase (ACCase)-inhibiting herbicides, 51 populations of L. chinensis were collected from the rice fields in Shanghai. Whole-plant single-dose experiments were conducted to investigate the resistance level of different populations to ACCase-inhibiting herbicides, including cyhalofop-butyl at 105 g (a.i.)/hm², metamifop at 120 g (a.i.)/hm² and fenoxaprop-P-ethyl at 62.1 g (a.i.)/hm² in the greenhouse. Meanwhile, the sequences of the target gene ACCase in resistant populations were analyzed. The results showed that of the 51 populations tested, eight populations were found to be resistant to clodinafop-propargyl, four populations resistant to metamifop, and six populations resistant to fenoxaprop-P-ethyl; six, five and two populations were found to be developing resistance to cyhalofop-butyl, metamifop and fenoxaprop-P-ethyl, respectively. Sequencing results showed that nine of fifteen resistant populations showed four different kinds of mutations in ACCase sequence, namely Trp (TGG)-1999-Ser (TCG), Trp (TGG)-1999-Cys (TGT), Trp (TGG)-2027-Ser (TCG) and Trp (TGG)-2027-Cys (TGT/TGC), but there were no mutations in other populations. Besides, five populations had mutant frequencies higher than 60%. Our results indicated that L. chinensis was extensively resistant to ACCase-inhibiting herbicides in some rice fields in Shanghai, and the mutations in the ACCase gene were one of the main causes of the resistance of L. chinensis populations to ACCase-inhibiting herbicides.