Characterization of Cyhalofop-butyl metabolism and identification of resistance genes in Barnyardgrass (Echinochloa crus-galli (L.) P. Beauv.).

Barnyardgrass (Echinochloa crus-galli (L.) P. Beauv.) is a dominant weed in paddy field worldwide causing yield losses and labor consumption. Years of extensive and continuous use of herbicides with one mode of action has resulted in the development of resistant weeds to the target herbicides and cross-resistant weeds to the herbicides with same mode of action in many regions. In our previous study, a metamifop-resistant barnyardgrass population (JS-R) demonstrated survival under recommended doses of cyhalofop-butyl. This study aimed to elucidate the underlying resistance mechanisms. Bioassays and molecular analysis showed that JS-R exhibited 7.59-fold resistance to cyhalofop-butyl, without ACCase target-site mutations or overexpression. The glutathione S-transferase (GST) inhibitor 4-chloro-7-nitrobenzoxadiazole (NBD-Cl) significantly reversed resistance, and GST activity in JS-R was significantly higher on the 3rd and 5th days post-treatment. UPLC-MS/MS analysis revealed a higher metabolic capacity to cyhalofop-butyl and cyhalofop acid in JS-R from 1 to 9 d after treatment. Transcriptome and qRT-PCR analyses identified significant upregulation of two ABC transporter genes, two cytochrome P450 genes, four GST genes, and three hydrolase genes in the resistant population. Notably, this study provides the first evidence that ehydroascorbate reductase (DHAR) and specific hydrolase genes were upregulated in resistant barnyardgrass, and may be involved in non-target-site resistance mechanism to cyhalofop-butyl.