Analysis of the resistance level and its resistant molecular mechanism of Echinochloa crus-galli population JS12 to metamifop

Barnyardgrass (Echinochloa crus-galli) is one of the most problematic weeds infesting rice fields and causes huge crop yield losses. To clarify the resistance pattern and possible mechanisms of resistance in barnyardgrass population JS12 in Jiangsu Province, whole-plant dose-response experiments were conducted to determine the sensitivity to metamifop, and its target- and non-target-based mechanisms were clarified by gene sequencing and expression analysis of ACCase gene, as well as synergistic effects on resistance of two metabolic enzyme inhibitors. Finally, the sensitivities of JS12 population to ACCase inhibitors and other herbicides with different modes of action were analyzed to determine the cross- and multi-resistance patterns. Results showed that the JS12 population exhibited 13.71 times high-level resistance to metamifop. No amino acid substitutions conferring metamifop resistance were detected in six copies of ACCase genes in JS12 population, and the gene expression levels of ACCase were significantly lower than that of the susceptible population after herbicide treatment. Both cytochrome P450 inhibitor malathion and glutathione-S-transferase (GST) inhibitor NBD-Cl could significantly increase the susceptibility of JS12 population to metamifop, causing the GR₅₀ (herbicide rate causing growth reduction by 50%) value to decrease from 227.90 g/hm² to 77.51 g/hm² and 137.93 g/hm², respectively. In addition, the resistant population JS12 had evolved cross-resistance to ACCase inhibitors cyhalofop-butyl, fenoxaprop-p-ethyl, clethodim, and pindoxaden, and multi-resistance to acetolactate synthase (ALS)-inhibiting herbicide penoxsulam and auxin herbicide quinclorac. Nevertheless, it was still susceptible to the new herbicides florpyrauxifen-benzyl and triadimefon. This study suggested that the enhanced herbicide metabolism mediated by cytochrome P450 and GST might be an important reason for herbicide resistance in JS12 population. Florpyrauxifen-benzyl and triadimefon can be used to control the resistant population.