Target-site mutation and cytochrome P450s confer resistance to multiple herbicides in Italian ryegrass (Lolium multiflorum Lam.) from China

Italian ryegrass (Lolium multifiorum Lam.) is a highly competitive grass weed capable of severely infesting wheat fields worldwide. In recent years, Chinese farmers are finding it increasingly difficult to control L. mulaflorum when using acetyl-CoA carboxylase (ACCase)-inhibiting herbicides. Accordingly, clarifying the resistance pattern of putative resistant populations of L. multiflorum is important for selecting alternative herbicides for effective weed control. In this study, a putative resistant L. multiflorum population, HN-03, which apparently has survived clodinafop-propargyl treatment under the recommended field application rate, was collected from a wheat field in Zhumadian, Henan, China. Whole-plant bioassay revealed that the HN-03 population had evolved high-level resistance to clodinafop-propargyl. Sequencing of the ACCase gene revealed a point mutation, of TGG to TGT, at codon position 1999, causing a Trp-to-Cys substitution in the resistant plants. The HN-03 population also exhibited cross-resistance to fenoxaprop-P-ethyl, clethodim, and pinoxaden and multiple-resistance to mesosulfuron-methyl and bixlozone, but it remained susceptible to cypyrafluone. Pre-treatment with piperonyl butoxide and malathion considerably increased the susceptibility of the HN-03 population to fenoxaprop-P-ethyl and mesosulfuron-methyl, by 25.3% and 36.6%, respectively. This study shows the L. multiflorum population HN-03 has evolved multiple herbicide resistance due to both a target-site mutation and P450s-mediated enhanced metabolism. Cypyrafluone can be used as an alternative herbicide to control resistant L. multiflorum, and it might be potentially helpful for improving the management of herbicide resistance in other aggressive weeds.

Automated summary

This study reveals that the L. multiflorum population HN-03 has evolved high-level resistance to the herbicide clodinafop-propargyl due to a target-site mutation. The population also exhibits cross-resistance and multiple-resistance to other herbicides, but remains susceptible to cypyrafluone. Pre-treatment with piperonyl butoxide and malathion enhances the susceptibility of the HN-03 population to certain herbicides. Cypyrafluone can be used as an alternative herbicide for resistant L. multiflorum.