Ile-1781-Leu Target Mutation and Non-Target-Site Mechanism Confer Resistance to Acetyl-CoA Carboxylase-Inhibiting Herbicides in var. .

var. is a xerophytic weed severely invading rice fields along with the application of rice mechanical direct seeding technology in China. This study identified one resistant population (M5) with an Ile-1781-Leu substitution in showing broad-spectrum resistance to three chemical classes of ACCase-inhibiting herbicides, including metamifop, cyhalofop-butyl, fenoxaprop--ethyl, haloxyfop--methyl, clethodim, sethoxydim, and pinoxaden. The other two populations, M2 and M4, without any resistance-responsible mutations, only exhibited resistance to aryloxyphenoxypropionate (APP) herbicides cyhalofop-butyl and fenoxaprop--ethyl. Pre-treatment with the cytochrome P450 monooxygenase (P450) inhibitor PBO significantly reduced the cyhalofop-butyl resistance by 43% in the M2 population. Pre-emergence weed control with soil-applied herbicides, such as pretilachlor, pendimethalin, and oxadiazon, can effectively inhibit the germination and growth of var. . The present study reported a xerophytic weed species invading rice fields featuring broad-spectrum resistance to ACCase-inhibiting herbicides as a result of Ile-1781-Leu mutation of . Both target- and P450-involved non-target-site mechanisms may be contributing to resistance in var. species.