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

Digitaria ciliaris var. chrysoblephara is a xerophytic weed severely invadingrice fields along with the application of rice mechanical direct seedingtechnology in China. This study identified one resistant population(M5) with an Ile-1781-Leu substitution in ACCase1 showing broad-spectrum resistance to three chemical classes of ACCase-inhibitingherbicides, including metamifop, cyhalofop-butyl, fenoxaprop-p-ethyl, haloxyfop-p-methyl, clethodim,sethoxydim, and pinoxaden. The other two populations, M2 and M4, withoutany resistance-responsible mutations, only exhibited resistance toaryloxyphenoxypropionate (APP) herbicides cyhalofop-butyl and fenoxaprop-p-ethyl. Pre-treatment with the cytochrome P450 monooxygenase(P450) inhibitor PBO significantly reduced the cyhalofop-butyl resistanceby 43% in the M2 population. Pre-emergence weed control with soil-appliedherbicides, such as pretilachlor, pendimethalin, and oxadiazon, caneffectively inhibit the germination and growth of D.ciliaris var. chrysoblephara. The present study reported a xerophytic weed species invading ricefields featuring broad-spectrum resistance to ACCase-inhibiting herbicidesas a result of Ile-1781-Leu mutation of ACCase. Bothtarget- and P450-involved non-target-site mechanisms may be contributingto resistance in D. ciliaris var. chrysoblephara species.