Resistance and Hormetic Responses to Acetyl‐Coenzyme A Carboxylase‐Inhibitors Observed in a <scp><i>Beckmannia syzigachne</i></scp> Population Holding the <scp>I1781L</scp> Target‐Site Mutation

ABSTRACT China is one of the countries suffering the biggest challenge of herbicide‐resistant weeds. Hormetic effects of herbicides on weeds may further facilitate the evolution and spread of herbicide‐resistant weeds. We investigated hormetic responses of fenoxaprop‐p‐ethyl and pinoxaden on a putative acetyl‐coenzyme A carboxylase (ACCase)‐inhibitor‐resistant Beckmannia syzigachne (JDR, collected from Jiangdu county) population by comparing it with a sensitive population (LHS, collected from Luhe county) in responses of whole‐plant bioassays, ACCase sequences, and biomass and seed productivity of plant individuals surviving fenoxaprop‐p‐ethyl treatments. We found that the GR 50 doses (doses of herbicides causing a 50% reduction in fresh weight of above‐ground parts) of fenoxaprop‐p‐ethyl and pinoxaden on LHS were 9.5 and 6.1 g ai ha −1 , respectively. In JDR, fresh weights of above‐ground parts of seedlings increased in fenoxaprop‐p‐ethyl treatments with doses from 7.8 to 124.2 g ai ha −1 and pinoxaden treatments with doses from 7.5 to 15 g ai ha −1 , compared with the control treatment which was not treated with herbicides. All 95 seedlings of JDR tested showed an I1781L mutation in the ACCase. Moreover, seedlings surviving fenoxaprop‐p‐ethyl treatments also showed hormetic effects on the dry weight of above‐ground parts, seed production per plant individual, and 100‐seed weights in the JDR population. This study implied the potentially important role of hormesis in the infestation of ACCase‐inhibitor‐resistant B. syzigachne in China, which has been overlooked.