Ala‐205‐met mutation in acetolactate synthase ( ALS ) of Bromus japonicus confers resistance to ALS ‐inhibiting herbicides

BACKGROUND: Acetolactate synthase (ALS)-inhibitor-resistant Bromus japonicus populations are widespread in wheat fields in China. A novel population BD-R has evolved resistance to flucarbazone-sodium, whereas its underlying resistance mechanism remains unclear. The objectives of this study were to (i) determine the resistance and cross-resistance levels to ALS inhibitors; (ii) investigate the resistance mechanisms; (iii) evaluate response to herbicides with other modes of action; and (iv) develop a CAPS molecular marker for rapid resistance detection. RESULTS: values of BD-R and HS-S to flucarbazone-sodium were 7753.82 and 144.12 nm. 3D modelling and molecular docking results revealed the Ala-205-Met mutation reduced the binding affinity between ALS and the three ALS inhibitors. Homozygous transgenic Arabidopsis thaliana lines harboring ALS from BD-R exhibited resistance to flucarbazone-sodium, with FW inhibition merely 4.93%. Haloxyfop-P-methyl and quizalofop-P-ethyl showed excellent control of BD-R, whereas topramezone and mesotrione exhibited no efficacy. A CAPS-ALS marker with the primers CAPS-ALS-F (5'-TCATCACCAACCATCTCTTCC-3') and CAPS-ALS-R (5'-ATCAGAGTAGTTGTAACTGGAATC-3') was developed and could reliably identify the resistant BD-R plants. CONCLUSION: BD-R conferred high-level resistance and cross-resistance levels to ALS-inhibitors. Haloxyfop-P-methyl and quizalofop-P-ethyl can be used for effective control BD-R. This study is the first report of the Ala-205-Met mutation conferring resistance to ALS inhibitors in weeds, indicating the complexity of the evolution of herbicide resistance in weeds. © 2026 Society of Chemical Industry.