Target‐site mutations and non‐target‐site detoxification confer ALS ‐inhibitor resistance in Bromus japonicus populations in China

BACKGROUND: The emergence of herbicide-resistant Japanese brome (Bromus japonicus) populations has been increasingly documented throughout China. Two such populations, DZ-R and XL-R, exhibit resistance to acetolactate synthase (ALS)-inhibiting herbicides, yet their resistance level and mechanism remain undetermined. This study sought to: (i) quantify resistance levels to flucarbazone-sodium, mesosulfuron-methyl, and pyroxsulam; (ii) screen for ALS mutations conferring target-site resistance (TSR); and (iii) characterize non-target-site resistance (NTSR) mechanisms using a multi-omics approach. RESULTS: Whole-plant bioassay results indicated that the resistance indices of DZ-R and XL-R populations were 111.3 and 90.5 to flucarbazone-sodium, 36 and 206.4 to mesosulfuron-methyl, and 109.8 and 429.5 to pyroxsulam. The TSR mechanism was mediated by distinct ALS gene mutations: a Pro197-Ser substitution in DZ-R and a Pro197-Thr substitution in XL-R. Integrated transcriptomic, metabolomics and malathion-inhibited bioassay analyses revealed the NTSR mechanism, identifying two ABCB4, ABCG48, ABCB11 genes, two unnamed ABC, POD 35, POD P7-like, GST1, GSTU17, 2 GSTU6, IN2-1-like isoform X3 genes, three unnamed GST, GT 73C6-like, ZWY2020_001091, cis-zeatin O-GT, CYP74A15, noroxomaritidine synthase 2-like, indole-2-monooxygenase-like genes and four unnamed CYP450 genes as candidate genes. These genes participated in ATP-binding cassette transporters, phenylpropanoid biosynthesis, glutathione metabolism and zeatin biosynthesis metabolic pathways that synergistically mediate herbicide detoxification. Notably, two putative flucarbazone-sodium degradation pathways were deduced in the resistant populations. CONCLUSION: Collectively, these findings demonstrated that both TSR and NTSR mechanisms contributed to herbicide resistance in the DZ-R and XL-R populations. Future research should prioritize functional validation of the identified candidate genes to elucidate their specific roles in herbicide metabolism. © 2026 Society of Chemical Industry.