Characterization of a novel R98Q mutation that confers resistance to sulfentrazone in common ragweed (Ambrosia artemisiifolia) populations from Michigan.

BACKGROUND: In 2023, soybean growers in Eaton County, Michigan, USA, reported repeated failures to control common ragweed (Ambrosia artemisiifolia L.) with protoporphyrinogen IX (PPO)-inhibiting herbicides, sulfentrazone and fomesafen, in soybean plants. This study aimed to investigate resistance levels and mechanisms of resistance in two suspected resistant populations (R1 and R2). RESULTS: Dose-response assays revealed resistance to sulfentrazone in both populations, with median lethal dose (LD50) values 36- and 24-fold higher than the susceptible population for R1 and R2, respectively, and reduced sensitivity to fomesafen in both populations. Nanopore sequencing identified two PPO2 target-site substitutions at codon 98: Arg-98-Leu (R98L) and a novel Arg-98-Gln (R98Q) mutation. Both substitutions were associated with reduced herbicide binding affinity in computational modeling simulations. R98Q substitution conferred strong and selective resistance in the PPO2 enzyme inhibition assays, supporting its role as a key resistance mechanism. CONCLUSION: This study reports the first field occurrence of the R98Q substitution in PPO2 of Ambrosia artemisiifolia populations and demonstrates its association to PPO inhibitor resistance. These findings highlight the rapid evolution of target-site resistance and the need for continued monitoring and rapid diagnostic tools to detect emerging mutations. Further research is needed to clarify the contribution of additional resistance mechanisms. © 2026 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.