Characterization of a novel R98Q mutation that confers resistance to sulfentrazone in common ragweed (Ambrosia artemisiifolia) populations from MichiganShort title: PPO resistance in common ragweed

BACKGROUNDIn 2023, soybean growers in Eaton County, Michigan, reported repeated failures to control common ragweed (Ambrosia artemisiifolia L.) with (PPO)-inhibiting herbicides, sulfentrazone and fomesafen, in non-genetically modified soybeans. This study aimed to investigate resistance levels and mechanisms of resistance in two suspected resistant populations (R1 and R2). RESULTSDose-response assays revealed resistance to sulfentrazone in both populations, with LD50 values 24 and 36-fold higher than the susceptible population and reduced sensitivity to fomesafen. 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 modelling simulations. R98Q substitution conferred strong and selective resistance in the PPO2 enzyme inhibition assays, supporting its role as a key resistance mechanism. CONCLUSIONThis study reports the first field occurrence of the R98Q substitution in PPO2 of A. artemisiifolia populations and demonstrates its association with 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.