Functional synergy and genomic linkage of glyphosate resistance traits in <scp>Canada</scp> fleabane

This study provides the first explicit quantitative analysis of gene × gene interactions underlying herbicide resistance in C. canadensis. By disentangling TSR and NTSR, we show that single copies of the TSR and NTSR alleles confer approximately nine-fold and seven-fold glyphosate resistance, respectively. When combined, these mechanisms exhibit synergism, resulting in resistance levels that exceed additive LD₅₀ expectations by more than two-fold. Both TSR and NTSR loci have been mapped to chromosome 4, and moderate genomic linkage (~27% recombination) between them will likely contribute to the persistence and spread of high-level resistance, even under low selection pressure. © 2025 His Majesty the King in Right of Canada. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. Reproduced with the permission of the Minister of Agriculture and Agri-Food Canada.