Survey of ACCase and ALS resistance in winter annual grasses identifies target-site and nontarget-site imazamox resistance in Secale cereale

Neeta Soni, Eric P. Westra, Giuseppe Allegretta, Andre L. S. Araujo, Camila F. de Pinho, Sarah Morran, Jens Lerchl, Franck E. Dayan, Philip Westra, Todd A. Gaines

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)


Background Early detection of herbicide resistance in weeds is crucial for successful implementation of integrated weed management. We conducted a herbicide resistance survey of the winter annual grasses feral rye (Secale cereale), downy brome (Bromus tectorum), and jointed goatgrass (Aegilops cylindrica) from Colorado winter wheat production areas for resistance to imazamox and quizalofop. Results All samples were susceptible to quizalofop. All downy brome and jointed goatgrass samples were susceptible to imazamox. Out of 314 field collected samples, we identified three feral rye populations (named A, B, and C) that were imazamox resistant. Populations B and C had a target-site mechanism with mutations in the Ser653 residue of the acetolactate synthase (ALS) gene to Asn in B and to Thr in C. Both populations B and C had greatly reduced ALS in vitro enzyme inhibition by imazamox. ALS feral rye protein modeling showed that steric interactions induced by the amino acid substitutions at Ser653 impaired imazamox binding. Individuals from population A had no mutations in the ALS gene. The ALS enzyme from population A was equally sensitive to imazamox as to known susceptible feral rye populations. Imazamox was degraded two times faster in population A compared with a susceptible control. An oxidized imazamox metabolite formed faster in population A and this detoxification reaction was inhibited by malathion. Conclusion Population A has a nontarget-site mechanism of enhanced imazamox metabolism that may be conferred by cytochrome P450 enzymes. This is the first report of both target-site and metabolism-based imazamox resistance in feral rye. (c) 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.
Original languageEnglish
Pages (from-to)5080-5089
Number of pages10
JournalPest Management Science
Issue number12
Early online dateSept 2022
Publication statusPublished - Dec 2022
Externally publishedYes


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