First report of target‐site resistance to ACCase‐inhibiting herbicides in Bromus tectorum L.

Abstract

AbstractBackgroundThe prevalent and repeated use of acetyl‐coenzyme A carboxylase (ACCase)‐inhibiting herbicides for Bromus tectorum L. control in fine fescue (Festuca L. spp) grown for seed has selected ACCase‐resistant B. tectorum populations. The objectives of this study were to (1) evaluate the response of nine B. tectorum populations to the ACCase inhibitors clethodim, sethoxydim, fluazifop‐P‐butyl, and quizalofop‐P‐ethyl and the acetolactate synthase (ALS) inhibitor sulfosulfuron and (2) characterize the resistance mechanisms.ResultsBromus tectorum populations were confirmed to be resistant to the ACCase‐inhibiting herbicides tested. The levels of resistance varied among the populations for clethodim (resistance ratio, RR = 5.1–14.5), sethoxydim (RR = 18.7–44.7), fluazifop‐P‐butyl (RR = 3.1–40.3), and quizalofop‐P‐ethyl (RR = 14.5–36). Molecular investigations revealed that the mutations Ile2041Thr and Gly2096Ala were the molecular basis of resistance to the ACCase‐inhibiting herbicides. The Gly2096Ala mutation resulted in cross‐resistance to the aryloxyphenoxypropionate (APP) herbicides fluazifop‐P‐butyl and quizalofop‐P‐ethyl, and the cyclohexanedione (CHD) herbicides clethodim, and sethoxydim, whereas Ile2041Thr mutation resulted in resistance only to the two APP herbicides. All B. tectorum populations were susceptible to sulfosulfuron (RR = 0.3–1.7).ConclusionsThis is the first report of target‐site mutations conferring resistance to ACCase‐inhibiting herbicides in B. tectorum. The results of this study suggest multiple evolutionary origins of resistance and contribute to understanding the patterns of cross‐resistance to ACCase inhibitors associated with different mutations in B. tectorum. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.