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

Abstract

BackgroundThe 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.

Target‐site mutations Ile1781Leu and Ile2041Asn in the ACCase2 gene confer resistance to fluazifop‐p‐butyl and pinoxaden herbicides in a johnsongrass accession from Arkansas, USA

“…Research into the molecular resistance mechanisms to ACCase‐inhibiting herbicides in downy brome ( Bromus tectorum L.), has shown the presence of two different mutations, and authors have suggested a multiple evolutionary origin of ACCase resistance. Mutations described correspond to Ile2041Thr and Gly2096Ala which rendered a different pattern of ACCase‐resistance (Ribeiro et al, 2023 ).…”

Herbicide resistance in Bromus spp.: a global review

“…The population exhibited high levels of resistance to fluazifop-P-butyl (RF > 16) and sethoxydim (RF > 23) and low levels of resistance to clethodim (RF > 2) and quizalofop-P-ethyl (RF > 3). Fifteen years later, nine more ACCase-resistant B. tectorum populations were found in fine fescue seed production fields in the same area (Ribeiro et al 2023). The levels of resistance varied among the populations for clethodim (RF = 5.1 to 14.5), sethoxydim (RF = 18.7 to 44.7), fluazifop-P-butyl (RF = 3.1 to 40.3), and quizalofop-P-ethyl (RF = 14.5 to 36).…”

“…spp.) fields in Oregon (Ball et al 2007;Ribeiro et al 2023). In 2005, Ball et al (2007 identified an ACCaseresistant B. tectorum population in a creeping red fescue (Festuca rubra L. ssp.…”

“…Cross-resistance is prevalent in Bromus spp., with 20 reports confirmed in six countries, including Australia, the Czech Republic, France, Germany, the United Kingdom, and the United States. Instances of cross-resistance include resistance to ACCase and ALS inhibitors (Ball et al 2007;Davies et al 2020;Kumar and Jha 2017;Owen et al 2012Owen et al , 2015Ribeiro et al 2023;Sen et al 2021). Multiple resistance is less common, with four cases confirmed in Bromus spp.…”