volunteers and quizalofop-ethyl

The 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.. Bromus 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).. This 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.

Topics: Acetyl-CoA Carboxylase; Bromus; Enzyme Inhibitors; Herbicide Resistance; Herbicides; Mutation

Shortawn foxtail (Alopecurus aequalis) is a troublesome grass weed infesting winter wheat and oilseed rape productions in China. Fenoxaprop-p-ethyl and mesosulfuron-methyl failed to control shortawn foxtail of AHSX-1 population collected from a wheat field in Shou County, Anhui province. Molecular analyses revealed that Asp2078Gly mutation of ACCase and Trp574Leu mutation of AHAS were present in plants of the AHSX-1 population. The homozygous plants were isolated and cultured until seed maturity. Whole-plant herbicide bioassays were conducted in the greenhouse using the purified seeds of F1 generation. Dose-response experiments showed that the AHSX-1 population has evolved a very high level resistance to fenoxaprop-p-ethyl (RI = 275) and mesosulfuron-methyl (RI = 788). To determine the sensitivity to other herbicides, assays were conducted at the single recommended rate of each herbicide. Based on the results, the AHSX-1 population was considered to be highly resistant to clodinafop-propargyl, pyroxsulam and flucarbazone-sodium, moderately or highly resistant to quizalofop-p-ethyl, clethodim, sethoxydim and pinoxaden, and susceptible to isoproturon and chlorotoluron. This is the first report of Asp2078Gly mutation in shortawn foxtail and the two robust dCAPS markers designed could quickly detect Asp2078 and Trp574 mutations in ACCase and AHAS gene of shortawn foxtail, respectively.

Topics: Acetolactate Synthase; Acetyl-CoA Carboxylase; China; Cyclohexanones; Herbicide Resistance; Herbicides; Heterocyclic Compounds, 2-Ring; Mutation; Oxazoles; Propionates; Pyridines; Quinoxalines; Sulfonylurea Compounds