title: Field-evolved resistance to four modes of action of herbicides in a single kochia (Kochia scoparia L. Schrad.) population.
abstract: BACKGROUND
  Evolution of multiple herbicide resistance in weeds is a serious threat to weed management in crop production. Kochia is an economically important broadleaf weed in the U.S. Great Plains. This study aimed to confirm resistance to four sites of action of herbicides in a single kochia (Kochia scoparia L. Schrad.) population from a crop field near Garden City (GC), Kansas, and further determine the underlying mechanisms of resistance.
  
  
  RESULTS
  One-fourth of the GC plants survived the labeled rate or higher of atrazine [photosystem II (PSII) inhibitor], and the surviving plants had the Ser-264 to Gly mutation in the psbA gene, the target site of atrazine. Results showed that 90% of GC plants survived the labeled rate of dicamba, a synthetic auxin. At least 87% of the plants survived up to 72 g a.i. ha(-1) of chlorsulfuron [acetolactate synthase (ALS) inhibitor], and analysis of the ALS gene revealed the presence of Pro-197 to Thr and/or Trp-574 to Lue mutation(s). Most GC plants also survived the labeled rate of glyphosate [5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) inhibitor), and the resistant plants had 5-9 EPSPS gene copies (relative to the ALS gene).
  
  
  CONCLUSIONS
  We confirm the first case of evolution of resistance to four herbicide sites of action (PSII, ALS and EPSPS inhibitors and synthetic auxins) in a single kochia population, and target-site-based mechanisms confer resistance to atrazine, glyphosate and chlorsulfuron.
authors.affiliation: Department of Agronomy, Kansas State University, Manhattan, KS, USA.
authors.forename: Vijay K
authors.initials: VK
authors.lastname: Varanasi
authors.affiliation: Department of Agronomy, Kansas State University, Manhattan, KS, USA.
authors.forename: Amar S
authors.initials: AS
authors.lastname: Godar
authors.affiliation: Southwest Research and Extension Center, Kansas State University, Garden City, KS, USA.
authors.forename: Randall S
authors.initials: RS
authors.lastname: Currie
authors.affiliation: Department of Agronomy, Kansas State University, Manhattan, KS, USA.
authors.forename: Anita J
authors.initials: AJ
authors.lastname: Dille
authors.affiliation: Department of Agronomy, Kansas State University, Manhattan, KS, USA.
authors.forename: Curtis R
authors.initials: CR
authors.lastname: Thompson
authors.affiliation: Agricultural Research Center - Hays, Kansas State University, Hays, KS, USA.
authors.forename: Phillip W
authors.initials: PW
authors.lastname: Stahlman
authors.affiliation: Department of Agronomy, Kansas State University, Manhattan, KS, USA.
authors.forename: Mithila
authors.initials: M
authors.lastname: Jugulam
mesh_terms: D001280:Atrazine; D027467:Bassia scoparia / Q000235:genetics / Q000502:physiology*; D018744:DNA, Plant / Q000235:genetics; D003996:Dicamba; D005998:Glycine / Q000031:analogs & derivatives; D053209:Herbicide Resistance; D006540:Herbicides; D007615:Kansas; D009154:Mutation; D057685:Plant Weeds; D013449:Sulfonamides; D014227:Triazines; D000097797:Glyphosate
chemical_list: D001280:Atrazine; D018744:DNA, Plant; D003996:Dicamba; D005998:Glycine; D006540:Herbicides; D013449:Sulfonamides; D014227:Triazines; D000097797:Glyphosate; C037137:chlorsulfuron
keywords: ALS gene; EPSPS gene; Kochia scoparia; dicamba; mechanism of resistance; multiple herbicide resistance; psbA gene