title: Glyphosate resistance in Ambrosia trifida: Part 1. Novel rapid cell death response to glyphosate.
abstract: BACKGROUND
  Glyphosate-resistant (GR) Ambrosia trifida is now present in the midwestern United States and in southwestern Ontario, Canada. Two distinct GR phenotypes are known, including a rapid response (GR RR) phenotype, which exhibits cell death within hours after treatment, and a non-rapid response (GR NRR) phenotype. The mechanisms of resistance in both GR RR and GR NRR remain unknown. Here, we present a description of the RR phenotype and an investigation of target-site mechanisms on multiple A. trifida accessions.
  
  
  RESULTS
  Glyphosate resistance was confirmed in several accessions, and whole-plant levels of resistance ranged from 2.3- to 7.5-fold compared with glyphosate-susceptible (GS) accessions. The two GR phenotypes displayed similar levels of resistance, despite having dramatically different phenotypic responses to glyphosate. Glyphosate resistance was not associated with mutations in EPSPS sequence, increased EPSPS copy number, EPSPS quantity, or EPSPS activity.
  
  
  CONCLUSIONS
  These encompassing results suggest that resistance to glyphosate in these GR RR A. trifida accessions is not conferred by a target-site resistance mechanism. © 2017 Society of Chemical Industry.
authors.affiliation: Department of Bioagricultural Sciences and Pest Management, Colorado State University, Fort Collins, CO, USA.|United States Department of Agriculture-Agricultural Research Service, San Joaquin Valley Agricultural Sciences Center, Parlier, CA, USA.
authors.forename: Christopher R
authors.identifier: http://orcid.org/0000-0003-2761-4662
authors.initials: CR
authors.lastname: Van Horn
authors.affiliation: Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN, USA.|Department of Horticulture, Oregon State University, Corvallis, OR, USA.
authors.forename: Marcelo L
authors.identifier: http://orcid.org/0000-0001-8313-9195
authors.initials: ML
authors.lastname: Moretti
authors.affiliation: Department of Horticulture and Landscape Architecture, West Lafayette, IN, USA.
authors.forename: Renae R
authors.initials: RR
authors.lastname: Robertson
authors.affiliation: Department of Horticulture and Landscape Architecture, West Lafayette, IN, USA.|Department of Plant Science and Landscape Architecture, University of Maryland, College Park, MD, USA.
authors.forename: Kabelo
authors.initials: K
authors.lastname: Segobye
authors.affiliation: Department of Horticulture and Landscape Architecture, West Lafayette, IN, USA.
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Weller
authors.affiliation: Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN, USA.
authors.forename: Bryan G
authors.initials: BG
authors.lastname: Young
authors.affiliation: Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN, USA.
authors.forename: William G
authors.initials: WG
authors.lastname: Johnson
authors.affiliation: Department of Horticulture and Landscape Architecture, West Lafayette, IN, USA.|Department of Plant Science and Landscape Architecture, University of Maryland, College Park, MD, USA.
authors.forename: Burkhard
authors.initials: B
authors.lastname: Schulz
authors.affiliation: Department of Plant Agriculture, University of Guelph, Guelph, ON, Canada.
authors.forename: Amanda C
authors.initials: AC
authors.lastname: Green
authors.affiliation: Department of Plant Agriculture, University of Guelph, Guelph, ON, Canada.
authors.forename: Taylor
authors.initials: T
authors.lastname: Jeffery
authors.affiliation: Department of Plant Agriculture, University of Guelph, Guelph, ON, Canada.
authors.forename: Mackenzie A
authors.initials: MA
authors.lastname: Lespérance
authors.affiliation: Department of Plant Agriculture, University of Guelph, Guelph, ON, Canada.
authors.forename: François J
authors.initials: FJ
authors.lastname: Tardif
authors.affiliation: Department of Plant Agriculture, University of Guelph, Guelph, ON, Canada.
authors.forename: Peter H
authors.initials: PH
authors.lastname: Sikkema
authors.affiliation: Department of Plant Agriculture, University of Guelph, Guelph, ON, Canada.
authors.forename: J Christopher
authors.initials: JC
authors.lastname: Hall
authors.affiliation: Department of Plant Agriculture, University of Guelph, Guelph, ON, Canada.
authors.forename: Michael D
authors.initials: MD
authors.lastname: McLean
authors.affiliation: Monsanto Company, Guelph, ON, Canada.
authors.forename: Mark B
authors.initials: MB
authors.lastname: Lawton
authors.affiliation: Monsanto Company, St Louis, MO, USA.
authors.forename: R Douglas
authors.initials: RD
authors.lastname: Sammons
authors.affiliation: Monsanto Company, St Louis, MO, USA.
authors.forename: Dafu
authors.initials: D
authors.lastname: Wang
authors.affiliation: Department of Bioagricultural Sciences and Pest Management, Colorado State University, Fort Collins, CO, USA.
authors.forename: Philip
authors.initials: P
authors.lastname: Westra
authors.affiliation: Department of Bioagricultural Sciences and Pest Management, Colorado State University, Fort Collins, CO, USA.
authors.forename: Todd A
authors.identifier: http://orcid.org/0000-0003-1485-7665
authors.initials: TA
authors.lastname: Gaines
mesh_terms: D031164:Ambrosia / Q000187:drug effects* / Q000235:genetics / Q000502:physiology; D016923:Cell Death / Q000187:drug effects*; D005998:Glycine / Q000031:analogs & derivatives* / Q000494:pharmacology; D053209:Herbicide Resistance; D006540:Herbicides / Q000494:pharmacology*; D015146:Midwestern United States; D009864:Ontario; D057685:Plant Weeds / Q000187:drug effects* / Q000502:physiology; D013714:Tennessee; D000097797:Glyphosate
chemical_list: D005998:Glycine; D006540:Herbicides; D000097797:Glyphosate
keywords: 5-enolypyruvyl shikimate 3-phosphate synthase; giant ragweed; glyphosate resistance; rapid response; shikimate; target site