title: Interspecific hybridization transfers a previously unknown glyphosate resistance mechanism in Amaranthus species.
abstract: A previously unknown glyphosate resistance mechanism, amplification of the 5-enolpyruvyl shikimate-3-phosphate synthase gene, was recently reported in Amaranthus palmeri. This evolved mechanism could introgress to other weedy Amaranthus species through interspecific hybridization, representing an avenue for acquisition of a novel adaptive trait. The objective of this study was to evaluate the potential for this glyphosate resistance trait to transfer via pollen from A. palmeri to five other weedy Amaranthus species (Amaranthus hybridus, Amaranthus powellii, Amaranthus retroflexus, Amaranthus spinosus, and Amaranthus tuberculatus). Field and greenhouse crosses were conducted using glyphosate-resistant male A. palmeri as pollen donors and the other Amaranthus species as pollen recipients. Hybridization between A. palmeri and A. spinosus occurred with frequencies in the field studies ranging from <0.01% to 0.4%, and 1.4% in greenhouse crosses. A majority of the A. spinosus × A. palmeri hybrids grown to flowering were monoecious and produced viable seed. Hybridization occurred in the field study between A. palmeri and A. tuberculatus (<0.2%), and between A. palmeri and A. hybridus (<0.01%). This is the first documentation of hybridization between A. palmeri and both A. spinosus and A. hybridus.
authors.affiliation: Department of Bioagricultural Sciences and Pest Management, Colorado State University Fort Collins, CO, USA.
authors.forename: Todd A
authors.initials: TA
authors.lastname: Gaines
authors.affiliation: Department of Soil and Crop Sciences, Colorado State University Fort Collins, CO, USA.
authors.forename: Sarah M
authors.initials: SM
authors.lastname: Ward
authors.affiliation: Department of Bioagricultural Sciences and Pest Management, Colorado State University Fort Collins, CO, USA.
authors.forename: Bekir
authors.initials: B
authors.lastname: Bukun
authors.affiliation: School of Agriculture, Food, and Wine, University of Adelaide Glen Osmond, SA, Australia.
authors.forename: Christopher
authors.initials: C
authors.lastname: Preston
authors.affiliation: Department of Bioagricultural Sciences and Pest Management, Colorado State University Fort Collins, CO, USA.
authors.forename: Jan E
authors.initials: JE
authors.lastname: Leach
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
keywords: 5-enolpyruvyl shikimate-3-phosphate synthase; Palmer amaranth (Amaranthus palmeri S. Wats.); evolution; evolutionary adaptive change; gene amplification; gene flow; genetic introgression; glyphosate; transgenic crops