title: Occurrence of an herbicide-resistant plant trait in agricultural field margins.
abstract: Agricultural environments allow study of evolutionary change in plants. An example of evolution within agroecological systems is the selection for resistance to the herbicide glyphosate within the weed, Conyza canadensis. Changes in survivorship and reproduction associated with the development of glyphosate resistance (GR) may impact fitness and influence the frequency of occurrence of the GR trait. We hypothesized that site characteristics and history would affect the occurrence of GR C. canadensis in field margins. We surveyed GR occurrence in field margins and asked whether there were correlations between GR occurrence and location, crop rotation, GR crop trait rotation, crop type, use of tillage, and the diversity of herbicides used. In a field experiment, we hypothesized that there would be no difference in fitness between GR and glyphosate-susceptible (GS) plants. We asked whether there were differences in survivorship, phenology, reproduction, and herbivory between 2 GR and 2 GS populations of C. canadensis in agrestal and ruderal habitats. We found that geographic location was an important factor in the occurrence of GR C. canadensis in field margins. Although not consistently associated with either glyphosate resistance or glyphosate susceptibility, there were differences in phenology, survivorship, and herbivory among biotypes of C. canadensis. We found equal or greater fitness in GR biotypes, compared to GS biotypes, and GR plants were present in field margins. Field margins or ruderal habitats may provide refugia for GR C. canadensis, allowing reproduction and further selection to occur as seeds recolonize the agrestal habitat. Agricultural practices may select for ecological changes that feed back into the evolution of plants in ruderal habitats.
authors.affiliation: Department of Plant, Soil, and Agricultural Systems Southern Illinois University Carbondale Illinois 62901 ; Department of Plant Biology Center for Ecology Southern Illinois University Carbondale Illinois 06460.
authors.forename: Karla L
authors.identifier: 0000-0002-6235-8804
authors.initials: KL
authors.lastname: Gage
authors.affiliation: Department of Plant Biology Center for Ecology Southern Illinois University Carbondale Illinois 06460.
authors.forename: David J
authors.identifier: 0000-0002-0308-7506
authors.initials: DJ
authors.lastname: Gibson
authors.affiliation: Department of Plant, Soil, and Agricultural Systems Southern Illinois University Carbondale Illinois 62901.
authors.forename: Bryan G
authors.initials: BG
authors.lastname: Young
authors.affiliation: Department of Plant, Soil, and Agricultural Systems Southern Illinois University Carbondale Illinois 62901.
authors.forename: Julie M
authors.initials: JM
authors.lastname: Young
authors.affiliation: Department of Plant, Soil, and Agricultural Systems Southern Illinois University Carbondale Illinois 62901.
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Matthews
authors.affiliation: Department of Horticulture and Landscape Architecture Purdue University West Lafayette Indiana 47907.
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Weller
authors.affiliation: Department of Agronomy and Horticulture University of Nebraska Scottsbluff Nebraska 69361.
authors.forename: Robert G
authors.initials: RG
authors.lastname: Wilson
keywords: Benchmark Study; contemporary evolution; field margins; refugia