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Low crop plant population densities promote pollen-mediated gene flow in spring wheat (Triticum aestivum L.)


Transgenic wheat is currently being field tested with the intent of eventual commercialization. The development of wheat genotypes with novel traits has raised concerns regarding the presence of volunteer wheat populations and the role they may play in facilitating transgene movement. Here, we report the results of a field experiment that investigated the potential of spring wheat plant population density and crop height to minimize gene flow from a herbicide-resistant (HR) volunteer population to a non-HR crop. Pollen-mediated gene flow (PMGF) between the HR volunteer wheat population and four conventional spring wheat genotypes varying in height was assessed over a range of plant population densities. Natural hybridization events between the two cultivars were detected by phenotypically scoring plants in F1 populations followed by verification with Mendelian segregation ratios in the F1:2 families. PMGF was strongly associated with crop yield components, but showed no association with flowering synchrony. Maximum observed PMGF was always less than 0.6%, regardless of crop height and density. The frequency of PMGF in spring wheat decreased exponentially with increasing plant population density, but showed no dependence on either crop genotype or height. However, increasing plant densities beyond the recommended planting rate of 300 cropped wheat plants m−2 provided no obvious benefit to reducing PMGF. Nevertheless, our results demonstrate a critical plant density of 175–200 cropped wheat plants m−2 below which PMGF frequencies rise exponentially with decreasing plant density. These results will be useful in the development of mechanistic models and best management practices that collectively facilitate the coexistence of transgenic and nontransgenic wheat crops.

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Adventitious presence


Extra sum of squares


Herbicide resistant




Pollen-mediated gene flow


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Funding for this project was provided by the Natural Sciences and Engineering Research Council of Canada (NSERC), the Canadian Wheat Board, the Agri-Food Research and Development Initiative of Manitoba (ARDI), the Canadian Seed Growers Association, and the Canadian Food Inspection Agency. The authors are grateful to Lyle Friesen and Andrea Bartlinski for their technical assistance.

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Correspondence to Christian J. Willenborg.

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Willenborg, C.J., Brûlé-Babel, A.L. & Van Acker, R.C. Low crop plant population densities promote pollen-mediated gene flow in spring wheat (Triticum aestivum L.). Transgenic Res 18, 841–854 (2009).

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  • Biosafety
  • Herbicide-resistant
  • Plant population density
  • Pollen-mediated gene flow
  • Spring wheat
  • Volunteer crop