Hugh J. Beckie
Research Centre, Agriculture and Agri-Food Canada (AAFC), Saskatoon
Suzanne I. Warwick
Research Centre, AAFC, Ottawa
Linda M. Hall
University of Alberta, Edmonton
K. Neil Harker
Research Centre, AAFC, Lacombe

Crop intraspecific pollen-mediated gene flow (PMGF) can be scale-dependent. A study was conducted in western Canada to examine PMGF in commercial spring wheat (Triticum aestivum L.) fields. At each of two sites located in the semiarid Grassland region of Saskatchewan, PMGF was measured from a 16-ha (400 × 400 m) field of imidazolinone (IMI)-resistant wheat (cultivar CDC Imagine) to an adjacent field of conventional (non-IMIresistant) wheat (cultivar AC Barrie) with the same dimensions. Wheat grain samples of AC Barrie were collected at varying distances up to 400 m along five equally-spaced transects oriented perpendicular to the common border with CDC Imagine. A total of 2,000 seedlings per sample were screened for resistance to imazamox at 200 μM in a 7-d soil-less bioassay. Putative-resistant hybrids were confirmed by two allele-specific analyses: cleaved amplified polymorphic sequence (CAPS) marker detection of the IMI-resistance allele, TaAhasL-D1, and polymerase chain reaction detection of heterozygotes. Averaged across transects and sites, PMGF was 0.20% at the common border and declined exponentially with increasing distance; the maximum distance that PMGF was detected was 80 m from the donor field. Within 5 m of the common border, hybridization frequency averaged 0.14%. Averaged across the entire field, hybridization frequency averaged 0.006%; when grain from a 5- m harvested strip adjacent to the donor field was excluded from the harvest-blended seedlot, hybridization frequency was reduced by 33% to 0.004%. The largest contributor to adventitious presence in wheat is likely not PMGF, but seed-mediated gene flow. Frequency and distance of PMGF can guide grower stewardship practices for identity preservation in wheat cultivars possessing different traits.

Key words: Adventitious presence, gene flow, GM crops, identity preservation, outcrossing, plants with novel traits, pollen flow, threshold, Triticum aestivum.