Gene Flow in Wheat at the Field Scale

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In wheat (Triticum L.), large‐scale field studies were conducted to assess the level of intra‐ and interspecific pollen‐mediated gene movement that may exist at varying distances from a pollinator source. The objectives of this research were to measure gene flow rates from a blue‐grained pollinator (T. aestivum cv. Purendo‐38) to (i) red‐grained spring wheat cv. CDC Teal (T. aestivum) over distances of 0.2 to 160 m, (ii) amber durum wheat cv. AC Navigator (T. turgidum L.) over distances of 0.2 to 260 m, and (iii) CDC Teal and AC Navigator over distances of 180 to 2760 m. In 2000 and 2001, 50‐ by 50‐m blue‐grained pollinator blocks were sown and surrounded by recipient fields of either CDC Teal or AC Navigator at Saskatoon, SK. At maturity, 0.5‐ by 4‐m strips were harvested at specified distances between 0.2 and 160 m or 260 m along eight transects (N, E, S, W, NE, SE, SW, NW) radiating out from Purendo‐38. In addition, random sampling was conducted in 2000 and 2001 from surrounding wheat fields to estimate gene flow rates over distances of 180 to 2760 m. Gene flow from Purendo‐38 to recipient plants was identified by the expression of a light‐blue pigment in the aleurone layer of F1 hybrid seed. Confirmed intra‐ and interspecific pollen‐mediated gene flow rates remained below 0.5% and declined rapidly with distance from the pollinator. Elevated gene flow rates to the N, W, and NW of the pollinator were associated with prevalent winds in 2000, but not in 2001. In 2000, long distance intraspecific gene flow was confirmed at a frequency of 0.005% at a position 300 m northwest of the pollinator. No evidence of interspecific gene flow was observed at ≥40 m from the pollinator. The results suggest that gene flow occurrence in spring wheat is relatively low but that a tolerance level of 0% transgenic wheat in nontransgenic wheat grain is unrealistic.