Pollen movement and gene migration at macro-geographic scales

Background/Question/Methods 

The transfer of GM genes out of modified crop plants into wild relatives requires the transfer and successful fertilization from GM pollen into a non-GM host.  Pollen transfer in canola is thought to occur primarily with insects, but pollen morphology and documented occurrence of Brassica napus allergies suggests that the pollen does become air-born at relatively high concentrations.  The entrainment of Brassica sp. pollen into the atmosphere and transport downwind therefore cannot be ruled out as a contributor to out-crossing events, potentially at some distance.  Long-distance fertilization was documented in eastern Oregon with GM-pollen producing GM-seed in non-GM Agrostis stolonifera at some 20 km from the nearest fields.  In a non-GM system, pollen concentrations greater than 2000 pollen grains per m³, have been recorded at 200 to 600 km downwind of pollinating populations in the southern Great Plains.  These high concentrations result from a dense pollen source and specific atmospheric conditions where meso-scale weather systems interact over large regional areas.  Similar weather systems are common in the upper Great Plains during the growing season.  Modeled wind trajectories for select years are calculated to characterize the prevalence of atmospheric conditions that correlate with long distance transport events in other systems.  The distance at three hour time intervals was calculated to determine potential areas in which plants on the ground may be susceptible to GM-pollen fertilization.  In addition the general direction of the wind trajectories were determined.

Results/Conclusions 

The current GM-canola study area, along the northern tier counties in North Dakota, is renowned for its consistent and elevated wind speeds.  During periods where the atmosphere is heavy and has little buoyancy pollen entrained within the atmosphere can move but is subject to impaction on neighboring plants and other obstacles, removing it from the air stream.  Times in which a buoyant atmosphere occurs, however, pollen can be lifted into the atmosphere and deposited at some distance downwind.  Wind trajectories from northern North Dakota routinely cover a distance greater than 600 km during a 24 hour period.  The general wind direction is from the north to northwest, thus areas to the south to southeast have the greatest potential for GM-Pollen out crossing events from wind entrained pollen.  In conclusion, the escape of GM-genes from crop areas must be considered to be both at the local as well as long-distance wind direction, especially in systems in which the pollen is known to be transferred by both mechanisms.