NDSU Agronomist:

“Wheat Outcrossing Limited, Manageable”

There are a number of factors that can affect gene flow via pollen drift in wheat, including distance between varieties, temperature, humidity, wind, insects, and synchronization of flowering. Varietal characteristics – glume opening, extrusion of anthers, and whether spikelets are open or dense – can also impact cross-pollination.

Generally, however, the chances of outcrossing are remote if a minimal separation distance is maintained. Wheat pollen is viable for only between 2 and 20 minutes, and is heavy, limited in how far it can travel.  NDSU extension agronomist Joel Ransom points to research data which indicates that a distance of 33-59 ft gave zero outcrossing in hard red spring wheat.  Research data further suggests that:

• With an isolation distance of 60-90 ft (conservative, based on the most ‘promiscuous’ cultivar) there is limited risk of gene flow via pollen between spring wheat cultivars.
• An isolation distance of greater than 90 ft has a high probability of zero outcrossing, although zero cannot be guaranteed, as pollen has been shown to be capable of much farther movement – research in the late 1960s in Kansas recorded movement over 150 ft.
• Current IP systems frequently have isolation distances approaching 60 ft, but sometimes much less. However, isolation distances in IP, organic, and seed production would likely not be difficult to achieve. Relying on natural boundaries alone for isolation would not be workable due to the fact that farmers often plant more than one variety within a field.
• Given limited outcrossing and current field layouts, gene flow from biotech to non-biotech wheat will likely be minimal and manageable.

The data on this page shows that outcrossing can vary by wheat variety and by seasonal conditions, and while pollen spread has been shown to be capable of traveling over 150 ft, other research indicates that the chance of cross pollination occurring drops to virtually zero much beyond 30 ft.

Preliminary data from research conducted at NDSU (Mohamed Mergoum, NDSU spring wheat breeder, principal investigator) provides further evidence that the outcrossing ability of wheat varieties is limited. One experiment near Prosper, N.D. in 2004 examined the effect of spatial separation on outcrossing in four varieties: Alsen, Granite, Oslo, and Explorer, a hard white spring wheat variety. Percent outcrossing with a separation distance of 1.1 ft was under 2% for all four varieties.  The outcrossing percentage at a distance of 1.1 ft was about 1.7% for Granite; Explorer, 0.5%; Alsen, 0.375%; Oslo, under 0.1%. At a separation distance of 13 ft, there was a detectable trace of outcrossing for Alsen and Granite, although it was near zero. No outcrossing of any of the varieties was detected at a separation distance of 33 ft and 110 ft.

Effect of variety and year on outcrossing (92-93), HRSW, Canada (Adapted from Hucl, 1996)

Effect of isolation distance on outcrossing of four Canadian wheat cultivars, 1995 (Adapted from Hucl & Matus-Cadiz, 2001)

How far can wheat pollen move? (Adapted from Khan et al, 1973 (Kansas)