Colorado State Studies Wheat Cross-Pollination to Other Wheat Crops and Related Weeds

A Colorado State University study has identified wheat pollen drift patterns in eastern Colorado, providing initial information to farmers and residents about how far wheat pollen – including pollen from wheat varieties that are genetically modified — will drift in typical conditions in that area of the state.

The study, which looked at natural drift patterns of wheat pollen, has preliminary results based on two years of testing, but will also eventually include several additional years to continue to give researchers a better average of "typical" climate conditions in eastern Colorado.

When evaluating wheat drift, the two-year study measured cross-pollination by tracking the drift — or spread — of a genetic trait for herbicide resistance to nearby wheat without the resistant gene. The study indicates that genetic traits from one field of wheat can be transferred at a low frequency to neighboring wheat plants as far away as 200 feet.  

The rate of cross-pollination was impacted by the direction of wind and the variety of the non-resistant crop. Study results indicate that some wheat varieties are more susceptible to cross-pollination than other varieties planted in the same area. The level of cross-pollination also is affected by distance from the pollen source.

"This study indicates that cross-pollination occurs in wheat at levels and distances greater than are usually assumed," said Pat Byrne, a researcher in Colorado State University’s Department of Soil and Crop Sciences.  "Seed producers and other growers interested in preserving the identity of their crops will likely be interested in these results."

The study specifically traced herbicide tolerance in Above, a non-genetically engineered winter wheat variety that is resistant to the herbicide imazamox, and cross-pollination with 20 other wheat varieties that are not herbicide-resistant. The non-resistant crops were planted in farmers’ fields immediately adjacent to the Above plots.  

Researchers collected seed samples from non-resistant fields then germinated new plants from those seeds. They then sprayed the seedlings with the herbicide, and evaluated the number of plants that survived after they were sprayed, assuming that the plants that survived were resistant to imazamox because of cross-pollination. The group found evidence of cross-pollination in 70 percent of the wheat samples, but 95 percent of the samples had very low cross-pollination rates of less than one-half percent. Decreasing numbers of plants were affected from the border of the resistant wheat to wheat as far away as 200 feet. Rates were highest closest to the resistant field, with a maximum of 5 percent of the plants displaying resistance in one sample collected a foot away from the Above plot. At 200 feet from the resistant wheat, a maximum of one-tenth of one percent cross-pollination, or 1 seed in every 10,000 seeds, was found.

In addition to investigating the rate of cross-pollination from wheat crop to wheat crop, the study also looked at how jointed goatgrass, an invasive weed that is related to wheat and can be susceptible to cross-pollination from wheat, is affected by drifting pollen from Above. Jointed goatgrass grows on much of the Great Plains, where wheat is a prominent crop.

"The susceptibility of jointed goatgrass to wheat cross-pollination has raised concerns about the ecological consequences that may arise if traits from wheat such as herbicide or drought resistance are transferred to goatgrass," said Byrne. "We wanted to quantify the amount of cross-pollination that occurs in jointed goatgrass found within Above wheat fields and at distances from the field as far away as 174 feet."

The study found that cross-pollination between goatgrass and the herbicide-resistant Above wheat did occur, but was limited to weeds within 5 feet of the resistant wheat. Within that 5 feet, cross-pollination ranged from one to 16 seeds per 1,000 seeds.

"The potential impacts of this wheat-to-goatgrass gene flow will depend on several factors, including the fertility of the hybrid plants, the competitive advantage that the transferred gene provides to goatgrass, and the rate of spread of the gene within goatgrass populations," Byrne said.

This study was funded by the U.S. Department of Agriculture’s Biotechnology Risk Assessment Grants Program, with participation from Colorado State University Cooperative Extension specialists, U.S. Department of Agriculture – Agricultural Research Service scientists and cooperating farmers.