Final data from an Iowa State University research project looking at corn pollen drift supports the notion that an effective way to decrease unintended pollination is to use buffer strips of corn.
Last spring, researchers planted a strip of 24 rows of purple popcorn within a 15-acre field of standard yellow corn on Iowa State's Allee Farm near Newell. Separation distances of 30 to 150 feet were cut out of the yellow corn, leaving an open area between the yellow and purple corn. Because the purple seed color is a dominant trait, any outcrosses in the yellow buffer areas produced a purple kernel.
As expected, the yellow corn near the popcorn developed the largest number of purple kernels. "Outcrossing was high at the edge of the open area all around the purple corn," says Mark Westgate, agronomy professor. "Increasing the distance to 150 feet from the purple corn did not make much of a difference when the space between them was open."
Westgate says the project results provide support for using corn rows as a buffer area to decrease potential outcrossing. "The 60 feet of open area minimizes chemical drift, but it provides no protection from pollen drift," he says. Weather was monitored during pollination to study the relationship between pollen drift and prevailing winds. "As we expected, outcrossing percentages were greater downwind," Westgate says. "About 100 feet of corn buffer was needed to reduce the outcrossing to less than 1 percent. Upwind of the purple corn, outcrossing decreased to this low level within 30 feet."
Some purple kernels were found in one sample at the edge of the buffer strip, 240 feet downwind of the purple popcorn. A few purple kernels also were seen up to 1,600 feet away in a nearby field of standard yellow corn reportedly planted 19 days earlier. But Westgate cautions the demonstration plot design favored outcrossing because the purple popcorn produces about five times as much pollen as a typical yellow hybrid.
Tom Olsen, an ISU Extension ag business specialist, had the idea for the initial project. He says the results aren't surprising when you understand corn breeding behavior. "Each individual kernel on an ear of corn is a different cross. The mother is the same, but the father could be a different plant. There could be 350 different corn plants that pollinated this ear," Olsen says.
Olsen said the project was a good way to demonstrate the economic considerations of pollen drift. "Corn producers need to consider the risks of undesired characteristics showing up in their fields. There are opportunities to enter into contracts to produce specialty corn. But producers must look at the amount of risk involved versus the return," he saiys
Westgate agrees. "The corn seed industry has used isolation time and distance very effectively to produce hybrid seed products that are 99.5 percent, or better, genetically pure. But even at isolation distances of 660 feet, which is the standard for producing certified seed, there still is a small probability that outcrossing will occur," he says.
Westgate said if the specialty corn must be completely free of any genetically modified organism (GMO) to be acceptable to the buyer, that small probability carries large economic consequences. "The expanded use of corn hybrids that carry transgenes for herbicide and insect resistance will make the goal of delivering GMO-free corn increasingly difficult for producers," he said. "Developing minimum tolerances greater than zero percent for the presence of transgenes in these products would make a big difference."
The research was funded by an ISU agronomy department endowment and a federal biorisk assessment program grant. Westgate said a future project might look at how much of a buffer zone would be needed if there was no open space between the purple and yellow corn, and if both hybrids produced similar amounts of pollen.