Ames, Iowa
June 1, 2004
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," said 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 said 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 said.
Weather was monitored during pollination to study the
relationship between pollen drift and prevailing winds. "As we
expected, outcrossing percentages were greater downwind,"
Westgate said. "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 said 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 said.
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 said.
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 said.
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.
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