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2-Plants: New U.S. research on pollen drift in maize

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SOURCE: Iowa State University, USA, Press Release
DATE:   1 Jun 2004

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AMES, Iowa -- 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
Demonstration 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

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

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.

Mark Westgate, Agronomy, (515) 294-9654,
Tom Olsen, Economics, (712) 732-5056,
Susan Thompson, Communications Service, (515) 294-0705,


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