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Corn+Soybean Digest

Plotting Pollen Drift

Plant biotechnology is poised to enter its “third wave” — the production of plant-made pharmaceuticals (PMP).

Biotechnology companies are developing genetically specialized crops designed to produce feedstocks for vitamins, pharmaceuticals and perhaps even vaccines.

“Corn and tobacco have gotten the most attention as potential green factories for producing medicines and vaccines,” says Gene Stevens, crops production specialist at the University of Missouri's Delta Center.

“This, in effect, is an industrial process with scrupulous controls and regulatory oversight by at least three government agencies,” he adds.

But science has hit a couple of snags. Last fall, Nebraska-grown soybeans were found contaminated with residue from volunteer corn following a field trial of pharmaceutical corn. (See “The Market That Never Was,” January issue, page 64.)

Partly in response the Biotechnology Industry Organization (BIO) banned the growing of PMP corn in Midwestern states. It relented in December and will follow federal guidelines on the production and handling of “pharma” corn.

“Safe production and manufacturing dictate the principle of confinement with these crops,” says Stevens. “That means keeping the crop and its products on the land where it's grown until it's removed for processing, with no inadvertent exposure to food or feed crops.”

For the past two years, Stevens has conducted corn field trials to mimic a PMP production system. Funded partly by a grant from Monsanto, Stevens' research studies ways to protect specialized corn from cross-pollination with field corn.

Since gene flow both to and from PMP crops is a strict no-no, Stevens set up three sites at varied distances from conventional corn fields. He isolated and detasseled the crop to reduce pollen movement from plots set up to mimic PMP sites. Each test plot was surrounded by cotton or soybean fields.

“We planted yellow-kernel corn (yellow seed color is dominant over white) in 10-acre pollen blocks and detasseled different percentages of the plants,” he says. “We also planted four-row strips of a white corn hybrid at distances of 660' and 900' from the yellow corn plots. This way, any yellow kernels found in the strips of white corn must have been pollinated by yellow corn in the pollen block.

“Detasseling can be effective, unless some tassels are missed,” Stevens adds. “Regulatory agencies want to know what kind of separation distance is needed at different levels of detasseling to prevent gene flow to other corn fields.”

When the corn was harvested, Stevens and his colleagues looked at thousands of ears of white corn, searching for a stray yellow kernel. They also used a specific genetic marker in the yellow corn.

“With this system, any yellow kernels found in the white corn strips can be traced back to pollen from a specific detasseling treatment,” says Stevens.

His experiments show that, at 660' away from a plot not detasseled, three yellow kernels were found in every 10,000 white-corn seeds. When the strips were 900' away from 90% of detasseled plots, only 1.3 kernels out of every 100,000 were yellow.

“If an average ear of corn contains 500 kernels, the incidence of cross-pollination at the 900' distance would be one seed for every 150 ears of corn,” Stevens notes.

No yellow kernels were found at 900' when the yellow hybrid was 100% detasseled.

“This shows us that detasseling, plus distance, are valuable tools in preventing gene flow in corn,” Stevens concludes. “With detasseling, we may not need to grow PMP corn at quite so great distances from regular field corn.”

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