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Corn+Soybean Digest

Transgenic Corn Boosts Yields

A new kind of transgenic hybrid - called glutamate dehydrogenase (GDH) corn - does more than provide crop protection, the usual biotech feature.

"The GDH gene is novel in that it boosts yield rather than simply protects it," says David Lightfoot, a plant biotechnologist at Southern Illinois University (SIU).

"GDH corn increases nitrogen uptake, yields and protein content, as well as helps the corn plant overcome stresses, especially early in the growing cycle."

Developed at SIU, the transgenic hybrid incorporates GDH, a gene isolated from soil-borne microorganisms and then inserted into corn tissue.

Lightfoot's initial research, begun in 1991, was partially funded by the Illinois Corn Promotion Board to find a way to reduce nitrogen runoff from cornfields.

"In the typical field, a seedling corn plant is in contact with a lot of nitrogen - more than it can make use of right away," says Lightfoot.

"In even the best-managed growing systems, 10% or more of the nitrogen is lost. We saw GDH as a way to let young corn plants utilize more nitrogen. That would reduce the loss of nitrogen that a farmer buys and also reduce the amount of environmental damage caused by nitrogen runoff."

GDH has fulfilled that promise and then some. For reasons he doesn't completely understand, Lightfoot finds that corn plants equipped with the gene are bigger and more productive all the way through the growing season.

"This gene makes a corn plant metabolically more efficient throughout the growing period," he explains. "The entire corn plant - stalks, ears, roots - grows about 10% bigger than comparable hybrids. And GDH produces grain that is 10-11% higher in protein than normal corn."

In 1998, Lightfoot grew the hybrid with three nitrogen fertility levels: 125, 175 and 225 lbs/acre.

"The GDH corn performs well with below-optimum fertility. We take some yield hit at lower rates of N, but GDH performs nearly as well at a lower rate as regular hybrids do at a normal rate of N."

This should mean that a grower could trim back on the amount of nitrogen applied and still produce a normal corn crop.

How well GDH corn performs as livestock feed is still an open question. Besides being somewhat higher than normal in protein content, the corn may also be higher in some essential amino acids.

"We're conducting small-animal feeding studies with GDH corn this winter," says Gary Apgar, an SIU swine nutritionist.

"In another year, we should produce enough volume to hold mass feeding trials," he says.

GDH corn is just a tip of the biotechnology iceberg, says Lightfoot.

"I think yield-boosting genes will be bred into more hybrids in the next few years. And we will be able to tackle some other yield-limiting factors genetically - the limit on yields from moisture shortage, for example."

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