Bt Corn Does Double Duty on Threats to Corn Crop

Date: June 17, 1999
Contacts:
Gary Munkvold, Plant Pathology, 515-294-6708
Richard Hellmich, ARS/Entomology, 515-294-4509
Danelle Baker-Miller, Office of Biotechnology, 515-294-7356

Bt CORN DOES DOUBLE DUTY ON THREATS TO CORN CROP

AMES, Iowa -- Researchers at Iowa State University and USDA have confirmed that Bt corn reduces two threats to corn plants: corn borers and toxic fungi. The genetically engineered corn hybrid is designed to ward off the corn borer, and scientists recently discovered that it can lessen damage from toxic fungi as well.

Bt corn contains genes from the bacterium Bacillus thuringiensis that express proteins deadly to the corn borer, a common pest in cornfields. When borers bore holes, as their name suggests, into the stalks and ears of plants, they reduce crop quality and yield. Borers can also carry Fusarium fungi into the plants, leading to ear and kernel rot. The fungi can release mycotoxins, chemicals toxic to both animals and humans.

"Corn borer larvae cause physical injury to the plants, and that's where Fusarium infections occur. Larvae can also carry Fusarium spores from the leaf surface and transmit them to their feeding sites on the plants," said Gary Munkvold, a plant pathology professor and researcher on the project.

Bt corn's protective design diminishes the likelihood of this chain reaction. Cry protein genes from Bt bacteria serve as insecticides, poisoning the hungry borers. Because the borers are killed off before they can do much damage, they don't transmit as much fungi to corn stalks and ears.

Munkvold, Richard Hellmich, a USDA-ARS researcher, and Larry Rice, a USDA-APHIS researcher, discovered that some hybrids of Bt corn are more effective than others in reducing levels of fungi because of variations in the type of Cry protein and location in the plant. Nonetheless, Cry proteins have a significant effect on the amount of corn borer feeding, ear rot and toxins on the plant.

The scientists' findings offer good news for animal and human health. Some species of Fusarium produce fumonisin, a dangerous toxin that can lead to fatal diseases in horses and swine that ingest infected corn. The same toxins are associated with esophageal cancer in humans.

"The difference in the amount of fumonisin in standard corn hybrids and Bt corn in our study was significant. Fumonisins in the standard hybrids were sometimes high enough to make corn kernels toxic to horses and humans. When corn borers attack, fumonisin levels go up in standard hybrids, but not in the Bt hybrids," Munkvold said. Related research by USDA researchers in Illinois also supports that fumonisin levels are reduced in Bt corn.

"Our results indicate that under some conditions, genetic engineering of maize for insect resistance may enhance its safety for animal and human consumption," he said.

The team is expanding their research to examine levels of other mycotoxins on different Bt corn hybrids and the influence of Bt gene expression on corn stalk rot.

A report of the team's findings was recently published in Plant Disease, a publication of the American Phytopathological Society.

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