Pressure is growing on Monsanto Co. to withdraw from the heart of the farm belt a genetically modified corn seed it hopes will become a blockbuster product.

Joe Hampton, director of the Illinois Department of Agriculture, sent a letter last week asking hundreds of seed dealers in the nation's No. 2 corn-producing state to stop selling "seed varieties that are not approved for all uses in all major markets."

While the letter doesn't mention Roundup Ready corn by name, government, industry and Monsanto officials said Wednesday the Monsanto seed, which isn't approved for use in Europe, is clearly a target of the letter.

An Unusual Request

Mr. Hampton, who couldn't be reached for comment, doesn't have the legal authority to prevent Illinois farmers from buying Roundup Ready corn seed. But some independent seed dealers said the unusual request could have a chilling effect on the seed, which grows into a corn plant able to tolerate exposure to Monsanto's Roundup herbicide.

The letter was written because Illinois grain processors and state farm groups are worried that Roundup Ready corn might accidentally end up in products being exported to Europe, which has yet to approve the use of corn grown from that specific genetically modified seed. The agriculture sector is particularly sensitive in the wake of last year's Starlink debacle, the Aventis SA bio-engineered corn that prompted recalls of dozens of U.S. corn products.

Two of Illinois' biggest corn processors -- Archer-Daniels-Midland Co. and A.E. Staley Manufacturing Co., both in Decatur, Ill. -- supply much of the U.S. corn gluten, valued at $1 billion, that Europe buys annually for making livestock rations.

Public sentiment in Europe is so negative toward bio-engineered food that those corn-gluten shipments would probably shrink if Roundup Ready corn were ever detected in Europe's livestock feed, a development that would depress U.S. corn prices.

Danger of a Market Backlash

A market backlash has happened before. U.S. exports of raw corn to Europe evaporated a couple years ago over a biotech dispute, essentially closing what had been a $200 million market for U.S. corn farmers.

Some millers in Iowa, the leading corn-producing state, and in Illinois are warning farmers not to bring them Roundup Ready corn and the Illinois Farm Bureau passed a resolution in December asking that seed companies stop selling varieties not yet approved by major foreign customers. Those calls prompted some seed firms, such as DuPont Co.'s Pioneer Hi-Bred International unit, to postpone selling six lines of genetically modified corn seed.

Monsanto, a St. Louis crop-biotechnology concern that is 85%-owned by Pharmacia Corp., Peapack, N.J., is resisting calls to withdraw the three-year-old Roundup Ready corn line. It was grown last year on just a few million of the 79.6 million acres planted by U.S. corn farmers, and most of that was raised on the Great Plains for livestock feed.

Finding Appropriate Buyers

But Monsanto hopes that Roundup Ready corn will eventually be planted on tens of millions of acres, which would make it one of the company's biggest bio-crops.

The company is trying to reduce the chance that Roundup Ready corn might end up in the wrong place by helping farmers find appropriate buyers for the crop, which is approved in the U.S. for use in food and feed. Japan, the biggest importer of U.S. corn, accepts Roundup Ready corn, for example.

Brett Begemann, Monsanto vice president of marketing, said Wednesday that the company plans to continue marketing Roundup Ready corn throughout the Farm Belt. "We think farmers want that choice," he said.

Write to Scott Kilman at scott.kilman@wsj.com

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