(Reuters) - A U.S. wheat farmer has sued Monsanto Co, accusing the biotech seed giant of gross negligence for not containing an experimental genetically modified wheat discovered in an Oregon field that has put U.S. wheat export sales at risk.

Farmer Ernest Barnes, who grows wheat in Morton County in the southwest corner of Kansas, filed suit Monday in U.S. District Court in Wichita, Kansas, alleging that he and other wheat farmers have been hurt financially by the discovery of the unapproved biotech wheat that Monsanto said it stopped testing and shelved nine years ago.

“Monsanto has released GE (genetically engineered) wheat into the non-genetically modified wheat population,” the petition states.

The “plaintiff has been harmed by any and all Monsanto GE wheat because it has impacted wheat exports and the price of wheat,” the petition also states.

It is not known how widespread the unapproved wheat is, or if it has contaminated food supplies. But some buyers of U.S. wheat have backed away from purchases. South Korea and Japan immediately suspended their U.S. wheat purchases and European Union officials have said they want to test all incoming shipments and block any containing genetically modified wheat.

The suit does not state a specific claim for damages but says the amount in dispute exceeds $75,000.

More lawsuits are likely, the plaintiff’s attorney said. Monsanto said the lawsuit was a “wild swing” that lacked basis.

“Tractor-chasing lawyers have prematurely filed suit without any evidence of fault and in advance of the crop’s harvest,” David Snively, Monsanto executive vice president and general counsel, said in a statement.

Monsanto said it had followed a “government-directed, rigorous, well-documented and audited” program in conducting its wheat field trials and it is likely that the presence of its biotech trait in wheat is very limited.

“Given the care undertaken, no legal liability exists and the company will present a vigorous defense,” the Monsanto statement said.

The petition filed by Barnes claims Monsanto knew there was a high risk the genetically modified wheat it was testing could contaminate other varieties of wheat, and the company failed to follow proper procedures to keep the wheat contained.

Monsanto tested the wheat in many states, including Kansas, the top U.S. wheat-producing state, but did not disclose to farmers in those states that it was testing the controversial wheat there, the petition states.

The U.S. Department of Agriculture announced May 29 that a wheat farmer in Oregon had discovered Monsanto’s experimental wheat growing on his farm.

The wheat was developed by Monsanto to withstand treatments of the Roundup weed killer, but the firm never commercialized the product because of widespread industry opposition. International buyers threatened to boycott U.S. wheat if the biotech wheat was introduced to the marketplace, and Monsanto said in 2004 that it would discontinue testing and efforts to commercialize the “Roundup Ready” wheat.

The field testing that Monsanto had been doing in many states across the country was supposed to contain the biotech wheat and keep it from contaminating conventional wheat supplies, so the discovery of the experimental Roundup Ready wheat immediately triggered harsh reactions from international buyers of U.S. wheat.

U.S. wheat exports, forecast this year at about $9 billion, are at further risk if unapproved wheat is found to be more widespread than the few plants in Oregon.