WASHINGTON (AP) -- The Agriculture Department says it has no indications that genetically modified wheat found in Oregon last month has spread beyond the field in which it was found.
No genetically engineered wheat has been approved for U.S. farming, and the department is investigating how the engineered wheat got in the field.
USDA spokesman Matt Paul said in a statement Friday that the department "has neither found nor been informed of anything that would indicate that this incident amounts to more than a single isolated incident in a single field on a single farm."
Agriculture Department officials have said the wheat is the same strain as a genetically modified wheat that was designed to be herbicide-resistant and was legally tested by seed giant Monsanto a decade ago but never approved.
Japan, Korea and Taiwan have suspended imports of western white wheat from the Pacific Northwest as the USDA investigates.
Paul said that investigators have interviewed the farmer who harvested the wheat from his field, interviewed the supplier who sold the producer wheat seed, obtained samples of the seed and obtained samples of other wheat grown by the farmer. All of the samples have tested negative so far, Paul said, and there is no indication that the engineered wheat entered commerce.
USDA said the investigation is continuing and inspectors are conducting interviews with approximately 200 area growers. The department also has given trading partners a copy of the test developed by Monsanto so they can identify the engineered strain.
The modified wheat was discovered when field workers at an Eastern Oregon farm were clearing acres for the bare offseason when they came across a patch of wheat that didn't belong. The workers sprayed it but the wheat wouldn't die, so the farmer sent a sample to Oregon State University to test.
A few weeks later, Oregon State wheat scientists discovered that the wheat was genetically modified. They contacted the USDA, which ran more tests and confirmed their discovery.
On Friday, a group of Oregon legislators urged Oregon Gov. John Kitzhaber to direct the state attorney general to pursue compensation for money lost by Oregon wheat farmers because of the discovery.
"It's not an easy thing to rebuild trust in the marketplace," said Oregon state Rep. Brian Clem. "You can't just flip a switch."
Clem said that, if the USDA fails to find a party responsible for the emergence of the modified wheat, Monsanto Co. should be held financially responsible because the company developed the wheat, a soft white winter variety.
Most of the corn and soybeans grown in the United States are already modified, or genetically altered to include certain traits, often resistance to herbicides or pesticides. But the country's wheat crop is not, as many wheat farmers have shown reluctance to use genetically engineered seeds since their product is usually consumed directly. Much of the corn and soybean crop is used as feed.
The USDA has said the wheat would be safe to eat if consumed. But American consumers, like many consumers in Europe and Asia, have shown an increasing interest in avoiding genetically modified foods.
There has been little evidence to show that foods grown from engineered seeds are less safe than their conventional counterparts, but several state legislatures are considering bills that would require them to be labeled so consumers know what they are eating.
The Agriculture Department said that during a seven-year period, it authorized more than 100 field tests with the same herbicide-resistant wheat variety. Tests were conducted in in Arizona, California, Colorado, Florida, Hawaii, Idaho, Illinois, Kansas, Minnesota, Montana, Nebraska, North Dakota, Oregon, South Dakota, Washington and Wyoming.
During that testing and application process, the Food and Drug Administration reviewed the variety found in Oregon and said it was as safe as conventional varieties of wheat.
USDA officials have so far declined to speculate whether the modified seeds blew into the field from a testing site or whether they were somehow planted or taken there. They also declined to identify the farmer or the farm's location. They said they had not received any other reports of discoveries of modified wheat.
Representatives for Monsanto Co. said June 5 that they believe the emergence of the genetically modified strain was an isolated occurrence.
Sabotage is a possibility, said Robb Fraley, Monsanto chief technology officer.
"We're considering all options and that's certainly one of the options," Fraley said.
The USDA has so far declined to respond to the suggestion of sabotage.
Follow Mary Clare Jalonick on Twitter at https://twitter.com/mcjalonick
Associated Press writer Nigel Duara contributed to this story from Portland, Ore.