PORTLAND, Ore. » A genetically modified test strain of wheat that emerged to the surprise of an Oregon farmer last month was likely the result of an accident or deliberate mixing of seeds, the company that developed it said today.

Representatives for Monsanto Co. said during a conference call that the emergence of the genetically modified strain was an isolated occurrence. It has tested the original wheat stock and found it clean, the company said.

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.

Fraley said the company has a test it has shared with other countries that could "fingerprint" the exact variety of wheat that carried the gene, and it’s awaiting samples from the U.S. Department of Agriculture or the Oregon farmer to test for the exact variety that emerged.

The USDA has said the Oregon wheat is safe to eat and there is no evidence that modified wheat entered the marketplace. No genetically engineered wheat has been approved for U.S. farming.

Agriculture Secretary Tom Vilsack said he would not address Monsanto’s suggestions that it could have been sabotage.

"I’m not going to speculate on what could or couldn’t have happened," Vilsack told reporters in Washington, D.C., today. "Because you could go down that road and we’d be here all day."

Fifteen inspectors from the USDA’s Animal and Plant Health Inspection Service are working on the investigation.

Vilsack said the department’s priorities are to investigate and also to focus on getting markets open as quickly as they can after some overseas markets balked at the discovery of the modified crop. He said the department believes it is an isolated situation because tests in the farmer’s adjoining fields have turned up negative, as have tests on neighboring fields so far.

He said the South Korean government had notified USDA today that tests so far on wheat and flour had showed no indication of contamination.

Consumers’ unease with genetically modified crops, particularly those in Europe and Asia, led St. Louis-based Monsanto to end the testing of modified wheat in 2005.

Many countries will not accept imports of genetically modified foods, and the United States exports about half of its wheat crop. Since the announcement of the discovery of the genetically modified wheat in Oregon, Japan — one of the largest export markets for U.S. wheat growers — suspended some imports. South Korea said it would increase its inspections of U.S. wheat imports.

Supporters of splicing in beneficial genes to modify crops say modifications could help wheat grow in places where it’s needed. New traits could make it resistant to disease, pests and, like the rogue strain discovered in Oregon, herbicides.

Opponents argue that genetic modifications carry potential unknown consequences to the humans that consume them and the areas in which they’re grown. Changes to the genes of the crops could affect the durability of weeds, making them harder to kill, or the pests that feed on the crops.

The wheat emerged in an Eastern Oregon field in early May and was resistant to the herbicide Roundup. Oregon State University researchers found the wheat had a genetic modification Monsanto used in field testing.

When the test fields were cleared in Oregon in 2001, the seed samples were sent to a USDA deep-storage facility in Colorado. The company’s research director, Claire Cajacob, said the company also keeps some samples it is able to test. The rest of the seed is destroyed, she said.

"We’ve been very careful of how seed is stored and where it’s stored," Cajacob said.

The company conducted follow-ups with any entity that possessed the seed with the so-called Roundup Ready gene and confirmed that they shipped it to Colorado or destroyed it, she said.

Testing ended in Oregon in 2001, four years before testing ended nationally. Company representatives said the average wheat seed only stays viable for one to two years in a harsh climate like Eastern Oregon’s.

The wheat emerged in a rotational field that was supposed to be fallow in 2013.

Fraley said it’s unlikely that other parent stocks were corrupted, or "probably we would have seen it for many, many years over the last decade."

Ninety percent of soft white wheat grown in Oregon, Washington and Idaho is exported, making the states reliant on relationships with foreign markets, specifically those in Asia.

Oregon wheat farmers convened by the Oregon Wheat Commission on Tuesday in Portland said their private conversations center on one question: How did it happen?

"We need to know," said Blake Rowe, chief executive of the Oregon Wheat Commission. "Somehow this gene is out in the environment, but we’re waiting for USDA to know how it could have happened."

AP Writer Mary Clare Jalonick contributed to this story from Washington, D.C.