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 http://twitter.com/mcjalonick
Associated Press writer Nigel Duara contributed to this story from Portland, Ore.