ST. LOUIS — Monsanto officials during a June 5 conference call with reporters provided an update on information gleaned from the company’s inquiry into the discovery of volunteer glyphosate-resistant wheat growing on an Oregon farm. Monsanto was very much at the center of the controversy because it was its Roundup Ready event that the U.S. Department of Agriculture confirmed was present in wheat samples taken from the farm. Monsanto had field tested Roundup Ready wheat in Oregon and several other states from 1998 through 2005 but discontinued that program in 2005 when the company determined the market was not yet ready to accept a bioengineered wheat.

Robb Fraley, Monsanto’s chief technology officer, said the Oregon farmer who found the glyphosate-resistant wheat had planted two fields with a mixture of two western white winter wheat varieties, ROD and WestBred 528, in the fall of 2011. He harvested the wheat in the summer of 2012. The 125-acre field in question was left fallow for the current growing season. In the spring of this year, the farmer sprayed weeds and wheat plant volunteers with glyphosate instead of tilling. The wheat volunteers that survived the glyphosate application attracted his attention.

On its own initiative, Monsanto tested the ROD and WB-528 parent seed stocks and found both to be free from the Roundup Ready trait. Monsanto then expanded its testing to include 50 parent seed stocks of other commercial wheat varieties representing 60% of the white wheat acres planted in Oregon and Washington in 2011 and discovered no presence of the Roundup Ready event in any of the varieties. The company was continuing its testing.

Monsanto said it had not been provided wheat samples from the Oregon farm where the bioengineered wheat had been discovered by any party, including the farmer, O.S.U. or the U.S.D.A., but the company presumed the U.S.D.A. test results to be accurate.

Dr. Fraley said Monsanto has an event-specific test that identifies the specific region of the wheat genome containing the original Roundup Ready wheat event, and this test was the only one that could absolutely eliminate false positives that may occur if the test methodology employed was not wheat-specific. He confirmed Monsanto had shared the wheat-specific testing methodology with the U.S.D.A. and regulatory agencies in Japan, South Korea, Taiwan and the European Union at their request.

Dr. Fraley also affirmed Monsanto’s earlier assessments that neither seed left in the soil nor wheat pollen flow would serve as a reasonable explanation for the glyphosate-resistant wheat found on the Oregon farm. He said seeds may remain viable in the soil for only one or two years, and that 99% of wheat pollen moves less than 30 feet from its source.

Dr. Fraley suggested a much more likely scenario was the wheat germinated as the result of accidental or purposeful mixing of bioengineered seed from some source with approved wheat seed. Correspondents asked if this implied the mixing might have constituted “sabotage.” Dr. Fraley and his associates said they were not in position to rule out any scenario, but like everyone else, Monsanto would have to await the results of the U.S.D.A. investigation.