MEXICO CITY – A major Mexican tomato-growers' association says shipments to the United States have stopped as U.S. authorities investigate the origin of a salmonella outbreak.

But a spokesman for the Sinaloa state Tomato Growers Association says it's just a precaution; there's no evidence so far that the salmonella originated in Mexico, which accounts for about a third of winter tomatoes in the United States.

Spokesman Mario Robles says the association ships 44 percent of Mexican tomatoes imported into the United States and Canada. Its importer voluntarily stopped shipments during the probe. The tomatoes are being sent to Mexican markets, where they will be sold at a lower price.