A group representing all 2,500 rice farmers in California has called for a statewide moratorium on field-testing of genetically modified rice in order to prevent contamination.

The decision was prompted by recent discoveries of unapproved genetically modified long grain rice - varieties not found in California - mixed into commercial grain and seed supplies in states such as Arkansas and Missouri.

California, which primarily produces medium grain rice, relies heavily on export markets in Japan, South Korea, Taiwan and Turkey.