There is a "vanishingly small" risk that crops genetically engineered to resist disease will accidentally create new plant diseases, according to two plant disease experts at UC Davis. Research elsewhere has indicated that when genes from a viral disease are inserted into a plant in order to make the plant resistant to that specific virus, those genes can mix with genes from another virus infecting the plant, thus generating a new virus. "Under typical agricultural conditions, plant viruses already have many opportunities to interact genetically as viral genes are distributed over vast acreages by insects, seeds and plant cuttings," says Bryce W. Falk, a professor of plant pathology. There is no reason to believe that genetically engineered plants will result in a greater number of new -- or more potent -- viruses than already occur through traditional plant breeding and under the normal processes of infection in the field, he says. Falk and colleague George E. Bruening, also a professor of plant pathology, presented their overview in a recent issue of the journal Science.