Do virus-resistant transgenic plants favour virus emergence?

The development of virus-resistant transgenic plants (VRTPs) in the 1980s was one of the early success stories in the development of Genetically Modified (GM) crops, and the vast majority of VRTPs express viral sequences, usually a gene encoding the viral coat protein. However, since the 1990s, scientists have expressed concerns about potential risks associated with this type of VRTP. Of the issues raised, one particularly complex question has remained incompletely resolved, whether recombination between viral sequences expressed in the VRTP and the genome of an infecting non-target virus would generate new virus genotypes resulting in emergence of novel viral diseases. In this paper evidence on this issue is examined focusing on Cucumber mosaic virus (CMV), which is a particularly pertinent choice, since it is both a major plant pathogen and also the virus with which this question has been studied in the most detail. We use an improved strategy for evaluating GMO biosafety issues in which particular prominence is given to formulation of the risk hypothesis, and to hypothesis-testing via examination of the potential pathway to harm. Then we use recent results from our laboratories on recombination in CMV both in GM crops and in multiple-infected wild-type crops to address each step in hypothesis testing. Results allow us to conclude with greater certainty that the likelihood of this potential harm, emergence of novel viruses, is low.