able in assessing inadvertent risks (sections 2.5.2 and 3.2.4) These databases could be used to catalog potential toxicants and their concentrations in edible portions of prominent cultivars grown under standardized conditions. New cultivars, regardless of how they were produced, could be tested for known or suspected toxicants and compared with established cultivars that are already being consumed.
Because viruses of edible plants are common components of the food supply and no associations between such viral infections and adverse health effects have emerged, transgenic plants that express parts of viral genomes are generally considered not to represent an important human health risk because there is little chance of exposure to a novel virus gene product. The concentration of some viral gene products might be higher in a transgenic plant than in a naturally infected plant; but in the case of coat-protein-expressing plants, the concentrations will likely be lower.
Plants containing virus-derived transgenes that confer protection from pests because of activation of gene silencing generally produce very low concentrations of transgene-encoded protein, because the transgene mRNA is inactivated (section 2.3.2). From the standpoint of exposure to new or enhanced levels of viral protein, transgenic plants that contain silenced transgenes have little chance of causing problems.
Experience with pathogen-derived or pest-derived protection from organisms other than viruses is sparse. It is difficult to assess this class of potential protective genes with regard to risk. New exposures could result, depending on the pathogen or pest, and potential toxicity to non-target organisms is conceivable. Those examples will require relative-risk assessments case by case.
The various genes from novel genetic resources that confer pest-protection cannot be grouped from the standpoint of health risks. Transgenes that encode protective compounds from nonplant sources, such as Bt delta endotoxin, will probably present novel exposures and must be assessed on a case by case basis.