Food and Drug Administration (FDA) has approved many crops with transgenic kanamycin resistance. FDA continues to examine the safety of antibiotic-resistance genes and issued the following draft statement in 1998 (FDA 1998):
FDA acknowledges that the likelihood of transfer of an antibiotic resistance marker from plants to microorganisms in the gut or in the environment is remote and that such transfer, if any, would likely be insignificant when compared to transfer between microorganisms and, in most cases, would not add to existing levels of resistance in bacterial populations in any meaningful way.
Nevertheless, in the future, it may not be necessary to take even the small risks associated with the use of antibiotic resistance markers, since other types of markers could be substituted in future transgenic crops (for example, Kunkel et al. 1999).
The major environmental risks that have been discussed in connection with virus-protected crops pertain to effects of viral coat protein genes on the pathogenicity of other viruses (Falk and Bruening 1994) and consequences of crop-to-wild gene flow that could allow beneficial transgenes to move into feral-crop plants or closely related weeds, as described in section 2.7. The first issue was studied experimentally at Cornell University by Dennis Gonsalves, who helped Asgrow to develop the virus-protected squash; he and his collaborators concluded that the risks that other viruses would become transmissible (from heteroencapsidation) or that the nonpathogenic viruses would become more virulent (from recombination) were exceedingly small (Fuchs et al. 1998; also see section 2.8).
The second issue—whether wild relatives could benefit from disease-protection genes —was more controversial. An important precedent for USDA in dealing with this potential problem was established in the following example. To get more information on the ecology and systematics of weedy, free-living Cucurbita pepo (FLCP), the USDA Animal and Plant Health Inspection Service (APHIS) commissioned a report on the risks that may be posed by crop-to-wild gene flow by Dr. Hugh Wilson, an expert on cucurbit taxonomy and ecology. Wilson concluded that FLCP is a significant agricultural pest that might benefit ecologically from protection from ZYMV and WMV2 (Wilson 1993). Key information about squash and its weedy North American relatives is summarized below with an evaluation of USDA 's conclusions.
Volunteer squash plants are not known to spread and become weeds, but C. pepo crosses freely with a wild weedy species that is variously known as C. texana (Texas gourd) or, more recently, wild or free-living C. pepo (FLCP), and C. pepo subspecies ovifera (same species as zucchini and