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GENETICALLY MODIFIED PEST-PROTECTED PLANTS: SCIENCE AND REGULATION
crookneck squash; Decker 1988, Wilson 1993). FLCP is an agricultural weed in cotton and soybean fields, where its tough gourds interfere with harvesting machinery (Harrison et al. 1977; McCormick 1977; Oliver et al. 1983; Bridges 1992). Cultivated squash and free-living squash co-occur in many regions of Texas, Louisiana, Alabama, Mississippi, Missouri, and Arkansas (Wilson 1993). The bouyant gourds of FLCP are widely dispersed during floods, and this leads to periodic infestations of crops along river floodplains. Once FLCP becomes established in an area, it can be difficult to eradicate, because some seeds germinate throughout the growing season, other seeds remain dormant for long periods, and the plants spread laterally by branching and producing roots along the nodes of their long, viny stems. USDA asserts that FLCP is only a minor weed that can be easily controlled with herbicides (such as Cobra, bromoxynil, and glyphosate; USDA 1994b and 1996b). Nonetheless, FLCP is clearly a weed that merits close attention from regulatory agencies. It was previously listed as one of the top 10 most important weeds in Arkansas (McCormick 1977). Additional fitness-related traits such as virus-protection could potentially increase the agricultural impacts of this weed.
Hybridization between cultivated squash and FLCP is known to occur across distances of 1 km or more. Cultivated squash and wild squash have single-sex flowers that make them dependent on insect pollinators for seed set, and bees are known to carry crop pollen to wild plants as far as 1.3km (Kirkpatrick and Wilson 1988). Although cultivated squash hybridizes and backcrosses with weedy FLCP, USDA stated that “there is no scientific or anecdotal evidence that supports the contention that hybrids between yellow crookneck squash and FLCP plants are weeds and are persistent” (USDA 1994b). That statement appears to overlook the fact that after the first hybrid generation, spontaneous backcrossing with wild plants can allow crop genes to spread into FLCP populations, which are clearly persistent weeds. Crop-wild hybrids and their offspring are vigorous and fertile, so neutral or beneficial transgenes could probably persist in wild or weedy populations (Fuchs and Gonsalves 1999). Furthermore, virus-protection transgenes confer strong protection in crop-wild hybrids and backcrossed generations, as expected (Fuchs and Gonsalves 1999). The environmental question posed by this situation is “will genes for virus-protection be beneficial enough to cause this weed (FCLP) to become more common?”
Wild C. pepo and cultivated C. pepo are susceptible to the same viruses (Provvidenti et al. 1978). To check for viral infections in FLCP populations, Asgrow conducted a survey in 1993. Its analyses of 14 FLCP patches in nine locations did not detect viral infections in wild plants; one plant was sampled at each location (USDA 1994b). No information was given on whether cultivated squash in these areas were infected with ZYMV or