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Environmental Effects of Transgenic Plants: The Scope and Adequacy of Regulation
Yellow crookneck squash belongs to the species Cucurbita pepo. As discussed above, the squash itself is not a weed. However, squash freely crosses with wild weedy plants known as Texas gourd (originally classified as C. texana but now considered a subspecies of C. pepo) and as FLCP. An experiment by Kirkpatrick and Wilson (1988) demonstrated that squash and FLCP naturally hybridize freely; the crop sired 5% of the seed set by FLCP, growing 1,300m from cultivated squash. Hybrids between the crop and FLCP are fully fertile (Whitaker and Bemis 1964). Clearly, if the crop and FLCP grow in the same region, natural hybridization will occur, and crop alleles will readily enter the natural populations. Indeed, cultivated squash and FLCP co-occur in many regions of Texas, Louisiana, Alabama, Mississippi, Missouri, and Arkansas (Wilson 1993). APHIS concludes that natural hybridization will move the virus resistance genes from the transgenic crop to the wild populations (USDA 1994b, 1996).
FLCP is an agricultural weed in cotton and soybean fields. At one time it was one of the 10 most important weeds in Arkansas (McCormick 1977). APHIS contacted three weed experts for their opinions on the current status of FLCP as a weed. The three experts noted that FLCP plants appeared to be “less a problem” in 1994 than during the 1980s because of new herbicides not available in the 1980s and suggested that new herbicide-tolerant crops would “further expand the tools for effective control of FLCP plants” (USDA 1994b). APHIS concluded that “FLCP plants are not a serious weed in unmanaged or agricultural ecosystems [because] “the registration of new herbicides now allows effective management of these plants” (USDA 1994b). However, two of the three weed experts reported that FLCP is less of a problem; it is not clear how serious a weed they still consider it to be.
The key issue raised by the foregoing data is whether virus resistance genes will provide enough of a benefit that FLCP becomes a more difficult weed. Wild and cultivated C. pepo are susceptible to the same viruses (e.g., Provvidenti et al. 1978). To determine whether viruses limit the population size and number of FLCP, Asgrow conducted a survey in 1993. Fourteen FLCP populations (two in Arkansas, four in Louisiana, and eight in Mississippi—a severe drought precluded sampling in Texas) in nine locations were visited once (when plants were at maturity); no visual symptoms of viral infection were noted. Some of these sites were within a mile of cultivated squash. But it was not reported whether the nearby cultivated plants were infected with virus; that information would have shown whether viruses were present that year. A single plant was sampled from each population. Each plant was subjected to multiple analyses to check for asymptomatic viral infection, and all were found to be virus free. On the basis of these data and qualitative anecdotal reports