ARS | Publication request: Population Structure and Incidence of Virus Infection in Free-Living Populations of Cucurbita Pepo

Submitted to: Environmental Biosafety Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 20, 2008
Publication Date: N/A

Interpretive Summary: Transgenic crop plants (plants that have foreign genetic material placed in them by biotechnological tools) have been commercialized since 1994 (e.g., corn, soybean, rice, canola, cotton, and squash), and are responsible for significant and demonstrate economic benefits in areas where they have been commercially adopted. Thus far, these crops have had a record of safety, both from a human/animal health and environmental perspective. Nevertheless, scientific issues surrounding the safety assessment of these crops receive continued consideration. These continuing risk appraisals provide feedback for decision-making by testing the assumptions and conclusions during the pre-market risk assessment process (before commercialization of plants for human consumption) and thereby improve the quality, efficiency and effectiveness of those risk assessments. Of considerable ecological importance is the potential impact that transgenes (genes from foreign plants are genetic material that are on chromosomes which are in the nucleus of each cell) might have on the structure and competitiveness of natural populations into which the transgenes are transferred by natural means. Several transgenic squash cultivars that have been commercialized have been evaluated for these impacts. Commerical transgenic squash (with virus resistance) has had the longest history of unrestricted regulatory approval in areas where wild relatives may be present. It is important to obtain historical information regarding the introduction of transgenes into the environment, and thus a study was designed to determine the frequency of transgenes in wild squash populations which growing close to commercial agricultural production of transgenic squash. It was determined that the frequency of viruses in natural populations was relatively low indicating that the inclusion of virus resistance from transgenic plants does not provide significant genetic changes in wild squash populations or effect their size. This information is critical to agricultural production of transgenic squash since it indicates that their use will not adversely affect natural squash populations growing in close proximity. As a result, U.S. growers can continue to use transgenic squash varieties knowing that their use does not negatively impact the ecology of native wild squash populations. Since transgenic squash produce more yield under virus conditions, U.S. growers can continue to remain competitive in a global economy.

Technical Abstract: To assess the imact of virus resistance transgene introgression into wild, free-living populations, it is important to characterize the potential benefit(s) that those transgenes might confer on such poulations. Transgenic virus-resistant Cucurbita pepo L. (squash) cultivars have been commercialized, and might be cultivated in close proximity to cross-compatible wild, free-living Cucurbita pepo. Therefore, the potential benefit of virus resistance transgenes was studied by surveying the incidence and fluctuations of virus infection and population size in selected free-living Cucurbita pepo subsp. pepo var. ozarkana and texana populations in Illinois, Missouri, Arkansas, Mississippi, Louisiana, and Texas. Populations were surveyed for the presence of cucumber mosaic virus (CMV), zucchini yellow mosaic virus (ZYMV), watermelon mosaic virus (WMV2), papaya ringspot virus (PRSV), and other poty viruses. The infection level in free-living populations was consistent with levels that were considered "low" in previously reported field experiments, leading to the conclusion transgenic virus resistance should provide no significant fitness advantage to the free-living populations examined. Furthermore, patterns of infection in relation to population size support the conclusion that these viruses do not impose limitations on the size of free-living populations. CMV, ZYMV and WMV2 were not the only viruses infecting these populations, further reducing the likelihood that resistance to CMV, ZYMV amd WMV2 would release popluations from constraints imposed by virus diseases.