The Effect of Transgenic Squash on the Ecosystem
Genetically Modified Crop Impacts Wild Squash Population
Commercial squash production has benefited greatly from the introduction of the transgenic squash. The genetically modified crop is able to resist the ravages of viral diseases caused by the mosaic viruses. An infection with the mosaic viruses slows the growth of the squash plants and the plants produce misshapen fruits.
How Squash Plants are Genetically Modified
Virus resistant squash ZW-20 was developed by taking two different squash virus’s genes and incorporating then into the genes of the wild type of squash. The inserted virus genes code for the virus's coat protein (CP). The genes were then transferred into the squash's genes by a bacterial plant pathogen. The inserted virus’s coat protein gene produces a protein that protects the ensuing plant from viral infection via a process of viral cross-protection.
The transgenic squash variety is for the most part resistant to the dreaded and costly mosaic viruses. This has been extremely beneficial to commercial squash farmer’s squash yields. However, there has always been the concern that these genetically modified squash plants may have an impact on the wild squash population that occupies the same ecosystem as the transgenic variety.
Modified Gene Transfers to Wild Squash
Commercially grown transgenic squash are able to pass on the resistance by transferring the genetically modified gene to wild squash types. Researchers determined this in a study where wild squash and genetically modified squash were grown in close proximity. The transfer was via pollen across the field. Researchers found that wild squash population's second generation of plants had acquired the mosaic virus resistance gene (Fuchs, M., Chirco, E.M., Gonsalves, D. “Movement of coat protein genes from a commercial virus-resistant transgenic squash into a wild relative”. Environmental Biosafety Research. 3(1):5-16 2004 abstract).
Effect of Cross-Pollination by Genetically Modified Plants
As expected the viral gene acquired within the wild population conferred resistance to the mosaic viruses. However, another ecological effect was observed in a different study. In this study a viral infection was also introduced into a field where both transgenic and wild squash were within pollination proximity. The gene was transferred to some wild squash in the second generation. The mosaic viruses affected all plants that were not genetically modified.
Cucumber Beetles Prefer Healthier Squash Plants
The researchers also introduced cucumber beetles into the fields. The beetles feed on squash plants leaving open wounds where they leave their bacteria containing feces causing bacterial wilt. In this study, the beetles preferred the healthier plants; concentrating their infestation on the genetically modified plants (Sasu MA et al., “Indirect costs of a nontarget pathogen mitigate the direct benefits of a virus-resistant transgene in wild Cucurbita.” Proc Natl Acad Sci U S A. Oct 26 2009). This study shows that while the plants were protected from viral infections they were targeted by cucumber beetles and eventually succumbed to bacterial wilt.
As more researchers continue to conduct studies into the ecological impact of genetically engineered plants, there will more cases of the negative impacts uncovered. Scientists may need to find a way to restrict gene transfer from transgenic plants to wild types within the ecosystem.
Cucumber Beetles Feed on GM Squash Plant
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