PROS and CONS of Transgenic Crops: Environmental Considerations

    One of the key arguments in favor of certain transgenic crop varieties is their potential to improve crop quality and yield normally lost to pests. Some transgenic plant varieties -- such as those with resistance to the herbicide Roundup and those producing the protein Bt -- have great potential to reduce the amount of land needed for farming and to also reduce the use of chemical pesticides while reducing the incidence of pesticide resistance. However, these benefits are dependent upon the ultimate adoption of these crops by farmers and the larger problem of keeping pace with the ever-growing world population while overcoming skeptics' doubts about the safety of these plants for use as food.

    Much of the controversy over transgenic crops or genetically modified organisms (GMOs) is grounded in the potential for (and/or perceived) adverse impacts on the natural environment. One of the most contentious issues is the fear that a transgenic crop will become a potential conduit for transmission of genes to non-GMO plants of the same or a closely related species.

Why does this matter? First, such genes could have unpredictable effects when inserted into other species without rigorous scientific control. When a transgenic crop is approved for a certain purpose, testing has been undertaken to understand what effect the introduction of a gene(s) will have on the phenotype and fitness of that particular organism. Once that gene transfers into a separate species in the natural environment, the gene might produce a unique phenotype that was not present in the original GMO crop. Because introduced genes often confer advantageous traits, environmentalists worry that their transfer into native species could produce “super weeds” that would be invasive and hard to control - with long-term effects on local biodiversity.

    Second, if gene transfer occurs from the transgenic to a non-GMO crop line, it could adversely affect farmers who sell to customers and entities who wish to consume non-GMO crops.

    Effective measures to block transmission of transgenic genes are needed to solve both of these problems. One common and simple method employed is an actual physical separation, either by distance or enclosure. Enclosures can be expensive and are of limited utility for plants grown on large acreages such as corn, wheat, or soybeans and for trees and other large plants. A distance-based approach requires detailed knowledge about the range of pollen flow, whether carried by animals or the wind, to insure that transgenic plants are a sufficient distance from other plants -- and farmers would need to cooperate with their neighbors to plan the distribution of transgenic materials to minimize contamination.

    A second method, one that is utilized specifically for corn, is to simply remove the male inflorescence (tassel) before pollen shed occurs, called "de-tasseling". This method is commonly used in the production of hybrid corn, although it requires both expensive machinery to carry workers through the field and manual labor to pull each tassel from the plants; and this method is not foolproof because tassels that emerge very early or very late may send pollen into the environment. Ironically, perhaps one of the most promising techniques to curtail the transmission of transgenes into other species or non-GMO crop lines relies on a transgenic approach. This would involve engineering male sterility into the transgenic plants to prevent the production and transmission of pollen. Assuming that the genetically modified male sterility is absolute, the transgenes should be able to be effectively "quarantined". This method has some drawbacks, too: there is the fear that farmers, especially in the developing world, will become dependent on large seed companies who develop and market the seed. A combination of techniques may emerge as the most fail-safe option.


    Even without gene transfer into wild species, transgenic plants might disrupt an ecosystem. For instance, an introduced gene could confer pest or herbicide resistance in the field in order to improve overall crop yield.     Ecosystems involve complex, integrated connections among organisms in the environment. The introduction of a new variable could be significant enough to affect non-target organisms living in the same environment as the transgenic crop. Often these consequences are not studied or elucidated until after the crop has already been introduced into an ecosystem. See the example of Bt corn and monarch butterflies for conflicting arguments surrounding this overall issue.

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