Rakesh S. Chandran, Ph.D.
WVU Extension Service
This article was published in the February 2001 issue of West Virginia Farm Bureau News.
Genetically modified crops (transgenic crops) are best known for their abilities to resist pests (weeds, insects, and diseases) or for produce containing high nutrient levels. Transgenic crops capable of manufacturing vaccines and other pharmaceuticals are also in the pipeline. Some of the well-known transgenic crops on the market today are Roundup Ready Soybean, Roundup Ready com, Bt Corn, IMI corn, etc.
In the previous article (Farm Bureau News; vol. 8, no. 11), I discussed the basic principles of genetic engineering. Now that we have the background information, let's examine some of the pros and cons of the technology in agriculture.
Allergies. Eating certain transgenic foods has occasionally led to the development of allergies. A study reported in the New England Journal of Medicine in 1998 showed that people consuming transgenic soybean intended as animal feed developed certain allergic reactions. Transgenic crops marketed for human consumption have not been linked directly to causing widespread allergies.
Monarch butterfly mortality. Recent studies reported in Science and Oecologia journals suggested that pollen from the transgenic Bt com may be fatal to monarch butterflies, which feed on milkweed coated with com pollen. Scientists have confirmed the mortality of monarch butterflies exposed to Bt com pollen under both laboratory and field conditions. Proponents of the technology claim that under field conditions the concentration of pollen on milkweed may not reach levels that cause lethal effects. Scientists from Iowa State University are examining this more closely, and their findings should be published soon. A study published in Nature (1999) indicated that secretions from remains of Bt com adversely affected certain other soilborne nontarget insect species.Soil Erosion. Herbicide-tolerant crops are used for post-emergent weed control in no-till farming. This reduces the need for tillage, which in turn reduces soil erosion and nutrient losses. A potential environmental risk comes with this technique because it involves total vegetation control, which may affect an ecosystem's species diversity.
Herbicide-resistant weeds. The evolution of "superweeds" capable of resisting herbicides as a result of using herbicide-tolerant crops has been a topic of public interest. Such a phenomenon is highly unlikely because there are more than 12 distinct groups of herbicides displaying different sites and modes of action (Herbicide Handbook, Weed Science Society of America). The popular herbicide, Roundup, is only one member of one of these herbicide groups. Therefore, the likelihood of a weed becoming resistant to all known herbicides is almost impossible. The same argument and counter- argument are true for "escapes" of transgenic plants into the surrounding habitat.
Food Supply and Pesticide Usage. Transgenic crops may provide increased profits to the farmer while providing cheaper and more nutritious food. Genetic engineering also has helped make crops available that could not otherwise tolerate adverse environmental conditions (drought, cold, high salt levels in the soils, etc.). Such crops are capable of resisting pests, generating higher yields, and producing food with high nutrient content. They are considered an effective means of dealing with pest problems while reducing production costs.
Opponents of the technology argue that transgenic crops would increase our dependence on pesticides. This may be true in some instances but not in others. For example, Bt com reduces the need for insecticides since this transgenic corn can produce toxins to kill the European com borer pest, which otherwise would require insecticide applications. Indirect benefits of reduced insect damage include lower levels of fungal toxins associated with insect-damaged com.
Gene flow. The flow of transgenes into other organisms through pollution (termed "genetic pollution") may pose unknown risks to the ecosystem. Once these genes are released, it is difficult to recall them. Proponents of the technology claim that this form of gene pollution is similar to introducing alien species into an ecosystem. The ecosystem is dynamic, and human interference caused it to change throughout history. Some organisms have become a nuisance although they were originally introduced as a biological control agent (e.g., Japanese ladybug).
Crop diversity. Because genetic engineering focuses on crops with certain highly desirable traits, genetic diversity within the crop could be diminished. This can make crops more susceptible to natural calamities such as disease outbreaks. Such problems also have been encountered with hybrids generated by traditional breeding techniques.
Faster breeding. A possible benefit of transgenic crops or animals is that they can be bred for desirable traits very precisely and much faster than when traditional methods are used. The related disadvantage is that because the actual "breeding" in genetic engineering is carried out under laboratory or sterile conditions, the implications under field conditions may not be fully understood until a problem arises.
Nutrient levels. Certain transgenic crops (e.g., "golden rice" capable of synthesizing the precursor of Vitamin A) are capable of producing higher amounts of nutrients and vitamins, which could be have a great impact on solving nutrition problems in heavily populated and underdeveloped countries.
Resistant microbes. Although there is no evidence, there are claims that transgenic crops may lead to the release of resistant strains of microbes into the environment by plants. This has been contradicted by proponents of the technology who state that such risks are highly unlikely compared to similar releases from medical or veterinary practices.
Pharmaceuticals. Researchers are testing transgenic plants that are valuable to farmers and consumers now. They are capable of producing vaccines, pharmaceuticals, and other materials used in the medical industry. But their ability to safely contain such products has been questioned.
Disease pathogens. Plant pathogens capable of causing cancers (Agrobacterium tumefaciens) are used sometimes to carry the novel genes into the transgenic plants. There is a low likelihood that such pathogens could recombine with their equivalents in the plant and cause new plant diseases. Other techniques (e.g., "gene gun") can be used to insert genes into the DNA of an organism, which may rule out the possibility of such recombining.
Several more arguments for and against the use of this technology are found in the media today. Most of them are subjective and speculative. The topic is a very complex one, the ramifications of which may involve many disciplines. Therefore, future research may provide answers to some of the uncertainties we face now.