Genetic engineering and the supermarket: Which crops are actually GE and why?

Product labeling at the supermarket has become very misleading. So many products are labeled with the words ‘Non-GMO’ or ‘GMO-free’ when this label is absolutely unnecessary. While this labeling is correct (the product truly doesn’t contain GE crops), lately we see these phrases on a majority of the packages on the supermarket shelves, regardless of what the product is made of and if GE varieties of these crops even exist. By labeling foods as ‘GMO-free’ when it is not possible for them to contain products from genetically engineered crops is misleading to consumers and proliferates a fear-based marketplace where ‘GMO-free’ has gained an unsubstantiated reputation of being healthier and safer.

For example, you pick out a bottle of grape juice from the store shelf and see that one brand is labeled ‘GMO free’ and the other isn’t, because of this you may assume that the second brand uses genetically engineered grapes, because if they didn’t why wouldn’t they label their bottle as ‘GMO-free’ too? Well, they wouldn’t because there are no genetically engineered grapes, they haven’t even been developed. So labeling grape juice as ‘GMO-free’ is almost the same as labeling it as ‘dairy-free’. We know that grape juice is dairy-free, so a label stating as much is unnecessary. The same goes for labeling things as ‘GMO-free’, but because of the atmosphere of fear and misinformation being proliferated in the media, companies can make use of marketing approaches that capitalize on people’s fears. By saying that their product doesn’t contain genetically engineered crops, they can take advantage of consumers who have been swayed by mass media’s negative portrayal of genetic engineering. This applies to both processed products and fresh fruits and vegetables. You can easily find fresh produce labeled as ‘Non-GMO’, even though genetically engineered varieties of nearly all of those crops don’t exist, again illustrating how misleading and unnecessary the current labeling practices are.

Globally, the four main crops in which genetic engineering technologies have been implemented are cotton, corn, soybean, and canola. In these crops, the traits that have been introduced are Bt insect resistance and herbicide tolerance, which have been introduced as single genes or combined as a pair, providing increased options to meet growers needs. GE varieties of other crops have been developed but most are not commercially available or they are grown in very small numbers. Some of these crops have been specifically developed to address challenges being faced in rural communities of developing nations and are not grown in countries like the U.S..

Bt Insect Resistance

This trait is derived from the soil bacterium Bacillus thuringiensis, which is present in soils all around the world. It was discovered that this bacterium produces crystalline proteins that are toxic to certain insects. When eaten by an insect, the proteins bind to receptors in the insect’s gut wall and cause it to breakdown, leading to the death of the insect. Because these proteins bind to receptors in the gut, this toxic effect only occurs in specific types of insects with the appropriate receptors. These proteins, frequently called Bt proteins, can be applied to crops as a biologic pesticide, have been used as a pesticide since 1920, and are approved for use in organic production systems. Crops that have been genetically engineered to produce the Bt proteins work in the exact same way, except that the pesticide does not have to be applied to the plants because they now have the genetic code needed to produce the protein themselves. When a pest insect eats from a Bt plant, it consumes the protein and is affected by the toxins. Bt targets primarily Lepidopteran insects, or caterpillars. This includes bollworms in cotton, European corn borer in corn, armyworms in soybean, diamondback moth in canola, and many other pest species. Crops engineered to contain the Bt gene have substantially reduced the need for insecticides and all Bt products are safe for the environment and have no effect on non-target insects and other animals, including humans.

bt-soybean
Soybean plants in a screen house, infected with velvetbean caterpillars. Left: Insect resistant Bt soybeans. Right: Soybeans susceptible to insect feeding damage. Source: AgBio Forum, Volume 7

Herbicide Tolerance

Herbicide tolerance is the ability of a plant to withstand exposure to herbicide chemistries that would be otherwise harmful. Herbicides can function to damage a plant in several different ways, and although some herbicides are effective on certain plants and not others (for example grasses vs. broadleaf plants), they do not discriminate between weeds and crop plants. This presents a big challenge for growers because it limits their options in choosing a herbicide chemistry as well as restricting them to applying herbicides at specific times in the season to avoid harming their crop plants. One of the most effective herbicides is glyphosate, or Roundup, which acts on nearly all types of plants. Due to its common use in production systems, crop tolerance to glyphosate was the first herbicide tolerance trait to be introduced. Glyphosate works by binding to an enzyme (called EPSPS) in plants and blocking its ability to synthesize certain amino acids, halting the plant’s growth and development and causing it to die. Plants that have been engineered to be glyphosate tolerant have an altered gene that produces the EPSPS enzyme with a slightly different shape. This different shape prevents glyphosate from binding and allows the enzyme to continue working to build the amino acids needed by the plant. By having crop plants that can tolerate exposure to glyphosate, growers can use the herbicide more effectively and efficiently to control weed pests.

monsanto_shows_off_dicamba_resistant_soybeans_farmers_1_635427514411052098
GE crops with herbicide tolerance allow growers to control weeds using herbicide without harming their crop. Left: Traditional soybeans cannot be safely treated with herbicide and are overcome with weeds. Right: Improved weed control in GE soybeans with herbicide tolerance. Source: Farm Week Now

 

 

Disease Resistance

Many scientists are working to develop genetically engineered crops that are resistant to diseases, which cause large yield losses and frequent pesticide applications in many crops. Disease resistant GE crops have not yet become widespread, however, one success story we’ve seen so far is the papaya with resistance to papaya ringspot virus. Papaya is a perennial herbaceous tree grown in tropical countries and most traditional cultivars are susceptible to papaya ringspot virus. This virus causes stunted trees and other symptoms, which lead to unmarketable fruit. In Hawaii, this disease was so serious that the papaya industry was nearly eliminated. The introduction of papaya cultivars with resistance to papaya ringspot virus saved the Hawaiian papaya industry and these cultivars are becoming more widespread in other papaya-growing regions of the world.

papayaringspotvirus07
Left: Non-GE papaya trees susceptible to papaya ringspot virus. Right: GE papaya with resistance to the virus. Source: American Phytopathological Society

Refuge Areas

When growers use crops engineered with Bt insect resistance or herbicide tolerance, they plant several rows of non-engineered crops nearby. Growers do not anticipate any yield or profit from the plants in these rows because their purpose is to serve as a refuge area for the pest species. By introducing genetically engineered crops to their fields, growers are introducing a new selection pressure for the pest populations being targeted: for example, if there is only Bt corn available for corn borer larvae to feed on, eventually the individuals that are not killed by the Bt protein, due to a natural mutation or some other factor, will evolve and reproduce to the point that the protein is no longer toxic to them. Planting non-engineered crops in nearby refuge areas allows enough of the pest population to survive in order to avoid evolution in response to the engineered crops, thus ensuring that the GE traits will continue to be effective.

Takeaway Points:

  • Food labels claiming a product to be ‘Non-GMO’ or ‘GMO-free’ are often unnecessary and added just for marketing purposes. Learning more about how your food is produced is essential to make sense of all the marketing claims and make the healthiest and most cost-effective choices for you and your family.
  • The major crops with commercially available genetically engineered varieties are cotton, corn, soybean, and canola. There are no commercially available GE varieties of most vegetable and fruit crops.
  • The main GE crops being grown have been engineered to be insect and herbicide resistant, traits which work by affecting physiological pathways specific to certain insects and plants, respectively. Therefore, the environment, non-target insects, animals, and humans cannot be harmed by this technology.
  • Growers who use GE crops take care to ensure that there are refuge areas available for pest species, thereby maintaining genetic diversity within pest populations and ensuring the future efficacy of these GE crops.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s