Genetic engineering can be used in a variety of ways to protect plants from damaging pests and diseases. Why is it important to protect plants from pests and diseases? In commercial agriculture, plants are typically grown in genetic monocultures, especially staple crops like corn, wheat, rice and others. If a pest or pathogen is present or introduced and conditions are favorable, the crop is quite vulnerable. If not addressed, serious crop losses can occur.
Agricultural crops are not the only plants that can be protected with the use of genetic engineering. In the first half of the twentieth century, the American chestnut, a major component of the eastern hardwood forest, was all but eliminated following the introduction of an Asian fungal disease, chestnut blight. Unlike Asian chestnut, American chestnut has absolutely no genetic resistance to the disease. Why is this important? American chestnut once made up 25% of the forest throughout much of its natural range. The leaves were a food source for many insects and the nutritious nuts provided food for animals including turkeys, bears, squirrels and more. And, of course, people enjoyed eating them, too. The wood was valued as a source of decay resistant lumber for construction and many other uses. Both traditional cross breeding and genetic engineering are possible solutions in the effort to bring back this significant species.
Farmers use many tools and techniques to prevent or manage plant pests and diseases. These include:
- Monitoring to detect pests early
- Cultural practices such as crop rotation or trap crops
- Resistant plant varieties (traditional breeding)
- Appropriate fertilization and irrigation
- Physical barriers and traps
- Biological controls
- Chemical controls (organic and conventional)
- Genetically engineered crops
Genetic engineering may be used when other available tools are ineffective, unavailable, or when a clear benefit, such as reduced reliance on pesticides or increased yield, can be achieved.
Let’s look at three examples of traits used in agricultural crops today, what they do, how they work, which crops have them and why.
Trait I. Bt (Bacillus thuringiensis) toxin
What does it do? It kills caterpillars (in most cases) that eat it (or genetically engineered plants that contain it). Other insects, including pollinators, are unaffected.
How does it work? Bacterial genes that result in production of a protein harmful to insect cells are inserted into genes of the plant. The plant cells now contain the toxic protein and caterpillars that feed on the plant will be killed.
Which crops have Bt toxin genes? Corn, cotton, and eggplant (Bangladesh) (not all seed/plants are genetically modified).
Why was this trait introduced? Some of the most damaging pests of these crops, typically requiring regular applications of insecticides, are caterpillars. By making the plant toxic to the pest, chemical insecticide applications can be reduced. This can reduce harmful effects of pesticides on non-target organisms, handlers and the environment while reducing costs. Read more: http://sitn.hms.harvard.edu/flash/2015/insecticidal-plants/
Trait II. Resistance to papaya ringspot virus (PRSV).
What does it do? Transgenic (genetically engineered) papaya is resistant to PRSV.
How does it work? Genes from part of the virus itself have been incorporated into the papaya genome to achieve resistance.
Which crops have PRSV resistance? Rainbow papaya.
Why was this trait introduced? No other preventive or curative options were available to protect papaya in Hawaii from this disease. It is credited with saving the papaya industry in Hawaii. Read more: http://www.apsnet.org/publications/apsnetfeatures/Documents/2004/HawaiianRainbow.pdf
Trait III. Resistance to potato late blight.
What does it do? Modified potato plants are resistant to the serious disease, late blight,that was responsible for the Irish potato famine of the 1800s and still causes major crop losses today. In addition, these potatoes are reported to have improved storage life and reduced amounts of a potentially carcinogenic chemical produced when potatoes are cooked at high temperatures.
How does it work? Genes from a South American potato with resistance to the disease have been added to the genome of these food crop potatoes. Consumers may be more receptive to plants modified using genes from the same or a closely related species.
Which potatoes have this trait? The new varieties are Russet Burbank, Ranger Russet and Atlantic.
Why was this trait introduced? For disease control. More info: https://www.usnews.com/news/business/articles/2017-02-28/us-approves-3-types-of-genetically-engineered-potatoes
By Joan Allen, Assistant Extension Educator, UConn Department of Plant Science and Landscape Architecture