Section Goals:

1. Learn examples and relevant details about genetically modified crops.
2. Relate the examples to a larger understanding of the benefits and risks of GMOs.

Case Studies of GMO crops

The goal of this section is to talk about specific examples of GMO crops because the details matter. GMO crops are all different, and the trait that has been modified will result in different outcomes, especially if we are measuring the environmental impact.

Glyphosate Resistant Crops

Roundup Ready is the Monsanto trademark for its patented line of genetically modified crop seeds that are resistant to its glyphosate-based herbicide, Roundup.

Glyphosate kills plants by interfering with the synthesis of the essential amino acids phenylalanine, tyrosine and tryptophan. These amino acids are called “essential” because animals cannot make them; only plants and micro-organisms can make them, and animals obtain them by eating plants. Therefore, the fundamental way that glyphosate works means that the health risks to humans are low. The consensus among national pesticide regulatory agencies and scientific organizations is that labeled uses of glyphosate have demonstrated no evidence of human carcinogenicity, though that does not mean it is “safe”.

In 1996, genetically modified Roundup Ready soybeans resistant to Roundup became commercially available, followed by Roundup Ready corn in 1998. Current Roundup Ready crops include soy, maize (corn), canola, sugar beets, cotton, and alfalfa, with wheat still under development.

While the use of Roundup Ready crops has increased the usage of herbicides measured in pounds applied per acre, it has also changed the herbicide use profile away from atrazine, which is more easily leached into groundwater and drinking water sources.

Bt Cotton

Bt cotton is a genetically modified pest resistant plant cotton variety, which produce an insecticide to combat bollworm, the primary pest of cotton.

Strains of the bacterium Bacillus thuringiensis produce over 200 different Bt toxins, each harmful to different insects. Most notably, Bt toxins kill to the larvae of moths and butterflies, beetles, cotton bollworms and flies but are harmless to other forms of life. The gene coding for Bt toxin has been inserted into cotton, allowing cotton to produce this natural insecticide in its tissues. In many regions, the main pests in commercial cotton are lepidopteran larvae, which are killed by the Bt protein when they eat the Bt cotton plant. This eliminates the need to use large amounts of broad-spectrum insecticides to kill lepidopteran pests. A secondary benefit is to spare natural insect predators in the farm ecology and further contributes to non-insecticide pest management.

Bt cotton is ineffective against cotton pests in other insect families, such as plant bugs, stink bugs, and aphids; depending on circumstances it may be desirable to use insecticides in prevention. A 2006 study done by Cornell researchers, the Center for Chinese Agricultural Policy and the Chinese Academy of Science on Bt cotton farming in China found that after seven years these secondary pests that were normally controlled by pesticide had increased, necessitating the use of pesticides at similar levels to non-Bt cotton.

Golden Rice

Golden rice is a variety of rice (Oryza sativa) produced through genetic engineering to biosynthesize beta-carotene, a precursor of vitamin A, in the edible parts of the rice. It is intended to produce a fortified food to be grown and consumed in areas with a shortage of dietary vitamin A. Vitamin A deficiency causes a range of eye conditions; from night blindness to more severe clinical outcomes such as keratomalacia, corneal scars, and permanent blindness. It also increases risk of mortality from measles and diarrhea in children. In 2013, the prevalence of deficiency was the highest in sub-Saharan Africa (48%; 25–75), and South Asia (44%; 13–79).

Although golden rice has met significant opposition from environmental and anti-globalization activists, more than 100 Nobel laureates in 2016 encouraged use of genetically modified golden rice.

Bananas

Bananas are a unique fruit because the ones we eat are sterile fruits: no seeds are produced within the fruit. These plants must be reproduced vegetatively, which means that all banana plants from the same parent are clones. The risk of this is that any type of infection to which the parent is susceptible will also be equally impactful to the clones.

The current banana variety that is most commonly sold is the Cavendish. The Cavendish banana replaced the previously preferred Gros Michel variety because the Gros Michel was susceptible to a fungal pathogen; all Gros Michel bananas were effectively wiped out by the pathogen (called Tropical Race 1) by 1965. Unfortunately, in 1989 a similarly deadly fungus variety (Tropical Race 4) was discovered to kill Cavendish bananas. It is only a matter of time before the Cavendish variety is wiped out, as happened to the Gros Michel.

A number of genetic-engineering techniques and labs are working on modifying the Cavendish to resist TR4. Though there are successful results, the resistance of the world to accept and buy these GMOs is the limiting factor to potentially save the Cavendish banana.

Are All GMOs the Same?

The two most common GMOs are Bt-enhanced crops and glyphosate-resistant crops. These two types of GMOs have differing, contrasting results: to reduce the use of pesticides and to increase the use of herbicides. Though there are slightly oversimplified conclusions, it highlights that if a person was concerned about the amount of chemical applications in agricultural settings, they should avoid glyphosate-resistant crops but should chose to use Bt crops. Golden Rice and the modification of Cavendish bananas similarly cannot be grouped together unambiguously. These examples highlight that knowledge of each type of GMO is necessary in order to evaluate the environmental risks and benefits. However, one thing is clear: all evidence shows that GMOs that have been approved are safe for human consumption. A similar conclusion can be made about the economic benefit to farmers. The adoption rate of many GMO crops is more positive than negative because the successful GMO crops outperform the non-GMO varieties. Though, as with all things, there are complexities and inequities by having specific GMO-varieties owned by a large company.

Are GE Crops the Solution We Need?

Significant resources, both financial and intellectual, have been allocated to answering the question: are GE crops safe? After many hundreds of scientific studies, the answer is yes. But a significant question still remains: are they necessary? Certainly, such as in instances like Hawaii’s papaya, which were threated with eradication due to an aggressive disease, genetic engineering was a quick and effective solution that would have been extremely difficult, if not impossible, to solve using traditional breeding practices.

However, in many cases, the early promises of GE crops – that they would improve nutritional quality of foods, confer disease resistance, and provide unparalleled advances in crop yields – have largely failed to come to fruition. NASEM’s GE Crop Report states that while GE crops have resulted in the reduction of agricultural loss from pests, reduced pesticide use, and reduced rates of injury from insecticides for farm workers, they have not increased the rate at which crop yields are advancing when compared to non-GE crops. Additionally, while there are some notable exceptions like golden rice or virus-resistant papayas, very few GE crops have been produced to increase nutritional capacity or to prevent plant disease that can devastate a farmer’s income and reduce food security. The vast majority of GE crops are developed for only two purposes: to introduce herbicide resistance or pest resistance.

Genetic engineering of crops represents in important tool in a world of rapidly changing climate and a burgeoning human population, but as you will see in the next chapter, it is only one of many tools that agriculturists can use to produce enough food for all humans while simultaneously working to conserve the environment.

Suggested Supplementary Reading

Bananas, by Matt Reynolds. Wired. Published 11-10-2018.

Attribution

Are GE Crops the Solution We Need? by Matthew R. Fisher is licensed under CC BY 4.0. Modified by Joni Baumgarten.

Atrazine by Wikipedia is licensed CCA-SA 3.0. Modified by Joni Baumgarten. Accessed 02-26-2023.

Bt Cotton by Wikipedia is licensed CCA-SA 3.0. Modified by Joni Baumgarten. Accessed 02-23-2023.

Genetically Modified Soybean by Wikipedia is licensed CCA-SA 3.0. Modified by Joni Baumgarten. Accessed 02-23-2023.

Glyphosate by Wikipedia is licensed CCA-SA 3.0. Modified by Joni Baumgarten. Accessed 02-26-2023.

Golden Rice by Wikipedia is licensed CCA-SA 3.0. Modified by Joni Baumgarten. Accessed 02-23-2023.

Roundup Ready by Wikipedia is licensed CCA-SA 3.0. Modified by Joni Baumgarten. Accessed 02-23-2023.