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Conventional and Transgenic Cassava

Image: fruitsandveggiesmatter.gov

There are areas of the world disproportionately affected by droughts, famines, and malnutrition. Although some argue that food shortages and malnutrition have political or economic roots, the fact remains that weather patterns and prevalence of pests both fall outside the purview of corrupt political systems – in this case, drought- and pest-resistant crops can be beneficial. And while still recognizing the need to advocate for social justice, many scientists believe they are employing one strategy of many in the fight against malnutrition when they use genetic engineering to create plants that are higher in nutrients than their artificially selected counterparts.

Cassava is a staple crop for 800 million people and is the No. 3 source of the world’s calories, behind rice and wheat (Nassar).[1] Further, cassava is No. 2, after sugarcane, in terms of calories produced per unit of land (Siritunga). The plant is hardy and drought-tolerant, and the roots are eaten cooked or raw, or may be further processed. Its greens are also a source of food. Despite its status as a staple crop for many residents of developing countries in the tropics, most of which are in Africa, it is not very high in nutrients (Nassar); of all staple foods, it has the lowest ratio of protein to energy. The roots contain no storage proteins and no amino acids that contain sulfur, which can lead to protein-deficiency diseases such as kwashiorkor (Abhary).

Cassava is very high in cyanogen, a type of cyanide that gives the plant some natural pest resistance but can also be toxic to humans. Its cyanogen content exceeds FAO recommendations, but can be reduced through processing (such as by cooking). Still, overconsumption can lead to death or chronic health problems – one reason for inadequate processing can be drought, which decreases the amount of available firewood needed for cooking (Siritunga).

Thus, the overreliance on cassava as a source of calories can contribute to malnutrition and other problems. Many botanists have attempted to increase its nutritional profile by cross-breeding it with wild relatives that have evolved different traits; in 1982 a Brazilian team created a hybrid with increased protein content – 5 percent, up from 1.5 percent (as a point of comparison, wheat is 7 percent protein). In recent years, the team has produced, through conventional breeding, cassava varieties that have up to 50 times the normal amount of beta-carotene (Nassar).

The seeds produced by the conventionally bred hybrid plants aren’t agriculturally useful (meaning that farmers can’t save their seeds), so successful varieties are propagated through cuttings, leaving the genetically homogeneous crops vulnerable to pests. In response to this, the Brazilian team has also had recent success in developing cassava that can reproduce both sexually and asexually; this variety has not yet been made available to farmers. Conventional breeding techniques have also resulted in varieties that are more drought-tolerant, have resistance to common cassava pests, and have higher yields. Still, in order to feed a hungry world, scientists and plant breeders must continue to improve this crop. Cassava’s genome has been sequenced, which can help plant scientists to create new varieties – both transgenically and traditionally (Nassar).

One project underway is to genetically engineer a cassava with decreased cyanide and increased protein, iron, zinc, and vitamins A and E, as well as an engineered resistance to diseases that afflict the crop (McNeil). The genes for BioCassava Plus come from algae, bacteria, and plants, and the transgenic cassava is in field tests in Puerto Rico, with plans to conduct field tests in Nigeria. Funding is provided by the Bill and Melinda Gates Foundation as well as Monsanto. Monsanto stipulated that they would have the right to charge farmers for using the transgenic seed if they had annual incomes in excess of $10,000. Fortunately, poor families and small farmers should be able to grow the enhanced cassava at no extra cost (Castelvecchi).

One version of the transgenic cassava currently under development is engineered to express a protein called zeolin, which is stored by the roots of the plant, giving it a dry weight of 12.5 percent protein after growing for 11 months. Zeolin is a recombinant protein made by combining a corn-derived protein (γ-zein) with a bean-derived protein (phaseolin), and the inclusion of this protein in transgenic cassava results in a more robust amino-acid profile, especially aspartate and glutamate. Additionally, cyanogen content in both the leaves and the roots was decreased by more than half. The transgene was inserted into embryonic cassava cells using Agrobacterium tumefaciens (strain LBA4404) as a vector (Abhary). A. tumefaciens is a bacteria species capable of inserting its own genes into the DNA of certain plants, causing tumors; it is used in biotechnology to insert small pieces of DNA containing desired genes into target plants (Tortota, 304-5).

However, the project faces resistance from certain environmental groups who are slowing field trials in Uganda and Nigeria. A Nigerian geneticist named Martin Fregene, project development manager for BioCassava Plus, believes they use fear-mongering tactics and that their intentions, however pure, are paternalistic at best: “They treat Africans as if we are kids and can’t make up our minds” (McNeil).

Western influence in African countries, both in the form of biotechnology and anti-GMO activism, raises questions about self-determination. Surely starvation and malnutrition arise from multiple sources and are complicated issues, but can transgenic cassava save lives? Do Africans need Western anti-GMO activists to rescue them from a technology the activists believe is harmful? For that matter, do Africans need Western scientists to rescue them from starvation? Or can they rescue themselves through political reform, scientific advancement, or both?


Abhary, M., Siritunga, D., Stevens, G., Taylor, N.J., Fauquet, C.M. (2011). Transgenic Biofortification of the Starchy Staple Cassava (Manihot esculenta) Generates a Novel Sink for Protein. PLoS ONE 6(1): e16256. doi:10.1371/journal.pone.0016256

Castelvecchi, D. (2010). The Biotech Way. Scientific American, 302(5), 84.

McNeil, D.G. Jr. (2010). “Five Years In, Gauging Impact of Gates Grants.” New York Times. Obtained from http://www.nytimes.com/2010/12/21/health/21gates.html?pagewanted=3

Moffat, A.S. (1999). PLANT BIOTECHNOLOGY: FOOD AND FEED: Crop Engineering Goes South. Science, Vol. 285  no. 5426  pp. 370-371.

Nassar, N., & Ortiz, R. (2010). Breeding Cassava to Feed the Poor. Scientific American, 302(5), 78-84.

Siritunga, D., & Sayre, R. (2007). Transgenic Approaches for Cyanogen Reduction in Cassava. Journal of AOAC International, 90(5), 1450-1455.

Tortora, G.J., Funke, B.R., Case, C.L. (2010). Microbiology: An Introduction. San Francisco: Pearson Benjamin Cummings.

[1] According to Science, cassava is the No. 3 source of calories behind rice and corn (Moffat).

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One Response to “Conventional and Transgenic Cassava”

  1. Unfortunately the Abhary paper has been retracted.

    Posted by jshoyer | June 3, 2013, 4:19 pm