Virus-Resistant Cassava Could Lead to Serious Problems: Biologists

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Virus-Resistant Cassava Could Lead to Serious Problems: Biologists

Several regions worldwide plant and cultivate cassava to supply the never-ending growth of populations / Photo by Getty Images


Cassava is one of the primary crops grown across the globe due to its nutritional values. However, the plant is prone to a particular disease that can cause plagues in farmlands. So, a team of biologists investigated the use of a gene-editing tool to counter the disease, but they discovered that doing so triggers serious consequences.

The investigation of gene-editing tool to create virus-resistant cassava plants has been conducted by biologists at the University of Alberta, the University of Liege, and the Swiss Federal Institute of Technology. Their findings unveiled the propagation of mutated viruses in controlled conditions. They published the results in the journal Genome Biology.


The Cassava Mosaic Disease

Cassava is a highly important crop grown in Africa, Asia, and South America. About one billion people obtain their daily calorie needs from this crop. So, several regions worldwide plant and cultivate cassava to supply the never-ending growth of populations.

Normally, cassava farmers only have to deal with drought and pests to keep their crops. But at times, situations get worse when the cassava mosaic disease (CMD) attacks farmlands. This disease can result in 20 percent of crop loss in affected fields.

According to CABI, the cassava mosaic disease is caused by a virus that belongs to the viral family Geminiviridae. Scientists have been able to define 10 species of CMD while 1 species is still under investigation, though it is known to exhibit the symptoms of the disease in infected cassava plants.

Downsides of cassava typically happen if consumed in large amounts or if prepared improperly / Photo by Phong Giap Van via 123RF


Since cassava plant is vegetatively propagated, the CMD can spread via movement of cuttings from infected plants. Once the cuttings are planted, the virus automatically establishes itself and spread across fields, with infectivity rate connected to available vectors in the area. The range of crop loss due to CMD infection is between 12 and 82 percent, varying from the infection type and cassava variety.


CRISPR Does Not Work with CMD in Lab Setting

With the availability of the gene-editing tool called CRISPR-Cas9, many experts wanted to create cassava varieties that have an inherent resistance to CMD. Although it is a noble goal to help farmers and their crop production, a group of biologists disagrees with the use of gene-editing. The implementation of CRISPR works differently in plants.

"We concluded that because this technology both creates a selection pressure on the viruses to evolve more quickly, and also provides the viruses a means to evolve, it resulted in a virus mutant that is resistant to our interventions," explained Devang Mehta, the lead author of the study and a postdoctoral fellow from the Department of Biological Sciences at UA.

The biologists applied the CRISPR to determine its potential in protecting cassava plants from CMD. The gene-editing tool was used to test if engineered cassava could cut the DNA of the virus and gain resistance from its adverse effects. Unfortunately, the modified plants could not do it and eventually became fully infected by the virus.

They investigated the mechanisms behind the unsuccessful gene-editing process. So, they sequenced hundreds of viral genomes found in every cassava plant. Their findings showed the following:

- The gene-editing tool has been discovered as a potential factor to mutate the virus. This promotes its resistance against functional interventions.

- The use of CRISPR resulted between 33 percent and 48 percent of edited genomes to mutate and resist the cutting effect of the tool.

- The Nicotiana benthamiana model plant used in the study showed that mutant viruses depend on the presence of a wild-type virus. This plant is a relative of tobacco and has been utilized to replicate the novel approach.

The team is determined to share their findings with other scientists who are using the same tool for making plants resistant to viruses. They wanted to urge them to test their plants for similar viral mutations found in the study.


Nutritional Facts of Cassava

Details at Fact Fish showed that Nigeria was the number one producer of cassava in 2017, with a production quantity of more than 59 million tons. The next massive producer of the crop was the Democratic Republic of Congo with more than 31 million tons. Collectively, over 291 million tons of cassava was produced in the same year.

Dr. Brianna Elliott at Healthline explained that consumption of cassava has pros and cons, depending on the amount and how it is prepared. Its number one nutritional benefit is calories with a score of 112 for every 100 grams of boiled cassava.

Next is its carbohydrates of 27 grams per 100 grams of boiled cassava. It is followed by other nutrients like fiber, thiamine, phosphorus, calcium, and riboflavin in reasonable amounts, and then, vitamin C, iron, and niacin in trace levels. Generally, the nutritional value of cassava is excellent, despite its minimal amount of vitamins and minerals.

Downsides of cassava typically happen if consumed in large amounts or if prepared improperly. If a person eats raw cassava, they are prone to cyanogenic glycosides that release cyanide into their body. This means they have to cook it properly to reduce the risk substantially.

In relation to that, eating a lot of cassava even if it is cooked will increase the risk of cyanide poisoning. This condition can damage the thyroid glands and the nerves.




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