News / Africa

Scientists Work to Control Cassava Plant Disease in Africa

A farmer digs up cassavas in Yamoussoukro, Ivory Coast, June 2008 file photo.A farmer digs up cassavas in Yamoussoukro, Ivory Coast, June 2008 file photo.
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A farmer digs up cassavas in Yamoussoukro, Ivory Coast, June 2008 file photo.
A farmer digs up cassavas in Yamoussoukro, Ivory Coast, June 2008 file photo.
Anne Look
Scientists and agriculture experts are meeting in Bellagio, Italy this week to work out how to fight a deadly plant virus that has been annihilating cassava crops in East Africa for nearly a decade.

Recent outbreaks of this "rapidly proliferating" virus in the Democratic Republic of Congo and Angola have sparked fears that the epidemic is pushing into West Africa, and could reach Nigeria, the world's largest producer and consumer of the cassava plant.

Cassava, a tropical root vegetable, could be the miracle crop of Africa. It grows well in poor quality soil and high temperatures, making it resistant to climate change. It requires little labor to grow.

Its roots are rich in carbohydrates, vitamins and minerals. It is already a dietary staple throughout the continent, and it could feed more.

Cassava can also be used as an industrial starch to produce plywood, textiles and paper - something that experts say could change African economies and that countries like Nigeria are already beginning to invest in.

Deadly disease

But cassava diseases have been shortchanging farmers in Africa for a century.

One particularly deadly virus, Cassava Brown Streak Disease, began ravaging cassava fields in East Africa 10 years ago and has now moved as far west as the Democratic Republic of Congo.

Brown streak disease is spread in two ways: by white flies, of which scientists say there are no shortage in affected countries, and by infected stem cuttings, which farmers use instead of seeds to plant their fields.

"The [brown streak] disease is not very obvious on the plant itself," explained Claude Fauquet, a plant virologist who heads the Global Cassava Partnership for the 21st Century. "The plant is growing fairly well, but the disease is obvious on the roots when they harvest, but when they harvest, it's too late. So in short, there is really nothing that farmers can do and therefore solutions have to come from scientists and different organizations that would be capable of offering farmers virus-free material and to select, to breed material, genotypes of cassava that would be resistant to the disease."

Virus resistant

He said scientists have developed a strain of cassava that is resistant to the virus and are trying it out in Tanzania. They do that by either breeding existing virus-resistant strains together or genetically engineering new ones in the laboratory. They then must go village-by-village, getting farmers to plant that new super strain.

Fauquet said this approach has been successful against Cassava Mosaic Disease, also known as CMD. It is the most common cassava disease in Africa and it is all over the continent. But CMD primarily damages the cassava plant, not the root. A farmer can usually salvage some of his harvest.

Fauquet said that is not the case with brown streak disease.

"The roots are completely necrotic. Therefore farmers, they lose absolutely everything. So, the plant is growing," he said. "They work in the field, they weed. They spend a lot of energy and a year or 18 months later when they harvest, all the roots are present but they are necrotic, and therefore they cannot eat them, they cannot process them. They cannot even feed animals. Animals will refuse to eat them as well… You go from having a harvest to having no harvest in one cycle."

Experts say brown streak disease could cut cassava production in half on the continent. As many as 300 million Africans could be affected.

Fauquet said they must act fast to keep it from reaching West Africa where nearly every country, and in particular Nigeria, counts on the crop.

"You would have an explosion of the disease and maybe we would need a decade before we could respond and offer farmers solutions. So the magnitude of the problem would be gigantic, and therefore the idea is can we prevent this? Can we put in place a system to prevent and to monitor if there was an importation or a spread?" he said.

Fauquet said all it takes is one farmer sharing infected stem cuttings with another across the border or across the continent to accelerate the spread of the disease.

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