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           Scientists Work to Control Cassava Plant Disease in Africa

   by 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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   [1]http://www.voanews.com/content/scientists-working-to-control-cassava
   -plant-disease-in-africa/1655179.html

References

   1. http://www.voanews.com/content/scientists-working-to-control-cassava-plant-disease-in-africa/1655179.html