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July 12, 2009

Viral disease threatens East Africa's cassava farming

by Halima Abdallah

Cassava Brown Streak Virus, a new disease that affects the tuber crop and that could jeopardise food security has been found in East Africa. The virus has the potential of becoming an epidemic.

Scientists said that the disease was first detected in Tanzania and spread to Kenya, Rwanda, Burundi, Democratic Republic of Congo, and Uganda.

The virus is spread through propagation and by a whitefly vector (Bemisia tabaci) predominant in the affected countries, and is associated with the Cassava Mosaic Disease too.

It is not yet known how the disease could affect humans because research on it is still in the early stage.

Preliminary research shows that it is predominant in varieties that have been improved to resist the mosaic disease — the worst cassava disease ever known — a disturbing finding that could divert scientists’ efforts to fight the mosaic.

The improved variety was preferred by farmers who wanted to avoid the mosaic disease, which ravaged parts of Uganda in the 1990s causing starvation in some communities.

Cassava affected by the brown streak virus is brown and harder than a healthy tuber, which makes it inedible. The virus has been known to affect entire farms once it strikes, scientists said.

Unfortunately, the brown streak virus symptoms are not as pronounced as those of the mosaic disease, which makes it difficult to detect until the crop is harvested.

Cassava is produced by small-scale farmers in over 90 countries in the developing world, with half of the farmers in Africa.

The Food and Agricultural Organisation of the United Nations (FAO) estimates that about 70 million people depend on cassava for food and livelihood in the developing world.

In Uganda, cassava farming ensures national food security. The country produces 5.5 million tonnes of the tuber annually from about half a million hectares of land.

The crop is relatively cheap to produce because it does not require expensive inputs such as fertilisers or improved seeds as farmers often replant cuttings from the previous crop. It is also drought resistant.

Besides being a source of food rich in carbohydrates, cassava is also used in the industrial production of livestock feeds, starch for textile manufacturing, pharmaceuticals and in the paper industry at both small and large scale.

So far, the disease has spread to 30 districts in Uganda and in Kenya the outbreak has been reported in a large multiplication site in Yala swamp in Nyanza province. In Malawi the disease is widespread around the shores of Lake Malawi.

The brown streak virus was primarily known as a diseases of the lowland cassava growing areas of East Africa but is now seen in higher lands of over 1,000 metres above sea level.

The disease was first detected in Uganda in 1945 in infected planting material from Tanzania, according to Dr Titus Alicai, a plant virologist.

He said the diseased plantlings were destroyed, but the disease has reappeared and spreading fast.

The virus poses regional threat that calls for combined strategies like minimising the movement of susceptible planting material across boarders and management at country levels.

In Uganda, scientists are currently doing research to understand the virus, and how to develop resistant varieties.

Robert Anguzo, the spokesman for the National Agricultural Research Organisation said that a project, the Virus Resistant Cassava for Africa is currently doing research using biotechnology and conventional methods to develop cassava varieties that are resistant to both the mosaic disease and the brown streak virus.

The project will run for five years before findings are released to the public.

The East African

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