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October 10, 2009

Gene-modified, virus-resistant cassava developed in South Africa

by Carol Campbell

South African scientists have engineered plants with resistance to a local cassava virus, potentially safeguarding one of the region's staple crops.

The South African cassava mosaic virus is one of seven such viruses affecting different cassava-growing areas of the world. It results in yellow and green patches on the leaves of plants which impede photosynthesis and stunt the growth of the edible tuber.

Sarah Taylor, a researcher in the cassava biotechnology programme at the University of the Witwatersrand's School of Molecular and Cell Biology in Johannesburg, presented her research at the Bio2Biz conference in Durban in September.

She says the new technology could be applied across the southern African region, as the same virus infects crops in Madagascar, Mozambique, the north eastern provinces of South Africa, Swaziland and Zimbabwe.

Resistance to the African cassava mosaic virus has already been achieved. Plants are rendered resistant by altering their genes in a way that disables the mosaic virus once it attacks, said Taylor. The researchers' work exploits a feature of the virus's genetic material — RNA.

Strands of RNA are inactivated when they meet a matching strand, so creating a plant that makes strands of RNA for a given virus gene eliminates the function of that gene — and therefore the virus — once the plant becomes infected and the strands meet.

"The plant is still attacked but the virus is unable to propagate and eventually peters out," said Taylor.

The first round of Taylor's research experimented on the tobacco plant, which grows well in the laboratory. Tobacco plants infected with the virus continued to grow normally and the researchers now hope to replicate these results using cassava plants, before moving on to field studies.

Cassava is one of Africa's principal foodstuffs, with every person in Africa estimated by the UN Food and Agriculture Organization to eat 80 kilograms per year.

The virus is easily passed between plants by whiteflies, which carry the virus in their saliva. One contaminated plant can lead to the loss of an entire crop, with severe infections wiping out 80 per cent of yields, said Taylor.

SciDevNet


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