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Scientists have sequenced the genome of the staple crop cassava, and say this should lead to the development of more virus-resistant and nutritious varieties.

The draft genome, of a single cassava variety, has pinpointed about 95 per cent of the genes and could accelerate breeding programmes.

The large roots of the cassava plant provide daily sustenance for more than 750 million people in Africa, Asia and Latin America. But the crop is susceptible to many viruses and is not very nutritious.

Steve Rounsley, associate professor at the School of Plant Sciences at the University of Arizona, who coordinated the project, says the sequence will make goals such as developing virus resistance and increasing shelf life more attainable.

A US$1.3-million follow-up project, funded by The Bill and Melinda Gates Foundation, will sequence other cassava varieties and develop a freely available database comparing the sequences. The University of Arizona will lead the project which will involve international collaboration, including some African partners.

Scientists will use the database to identify genes involved in traits such as resistance to cassava brown streak virus, a threat to food security in Eastern Africa.

"With the first cassava genome in hand we can cheaply and quickly sequence other varieties that will give us thousands of little signposts — mile markers if you like — that will help us identify key genes for increasing the plant's resistance to the virus," said Rounsley.

These signposts will make breeding easier because traits that are normally not observed until the plant is mature can be identified earlier with a simple DNA test.

Andrew Ward, senior adviser for the UK Department for International Development's Research into Use programme, said: "Access to cassava's genetic code will enable researchers to target specific traits valued by farmers so that more people will benefit".

But "this is a tool that needs to be used in conjunction with others to develop farmer-desired varieties," he said.

The sequence was created by the Community Sequencing Program of the US Department of Energy Joint Genome Institute and 454 Life Sciences, part of the Roche group, after a proposal by the Global Cassava Partnership.

Link to draft genome