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African scientists have uncovered how one of the world's most economically devastating crop diseases emerged, and hope to genetically engineer disease resistant crops using the information.

Researchers compared the genetic sequence of the virulent maize streak virus (MSV) with ten less harmful strains of the virus from across the continent, which infect other grass food crops such as wheat and oats.

"We found that two relatively mild grass viruses had merged through genetic recombination," says researcher Arvind Varsani, from the University of Cape Town (UCT), South Africa.

This merger resulted in an ancestral MSV far more potent than its parents, which moved into maize before spreading rapidly across the continent.

The researchers think that this occurred about a century ago, just when commercial agriculture was replacing subsistence farming and maize started to overshadow indigenous crops in Africa.

The findings, published in the September issue of the Journal of General Virology, highlight the importance of research into plant diseases.

"Our results mean that DNA viruses are evolving faster than was thought. This rapid mutation increases the possibility of new plant viruses emerging," Varsani told SciDev.Net.

"While plant diseases do not feature very highly in the public's consciousness, their impact on food production causes more suffering in the developing world than many high profile human diseases," says lead researcher Darren Martin of South Africa's Institute of Infectious Disease and Molecular Medicine.

Studying plant diseases can provide information about pathogens that can be used to develop resistant crops.

Each year, at least two hundred samples of infected maize are analysed by the UCT team. An analysis of virus-infected maize from Burkina Faso, the Central African Republic, Ivory Coast, Namibia and Zambia will begin this month and be placed in a database.

Dionne Shepherd of the Department of Molecular and Cell Biology at UCT is leading efforts to genetically engineer a type of maize resistant to the streak virus.

"We have developed maize that is resistant to the streak virus. Now we need to prove that it will hold up under different conditions throughout sub-Saharan Africa," Shepherd told SciDev.Net.

Link to full paper in the Journal of General Virology


Journal of General Virology doi 10.1099/vir.0.2008/003590-0 (2008)