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The surprising emergence of hybrid rice varieties in West Africa may partly have been caused by war, scientists say.

The region is unique in that African and Asian rice co-exist there.

It was assumed that the two (Oryza glaberrima Steud and Oryza sativa L.) could not interbreed because they produce sterile offspring – and when scientists successfully crossed them in the laboratory a decade ago to create New Rice for Africa (NERICA), it was hailed as a technological breakthrough.

But researchers writing in PLoS ONE this month (6 October) report that the two are spontaneously interbreeding and that farmers are actively involved in selecting and improving these varieties.

The discovery shows that it is important to involve farmers in plant-breeding — so far they have generally been passive testers of scientists' inventions, say the authors.

The researchers collected rice varieties from villages across West Africa's coastal rice belt — including those in the Gambia, Ghana, Senegal and Togo — and looked for genetic differences.

They found several new farmer varieties that could only have arisen by interbreeding in the fields.   

Offspring resulting from spontaneous breeding between species will have few seeds — but if they survive this may be enough eventually to produce plants that are fully fertile, says Edwin Nuijten of the Technology and Agrarian Development Group at Wageningen University in The Netherlands, a co-author of the research.

"Suppose a farmer sees a hybrid in the field: he'll think it's pretty useless and not harvest it. Those few seeds could drop in the field and if the farmer replants the field they could germinate and then pollinate the surrounding normal plants. After a few generations a plant that has full fertility could develop," says Nuijten.

"The farmer may then select such plants and plant them separately to test whether they would do well as a new variety."

Disasters such as war seem to accelerate the selection and spread of the hybrid varieties, say the researchers. Areas affected by war, such as Guinea-Bissau, southern Senegal and Sierra Leone, had many more farmer hybrids than others.

"In Sierra Leone farmers have been hiding in the forest to escape attacks by rebels to avoid being discovered … Normal practice is to slash a piece of forest and burn it to have fertile land. But burning would draw attention so farmers need to keep reusing fields so the soil fertility reduces — and the farmer hybrids can tolerate [this] quite well."

Other reasons behind the spread include farmers fleeing their homes with their hardiest varieties, and farmers being less careful in harvesting their crops — reluctant to linger in their fields for fear of being spotted by rebels.

Farmers' active role in this crop development bolsters calls to involve them more in the plant breeding process, says Nuijten. Rather than simply testing crops once they have been developed, he says, farmers should be allowed to help select the most promising varieties — resulting in tailor-made plants.

Link to full paper in PLoS ONE


PLoS ONE doi 10.1371/journal.pone.0007335 (2009)