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January 26, 2009

Over-reliance on a few crops threatening world crop biodiversity

Jeff Bentley

Centuries of crop diversification are at risk of being lost forever, warns Jeff Bentley. A growing dependency on just a few modern, high-yielding varieties is leaving the world's food supplies exposed.

A potato is not just a potato; there are thousands of local varieties still grown in their birthplace in the Andes. Some are long, thin and purple; others are lemon yellow and floury, or shaped like a bull's horn. Most crops have many varieties, a rich heritage that most urban dwellers are no longer aware of. The cultivated potato comes in six different species and perhaps 3,000 varieties, most found only in the Andes. That is a lot of genetic information. Until recently these local, native varieties were safe on the farm, but as farmers turn increasingly to modern, high-yielding varieties, the old ones are being abandoned.

For example, in the 1970s near Lake Titicaca, agronomists collected more than 200 varieties of quinoa, a native Andean grain. Now, no more than 50 of these are still grown. Our generation is snuffing out ancient races of crops which fed the Incas, the Mayans, the Sumerians, and the Tang dynasty.

The impoverished smallhold farmers who nurture crop diversity need to sell some of their harvest to make a living, but selling can be stressful. Villagers struggle to understand why the harvest that was so much work now fetches such a low price. The person who buys the product often gets the blame.

Researchers in Peru and Bolivia found that farmers and other people further up the food chain hardly knew each other. But when farmers, wholesalers, even chefs and supermarket staff all sat down together they learned about each others' concerns.

The invisible hand of the market, it seems, can favour the farmers and crop diversity. For example, heirloom potatoes are being sold to upscale Andean shoppers in smart little net bags. Because farmers can sell native spuds at a good price, they are planting more of them.

If humanity mourns the loss of wild plants, we should really worry about the extinction of cultivated ones.

West Africans domesticated a native species of rice, called Oryza glaberrima, 3,500 years ago. The grain was relative of the Asian rice Oryza sativa. Yet 450 years ago, the Asian species reached Africa and all but displaced the native rice, which had a thinner head of grain and thus brought in a smaller harvest. By the 1990s, native African rice was reduced to a few pockets on scattered farms.

Then in the 1990s, Sierra Leonean plant breeder Monty Jones and colleagues found a way to create a fertile hybrid between African and Asian rice. Called "Nerica" (New Rice for Africa), it could yield a bumper harvest like its Asian parent, but it was as tough as its African side, resistant to drought, pests and disease. Scientists have bred many varieties of Nerica and farmers all over West Africa are starting to grow them. This new rice, descended from an endangered species, is helping Africa to feed itself, yet this opportunity would have been lost if O. glaberrima had gone extinct.

As the Earth gets warmer, we will need to breed other hardy new crop varieties. Plant breeding is like playing cards: more hands are possible with a full deck. We'll only be able to create new varieties in the future if we save the old ones we have now. Many rare crop varieties are now grown on just a few farms, often by elderly people. The crops will be lost forever unless young people start to grow them.


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