Mercy Diebiru-Ojo's ambitions are straightforward -- increase Nigerian yam and cassava yields by 500 percent, fight hunger and raise her country's position on the agricultural value chain from a mere grower to a processor.

The first steps, at least, are already underway for the 44-year-old agronomist, who was awarded this year's prestigious Africa Food Prize for her research on yams and cassava, both major food staples in Africa.

Traditionally, farmers in Nigeria -- which produces 70 percent of the world's yams -- replant chunks of yams and cassava from the previous year's harvest, to grow this year's crop.

Gradually, the plants lose their resistance to diseases -- a serious problem for food security in a country where 30 million people are not getting enough to eat, according to the Un

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