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A Hungry World

Given these risks, why do so many of these scientists support the continued development of agricultural biotechnology? One answer is witchweed. Witchweed, the common name for three species in the genus Striga, is a parasitic plant that feeds on the roots of cereals and legumes in much of Africa. Attacking maize, sorghum and millet-the continent’s three most important cereal crops-Striga, in the view of Gebisa Ejeta, an agronomist at Purdue University, is a “scourge” of African agriculture. It has been estimated that the weed destroys 40 percent of the continent’s total cereals harvest-a staggering loss in the world’s hungriest places.

From a biological perspective, Striga is fascinating. Its seeds, smaller than grains of sand, lie dormant for as long as 20 years, waking only when aroused by a chemical emitted by the roots of the host plant. While still underground, the parasite plants develop root-like organs called haustoriums, which penetrate the host roots and siphon nutrients. Scores or hundreds of Striga plants can attack the same host. Witchweed eventually grows into fields of five-foot-tall plants with pretty pink flowers, but by that time it has long destroyed the crops it feeds on. Because each plant produces as much as 100,000 seeds, witchweed is almost impossible to eradicate-the United States spent four decades wiping out a single small outbreak in the Carolinas.

Because witchweed rapidly adapts to new hosts, losses in Africa keep growing. When the parasite made it impossible to grow sorghum in eastern Sudan, desperate farmers tried to grow pearl millet. At first millet was immune. But within a few years witchweed was wreaking havoc on the new crop, too. “People are literally starving because of Striga,” says Ejeta.

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Tagged: Computing, Biomedicine

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