A slender purple flower is a leading cause of the ever-rising death toll in Africa due to starvation. Appropriately named "witchweed,"it feasts on more than 70 percent of all corn crops in Kenya alone. A recently reported method for killing witchweed may be able to rescue this staple of the African diet from parasitic destruction.
"Witchweed attaches itself to the crop's roots,"says Prof. Jonathan Gressel of the Weizmann Institute of Science's Plant Sciences Department, "then drains it of life." The innovative method of attacking witchweed, conceived by Gressel and developed in collaboration with researchers at CIMMYT (the Spanish acronym for the International Maize and Wheat Improvement Center), kills the colorful weed in its early stages of growth. That is the key to its success.
Until now, African farmers commonly removed witchweed (Striga hermonthica) by hand, but by the time it emerged above ground it had already done its damage. Herbicides applied after its emergence were also ineffective for the same reason.
Gressel decided to test whether coating the corn seeds with herbicide before planting would have an effect. The result: When the seeds sprouted, the parasite unwittingly devoured the weed-killing chemical from the crop's roots or surrounding soil and died. By the time the crop ripened, the herbicide, applied at less than one-tenth the usual rate, had disappeared, leaving the corn unaffected.
Tested in four African countries over ten crop seasons, the technique has on average tripled corn harvests and dramatically cut the cost of growing this crop, sparing farmers the expensive process of air-spraying entire fields. In addition to saving lives, this method may be an economic blessing to Africa: Yields lost to witchweed are valued at approximately $1 billion annually.
For the method to work, the seed itself must be resistant to the herbicides. Gressel sought out strains of corn that resist these herbicides and found one in the United States. His African colleagues Drs. Alpha Diallo and Stephen Mugo crossbred those seeds, provided by Pioneer International, Inc., with local corn to endow them with resistance to other African afflictions as well. The seed treatment technology was perfected by Drs. Fred Kanampiu and Dennis Friesen.
The new technology was presented at a conference in Kenya in July. After viewing the results in the field, Kenyan authorities pledged to fast-track approval for the method.
Prof. Gressel's research is supported by the Virginia Polytechnic Institute; Mr. David M. Safer, San Francisco, CA; and the Charles W. and Tillie K. Lubin Center for Plant Biotechnology. He holds the Gilbert de Botton Chair of Plant Sciences.
- According to UN figures, as many as 24,000 people die every day of starvation around the world. This devastation is substantially concentrated in Africa.
- Since the beginning of 2002, the U.S. Government, by far the leading food donor to Africa, has provided more than $68 million in emergency humanitarian aid and plans to provide an additional $82 million by the year's end.