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New witchweed-fighting method, presented by CIMMYT and Weizmann Institute scientist


Technique could dramatically diminish hunger in Africa

Corn harvests on experimental plots and in farmers’ fields in four East and Southern African countries have yielded striking results in long-term trials of an innovative witchweed-fighting technology developed by a Weizmann Institute scientist in collaboration with researchers at CIMMYT (the Spanish acronym for the International Maize and Wheat Improvement Center). The new technology will be presented to seed producers, government representatives, regional scientists and regulatory agencies at a CIMMYT-sponsored meeting in Kisumu, Kenya on July 4-6, 2002.

The meeting, entitled "A Herbicide-Resistant Maize Method for Striga Control: A Meeting to Explore the Commercial Possibilities," will demonstrate the results of the new technology in the field, present the current status of this herbicide-resistant maize technology, assess its commercial and regulatory aspects and evaluate its future. The meeting is designed to expose interested parties in the public and private sectors to a powerful new weapon that could dramatically alleviate the Striga scourge.

At the UN-sponsored World Food Summit in Rome (June 10-13), UN Secretary General Kofi Annan stated that as many as 24,000 people a day die of starvation around the world. This devastation is substantially concentrated in Africa. A major contributor to the problem is Striga hermonthica, or witchweed, a parasitic weed that ravages grain crops in several parts of the world–particularly in sub-Saharan Africa, where the weed infests approximately 20 to 40 million hectares of farmland cultivated by poor farmers and is responsible for lost yields valued at approximately $1 billion annually. An estimated 100 million farmers lose from 20 to 80 percent of their yields to this parasite. In Kenya alone it severely infests 150,000 hectares of land (76 percent of the farmland in Western Kenya), causing an estimated annual crop loss valued at $38 million.

The weed thrives by attaching itself, hypodermic-like, to the roots of a suitable host crop. It sends up a signal that says "feed me," and not only sucks up the crop’s energy, but also competes for much of its nutrients and water, while poisoning the crop with toxins and stunting its growth.

Until now, other methods to control this parasitic weed have been long-term and often impractical and, hence, have not been widely adopted by farmers. African farmers commonly remove the witchweed by hand, but by the time it emerges above ground, it has already drained the crop and done its damage. Herbicides, applied during that same post-emergence period, are also ineffective for the same reason.

Prof. Jonathan Gressel of the Weizmann Institute’s Department of Plant Sciences proposed an innovative solution to the parasitic weed problem that relies on a new use for a certain type of corn that was developed, using biotechnology, in the U.S. The corn carries a mutant gene that confers resistance to a specific herbicide, leaving the corn plant unharmed when treated with this herbicide. As an alternative to spraying entire fields, Prof. Gressel suggested that herbicide-resistant seeds be coated with the herbicide before planting. Once the crop’s plants sprout from the seeds, the parasites unwittingly devour the weed-killing chemical from the crop roots or surrounding soil and die. By the time the crop ripens, the herbicide, applied in this way at less than 1/10th the normal rate, has disappeared, leaving the food product unaffected.

Dr. Fred Kanampiu, a CIMMYT scientist based in Kenya, has tested this approach for more than ten crop seasons while CIMMYT breeders crossed the gene into African corn to produce high-yielding varieties that are resistant to major African diseases, as well as to the herbicide. Witchweed was virtually eliminated in plots planted with herbicide-coated seeds, as will be shown at the Kisumu meeting. The experiments indicate that a low-dose herbicide seed coating on resistant corn can increase yields up to four-fold in fields highly infested with witchweed. The herbicide is coated on the seed together with the fungicide-insecticide mix that is normally used in Africa to provide healthy plants. With this technology the farmer does not have to purchase spray equipment and can continue interplanting legumes between the corn plants – a common practice among smallholder African farmers.

This research was supported in part by the Canadian International Development Agency (CIDA) through the CIMMYT East Africa Cereals Program and by the Rockefeller Foundation. Initial herbicide-resistant corn seeds for breeding into CIMMYT varieties were provided by Pioneer International, USA.

Prof. Gressel holds the Gilbert de Botton Chair of Plant Sciences at the Weizmann Institute.

The Weizmann Institute of Science in Rehovot, Israel is one of the world’s foremost centers of scientific research and graduate study. Its 2,500 scientists, students, technicians and engineers pursue basic research in the quest for knowledge and to enhance the quality of human life. New ways of fighting disease and hunger, protecting the environment, and harnessing alternative sources of energy are high priorities at Weizmann.

Jeffrey J. Sussman | EurekAlert!
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