New Witchweed-Fighting Method, Developed by CIMMYT and a Weizmann Institute Scientist, To Become Public in July

 

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 20–40 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% of their yields to this parasite. In Kenya alone it severely infests 150,000 hectares of land (76% 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 United States. 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 a crop ripens, the herbicide, applied in this way at less than 1/10^th 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.