REHOVOT, Israel -- April 17, 1996 -- Corn yields on experimental plots in Kenya have tripled thanks to an innovative weed-fighting strategy developed by a Weizmann Institute scientist in collaboration with Kenyan researchers.
These results will be reported on April 17 at the Sixth Parasitic Weed Symposium in Cordoba, Spain.
The experiments focused on eradicating a parasitic weed called Striga hermonthica, or witchweed, which ravages grain crops in several parts of the world, particularly sub-Saharan Africa. An estimated 100 million farmers lose half their yields to this parasite. In Kenya alone it severely infests 80,000 hectares (200,000 acres) planted with corn, causing an estimated annual loss of $10 million. Weeds also have an indirect but devastating effect on the environment because farmers often encroach upon nature reserves in search of uninfested land.
Witchweed thrives by attaching itself to the root of a suitable host crop. It sends up a signal that says "feed me," and sucks up not only the crop's energy but much of the soil's fertilizer and water.
Until now, there has been no effective way to control parasitic weeds. Farmers in Africa commonly remove them by hand, but by the time the weeds emerge above-ground, they have already drained the crop. Herbicides are ineffective for the same reason, and they also enter the food chain.
Prof. Jonathan Gressel of the Weizmann Institute's Department of Plant Genetics proposed an innovative solution to the parasitic weed problem, which relies on a new use for a certain type of corn that has been biotechnologically developed in the United States. This corn has a gene conferring resistance to a herbicide and is therefore unharmed when sprayed by this herbicide.
Rather than spraying entire fields, Prof. Gressel has suggested taking seeds that are resistant to a particular herbicide and soaking them in it 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 crops ripen, the herbicide has disappeared and does not affect the food supply.
Scientists George Odhiambo and Gordon Abayo from the Kenyan Agricultural Research Institute in Kisumu, in conjunction with Joel Ransom of CIMMYT (the Spainsh acronym for The International Maize and Wheat Improvement Center) in Nairobi, have tested this approach for five crop seasons.
Witchweed infestation was dramatically reduced in experimental plots planted with herbicide-soaked seeds, they will report at the Cordoba conference. As a result, crop yields were more than three times higher compared with yields from witchweedinfested plots planted with untreated seeds.
This research was supported in part by the Canadian International Development Agency (CIDA) through the CIMMYT East Africa Cereals Program. Seeds 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 is a major center of scientific research and graduate study located in Rehovot, Israel.