In Kenya, a parasitic plant known as witch weed (Striga hermonthica) can cripple a farmer’s maize crop. A remarkably efficient seed producer, a single witch weed plant can produce thousands of seeds—which in turn suppress the growth of maize the farmer has planted.
WEED WHACKERS Witch weed (top, purple flowers) chokes a maize field. When certain witch-weed-fighting legumes are interspersed (bottom), the maize grows tall. (Zeyaur Khan)
Previously, Zeyaur Khan of the International Center of Insect Physiology & Ecology (ICIPE) in Mbita found that interspersing maize with Desmodium legumes, which are commonly grown for fodder, prevents witch weed from taking hold. Salome M. Guchu, a student at ICIPE in Nairobi, described her team’s efforts to track down how these legumes keep witch weed in check.
The legume exerts its death grip on the parasitic weed by releasing a secondary metabolite (or mix of metabolites) that inhibits witch weed growth. By means of extraction, fractionation, and characterization of natural products from the legumes’ roots, Guchu eventually fingered a class of glycosylated flavones.
One might think the next step would be to use these isolated natural products for weed control. But Baldwyn Torto, a former USDA scientist who recently returned to his home country of Kenya to take a job at ICIPE, has different ideas. Kenyan farmers, he argued, are far more likely to plant a crop that blocks weed growth than to buy and use chemicals that inhibit witch weed growth. To that end, ICIPE scientists, in collaboration with Rothamsted Research, in the U.K., are now working to screen related legume species for those that boast the highest concentration of the most active glycosylated flavones.