Legumes and Striga suicide

IITA, inew

Morals aren't at the root of what these legumes do, but their promiscuity and knack for prompting suicide of weeds are of great help to African farmers. 

Legumes make the soil more fertile, and many cause the seeds of a noxious weed to germinate without the means to survive. IITA scientists are improving and promoting the virtues of legumes so African farmers will grow more of this high-protein, low-cost food. 

The soybean takes nitrogen from air in the soil and fixes it in nodules on its roots. To form these nodules, soybean roots need mutually beneficial associations with bacteria. Most soybean species only make these relationships with specific strains of bacteria, but some, called promiscuous soybeans, form nodules with a wide range of bacteria strains, making them much more efficient at enhancing soil fertility. 

Striga hermonthica attaches itself to the roots of a maize plant and holds back its growth.Suicidal germination controls Striga hermonthica, a flowering parasitic weed that attacks the roots of cereals and often destroys crops completely, forcing farmers to abandon fields. To germinate, these Striga seeds need to be stimulated by chemicals from the roots of crops. A young Striga seedling has five days to attach itself to a host root and start drawing nutrients and water. If it doesn't, it dies. Scientists from IITA and other organizations discovered crops such as soybean, cowpea, and groundnut will stimulate germination but will not host Striga hermonthica. So if a seed germinates, it commits suicide. 

As part of a project funded by the UK's Department for International Development, IITA scientists are encouraging farmers in northern Nigeria to plant legumes and cereals in rotation to lower the amount of Striga hermonthica seeds in the soil and to improve soil fertility. IITA scientists developed promiscuous soybeans and introduced them in Nigeria, where soybean production has tripled over the past 10 years. IITA's soybean breeders are even developing promiscuous soybeans with enhanced ability to cause suicidal germination of Striga hermonthica seeds. 

The population of Africa is expanding, and farmers are using the land more intensely to meet demand for food. They can't let fields lie fallow to build up nutrients and to keep weed infestations manageable, and they can't afford chemical fertilizers and pesticides. Promiscuous soybeans and suicidal germination are two practical ways for farmers to keep the land productive and to nourish families.


June 2003