US Scientists Help Africans Breed Disease-Resistant Plant

In its native region of western and central Africa, the black-eyed pea — known by the name “niebe” in Francophone countries and as “cowpea” in the English-speaking regions — is a primary protein source for millions of people. About 80 percent of the world's cowpea crop is grown there, mostly by subsistence farmers. The entire plant is used — the pea for soups, stews and breads, the leaves as fresh greens, the stems as hay and fodder for cattle.

Unfortunately, as the cowpea plant evolved over time, so did a parasitic plant that starves the cowpea plant to death by sucking nutrients from its roots. This parasitic plant, Striga gesnerioides, or  “witchweed,” is so virulent that farmers must relocate their cowpea crop to new soil every few years. But because Striga’s seeds are as fine as dust, farmers inadvertently carry the witchweed seeds wherever they plant their cowpeas. It's a major problem in a dry region where farmers lack money for herbicides and fertilizers and must continually rotate their crops back to tired dry soil already infested with Striga seeds.

Michael Timko, a U.Va. Professor of Biology, is working hard to solve ”the Striga problem,” as it's called in west Africa. He and other scientists have sequenced the cowpea genome and are using this information to help develop Striga-resistant cowpea plants.

“It is now possible for us to identify all possible genes for Striga resistance in cowpeas, as well as resistance to other cowpea pathogens,” Timko said. “We may even eventually breed a more drought-resistant plant and varieties that have higher levels and a better balance of nutrients. We've reached a point where we can manipulate this plant for the good of millions of people.”

Because of various political, social and ethical issues associated with introducing genetically modified crops in Africa, the use of transgenics is not an option at the present time. Therefore, Timko’s approach is to improve the performance of plants by identifying genes that control key characteristics, and then use this knowledge in selective breeding programs that emphasize those traits using associated genetic markers. The resulting product is the delivery of improved parasite-resistant hybrids to the farmer in shorter amounts of time.

Timko is working with African breeders and growers and training African scientists in his lab at U.Va. in the use of modern molecular breeding techniques. In recent years he has brought more than 20 African graduate students and postdoctoral fellows to study in his lab, most of them staying for three months to a year. Some of them are now department chairs and directors of major labs in Africa.

“We've created a great international environment,” Timko said. “Right now there are two students from Ghana and one from Zimbabwe working in the lab.”

Timko is also seeking funding to send U.Va. undergraduate and graduate students to west Africa to learn firsthand about African agricultural practices. “The Africans are coming here to learn, but our students should also be going there,” he said. Timko makes regular trips himself, visiting six times last year to build on his already strong relationships.

While Timko’s research is successful, it is complicated work that will take years to measure out. One challenge is that there are at least seven different races of Striga, each capable of adapting to changing varieties of cowpeas.

“We are trying to create a plant that is resistant across the board,” Timko said. ”But the parasite responds over time to whatever we do. Striga is hyper-virulent. This is warfare between the cowpea plant and its parasite, and we keep trying to stay ahead of the enemy.”

For centuries, farmers have been modifying and improving their crops through selective breeding, a trial-and-error approach. “We simply speed up and improve the breeding process by using modern molecular-based technologies,” Timko said. “It’s a logical progression of the hybridization process. It's satisfying work, knowing that we are able to take research from our lab to the field that can directly improve people’s lives and well-being.”