While armed thugs in Somalia hijack planeloads of relief food, asmaller, but more sinister, sneak thief is robbing much ofsubtropical Africa of half its population's principal home-grownfood crop.

This is the sweet potato (Ipomoea batatas), a nutritious, easy-to-grow tuber, which the continent's peasants cultivate to feedtheir families. The sweet potato is the fifth most important cropin the developing world, where it is sown on some 25 millionacres, mostly family plots. But each year, more than 50 percentof the harvest falls prey to a single-stranded RNA Potyvirus,the sweet potato feathery mottle virus (SPFMV).

On Feb. 14 in Boston, Florence Wambugu, a plant pathologistfrom Kenya, and Robert B. Horsch, a molecular plant biologistfrom Monsanto Corp., told an audience at the 93rd annualmeeting of the American Association for the Advancement ofScience (AAAS) how they are making African sweet potatoesresistant to the SPFMV.

Wambugu, who received her doctorate in virology from theUniversity of Bath, England, is in the second year of a three-year stint at Monsanto's Life Sciences Research Center in St.Louis. She is working there with Horsch and his team atgenetically engineering Ipomoea batatas to resist Potyvirusattack .

"I grew up in a poor family in Kenya, and watched my motherwork very hard to grow enough food to feed her children,"Wambugu told her AAAS audience. "I believe if I am successfulin improving this plant, I can make a big difference towardhelping my people better feed themselves."

Horsch declared that placing a scientist from a developingcountry in a private-sector laboratory to learn how togenetically improve crops "is a first of its kind for Monsanto,but it won't be the last." His company, he added, will not collectroyalties from Kenya for its proprietary sweet potato viralresistance technology.

The project is also a first for the U.S. Agency for InternationalDevelopment's new six-year, $6 million program called"Agricultural Biotechnology for Sustainable Productivity." Thiseffort made its initial three-year joint-development grant toco-fund the Monsanto/Kenya proposal.

At the end of 1994, Wambugu plans to take her virus-resistanttransgenic tuber cultivars and technology back to Nairobi.There, she will work with the Kenyan Agricultural ResearchInstitute to secure regulatory approval, and then distribute theimproved plants throughout Africa via farm extension services.

The anti-viral gene, transfected into a single totipotent sweetpotato leaf cell, encodes SPFMV's entire virion envelopeprotein, and was cloned by plant pathologist James W. Moyer atNorth Carolina State University, Raleigh. Its transformingconstruct was then developed for Monsanto by Roger N. Beachywhile he was at adjacent Washington University in St. Louis. Heis now head of plant biology at Scripps Research Institute in LaJolla, Calif.

"The gene represents about 10 percent of the viral genome,"Beachy told BioWorld. He added, "They will be able toregenerate an entire resistant plant from a single leaf cell."Beachy noted that "Florence Wambugu is an outstanding expertin sweet potato tissue culture."

At Monsanto, she and Horsch are transfecting the viralconstruct via a Ti plasmid of the workhorse plant expressionvector, Agrobacterium tumefaciens. Transferring the viral geneinto the plant has been shown to block infection and reduce thepathogen's replication and spread.

"Biotechnology promises lower input costs for Third Worldfarmers and higher yields, with lower pesticide exposure,"Horsch said at the AAAS session. "It doesn't require specialmachines or additional know-how because the technology willbe contained in the seed."

-- David N. Leff Science Editor

(c) 1997 American Health Consultants. All rights reserved.