Publications /  Annual Report 1997

Virus Cleanup Boosts Chinese Sweetpotato Production

Chinese SweetpotatoChina, the world's largest producer of root and tuber crops, is also the first developing country to benefit on a large scale from technology designed to eliminate virus diseases in sweetpotato planting materials. According to recent reports, Chinese sweetpotato farmers are planting an estimated 330,000 hectares of virus-free sweetpotato annually in Shandong Province alone. The value of this technology over the past four years is estimated at $80 million and growing.

CIP economist Thomas Walker notes that the work is an excellent example of how international research centers can broker technologies from industrialized countries and extend them to the developing world. The virus cleanup techniques being used in China, he says, are based on high technology tissue culture techniques developed in industrialized countries. "CIP's role," he says, "was to identify a technology that could be taken off the shelf, adapt it to developing country needs, and help China's scientists modify it to local conditions."

Impact Through Training

The origin of the project dates back to 1987 when CIP conducted a small training course on virus detection techniques. The next year, Center scientists, in cooperation with colleagues at the Asian Vegetable Research and Development Center, organized a tissue culture training workshop at the Xuzhou Sweetpotato Research Center on China's east coast. According to Dapeng Zhang, who served as a translator and now heads CIP's sweetpotato breeding project, 30 of China's top sweetpotato researchers attended. Its main focus was on developing symptom-free tissue culture plantlets. He attributes the success of the course to the fact that most participants were young scientists eager to apply high technology to the country's agricultural problems. "We also had excellent instructors from CIP," he adds, among them John Dodds and Masa Iwanaga, both of whom now serve as the directors of research at other CGIAR centers.

Following a five-year period of adaptive research by Chinese scientists, closely supported by CIP virologists, large-scale planting of virus-free sweetpotato began in 1994, mostly in Shandong Province. Presently, about 40 percent of Shandong's 700,000-hectare sweetpotato growing area is planted to virus-free materials. If extension targets are met, that figure will rise to 80 percent, covering more than half a million hectares by the end of 1998.

The production of virus-free cuttings begins with meristem tissue cultures that are used to produce virus-free plantlets in heated greenhouses during the winter. The plants are replanted to nethouses in the spring. From there, virus-free seed roots are produced in the autumn to generate vine cuttings, which then serve as a source of planting material for the summer crop. Because two field-multiplications per year are possible, 500 virus-free plantlets are sufficient to produce planting material for 13,000 hectares within two years, a highly impressive field multiplication rate for a root crop.

Impressive Yield Advantages

Yield advantages are equally impressive. In tests conducted at nine sites with five varieties, average productivity gains were about 40 percent, but ranged as high 160 percent. But productivity gains disappear after three or four years. For example, an older Chinese variety, cultivar Xindazi, showed a yield advantage of 350 percent in the first year, 130 percent in the second and third years, but only 14 percent in the fourth year. At that point, farmers need to be resupplied with fresh planting materials.

Walker notes that the program has been implemented without investment in specialized facilities. "You would be hard pressed to come up with better conditions for economic impact than those embodied in the Shandong virus-free propagation program," he says. That includes a limited gestation time for research (the results he notes were achieved largely through training), swift transfer of technology; huge potential for area coverage; and relatively high unit benefits. Added to that are high yields, emerging export demand, and the fact that farmers do not have to change any of their existing practices.

A back-of-the-envelope calculation gives the project a net present value of about $250 million at a 10 percent discount rate. The estimated internal rate of return is 120 percent, with annual net benefits already exceeding $40 million calculated over 30 years.

Assuming the diffusion data reflect reality, one could vary these assumptions by several orders of magnitude and still not affect the results all that much, Walker adds. "In all likelihood, this work has had more economic impact than any other project, perhaps even more than the aggregate of all other CIP projects combined," he says. Walker notes that a formal impact case study will be conducted in 1998 by the CIP economics and virology groups, in association with biologists at the sweetpotato program of the Shandong Crops Research Institute and economists at the Center for Chinese Agricultural Policy.

CIP has worked in China since the establishment of its scientific liaison office in the 1980s. Collaborative research is conducted under a formal agreement with the Chinese Academy of Agricultural Sciences of the Ministry of Agriculture.