by Peter Gregory

The 10-year, $25.5 million Global Initiative on Late Blight (GILB) to develop potato cultivars with durable resistance to all forms of the disease was launched this year followed urgent calls for action by farmers and the global research community. Their concern: the appearance of new forms of the fungus that within the past five years have spread to many of the world's major potato producing regions.

The disease, which was responsible for the Irish potato famine in the 1840s, causes estimated annual crop losses of nearly 14 million tons annually, equivalent to nearly $3 billion. Spread by infected potatoes and aloft by strong winds, the disease can destroy a healthy potato field in just a matter of days.

CIP Director General Hubert Zandstra says late blight has reached epidemic proportions in many areas. He notes that the disease is poised to strike hardest at millions of poor people in developing countries who rely on potatoes, but can least afford to buy expensive chemicals to keep the fungus in check.

"The late blight threat questions the ability of the potato crop to continue its unprecedented growth," Zandstra says, "especially in developing countries where production has soared by nearly 200 percent in the past 30 years and is expected to rise about another 3 percent a year by the turn of the century." CIP and FAO economists predict that developing countries will produce more than a third of the world's potato crop by the year 2000.

Origins of the Disease

Late blight, also known as Phytophthora infestans, began as a local disease of wild relatives of potato and tomato in Mexico's Toluca Valley. In the early 1950s, John Niederhauser, a World Food Prize laureate and a founding member of the CIP Board of Trustees, pinpointed the valley as the location now widely accepted as late blight's center of genetic diversity. There he discovered two mating types, called A1 and A2.

The A2 form of the fungus is believed to have spread from Mexico to Europe in the late 1970s. Many experts believe that it was then re-exported unintentionally through the sale of infected potatoes. This form of the disease can be more damaging and powerful than the A1 type, which escaped from Mexico in the 19th century and was responsible for the Irish famine of the 1840s. Both strains reproduce asexually, but when they occur in the same location, they combine sexually.

CIP scientists say losses from newer strains of late blight are likely to rise. Hard-hulled Oospores produced by sexual recombination of different late blight mating types are genetically more diverse than older strains of the disease. Their ability to survive in the soil over longer periods poses new threats to developing-country potato farmers. The A2 is known to be present on all continents except Australia and Antarctica.

GILB

The GILB initiative will draw on worldwide public and private research sources in its efforts to develop higher levels of durable host plant resistance and to use resistant varieties in integrated pest management programs. A meeting at CIP's headquarters in the Lima suburbs last March established project priorities and developed work plans.

During the first three-year phase of the project, 1998-2000, researchers expect to expand the genetic base for durable resistance of cultivated potatoes through the transfer of resistance genes from wild species, primitive cultivars, and to a limited extent from other organisms. This work is expected to both broaden and strengthen late blight resistance. Rapid progress is expected as CIP and national program scientists have already overcome most incompatibility barriers between wild species and cultivated potatoes. GILB research will also focus on efforts to promote the use of integrated pest management practices, including simple, but practical field sanitation practices that are frequently ignored by farmers who once relied solely on fungicides to control the disease.

From 2001 through 2003, the initiative will advance the transfer of broader-based durable resistance to locally adapted potato varieties and advanced breeding lines. During the project's final phase, years 2004-2007, emphasis will be directed to promoting widespread use of new late blight resistant varieties--an effort that will help farmers to control late blight through integrated pest management systems in which resistant varieties, rather than chemical fungicides, play the key role.

Projected Impact

CIP believes that there is a high chance of payoff from such investment because past CGIAR investments in late blight research have been highly profitable. Rates of return from CIP's collaborative research with East African NARS conducted over the past 15 years, for instance, have been estimated at 91 percent annually. Net benefits to the African farmers totaled $10 million in 1993 and more than $60 million over the past decade. Most of this impact was due to investment of only $5.6 million in the deployment of late blight resistant varieties and improved availability of planting materials.

But in the face of the new disease problems, similar progress in the future will not be possible without additional resources. For this reason, CIP has already increased its commitment to late blight research from $1.2 million per year to $1.5 million. To expedite the launching of this global project, CIP plans to reallocate an additional $500,000 in 1997 from its existing resources. These funds will be used to stimulate full-scale planning, improve communications, and expedite a small number of priority research projects. Assuming that additional funding needed to finance the project will become available, the Center predicts that payoffs in developing countries could eventually exceed $3 billion per year.

Expansion of Potato Production

Ironically, the new late blight threat comes at a time when developing country potato production is expanding. According to a recent FAO-CIP publication, annual potato production in developing countries grew from 30 million tons in the early 1960's to 85 million tons in 1993. Output is expected to rise further by nearly 3 percent per year for the foreseeable future. By 2000, economists predict that developing countries will produce more than a third of the world's potato crop.