CGIAR Scientists Develop New Potato Clones To Counter Late Blight, World’s Worst Agricultural Disease

Released exclusively in Washington, D.C.

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Ismail Serageldin, Chairman of CGIAR and World Bank Vice President for Special Programs, and Wanda Collins, Ph.D., Director of Research, International Potato Center, will be available for interviews in Washington DC on Wednesday, May 20th. Please call 703-820-2244 to schedule time.

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Scientists at the International Potato Center in Lima, Peru have harvested a new set of experimental potatoes expected to be resistant to all existing forms of late blight disease, the same pathogen that precipitated the Irish potato famine of the 1840s. Development of these clones comes at a time when late blight, including new, virulent strains, is cutting global potato production by 15 percent. In the world’s developing countries alone, the disease is causing $2.5 billion in production losses yearly and an additional $750 million in fungicide costs each year.

The International Potato Center (CIP, for its initials in Spanish) is one of the 16 research centers that make up the Consultative Group on International Agricultural Research (CGIAR), which seeks to mobilize the best in agricultural research for food security in developing countries.

CIP’s work in developing late-blight resistant potatoes is so crucial because potatoes are an important food and income source for poor people. If current trends continue, most of the world’s potatoes will be harvested in Asia, Africa, or Latin America over the next generation.

“Late blight, the world’s worst agricultural disease, not only affects food production in these regions, but also rural employment, income, and pesticide usage,” says Ismail Serageldin, Chairman of the CGIAR and World Bank Vice President for Special Programs. “Finding a new potato with lasting resistance to late blight is important for feeding the developing world and protecting the environment.”

These new, more aggressive strains of late blight have attacked potato crops in North and South America, Europe, Asia, and Africa, sparing only Australia. Currently, Sub-Saharan Africa, the world’s most impoverished region, is the area hardest hit by the fungus. It is estimated that, if the disease were controlled effectively through the use of stable resistant varieties, the value of potato production would increase as much as 40-50 percent in many potato producing countries in Sub-Saharan Africa. In other regions, especially Latin America, effective control through resistant varieties would result in significant reductions in the use of pesticides thereby increasing farmer incomes.

The environmental “cost” of the use of fungicides is also of great concern. This “cost” is manifested in poor, developing countries through health risks as a result of exposure and misuse of fungicides. In developed countries, the “cost” is more one of environmental pollution.

Both Canada and the U.S. have also seen lower crop yields because of the disease, which spreads rapidly, mainly by air-borne spores. The disease can also spread through shipment of infected potato tubers.

The International Potato Center

The International Potato Center based in Lima, Peru, has been working on late blight for 20 years. With its partners in national agricultural research programs, CIP has bred resistance to older forms of late blight in many strains of potatoes in commercial production around the world.

In 1990, the potato variety Canchán-INIAA was released to farmers. This variety, which Peru’s national potato program and CIP jointly developed, was highly prized in Peru for its high levels of resistance to late blight. In 1997, the resistance began to break down under a combined attack of humidity from El Niño, the appearance of a new, more aggressive form of Phytophthora infestans and the failure of the previously effective fungicide, metalaxyl, to control it.

One major complication is that the new forms of late blight are increasingly resistant to metalaxyl, especially in North America and Western Europe where potatoes with little native resistance to the disease are grown.

Another problem is that the new late blight strains are so powerful that they have overwhelmed potato varieties bred specifically to be resistant to the fungus, mainly planted in developing countries. The failure of previously resistant varieties and the ineffectiveness of modern fungicides have left developing world farmers with few options.

Although the fungus normally reproduces asexually, the recent migrations of P. infestans could lead to sexual crossing of the two mating types of the fungus, brought together for the first time outside of Mexico. The “old” populations of P. infestans consisted only of the A1 mating type. The “new” migrant populations consist of both the A1 and A2 mating types. Scientists fear that sexual crossing could produce progeny more virulent than the parental strains.

In 1997, CIP researchers confirmed the presence of a new A2 strain of P. infestans living on wild relatives of potato in Ecuador, near where potatoes originated and where they remain a major food for the poor. Based on DNA fingerprinting, this strain is strikingly different from the types hitherto found elsewhere. Scientists say this is a “bizarre strain” that could cross with the P. infestans strains infecting potatoes in Ecuador, which have the A1 mating type. This danger also occurs in Bolivia, according to a team of CIP researchers and scientists from the Bolivian national program. The staple food crop of millions of poor indigenous highland people may be at risk. In addition, the same process could occur in other regions of the world.

“The fresh outbreaks, while unlikely to lead to food shortages, are important because potatoes have rapidly become one of the world’s major food crops, especially in Asia and Africa,” says Mr. Serageldin. “Developing countries grew just 10 percent of the world’s potatoes in the 1960s, but will produce 40 percent by the year 2000. No other major food crop has experienced such a shift in production over this period.”

In 1996, CIP set up the Global Initiative on Late Blight (GILB), a consortium of potato researchers that include its own scientists in Africa, Asia and Latin America, and its partners in national programs, backed by industrialized country institutions. The GILB is also drawing upon the talents and the resources of universities, non-governmental organizations (NGOs), and the private sector.

CIP cooperates closely with another well-known research organization on the potato, the Mexican-based PICTIPAPA. Supported by the PULSAR group of Mexico, PICTIPAPA plays an important role in testing advanced materials and in studies on oospore behavior (sexual spores), and in testing advanced materials for which CIP has been providing advanced breeding lines with durable resistance from its breeding program.

CIP’s late blight team is producing new, blight-resistant potato varieties and developing strategies for integrated management of the disease that are suited to the conditions of poor farmers in developing countries.

“The good news is that the CIP team has now harvested the first commercially viable potatoes that we believe will provide long-lasting resistance to all forms of late blight,” Mr. Serageldin says. “By getting these resistant potatoes to the farmer, together with knowledge about how to manage the disease, we’re in an excellent position to have a dramatic impact on this devastating problem.”

The CIP team used a breeding method known as recurrent selection in developing the new, broadly resistant potatoes. The technique requires scientists to cross dozens of different potato clones, then identify and cross the progeny with the strongest resistance to late blight. The process is repeated several times, with the aim of accumulating as many so called “minor” resistance genes as possible.

“The CIP breeders who produced the new clones watched them grow up sound and healthy during the warm, wet El Niño conditions in 1997 that were so conducive to late blight, while watching potato fields all around the test sites shrivel and die under intense disease pressure,” says Wanda Collins, Ph.D., CIP Director of Research and a leading expert on root and tuber crops. “That is what gives us so much hope for the future of these improved potato varieties.”

In earlier CIP varieties, late blight resistance was carried at least in part by major genes, which, working alone, provided strong resistance to the disease. But naturally arising mutant strains of the fungus could easily overwhelm major disease resistance. The more complex resistance provided by minor genes is expected to be much more difficult for the pathogen to overcome.

Three sets of resistant potatoes are currently being bred at two separate CIP sites in Peru: European-style potatoes for Africa and many other parts of the world; yellow-fleshed Andean-style potatoes for parts of South America; and potatoes derived from crosses between the European and Andean types, intended for tropical countries.

“We are working hard to get these new potatoes to farmers around the world in a rapid-fire way, together with the knowledge that will help them reduce losses and cut down on fungicides,” says Dr. Collins. “By working in innovative ways with farmers and extension organizations, we aim to get the varieties out in five years, rather than the usual 10-20 years. One of these ways will be through farmer field schools.”

Farmer Field Schools

A vital component of CIP’s late blight strategy is farmer-participatory research and training. In 1997, CIP and CARE, the international NGO, launched a pilot field school program in central Peru involving about 100 farm families at four highland locations. The farmers worked directly with project personnel throughout the season conducting experiments to test new varieties and management techniques.

“The farmer field school concept has worked very well, for both farmers and for us,” Dr. Collins says. “The farmers are eager to try the new potatoes, and to learn more about how to manage the disease. For scientists, it is a cost-effective way to collect data on the new varieties, and to learn which management strategies work best in the field.”

Farmer field schools have already been in existence for many years in Asia, mostly focusing on managing insects with fewer pesticides in rice production. CIP plans to work with government extensionists and NGOs in Latin America, the Caribbean and Africa to set up similar schools for managing pests and diseases of potato.

“We foresee the need for thousands of field schools to be run by national programs and NGOs, using information and technology developed by CIP and its global partners,” says Mr. Serageldin. “By fostering collaboration with national research organizations, CIP can remain lean and cost conscious, while continuing to feed the latest technology into the pipeline.”

Late blight affects potato crops in the highlands and the lowlands, in temperate and tropical regions, on industrial farms and in small family farms. Dr. Collins says that the success of the farmer field schools depends on CIP’s understanding of how the disease functions in diverse ecosystems, and under diverse management practices.

CIP social scientists are collecting information about local late blight management from farmers in the Andes, Bangladesh and Uganda. They are combining their findings with data on weather, water and soil, to design computerized disease management strategies tailored to specific agro-ecological environments. At the end of 1997, CIP’s late blight team demonstrated to a meeting of international experts the first use of this technology, which combines the use of geographic information systems, crop modeling, and late blight simulation.

What Late Blight Is

Late blight is the same disease that destroyed Ireland’s potato crop in the 1840s, which led to the starvation and death by disease of one million people, out of Ireland’s then total population of eight million, and the emigration of 1.5 million others, most to the United States. The fungus is thought to have originated in Mexico. A new, “exotic population” — the more aggressive strain of the disease — traveled to Europe during the 1970s, probably in Mexican potato exports.

P. infestans has a complex life cycle that enables it to attack the potato plant in several different ways. The assault usually begins when air-borne spores arrive in a field. These spores land on the foliage, where they may germinate directly, or each may release a set of swimming zoospores. The fungus penetrates the leaf or stem tissue and grows there, forming a black and shriveled lesion. Thousands of new spores are produced, which are carried by wind or rain-splash to start new infections on the same plant, or its neighbors, or on other fields.

Zoospores can wash from the foliage to the potato tubers growing in the soil, causing them to rot in the field or later during storage. Infected seed tubers can be a source of the disease that may start a new cycle of infection in a following season.

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