Millions of poor people in developing countries who depend on potatoes for their food and livelihoods live in dread of a plant disease called late blight. When weather conditions are highly favorable to the pathogen, this disease can wipe out a potato crop in a mere few weeks. Potato late blight can also put millions of poor farm families at great risk by exposing them to the harmful effects of pesticides.

Losses to late blight in developing countries have reached a staggering $3.25 billion each year, $750 million of which is spent on pesticides alone. The greatest concern is that fear of the disease is preventing those most in need of the food and income that potatoes can provide from taking the risk of planting this important crop, despite its tremendous potential.

KNOWING THE PATHOGEN. Like any infectious disease, late blight is the product of a complex relationship between a pathogen (in this case Phytophthora infestans) and a host (the potato plant). CIP pathologists, in close collaboration with scientists in national programs, are working to track the ongoing movement and change in pathogen populations in key locations throughout the developing world. Scientists use DNA fingerprinting techniques and other state-of-the-art methods to detect variation among pathogen strains. These teams intend to keep one step ahead of this virulent disease by increasing their understanding of how pathogen populations evolve, and by being prepared to assist poor farmers to adapt to the changes brought on by late blight.

Pathogen studies also provide important tools for improving resistance. By studying the diversity of the late blight pathogen, pathologists and breeders are able to select strains for use both in analyzing resistance and breeding potato varieties with stronger and more long-lasting resistance. Resistance can only be detected through the plant’s exposure to the pathogen, and the choice of pathogen strain determines what aspect of resistance can be detected in an inoculation test.

BREEDING FOR LATE BLIGHT RESISTANCE. CIP potato breeders and their research partners are able to incorporate partial blight resistance genes from wild and cultivated potatoes into new breeding populations and, eventually, into new varieties. The technique most often used is called recurrent selection, a process through which scientists cross dozens of different potatoes and then identify and cross the progeny showing the strongest resistance to late blight. This process is repeated many times so that as many minor resistance genes as possible can be accumulated.

The culmination of this meticulous research is to make the most promising blight-resistant materials available to users through a multi-location testing scheme involving collaborators in South America, East Africa, Central America, and Southern China.

MANAGEMENT TECHNOLOGIES AND TOOLS. Improved computer simulation of the disease is provid-ing a better understanding of late blight epidemiology across diverse environments, and allows more rapid evaluation of disease management strategies. This important component of CIP’s arsenal against late blight is aimed at developing and testing simple decision-support systems that will help farmers make better decisions about fungicide treatments and other management tactics.

Likewise, a suite of computer programs, including a geographic information system (GIS)-linked forecaster, uses global weather data to assess the relative importance of late blight in different parts of the world. Scientists can then map the severity level of the disease at national, regional, or global levels. The effects of changes such as the deployment of resistant varieties or variations in global weather patterns can then be more reliably predicted.

PARTICIPATORY TRAINING FOR FARMERS. CIP scientists are also developing strategies, methods, and training materials for participatory research and farmer training aimed at developing integrated disease management components adapted to various regions where late blight is a major constraint. The first crucial step in this process is to analyze farmers’ knowledge, attitudes, practices, and perceptions of problems and options, all of which can vary greatly from one location to another.

Peruvian farmers search for late blight symptoms in a participatory trial during a farmer field school.

In order to cope with late blight effectively, farmers need access not only to suitable disease-resistant potatoes, but also to the knowledge of how best to complement the available resistance through management techniques. To address these needs, CIP and its partners have adopted the farmer field school (FFS) approach in several countries. In a short time, the FFS program has made a significant impact. It is estimated that as a result of knowledge gained through FFS, farmers could increase their income by US$235 per hectare. When they also use a resistant variety they could have an additional US$350 per hectare, making a total of US$585 per hectare of additional income. By serving as a platform for both participatory research and farmer training, the FFS program has successfully combined two essential elements of CIP’s overall research agenda.

IMPACT. CIP’s late blight project provides farmers with effective ways to combat and manage the risks associated with the disease. Researchers see successful disease management as the poor farmers’ key to increasing productivity, reducing production costs, and mitigating negative impacts on their health and environment.

By encouraging the use of resistant potato varieties and improved farmer decision making, the project aims to minimize production risk and decrease losses resulting from late blight.

CIP economists anticipate that the impact of the late blight project will be felt directly in at least 23 developing countries throughout Africa, Asia, and Latin America. With average benefits per hectare estimated at $585, they estimate the total potential impact worldwide could reach $1.5 billion per year.

For more information, please contact Greg Forbes, Global Iniative on Late Blight Coordinator, Apartado 1558, Lima 12, Peru, or at g.forbes@cgiar.org.