5.1.9S
POTATO BLIGHT: A WORLD PROBLEM

GA FORBES1, RJ HIJMANS2 and RJ NELSON2

1International Potato Center, PO 17-21-1977, Quito, Ecuador; 2International Potato Center, PO 1558, Lima 12, Peru

Background and objectives
Historically, late blight of potato, caused by Phytophthora infestans, has been one of the most widely studied plant diseases. Since the Irish potato famine, the importance of potato blight in both Europe and North America has been described repeatedly in the phytopathological literature [1]. Disease management strategies, including sophisticated forecasting models, have been developed for most industrialized countries [2]. In contrast, there has been much less scientific investigation of the importance and management of this disease in developing countries. Nonetheless, the information that does exist would suggest that the epidemiological and socio-economic factors may require disease management strategies which are different from those currently used in industrialized countries. The objective of this study is to compare potato blight in different parts of the world, with special emphasis on its role in developing countries. We make regional comparisons of pathogen biology, epidemiology, disease intensity and disease management.

Materials and methods
The information presented here was extracted from the literature, or generated by use of disease simulation and plant-growth models within a geographic information system (GIS) framework. This approach permitted us to explore the impact of different agro-ecological factors on the epidemiology of the disease, and as a result, on the appropriateness of different disease management strategies. This review also draws on a workshop held in late 1997 at the International Potato Center in Lima, Peru, on the role of agro-ecological factors in the development of potato blight management strategies.

Results
Populations of P. infestans are complex in North America and Europe, where a high degree of sexual recombination was found in several regions. In contrast, pathogen populations in many developing countries comprise one, two or a few clonal lineages. In North America and Europe, some genotypes are found on both tomato and potato, whereas genotypes in most developing countries appear to be highly host-specific. In humid tropical highland environments, potato production and potato blight are continuous all year round. In these areas, potatoes are an important source of nutrition and blight frequently constitutes a threat to food security. Record numbers of fungicide sprays have been registered for these regions, because plants must be protected from emergence until harvest. With wind-borne inoculum present all year round, sanitation, the basis of most conventional blight management strategies, probably will not work. Management strategies which reduce the rate of disease spread (e.g. host resistance) should be most effective. Tuber blight also appears to be dependent on agro-ecosystem, because it is a major problem of industrialized countries but of little or no importance in the northern Andes. GIS can assist researchers in determining which management strategies are appropriate for different agroecosystems.

References
1. Robertson NF, 1991. In lngram DS, Williams PH, eds, Advances in Plant Pathology: Phytophthora infestans, the Cause of Late Blight of Potato. Academic Press, London, pp. 1-30.
2. Fry WE, Doster MA, 1991. In Lucas JA, Shattock RC, Shaw DS, Cooke LR, eds, Phytophthora. Cambridge University Press, Cambridge, UK, pp. 326-336.