Late blight of potato, which is caused by Phytophthora infestans (Mont) de Bary is the major bottleneck in
potato production in Ethiopia (Bekele and Yaynu 1996) and other parts of the world (Fry and Goodwin 1997b).
It is the best known, highly studied and still the most destructive of all potato disease (Jones 1998). Late blight
is probably the single most important disease of potatoes and tomatoes worldwide (Son et al. 2008). Worldwide
losses due to late blight are estimated to exceed $5 billion annually and thus the pathogen is regarded as a
threat to global food security (Latijnhouwers et al. 2004). Late blight was responsible for the Irish potato
famine in the 1840s (Mercure 1998). The disease caused yield losses ranging from 31-100% in Ethiopia
depending on the variety used (HARC 2007). Cultural control measures such as eliminating cull piles and
volunteer potatoes, using proper harvesting and storage practices, can be used to reduce the pathogen populations
by reducing its survival, dispersal and reproduction (Garrett and Dendy 2001). Use of fungicides like metalaxyl
in controlling the disease was found to boost potato yield in various East African countries (Nsemwa et al. 1992;
Rees et al. 1992). Potato late blight management strategies have changed considerably following the migration
of metalaxyl resistant isolates of P. infestans from Mexico to North America (Fry and Goodwin 1997b) and
necessitated utilization of cultural control measures and modification of the previous chemical control practices.
Potato late blight is probably the most studied plant disease in the world; yet relatively fewer alternative
management options other than synthetic chemical fungicides are available. At a global level, the major
approach to prevent late blight development has been through application of fungicides (CIP 1989). But highly
aggressive strains of this disease many insensitive to popular synthetic fungicides, have surfaced and created
new challenges for potato and tomato producers (Powelson and Ingils 1998).