1. Introduction
Potato belongs to the botanical family Solanaceae, which is the third most important plant family,
marked after the cereals and legumes, with an annual production of over 300 million tons. Its nutritional
value was recognized by western countries, and is now one of the staple foods in Europe and Northern
America. The consumption of potato in developing countries shows an increased trend in recent years.
China now is the largest potato producer in the world, reaching an annual production of 68 million tons.
P.infestans is the cause of potato late blight. The worldwide losses in potato production caused by late
blight have been estimated to cost $3 billion annually[1].