In 1845, a disease known as late blight of potato caused by an oomycete (Phytophthora infestans) was responsible for a famine in Ireland.  At that time the cause of any disease of plants or animals ahd not been established. The Reverend Miles Joseph Berkeley, priest of the Church of England and mycologist, argured that the fungus-like organism growing in the plant tissue was the agent of the disease. The novel explanation was not to be widely accepted for several decades. Two prominant English scientists, John Lindley and Lyon Playfair, were brought in to try to solve the mystery of the potato disease, which they attributed to a reaction of the potatos brought on by unseasonably cool weather. Where did the oomycete originate? One broadly held view is the the organism came from Mexico, because both mating strains of the organism occur there. One discounted idea was that guano imported from the Americas used to increase crop yeilds was the source of infection.  The unusually cool and rainey summer helped the oomycete to spread like wildfire.  The Irish, who relied on the potato as their main source of food were stuck with black, smelly, rotten potatoes with withered leaves. During this outbreak one million people were killed by the potato blight fungus, either by starvation directly or by disease aflicting those in the process of starving to death. Not until 1882 was there a cure for the disease, Bordeaux Mixture, a solution of copper sulfate and lime, accidently developed for treatment of a disease of grapes caused by a related organism. Since 1845, Phytophthora infestans has spread from Ireland throughout Europe and to North America. Most recently, there has been spread of the second mating strain, and the widespread opportuinity for sexual reproduction likely will result in recombination and the lost of resistance developed by years of plant breeding. --K. E. Rutherford