Phytophthora infestans –the micro-organism responsible for potato blight, most horrifically with the Irish Potato Famine of 1845, which depleted the population of Ireland by 30%! (A million people quickly died, and over a million migrated to the U.S.A.) There is some interesting science behind the particular virulence of this outbreak. Scientists figured out that P. Infestans originated in Mexico: it thrives in cool damp conditions (like Ireland, especially in the year 1845). The Irish had become dependent on the potato because it supplied a condensed highly nutritious and caloric food, and most of the arable actually went to their absentee British landlords. Unlike warmer and drier South American growing conditions that allowed for the potato to sexually reproduce, giving it genetic variation, the potato in Ireland could only assexually reproduce, and so the potato had no genetic variety. When P. Infestans hit, the entire crop was wiped out because of this.
