Indeed, Ireland’s was surely the biggest experiment in monoculture ever attempted and surely the most convincing proof of its folly. Not only did the agriculture and diet of the Irish come to depend utterly on the potato, but they depended almost completely on one kind of potato: the Lumper. Potatoes, like apples, are clones, which means that every Lumper was genetically identical to every other Lumper, all of them descended from a single plant that just happened to have no resistance to Phytophthora infestans. The Incas too built a civilization atop the potato, but they cultivated such a polyculture of potatoes that no one fungus could ever have toppled it. In fact, it was to South America that, in the aftermath of the famine, breeders went to look for potatoes that could resist the blight. And there, in a potato called the Garnet Chile, they found it.
from Michael Pollan “The Botany of Desire”