Potato is the term which applies either to the starchy tuberous crop from the perennial plant Solanum tuberosum of the Solanaceae, or nightshade, family, or to the plant itself. Potato is the world's most widely grown tuber crop, and the fourth largest food crop in terms of fresh produce — after rice, wheat, and maize ('corn').The potato originated in the area of contemporary Peru and Bolivia, identified more specifically in research published by David Spooner in 2005 as an area of southern Peru, just north of Lake Titicaca. Potato was introduced to Europe probably in the 1570s, or approximately eighty years after the first voyage of Columbus in 1492, and subsequently by European mariners to territories and ports throughout the world as European colonization expanded in the seventeenth and eighteenth centuries. Thousands of varieties persist in the Andes, where over 100 varieties might be found in a single valley, and a dozen or more might be maintained by a single agricultural household. Once established in Europe, potato soon became an important food staple and field crop. Lack of genetic diversity, due to the fact that very few varieties were initially introduced, left the crop vulnerable to disease. In 1845, a fungal disease, Phytophthora infestans, also known as late blight, spread rapidly through the poorer communities of western Ireland, resulting in the Great Irish Famine. The potato is also strongly associated with Idaho, Maine, North Dakota, Prince Edward Island, Ireland, Jersey and Russia because of its large role in the agricultural economy and history of these regions. But in recent decades, the greatest expansion of potato has been in Asia, where as of 2007 approximately eighty percent of the world potato crop is grown. Since the dissolution of the Soviet Union, China has become the world's largest potato producer, followed by India.