Tuber

A tuber is a swollen, underground storage organ that develops on the roots of certain species of plants. Some types of tubers are highly nutritious, mostly because of their energy content in the form of starch.

Agricultural species of plants that develop edible tubers include the white potato (Solanum tuberosum), sweet potato (Ipomoea batatas), tapioca or cassava (Manihot esculenta), and yam (Dioscorea batatas).

The white potato is the most important and best-known of the agricultural tubers. The potato is a native of the Andean plateau of South America. In this species, tubers develop at the end of roots that emerge from underground stems, known as stolons. Potato tubers have stem buds known as "eyes" which can sprout and grow new, aboveground stems. It appears that potatoes have been cultivated by indigenous peoples of the Andean plateau for at least 6,500 years.

The varieties of potatoes that are most commonly cultivated in modern, industrial agriculture typically develop rather large tubers with white centers. However, there is a great diversity of other varieties of potatoes, especially in their native Andean range. These varieties commonly form relatively small tubers with brown, red, yellow, or purple skin, and white or darker-colored interiors.

Potato tubers are very nutritious, especially as a source of starch. However, they also contain about 2% protein and valuable minerals and vitamins, especially vitamins B and C. Interestingly, potato foliage is poisonous because of its content of a toxic alkaloid known as solanin. This chemical also occurs in green sprouts of the eyes of the tubers, which is why these should be excised and not eaten.

The potato was first discovered by Europeans in the mid-1530s when Spanish conquistadors observed its cultivation in Peru. The potato subsequently became a commonly cultivated food in Europe, initially as a food for livestock. Around the beginning of the seventeenth century, people also began to commonly eat the potato. Its high productivity and favorable nutritional qualities are believed to have been important in allowing population growth in Europe during the next several centuries. However, at the beginning of the nineteenth century a new disease of potatoes occurred. The potato blight, caused by the fungus Phytophthora infestans, became a recurrent disaster, and widespread famine resulted. In some regions such as Ireland, poor people ate little else but potatoes, and the blight caused mass starvation which to some degree was alleviated by massive immigration to North America. The potato blight is still an important disease. However, this disease is now controlled by growing resistant varieties of potatoes by managing the environment to make it less favorable to the fungus and by the use of fungicides.