Wild potatoes are thought to have originated somewhere around Mexico. They are now found growing from as far south as southern Chile, all up the western edge of South America, throughout Central America, and into southwestern North America. Around 200 wild species of potato have been identified.These different species survive in a wide variety of habitats: 4500 m above sea level on the freezing slopes of the Andean Mountains; in hot, dry, semi-deserts near the Peruvian coast; and in warm and humid subtropical rainforests found to the west of the Andes. One North American species even lives on the mossy branches of oak trees.
Wild potatoes also differ from each other in appearance and taste. They grow in a variety of shapes and colours and the tubers of some species taste extremely bitter. This bitter taste is due to the presence of poisonous alkaloids, chemical compounds that are found in many members of the potato or nightshade family (Solanaceae). The diversity of wild potato plants is a valuable resource for modern potato breeders, who may be able to breed useful traits found in wild potato species, such as the ability to resist disease, into the potato plants we grow as crops.
Domestication of the Potato
Domestication describes the changes that occur to species as a result of their deliberate cultivation by humans. The first humans to use potatoes would have collected them from the wild. The domestication of the potato began when humans stopped foraging for potatoes and started to grow them instead. The potatoes we eat today are descendants of the first potatoes to be grown for human use. Evidence suggests that it was in the Andes, on the borders of lake Titicaca, that humans first started to cultivate potatoes. The great importance of the potato plant to humans in this region is due in part to its ability to grow in the severe weather found at high altitudes. Potato remains have been found preserved underground in Peru that suggest potato cultivation started over 7000 years before present, nearly 2,000 years before the birth of Ancient Egypt. Potato cultivation has formed the basis of many civilisations in this region since then and is still important today.
The Andean peoples have an ancient method of preserving potatoes for up to several years: First they lay the potatoes out on the ground overnight to freeze them. Then, in the morning, they trample the potatoes with their feet and leave them exposed to the intense warmth of the sun. This process (repeated three times) is a primitive method of freeze-drying that drives the moisture out of the potatoes, enabling them to be kept longer before rotting. Potatoes that have been treated in this way are known as chuño. Modern freeze-drying methods are used today to preserve food for camping trips or even for space travel.
Spread of the Potato
From its origin in the highlands of Southern Peru the domesticated potato has been transported all around the world. The first diffusion of the domesticated potato was within the Americas. It started (possibly thousands of years ago) when early farmers from the highlands of southern Peru took their crop plants both farther north into Central America and south to southern Chile. The next major spread of the potato came as a result of the Spanish invasion of South America in the 1500s. An early account of the potato (published in 1551) by the Spanish explorer Cieza de Leon describes it as "… a kind of earth nut, which after it has been boiled, is as tender as a cooked chestnut, but it has no more skin than a truffle, and it grows under the earth in the same way."
Evidence from early herbarium (plant library) specimens indicates that the first potatoes introduced to Europe came from the northern highlands of South America, around Peru and Colombia. These areas were part of the Incan Empire, which was conquered by the Spanish in 1532. It therefore seems likely that it was the Spanish who first exported the potato from South America. However, it appears that rather than being introduced directly to mainland Europe, potatoes were first cultivated in the Canary Islands. From there they were then shipped to European countries including Belgium and France. The first known record of a potato on mainland Europe is found in the accounts of a Spanish hospital in 1573.
The cultivated potato was introduced to Bermuda by the British in 1613, from whence it was introduced into North America in 1621. The British were then responsible for spreading the potato to India and China in the late 1600s. Also in the late 1600s, potatoes appeared in Africa and Japan. They were introduced to New Zealand in 1769, being swiftly adopted by the Maoris who were already cultivating (unrelated) sweet potatoes.
Use of the Potato
The potato has been a vital food crop for Andean civilisations for hundreds (possibly thousands) of years. The arrival of the Spanish in the 1500s heralded the introduction of the potato to Europe. However, although the potato had been introduced to most of Europe by 1600, it didn't become part of the European diet until much later. At first, it was mainly grown by botanists as a curiosity or by physicians who used it in medicines. Ireland was the first place in Europe where the adoption of the potato was widespread. The potato was introduced to Ireland sometime before 1600 and it flourished in the Irish climate. It is possible that the famous explorer Sir Walter Raleigh personally supplied the first potatoes to Ireland. Potatoes were of great benefit to the poor, who had to support themselves on very small plots of land, as yields were high. The ease of growing, harvesting, and preparing potatoes also contributed to their rapid success. By 1650, potatoes had become the main crop in Ireland. Unfortunately this dependence on the potato, and the population explosion that followed its introduction, would lead to widespread famine when the crop failed due to disease.
In the colder areas of Europe, the delay in adoption of the potato could be attributed to climate. The potato plant, which had come to Europe from Peru, was adapted to the short days of summer near the equator and didn't produce potatoes in Northern Europe until the shorter days of autumn. In colder regions this was too late for successful potato growth. As a result, potatoes didn't become successful in the northern and colder areas of Europe until plants had been bred that would produce tubers earlier in the year. Even in the warmer climates farther to the south and west the adoption of the potato was slow. This was probably due to the resistance of rural communities to change. To plant a new crop was to risk food shortages in the event of failure. There were also rumours that the potato caused flatulence and diseases such as leprosy and scrofula (tuberculosis of the neck).
The adoption of the potato as a food crop throughout Europe really occurred during the 1700s. Europe was racked by conflict during this period and many politicians encouraged their citizens to grow potatoes as a way of preventing famine. Not only did potatoes often produce better yields than other crops but, because it was growing underground, the crop was less vulnerable to damage by hostile troops. Today, the potato is used in hundreds of ways all over the world, but perhaps the most famous is the humble chip (or, to Americans, French Fry). The invention of the potato chip is claimed by both the Belgians and the French.
How the Potato has Changed
Ever since humans first began to grow potatoes, we have been picking the 'best' potato plants (with the biggest or tastiest potatoes, for example) to grow for our use. Just by doing this we began to change potato plants to suit our needs. The potato has changed a lot since it was first domesticated, but these changes have not always been in the same direction. Over time, different features have been considered important to potato growers. The earliest potato cultivation seems to have occurred in the upland valleys and plains of Bolivia. At these altitudes, the ability of the potatoes to survive frosts would have been of major importance to farmers. As a result, after the initial domestication of the potato one of the first varieties to develop had a high frost resistance. Subsequently, as potato cultivation began to spread into other areas, different qualities became important. In lowland areas there was less need to select hardy potato plants and farmers could concentrate on yield and eating quality. As the potato spread southward from Peru, it began to change in other ways. The days in northern South America are always around 12 hours in length as these areas are close to the equator. Summer days in southern Chile are much longer and potato plants from farther north will not start to produce potatoes until autumn, when day length drops to around 12 hours. Over time, potato plants in Chile were bred so that they would produce potatoes much earlier in the year. Potatoes brought to Europe from northern South America went through the same change because Europe also has summer day lengths longer than 12 hours. By breeding and selection from just two varieties of potato, which were introduced to Europe in the 1500s, a wide variety of different potato plants were developed in the following centuries. Potatoes were bred for improved yield, quality, texture, and resistance to disease.
In the 1840s, the Irish potato crop was devastatingly infected with potato blight. A potato affected by blight has the outside shrunken and the inside corky and rotten. The resulting crop failures from potato blight caused widespread famine, mass emigration to the USA, and around 1 million deaths. The scale of this disaster drove plant breeders in the late 1800s to search for resistance to the disease in wild relatives of the potato. A wild species that was resistant to blight was eventually found in the early 1900s and after many attempts its natural resistance was bred into cultivated potato plants.
The use of the diversity of wild potato plants and ancient potato cultivars to breed desirable characteristics into modern potato crops has become commonplace, but the variety of wild potato plants is still underexploited. This is because of the long time needed to breed a trait from a purely wild plant into a plant suitable for agriculture. The fight against diseases is still an extremely important job for potato breeders, but potatoes are also being bred to cope with new demands. They have become more resistant to bruising so that they can be dug by machines and have a more regular size and shape. These demands are changing as new challenges emerge. Attributes attractive to plant breeders in the future may include the ability to resist drought or to grow in salty environments.