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Image credits: Tomato-The Ewan [CC BY-SA 2.0] (source); Potato-Scott Bauer [public] (source); Pepper-idaun [public] (source)

Tomatoes, Potatoes, and Peppers

What do tomatoes, potatoes, and peppers have in common? One obvious answer is that these are all food plants. We can grow these plants in farm fields or home gardens and then collect the edible results. Or we can visit a grocery to purchase fresh produce from these plants. But what else do these three plants have in common? In fact, there are multiple answers:

  • All three plants are members of the nightshade family (Solanaceae), which means that they are all related.
  • All three crops were first domesticated in the Americas by Native Americans, but spread around the world after Europeans began to explore (and conquer) the New World.
  • All three foods have become closely associated with various cuisines of Eurasia — although these plants were completely unknown in Europe and Asia just 500 years ago.

Can you imagine Italian cuisine without tomatoes? Yet Italians were unaware of tomatoes 500 years ago. Can you imagine German or Irish cuisine without potatoes? Yet there were no potatoes in Europe 500 years ago. And can you imagine Thai cuisine without spicy peppers? Yet such peppers were unknown in Asia 500 years ago.

Tomatoes

Domesticated tomatoes (Solanum lycopersicum) are the cultivated descendants of a wild plant that grows in the Andes region of southern Ecuador and northern Peru. This wild ancestor (Solanum pimpinellifolium) is often called a “currant tomato” or a “pimp”. This species, which is becoming increasingly scarce in the wild, should not be confused with escaped garden tomatoes. Wild currant tomatoes are tiny, typically less than a centimeter across — similar in size to a shelled green pea. This is notably smaller than our familiar cherry tomatoes. Yet currant tomatoes are quite flavorful, with a delightfully bright orange-red color.

The mystery behind tomatoes is that much of the early domestication of this crop occurred in Mesoamerica (Mexico and Central America), more than 1000 miles from its ancestral home. Apparently the species was first domesticated by Native American residents of the Andes, who collected the wild seeds and planted them in their gardens. Because of trade between people of the Andes and civilizations farther north, these same fruits were soon cultivated in Mesoamerica. It is not known when this cultivation began, but quite likely it was more than a thousand years before Columbus. When the Spanish arrived in Mexico on a mission of conquest, they soon became aware of domesticated tomatoes, which by this time were quite a bit larger than the wild ancestors. The Spanish took samples back to Europe, and eventually tomatoes were cultivated all over the continent.

In the following centuries, gardeners in Europe developed many new varieties — in various sizes, shapes, and colors — producing most of our “heirloom” tomatoes. These gardeners did not necessarily set out to develop new varieties. Instead, they simply saved seed each year for planting the following year. But of course they saved the seeds of the plants that performed the best or had the most pleasing fruits. This meant that gardeners in places with different climates — such as cool summers versus hot summers — were selecting for varieties that could successfully produce fruit in those specific climates. Furthermore, people in different locations tended to focus on certain sizes, shapes, and colors of fruit. Therefore the different heirloom varieties became distinct from one another.

You may think of heirloom tomatoes as representing a great deal of genetic diversity — and they are certainly more diverse than our commercial varieties. But in fact all of these heirloom varieties are genetically quite similar. Differences in just a tiny handful of genes produce the variations we see in these tomatoes. One reason for this lack of genetic diversity is that our domesticated tomatoes are twice removed from their original gene pool. First, a small sample of seeds was brought from South America to Mesoamerica — which means that all the varieties developed in Mesoamerica were based on a small gene pool. And then a small sample of seeds was brought from Mesoamerica to Europe, resulting in an even tinier gene pool.

In contrast, the gene pool in the wild currant tomatoes is vast. Furthermore, this wild species readily crosses with its domesticated brethren. This provides great opportunities for creating new varieties of tomatoes, with improved disease resistance and other desirable characteristics. But to take advantage of this genetic diversity, we must preserve many different examples of wild “pimps” before human activity pushes them to the brink of extinction. Furthermore, several closely related species of Solanum still grow wild in Latin America, providing additional sources of genes. Finally, old domesticated varieties of tomatoes in Latin America — including some that have escaped into the wild or hybridized with wild species — provide a third source of genes for plant breeding.

The issue of limited genetic diversity is not unique to tomatoes — although tomatoes provide an extreme example. Most of our popular crop plants, when compared to their wild ancestors, have very little genetic diversity. Therefore, for all major crop plants, agronomists are eager to identify and preserve populations of wild ancestors and other close relatives.

Today, the leading tomato-producing countries of the world are China, United States, India, and Turkey. China is by far the world leader, producing more tomatoes than the next three countries combined. Many of these tomatoes are eaten fresh, but a far larger quantity goes into making tomato sauce and canned tomatoes. It has been quite a leap from Native Americans harvesting the original wild currant tomatoes to our world of modern agriculture, with mechanized harvesting of vast acreages of large, domesticated tomatoes. This leap did not occur in a single bound, but in a long series of baby steps over many, many centuries, first in the Americas, and then in the world at large.

Potatoes

We think of potatoes and tomatoes as being quite different, and yet the two plants are closely related. Not only are both in the nightshade family (Solanaceae), but both are in the same genus (Solanum). There are approximately 2,700 species of plants in the family Solanaceae, about half of which are in the genus Solanum. The reason that these two names are so similar is that every botanical family is named after one genus in the family — and therefore Solanaceae got its name from Solanum.

The main reason that potatoes and tomatoes seem so different is that we eat a different part of the plant. In the case of tomatoes, we eat the fruit of the plant — in other words, the part that develops from a pollinated flower and that contains the seeds. In the case of potatoes, we eat a swollen, starchy part of the plant that is used for storing food and water underground. These reserves can help the potato plant survive periods of difficult conditions. Potatoes, because they are covered with tiny buds (the “eyes” of the potato), are capable of sprouting independently of the parent plant, even though they are genetically identical to the parent.

Domesticated potatoes (Solanum tuberosum) originated high in the Andes Mountains in southern Peru and northern Bolivia. The wild ancestor is Solanum brevicaule, along with several other closely related species. All of these related species are jointly called “the Solanum brevicaule complex”. Because the species in this complex are so closely related, they often interbreed, resulting in numerous hybrids. This makes it difficult to distinguish between the various species. A second difficulty is that some of the wild varieties have hybridized with ancient domesticated potatoes, making it difficult to determine which varieties are the pure wild ancestral potatoes and which are not.

Potatoes have been domesticated for at least 7,000 years, and perhaps even 10,000 years. This means that Native Americans were growing potatoes for many thousands of years before Europeans “discovered” the New World and brought samples of potatoes back to Europe. This long period of domestication, plus the continued gene exchange between wild and domesticated potatoes, resulted in several thousand varieties of domesticated potatoes prior to the European conquest. After the Conquest, potatoes spread to Europe and beyond. As a result, approximately 2000 varieties have been developed outside of South America. However, most of these later varieties — which dominate modern potato production — are descended from potatoes cultivated by Native Americans in the lowlands of south-central Chile, rather than the highlands of Peru and Bolivia. That’s nearly 2000 miles from where potatoes were first domesticated. So why is this?

It turns out that wild potato plants are quite sensitive to daylength. The plant can sense the length of a day (also called a photoperiod), and uses this information to determine when to bloom and when to grow potato tubers. This ability is not unique to potatoes. For example, most chrysanthemums are sensitive to daylength, and will start blooming in the autumn when the days become shorter than a particular threshold. This sounds almost magical, but the explanation is simple. During daylight hours a specific hormone builds up, while at night the hormone is gradually destroyed. The level of this hormone is therefore sensitive to daylength, and it is the level of the hormone that triggers key events in the lifecycle of the plant.

The original domesticated potatoes of the Andes, just like their wild ancestors, begin to produce tubers when the days grow short and the nights grow long. But this trigger is not appropriate for locations that are much farther from the equator, such as south-central Chile. Such a trigger would prevent the tubers from getting started until far too late in the autumn. The upshot is that Chilean potatoes do not have this trigger, and will begin to produce potatoes even when the days are still long. This characteristic is well-matched to the conditions in northern Europe and the northern U.S. The upshot is that most potatoes grown in cold-temperate zones are descended from samples collected in Chile.

Today the top five potato-producing countries of the world — in order — are China, India, Russia, Ukraine, and the U.S. China produces more potatoes than the next two countries combined.

Peppers

Peppers — including both hot peppers and sweet peppers — are yet another food crop in the family Solanaceae that originated in the Americas. However, unlike tomatoes and potatoes, peppers do not belong to the genus Solanum. Instead, they are members of the genus Capsicum.

Our word “pepper”, as applied to the genus Capsicum, is a confusing use of the term. The word itself has a very long history, and for many centuries referred only to pepper made from peppercorns — especially the black pepper that we put into pepper shakers. This kind of pepper is originally from Asia, and was known in Europe long before the discovery of the New World. Peppers from the New World are completely unrelated to pepper from the Old World, but because both are spicy, the same word was applied to both.

There are approximately two dozen wild species of Capsicum, all native to various parts of the Americas. Five of these species were domesticated by Native Americans. Of these five, the most commercially important species is Capsicum annuum — sometimes called “chili pepper” — which was originally domesticated in Mexico at least 9,000 years ago. This species has been bred to produce a wide range of varieties, both mild and spicy — including bell pepper, jalapeño, cayenne, paprika, serrano, sweet Italian, poblano, Hungarian wax, pimiento, Thai bird, and Santa Fe Grande. In other words, most of the peppers that you find in a North American grocery store are Capsicum annuum, descended from Mexican ancestors. Likewise, most of the spicy peppers that are routinely used in various Asian cuisines are also descended from Mexican ancestors, and were completely unknown in Asia 500 years ago.

However, there are four other species of Capsicum that were also domesticated by Native Americas, mostly in Peru and Bolivia where many different species grow wild. In particular, the species Capsicum chinense is the source of habaneros and scotch bonnets. The hottest peppers in the world, those with highest Scoville Heat Units, are all varieties of this species. Tabasco sauce is made from yet a third species, Capsicum frutescens. Other varieties of this species have become popular in Africa and in Asia.

Today, China is by far the world’s largest producer of Capsicum peppers, completely dwarfing the production of all other countries. The other four top producers of Capsicum peppers are Mexico, Indonesia, Turkey, and Spain. China produces almost ten times as much as Mexico, but China exports very little of its production. In contrast, Mexico is the #1 exporter of Capsicum peppers.

Other Foods from the Americas

A great number of other important foods crops are native to the Americas, and in most cases were domesticated by Native Americans long before the arrival of Europeans. These crops include corn (maize), common beans, pumpkins and squash, avocado, peanuts, sweet potato, quinoa, chocolate, pineapple, sunflower seeds, chia, amaranth, and cassava (also called tapioca, manioc, or yuca). Still other food crops native to the Americas include blueberries, strawberries, cranberries, wild rice, pecans, cashew nuts, and Brazil nuts. These later foods were well known to Native Americans, but were often collected in the wild rather than grown as domesticated crops. Furthermore, there are many other native fruits and vegetables that are popular in various parts of Latin America, but little-known in the United States.

Corn (Zea mays), also called “maize”, was first domesticated by Native Americans in Mexico more than 10,000 years ago. This crop gradually spread throughout the Americas, and was grown by Native Americans from Canada to Chile before the arrival of Europeans. With such a wide geographical range, and such a long period of domestication, Native Americans had already developed hundreds of varieties of corn prior to the Conquest. The wild ancestor of corn is teosinte (Balsas teosinte). But because an ear of corn looks so much different than an ear of teosinte, it took many years for scientists to piece together the history of domesticated corn. Today the top producers of corn are the United States, China, and Brazil.

Native Americans have grown domesticated beans for the past 8,000 years. The wild ancestors are all members of the genus Phaseolus, including at least four different species. The most commercially important species, by far, is the common bean (Phaseolus vulgaris), which was independently domesticated by Native Americans in two different places — in Mesoamerica, and also in South America. In a modern grocery store, you can typically find a wide variety of fresh, dried, and canned beans that have all been developed from this one species — including string beans (snap beans), kidney beans, white navy beans, black turtle beans, cannellini beans, and cranberry beans. A second native species of bean, Phaseolus lunatus, gave rise to lima beans and butter beans. Like corn, domesticated beans became a staple food among agricultural societies throughout the pre-Columbian Americas.

Squashes and pumpkins are the descendants of several different species of the genus Cucurbita, all domesticated by Native Americans long ago. The most commercially important species is Curcurbita pepo, first domesticated about 10,000 years ago in Mesoamerica. Varieties bred from this species include zucchini, yellow summer squash (straight-neck and crookneck), patty-pan squash, acorn squash, spaghetti squash, jack-o-lantern pumpkin, small sugar pumpkin, and certain ornamental gourds. The second most commercially important species is Curcurbita moschata, also domesticated about 10,000 years ago. Butternut squash is the best-known example of this species. All canned pumpkin in the United States is made from this species, using such varieties as Dickenson Field Pumpkin and Kentucky Field Pumpkin.

For more information on pumpkins and squashes, see Is That Really Pumpkin in my Pumpkin Pie?

Summary

Tomatoes, potatoes, and peppers have several attributes in common: All are members of the nightshade family (Solanaceae). All are native to the Americas and were first domesticated by Native Americans. After the European conquest of the Americas, all three crops gradually spread around the world. Now China is the world’s top producer for all three.

Given the American origin of these important crops, it is not surprising that all three are frequent ingredients in several Latin American cuisines. However, we often associate these foods with the cultures and cuisines of Europe or Asia — where these ingredients were completely unknown 500 years ago. Although surprising, in a way it makes sense — because these crops have indeed become essential to many cultures around the world. By the same token, certain Old World crops have become completely integrated into Latin American culture — including wheat, rice, bananas, oranges, and coffee.

Of the top 10 food crops of the world (ranked by tonnage), four were first domesticated by Native Americans — corn (maize), potatoes, cassava, and sweet potatoes. If you rank the food crops of the world by dollar value instead of weight, then tomatoes are also in the top ten. There are more than 20 distinct and well-known food crops — all familiar to the average North American — that originated in the Americas. All of these crops still have close relatives growing in the wild. If we find and preserve diverse wild populations for each of these crops, then we have made a huge investment in the future. These wild gene pools provide us with powerful tools to fight diseases and pests that attack our crops, to expand each crop’s ability to survive varied climatic conditions, and to produce new varieties with a wide range of helpful characteristics. Even without all of these economic benefits, it is nice simply to preserve aspects of the natural world that would otherwise be lost forever.

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