Table 1.  The Genus Lycopersicon [3, 7]
 

From Peru, an unidentified wild ancestor of the tomato made its way north at some time several thousand years prior to the Spanish exploration of Central America in the early 16th century [6]. Tomatoes of the species L. esculentum cerasiforme were in wide cultivation throughout Central America when the first conquistadors arrived in the Yucatan area of what is now Mexico. L. esculentum cerasiforme is thought to be the direct ancestor of cultivated tomato based on its wide presence in Central America and the presence of a shortened style length in the flowers [7]. Cultivated tomato, L. esculentum has since been classified into five botanical varieties (Table 2).

Table 2. Botanical varieties of cultivated tomato, L. esculentum

That the tomato originated in South America, and that the tomato was an important crop among New World Indians by the 15th century is supported by strong evidence. The riddle that has kept some botanists on edge for many years is the question of where and when the wild tomato became a domesticated tomato. 
 
Most evidence supports Central American domestication. The strongest evidence is cultural. Pre-Columbian cultures in Peru were inclined to decorate textiles and pottery with depictions of crops and figures important to their well being. It may be significant that depictions of tomatoes on artifacts have not been unearthed. If the tomato had undergone domestication there, one would expect to find tomato representations on artifacts [6]. Linguistic evidence also supports this theory. The Aztecs of Central America called it "xitomatl", and wild Central American tribes called it "tomati" [3]. The writings of ancient Peruvian tribes fail to mention a tomato-like fruit as being an important part of the diet or even a word meaning tomato, while Aztec writings in Central America mention dishes comprised of peppers, salt and tomatoes, a concoction which seems likely to be the original salsa recipe [1]. And finally, genetic evidence also exists in support of Central American domestication. Genetic analysis of old cultivars descended from the original stock brought out of the New World by the Spanish showed modern cultivars to be more closely related to a cultivar grown widely in Mexico at that time than any wild species in Peru [6]. This cultivar was subsequently named as a variety of the domesticated tomato, called cerasiforme, and is regarded to be the direct ancestor of the modern cultivated tomato. The cerasiforme variety still grows in a somewhat wild state in Central America, producing small, cherry-like fruits on a creeping vine, thus it is known commonly as a cherry tomato [3]. Since domesticates were known to be cultivated in Central America, the lack of a genetically similar cultivar in South America suggests that domestication took place only to the north. Taken together, it seems well founded that initial domestication of tomato occurred in Central America. 
 
As for how it traveled to Central America, the evidence is less conclusive. It could have spread as a weed of maize and beans cultivated by natives [8]. Many crops of worldwide importance, such as rye and oats, were considered weeds at one time or another. Over time, a weed in a crop production system begins to evolve under the same selection pressures as the crop, and soon, becomes dependent on the irrigation and fertile soil provided such that it, too, becomes domesticated. Alternatively, migrating natives feasibly traded seeds of maize and beans, and could have spread seeds of the small but tasty tomato as well. The evidence on this point is simply inconclusive. 
 
The Spanish explorer Cortez conquered the Aztec city of Tenochtitlan, later to be renamed Mexico City, in 1521. It is presumed that the tomato found its’ way across the Atlantic shortly after. The earliest mention of the tomato in European literature is found in an herbal written by Matthiolus in 1544 [3]. He described tomatoes, or as they were called in Italy, pomi d'oro (golden apple), and wrote that they were "eaten in Italy with oil, salt and pepper". This provides evidence that the first tomatoes to reach the Old World were a yellow variety, and that they were introduced via the Mediterranean. Red tomatoes were said to be introduced to Italy by two Catholic priests many years later [9]. Although not specifically documented, early tomatoes were probably small fruited, since they most likely were of the small-fruited cerasiforme variety cultivated by the Aztecs. Additionally, later emphasis on breeding for smooth-skinned cultivars [3] suggests that early cultivars had a rough skin. 
 
Undoubtedly it was initially received in Spain, and the name pome dei Moro (Moor's apple), was probably among the first [1]. Cultivation of perhaps several varieties became widespread in the ensuing decades in Spain, Italy, and in France, where it was called pomme d'amour (love apple) [9], perhaps because of suspected aphrodisiac properties, but more likely the result of a corruption of the early Spanish name, pome dei Moro. Although used in a limited manner as a food in Mediterranean countries, northern European countries regarded the tomato as a curiosity for over a century [6]. English authors referred to the tomato as a horticultural ornamental as early as 1578 [3]. One such English cultivator wrote in 1596, "these love apples are eaten abroad", but went on to describe them "of rank and stinking savour" [1]. By 1623, four types of tomatoes were known: red, yellow, orange and golden [3], with the distinction between yellow and golden perhaps only in the mind of different authors. The first cookbook to mention tomatoes was published in Naples in 1692 [1]. By 1700, seven types are mentioned in one article, including a large red type [3]. In 1752, English cooks used tomatoes sparingly in the flavoring of soups [1]. In 1758, a tomato recipe allegedly showed up in the popular British cookbook, The Art of Cookery by Hannah Glass [1]. Earliest records of marketing tomatoes are from the early 1800's in Europe [3].
 
The introduction of the tomato did not proceed peacefully in all areas of Europe. Northern cultures associated the tomato plant with poisonous members of the Solanceae family, specifically henbane, mandrake and deadly nightshade, which bore morphological resemblance. Deadly nightshade, Atropus belladonna, in particular bears good resemblance to a tomato plant (Fig 3). It is a poisonous plant which has been used as both a hallucinogenic drug and a beauty aid in different parts of Europe. The Latin name "belladonna" literally means beautiful woman, in reference to the practice of ladies in medieval courts who would apply a few drops of nightshade extract to their eyes to dilate their pupils, a look considered most fashionable at the time. The hallucinogenic properties of the plant, comprised of visions and the sense of flying, most likely led to the association of nightshade with witchcraft. Old German folklore has it that witches used plants of the nightshade family to evoke werewolves, a practice known as lycanthropy (Fig 4). The common German name for tomatoes translates to "wolf peach", and was avoided for obvious reasons. In the 18th century Carl Linnaeus conjured up binomial nomenclature to name species, and took note of this legend when he named the tomato Lycopersicon esculentum, which literally means, "edible wolf peach" [1]. 
 
Plants were brought to North America with colonists early on as ornamentals from Britain, the fruits of which were reportedly most valued for pustule removing properties [5]. In 1781, Thomas Jefferson brought tomatoes to his table, along with french fries (a visionary). George Washington Carver, the man who made peanut butter a household item, strongly advocated tomato consumption to his poor Alabama neighbors in an effort to improve their woefully vitamin-deficient diet, but met with limited success [11]. Early efforts by merchants to peddle their crops were not highly successful. One account has it that the fruit was brought to the liberal hamlet of Salem, Massachusetts in 1802 by a painter who had difficulty even convincing people to taste the fruit [3]. Although New Orleans cuisine is reported to have incorporated tomato by 1812, suspicion about the fruit remained in some areas [3]. Lingering doubts about the safety of the tomato were supposedly put to rest in 1820, when Colonel Robert Gibbon Johnson announced that at noon on September 26, he would eat a bushel of tomatoes in front of the Boston courthouse. The story goes that thousands of eager spectators turned out to watch the poor man die after eating the poisonous fruits, and were shocked when he lived [5]. The source of this story, an old farm journal, may be less reliable than it is entertaining. Nevertheless, around the western world, tomatoes began to steadily grow in popularity. 
 
Several cookbooks from the 1820's include tomatoes in recipes [1]. In 1835, tomatoes were sold by the dozen in Boston’s Quincy Market. In 1847, Thomas Bridgeman listed four varieties in his seed catalogue: Cherry, Pear, Large Yellow and Large Squash. A seed merchant named Buist in 1858 commented on the tomato: "In taking retrospect of the last eighteen years, there is no vegetable on the catalogue that has obtained such popularity in so short a period as the one now under consideration. In 1828-29, it was almost detested; in ten years most every variety of pill and panacea was extract of tomato. It now occupies as great a surface of ground as cabbage, and is cultivated the length and breadth of the country." Buist listed eight cultivars in his catalogue that year. In 1863, a popular seed catalogue listed 23 cultivars, among which was Trophy, the first modern-looking large, red, smooth-skinned variety which fetched 5 dollars for a packet of 20 seeds. Large scale breeding for particular traits became commonplace in the 1870's in both Europe and the US, and by the 1880's, several hundred cultivars had been named (Table 3). A study done at Michigan Agricultural College in the late 1880's showed that 171 named cultivars represented only 61 truly different lines, many of which were only marginally different [3]. By the late 1800's, it was clear that the tomato had firmly implanted itself in western culture. 
 
The original center of domestication was, as mentioned, Central America. However, further domestication on a much more intense level occurred throughout Europe in the 18th and 19th centuries, and later in North America. Eastern Europe seemed to produce a particularly large number of high quality cultivars. Tomato plants are naturally self pollinating, and a general characteristic of self-pollinating plants is that they become genetically homozygous after many generations. Since they do not naturally outcross very often, seeds of a tomato will produce plants resembling the parents. Early cultivars did not change much because of this property, and were kept in a family or community for long periods of time, thus earning the name heirlooms. Heirloom cultivars dating back over a hundred years are still grown today. Most heirloom varieties are unique in size, shape or color (Fig 5). Some are black, dark purple, or red with black shoulders (Fig 6). Many are green, some have green stripes (Fig 7). Some are rainbow colored, or shaped like peppers (Fig 8). Of course there are orange and yellow cultivars too, and everything in between. Some are cherry size, some are over 2 pounds.
 
Many heirloom cultivars have colorful histories as well. Consider the story regarding the cultivar Mortgage Lifter. A West Virginian named Charlie owned a radiator repair shop that fell on hard times in the Great Depression as people abandoned their cars. He used the four largest-fruited tomato plants he had and crossed them repeatedly among each other to create a plant that produced two pound fruits. He sold plants for a dollar each, claiming one plant would feed a family of six. Within four years, he had made enough money to pay off the four thousand dollar mortgage on his house [12]. 
 
Names of heirloom cultivars often reflect some of the history of the plant.  Polish is a cultivar said to have been smuggled into the US on the back of a postage stamp in the late 1800's. Soldacki came to the US with Polish immigrants who settled in Ohio in the early 1900's. First Pick was grown by generations of the Baptiste family in Reims, France. Picardy has a history that dates back to 1890 in France. Besser came from the Freiburg region of Germany. Schellenburg's Favorite comes from the Schellenburg family near Manheim, Germany. Elbe originated in 1889 near the Elbe River in Germany. Amish Paste is a cultivar that has been cultivated by the Amish in Pennsylvania since the 1870's. Brandywine was developed by Amish farmers near Brandywine Creek in Chester County, Pennsylvania in 1885. Hillbilly came from the hills of West Virginia (Fig 9). Old Virginia was grown by locals in Virginia since the early 1900's. Jeff Davis is an old cultivar from Alabama honoring the Confederacy's only president.  Ace was introduced by the Campbell Soup Company in 1953, and is still popular for canning today [13]. A cultivar found growing at Edgar Allan Poe’s estate in Pennsylvania bears his mother’s maiden name, Hopkins. 1884 was said to have been found growing in a pile of flood debris near Friendly, WV by a Mr. Williamson in 1884. D.J. Doster of Monroe, NC grew seeds he brought back from Germany after WWII for over 50 years, and named the cultivar Belgium. Broad Ripple Yellow Currant was found growing in a sidewalk crack near 56th and College in Indianapolis, IN, 1984 (Fig 10) [14]. Stories of immigrants smuggling seeds into the United States hidden in waistbands or hollow canes seem to pop up frequently in heirloom descriptions. Of course, the tendency toward exaggeration must be considered with all these stories. 
 

Table 3. Some Popular Early Cultivars in the United States [3]
 

As with any homozygous crop, hybrid breeding can result in terrific gains in production and quality. When two homozygous lines are crossed, the resulting progeny inherit a high degree of genetic variability which leads to heterosis, or hybrid vigor, and perform much better and/or produce much more than either one of the parents. In this case, 1+1=3. One of the first hybrid tomatoes, Mikado, was introduced in 1880 by Rice's Seed Company of New York (Fig 11) [5]. Like most early hybrids, the Mikado's claim to fame was increased fruit size. Soon, higher yields were incorporated. By the beginning of the twentieth century, disease resistance, bush type and determinate growth habits were also found in hybrid cultivars. These traits were mostly incorporated into cultivated tomato by crossing with a wild relative, since all will hybridize with varying amounts of success [6]. Hybrid cultivars have come to dominate every area of tomato production, from large scale to backyard. One drawback, as far as the home gardener is concerned, is that hybrid seed or plants must be purchased every year. Seed from hybrid plants, if propagated, will produce the F2 segregating generation, and plants will be very diverse and not at all like that parent. This is the very property that makes hybrids so attractive to seed producers since it ensures that customers must buy new seed each year. Heirloom cultivars grow true from seed, and are still propagated by many home gardeners and seed companies. Many people argue that new hybrid cultivars bred for size and yield have overlooked the taste, and that the flavor of heirloom cultivars can't be beat. Hybrid cultivars have historically looked and tasted very similar to each other. Heirlooms definitely present greater variety, but typically have lower yields and lower disease resistance.
 
Tomato production in western countries began to soar in the early 1920's with the advent of mass canning. Canning of tomatoes was first documented in 1847 by Harrison Crosby of Lafayette College in Easton, Pennsylvania [3]. Prior to 1890, all tomato canning was done by hand. Mechanized peeling tables were put into use in the 1890's. Juice extractors were invented in the 1920's. Shortly after, a young entrepreneur named Joseph Campbell found a ready market for canned tomato products, and went on to make millions with his soup company.  High-solids cultivars have been introduced to maximize paste and solids for canning. Roma is a backyard favorite spanning half a century of cultivation and has been widely used for sauces because of its high solids content.
 
As the potential for introducing new traits into tomato cultivars through hybridization with wild relatives became more lucrative, the Tomato Genetics Cooperative was established at Cornell University in 1951 to collect and disseminate useful germplasm for breeding projects [3]. A prominent tomato breeder named Charles Rick heads up the Tomato Genetic Resource Center at University of California at Davis. In addition, tomato germplasm is kept in storage at the USDA National Seed Storage Laboratory in Fort Collins, Colorado. 
 
The late sixties sci-fi flick Attack of the Killer Tomatoes scared no one, but entertained millions. Tomatoes have been subject to politicking as well. In 1981, the USDA chairman declared ketchup to be a vegetable in order to justify Reagan administration budget cuts in the school lunch program [1].
 
The most recent contribution to tomato breeding has been biotechnology. For years merchants have tried to balance a good tasting fruit with a tough, good-shipping fruit. Ripe tomatoes are very soft, bruise easy, and begin to decline in quality after only a few days. Tomatoes ripen off the vine in response to the chemical ethylene, which is produced by the fruit as the development of the seeds nears completion. Traditionally, growers pick the fruits in the green-mature stage just as the shoulders of the fruit lose their dark green color. The fruit is then shipped to other locations, sometimes thousands of miles, and resists bruising or rotting because of its immature stage. The fruits are usually red by the time they reach their destination, or they can be induced to ripen with the application of an ethylene spray. Consumers often complain that taste suffers because of this practice.  In the 1980's a project was undertaken by Calgene Fresh, Inc. using biotechnology to tweak the tomato genetics to inactivate the gene responsible for softening the tomato during ripeness. These tomatoes turned red, but remained firm indefinitely. The practice of picking tomatoes green could be discarded, and everyone would be happy. They called this cultivar Flavr Savr because vine-ripening supposedly gave it better flavor. It hit the produce sections of stores in the US during 1993 [1]. The Flavr Savr tomato represents one of the greatest public relations blunders of the decade. Industry executives severely underestimated the public's concern over biotechnology, and failed to anticipate the backlash from consumers over this new and potentially risky technology applied to human food. Although evidence suggesting any danger over genetically engineered food is lacking, consumers are nervous about potentially unknown and unforeseen side effects. The Flavr Savr tomato was soon removed from supermarket shelves, and has never been reintroduced. 
 
The latest buzz surrounding tomatoes is the purported benefit of lycopene, the major carotenoid contained in tomatoes that is responsible for the deep red color. Similar to beta-carotene, lycopene has been touted as a potent anti-oxidant, a molecule which snuffs out cancer-causing free radicals within mammalian systems [15]. Tomatoes are an excellent source of lycopene, and numerous studies have confirmed that people who consume increased amounts of tomato products experience marked reductions in cancer risk [16]. Results from cancer research has already driven tomato breeders at the University of Florida to produce high lycopene cultivars. L. esculentum's wild relative, L. pimpinellifolium, also known as the currant tomato, produces tiny fruits which contain over 40 times more lycopene than domesticated tomatoes (Fig 12). Since hybrids between the two are relatively simple to achieve, this source of genetic diversity is open for exploitation, and will most likely become a sought-after hybrid trait. 
 
The top five tomato producing countries of the world are United States, China, Turkey, Italy and India, in that order. Within the US, Florida, California and Georgia are the top commercial producing states, with about 200 square miles under cultivation in 1997. An estimated 35 million backyard gardens across the country grow tomatoes as well. Per capita yearly consumption of tomatoes in the US increased from 16.6 lb in 1985 to 18.8 lb in 1995 [11]. Continued increase in this figure is expected due to the purported health benefits associated with tomatoes in the diet.  Specifically, these include a ranking of 16th among all fruits and vegetables as a source of vitamin A, 13th in vitamin C, and when adjusted for consumption, the most important provider of these two vitamins in the western diet. It also contains significant amounts of lycopene, beta-carotene, magnesium, niacin, iron, phosphorus, potassium, riboflavin, sodium and thiamine. A University of California at Davis survey ranked the tomato as the single most important fruit or vegetable of western diets in terms of overall source of vitamins and minerals. 
 
After only a few hundred years in European culture, the tomato has firmly implanted itself as a major player in diets of many nationalities. Italian cooking has become synonymous with tomato sauce. Pizza would be lost without it. Where would Mexican restaurants be without salsa? Tomato soup, slices on a burger and ketchup are all highly integrated uses for the versatile fruit in American culture. Additionally, millions of Americans grow tomatoes in their backyards each year. From one continent to another, the tomato has crossed through a variety of cultural barriers to become one of the world's foremost vegetables. 
    

[1] Cutler KD. 1998. From Wolf Peach to Outer Space. www.bbg.org/gardening/kitchen/tomatoes/cutler.html
 
[2] Harlan JR. Agricultural Origins: Centers and Noncenters. Science 174: 468-473
 
[3] Gould WA. 1983. Tomato Production, Processing and Quality Evaluation, 2ed. AVI Publishing Company, Inc. Westport, CT. pp 3-50
 
[4] Rick CM, DeVerna JW, Chetelat RT. 1990. Experimental introgression to the cultivated tomato from related wild nightshades. In: AB Bennett and SD O'Neill (eds), Horticultural Biotechnology. New York. pp 19-30
 
[5] Simpson BB, Ogorzaly MC. 1986. Economic Botany: Plants In Our World. McGraw-Hill, New York
 
[6] Rick CM. Tomato. In: J Smartt and NW Simmonds (eds), Evolution of Crop Plants. Longman Scientific and Technical, Essex, England. pp 452-457
 
[7] Hancock JF. Plant Evolution and the Origin of Crop Species. 1992. Prentice Hall, Englewood Cliffs, NJ. pp 275-276
 
[8] Ucko PJ, Dimbleby GW. The domestication and expoitation of plants and animal. Aldine-Atherton, Inc.Chicago. p 25
 
[9] NMSU College of Agriculture and Home Economics Web Page                                                                                horizon.nmsu.edu/garden/history/tomatoes.html
 
[10] Heiser CB. 1973. Seed to Civilization. WH Freeman & Co., San Francisco, CA. p 176
 
[11] Jones JB. Tomato Plant Culture. 1999. CRC Press, LLC., Boca Raton, FL. pp 1-3
 
[12] www.heirloomseeds.com
 
[13] www.homegrowntomatoes.com
 
[14] Seed Savers 2000 Yearbook; Seed Saver’s exchange, Inc., Decorah, IA. pp 302-446
 
[15] DiMascio P, Kaiser S, Sies H, Arch. Biochem Biophys. 274 (1989) 532.
 
[16] Giovanucci IL, Ashcerio A, Rimm EB, Stampfer MM, Colditz GA, Willett WC, J. Natl.  Cancer Inst. 87 (1995) 1767.