Tomato

Tomato

The tomato is the edible, often red, berry of the plant Solanum lycopersicum, commonly known as a tomato plant. The species originated in western South America and Central America. The Nahuatl (Aztec language) word tomatl gave rise to the Spanish word tomate, from which the English word tomato derived. Its domestication and use as a cultivated food may have originated with the indigenous peoples of Mexico. The Aztecs used tomatoes in their cooking at the time of the Spanish conquest of the Aztec Empire, and after the Spanish encountered the tomato for the first time after their contact with the Aztecs, they brought the plant to Europe. From there, the tomato was introduced to other parts of the European-colonized world during the 16th century.

Tomatoes are a significant source of umami flavor. The tomato is consumed in diverse ways, raw or cooked, in many dishes, sauces, salads, and drinks. While tomatoes are fruits—botanically classified as berries—they are commonly used as a vegetable ingredient or side dish.

Numerous varieties of the tomato plant are widely grown in temperate climates across the world, with greenhouses allowing for the production of tomatoes throughout all seasons of the year. Tomato plants typically grow to 1–3 meters (3–10 ft) in height. They are vines that have a weak stem that sprawls and typically needs support. Indeterminate tomato plants are perennials in their native habitat, but are cultivated as annuals. Determinate, or bush, plants are annuals that stop growing at a certain height and produce a crop all at once. The size of the tomato varies according to the cultivar, with a range of 0.5–4 inches (1.3–10.2 cm) in width.

Botany

Description

decumbent, typically growing 180 cm (6 ft) or more above the ground if supported, although erect bush varieties have been bred, generally 100 cm (3 ft) tall or shorter. Indeterminate types are “tender” perennials, dying annually in temperate climates (they are originally native to tropical highlands), although they can live up to three years in a greenhouse in some cases. Determinate types are annual in all climates.

Tomato plants are dicots, and grow as a series of branching stems, with a terminal bud at the tip that does the actual growing. When that tip eventually stops growing, whether because of pruning or flowering, lateral buds take over and grow into other, fully functional, vines.

Tomato vines are typically pubescent, meaning covered with fine short hairs. These hairs facilitate the vining process, turning into roots wherever the plant is in contact with the ground and moisture, especially if the vine’s connection to its original root has been damaged or severed.

Most tomato plants have compound leaves, and are called regular leaf (RL) plants, but some cultivars have simple leaves known as potato leaf (PL) style because of their resemblance to that particular relative. Of RL plants, there are variations, such as rugose leaves, which are deeply grooved, and variegated, angora leaves, which have additional colors where a genetic mutation causes chlorophyll to be excluded from some portions of the leaves.

The leaves are 10–25 cm (4–10 in) long, odd pinnate, with five to 9 leaflets on petioles, each leaflet up to 8 cm (3 in) long, with a serrated margin; both the stem and leaves are densely glandular-hairy.

Their flowers, appearing on the apical meristem, have the anthers fused along the edges, forming a column surrounding the pistil’s style. Flowers in domestic cultivars can be self-fertilizing. The flowers are 1–2 cm (0.4–0.8 in) across, yellow, with five pointed lobes on the corolla; they are borne in a cyme of three to 12 together.

Although in culinary terms, tomato is regarded as a vegetable, its fruit is classified botanically as a berry. As a true fruit, it develops from the ovary of the plant after fertilization, its flesh comprising the pericarp walls. The fruit contains hollow spaces full of seeds and moisture, called locular cavities. These vary, among cultivated species, according to type. Some smaller varieties have two cavities, globe-shaped varieties typically have three to five, beefsteak tomatoes have a great number of smaller cavities, while paste tomatoes have very few, very small cavities.

For propagation, the seeds need to come from a mature fruit, and be dried or fermented before germination.

Classification

In 1753, Linnaeus placed the tomato in the genus Solanum (alongside the potato) as Solanum lycopersicum. In 1768, Philip Miller moved it to its own genus, naming it Lycopersicon esculentum. This name came into wide use, but was technically in breach of the plant naming rules because Linnaeus’s species name lycopersicum still had priority. Although the name Lycopersicum lycopersicum was suggested by Karsten (1888), this is not used because it violates the International Code of Nomenclature barring the use of tautonyms in botanical nomenclature. The corrected name Lycopersicon lycopersicum (Nicolson 1974) was technically valid, since Miller’s genus name and Linnaeus’s species name differ in exact spelling, but since Lycopersicon esculentum has become so well known, it was officially listed as a nomen conservandum in 1983, and would be the correct name for the tomato in classifications which do not place the tomato in the genus Solanum.

Genetic evidence has now shown that Linnaeus was correct to put the tomato in the genus Solanum, making Solanum lycopersicum the correct name. Both names, however, will probably be found in the literature for some time. Two of the major reasons for considering the genera separate are the leaf structure (tomato leaves are markedly different from any other Solanum), and the biochemistry (many of the alkaloids common to other Solanum species are conspicuously absent in the tomato). On the other hand, hybrids of tomato and diploid potato can be created in the lab by somatic fusion, and are partially fertile, providing evidence of the close relationship between these species.

Genetic modification

Tomatoes that have been modified using genetic engineering have been developed, and although none are commercially available now, they have been in the past. The first commercially available genetically modified food was a variety of tomato named the Flavr Savr, which was engineered to have a longer shelf life. Scientists are continuing to develop tomatoes with new traits not found in natural crops, such as increased resistance to pests or environmental stresses. Other projects aim to enrich tomatoes with substances that may offer health benefits or provide better nutrition.

An international consortium of researchers from 10 countries, among them researchers from the Boyce Thompson Institute for Plant Research, began sequencing the tomato genome in 2004, and is creating a database of genomic sequences and information on the tomato and related plants. A prerelease version of the genome was made available in December 2009. The genomes of its mitochondria and chloroplasts are also being sequenced as part of the project. The complete genome for the cultivar Heinz 1706 was published on 31 May 2012 in Nature. Since many other fruits, like strawberries, apples, melons, and bananas share the same characteristics and genes, researchers stated the published genome could help to improve food quality, food security and reduce costs of all of these fruits.

Breeding

The Tomato Genetic Resource Center, Germplasm Resources Information Network, AVRDC, and numerous seed banks around the world store seed representing genetic variations of value to modern agriculture. These seed stocks are available for legitimate breeding and research efforts. While individual breeding efforts can produce useful results, the bulk of tomato breeding work is at universities and major agriculture-related corporations. These efforts have resulted in significant regionally adapted breeding lines and hybrids, such as the Mountain series from North Carolina. Corporations including Heinz, Monsanto, BHNSeed, and Bejoseed have breeding programs that attempt to improve production, size, shape, color, flavor, disease tolerance, pest tolerance, nutritional value, and numerous other traits.

 

Cultivation

The tomato is grown worldwide for its edible fruits, with thousands of cultivars. A fertilizer with an NPK ratio of 5–10–10 is often sold as tomato fertilizer or vegetable fertilizer, although manure and compost are also used.

Production

In 2016, world production of tomatoes was 177 million tonnes, with China accounting for 32% of the total, followed by the European Union, India, the United States, and Turkey as the major producers. Global tomato exports were valued at 85 billion US dollars in 2016.

Varieties

There are around 7,500 tomato varieties grown for various purposes having been selected with varying fruit types, and for optimum growth in differing growing conditions.

Tomato varieties can be divided into categories based on shape and size.

  • Beefsteak tomatoesare 10 cm (4 in) or more in diameter, often used for sandwiches and similar applications. Their kidney-bean shape, thinner skin, and shorter shelf life makes commercial use impractical.
  • Plum tomatoes, or paste tomatoes (including pear tomatoes), are bred with a lower water /higher solids content for use in tomato sauceand paste, for canning and sauces and are usually oblong 7–9 cm (3–4 in) long and 4–5 cm (1.6–2.0 in) diameter; like the Roma-type tomatoes, important cultivars in the Sacramento Valley.
  • Cherry tomatoesare small and round, often sweet tomatoes, about the same 1–2 cm (0.4–0.8 in) size as the wild tomato.
  • Grape tomatoesare smaller and oblong, a variation on plum tomatoes.
  • Campari tomatoesare sweet and noted for their juiciness, low acidity, and lack of mealiness, bigger than cherry tomatoes, and smaller than plum tomatoes.
  • Tomberries, tiny tomatoes, about 5 mm in diameter
  • Oxheart tomatoes can range in size up to beefsteaks, and are shaped like large strawberries.
  • Pear tomatoesare pear-shaped and can be based upon the San Marzano types for a richer gourmet paste.
  • “Slicing” or “globe” tomatoes are the usual tomatoes of commerce, used for a wide variety of processing and fresh eating. The most widely grown commercial tomatoes tend to be in the 5–6 cm (2.0–2.4 in) diameter range.

Tomatoes are also classified as determinate or indeterminate. Determinate, or bush, types bear a full crop all at once and top off at a specific height; they are often good choices for container growing. Determinate types are preferred by commercial growers who wish to harvest a whole field at one time, or home growers interested in canning. Indeterminate varieties develop into vines that never top off and continue producing until killed by frost. They are preferred by home growers and local-market farmers who want ripe fruit throughout the season. As an intermediate form, there are plants sometimes known as vigorous determinate or semi-determinate; these top off like determinates, but produce a second crop after the initial crop. The majority of heirloom tomatoes are indeterminate, although some determinate heirlooms exist.

Early tomatoes and cool-summer tomatoes bear fruit even where nights are cool, which usually discourages fruit set. There are varieties high in beta carotenes and vitamin A, hollow tomatoes and tomatoes that keep for months in storage. In 1973, Israeli scientists developed the world’s first long shelf-life commercial tomato varieties.

Heirloom tomatoes are becoming increasingly popular, particularly among home gardeners and organic producers, since they tend to produce more interesting and flavorful crops at the cost of disease resistance and productivity. The definition of an heirloom tomato is vague, but unlike commercial hybrids, all are self-fertile varieties that have bred true for 40 years or more. Quite a few seed merchants and banks provide a large selection of heirloom seeds. Home cultivars are often bred for flavor to the exclusion of all other qualities, while commercial cultivars are bred for factors like consistent size and shape, disease and pest resistance, suitability for mechanized picking and shipping, and ability to ripen after picking. Hybrid plants remain common, since they tend to be heavier producers, and sometimes may combine unusual characteristics of heirloom tomatoes with the ruggedness of conventional commercial tomatoes.

Most modern tomato cultivars are smooth surfaced, but some older tomato cultivars and most modern beefsteaks show pronounced ribbing, a feature that may have been common to virtually all pre-Columbian cultivars. While virtually all commercial tomato varieties are red, some cultivars – especially heirlooms – produce fruit in blue, green, yellow, orange, pink, black, brown, ivory, white, and purple. Such fruits are not widely available in grocery stores, nor are their seedlings available in typical nurseries, but they can be bought as seed. Variations include multicolored fruit with stripes (Green Zebra), fuzzy skin on the fruit (Fuzzy Peach, Red Boar), multiple colors (Hillbilly, Burracker’s Favorite, Lucky Cross), etc.

Nutrition

A tomato is 95% water, contains 4% carbohydrates and less than 1% each of fat and protein. In a 100 gram amount, raw tomatoes supply 18 calories and are a moderate source of vitamin C (17% of the Daily Value), but otherwise are absent of significant nutrient content.

Potential health effects

No conclusive evidence indicates that the lycopene in tomatoes or in supplements affects the onset of cardiovascular diseases or cancer.

In the United States, supposed health benefits of consuming tomatoes, tomato products or lycopene to affect cancer cannot be mentioned on packaged food products without a qualified health claim statement. In a scientific review of potential claims for lycopene favorably affecting DNA, skin exposed to ultraviolet radiation, heart function and vision, the European Food Safety Authority concluded that the evidence for lycopene having any of these effects was inconclusive.

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