Blue tomatoes, sometimes referred to as purple tomato, are

tomato The tomato is the edible berry of the plant ''Solanum lycopersicum'', commonly known as the tomato plant. The species originated in western South America, Mexico, and Central America. The Mexican Nahuatl word gave rise to the Spanish word ...

es that have been bred to produce high levels of anthocyanins, a class of pigments responsible for the blue and purple colours of many fruits, including blueberries,

blackberries The blackberry is an edible fruit produced by many species in the genus ''Rubus'' in the family (biology), family Rosaceae, hybrids among these species within the subgenus ''Rubus'', and hybrids between the subgenera ''Rubus'' and ''Idaeobatus' ...

and

chokeberries ''Aronia'' is a genus of deciduous shrubs, the chokeberries, in the family Rosaceae native to eastern North America and most commonly found in wet woods and swamps. The genus Aronia is considered to have 3 species. The most common and wide ...

. Anthocyanins may provide protection for the plant against insects, diseases, and

ultraviolet radiation Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...

. Some of these tomatoes have been commercialized under the names "Indigo Rose" and "SunBlack".

Conventional breeding

While tomatoes have the genes for producing

anthocyanins Anthocyanins (), also called anthocyans, are water-soluble vacuolar pigments that, depending on their pH, may appear red, purple, blue, or black. In 1835, the German pharmacist Ludwig Clamor Marquart gave the name Anthokyan to a chemical com ...

, these genes are typically not expressed in the fruit in most commercial varieties. The result is that the pigments are limited to leaves and stems, where they are not eaten. As of the 2012 growing season,

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developed blue tomato seeds became commercially available under the cultivar name "Indigo Rose". The blue color is produced mostly by the anthocyanin

petunidin Petunidin (Pt), like Europinidin and Malvidin, is derived from Delphinidin and is an O-methylated anthocyanidin of the 3-hydroxy type. It is a natural organic compound, a dark-red or purple water-soluble pigment found in many redberries includin ...

on the outside of the tomato where the fruit is exposed to direct sunlight. The shaded side of the fruit is green when unripe, red when ripe, and the inside is red or deep pink. The tomatoes are small, about 2 inches across, round, and grow in clusters of 6 to 8. Flavor is described as slightly acidic. The vines are said to be indeterminate but compact, and disease resistant. While the concentration of anthocyanins is still very low compared to other fruits like blueberries, the pigments do improve the resistance of the fruits to the fungus ''

Botrytis cinerea ''Botrytis cinerea'' is a necrotrophic fungus that affects many plant species, although its most notable hosts may be wine grapes. In viticulture, it is commonly known as "botrytis bunch rot"; in horticulture, it is usually called "grey mould" o ...

''.

Biotechnology

The conventionally-bred varieties are similar to the "blue" tomatoes that have also been developed at the

John Innes Centre The John Innes Centre (JIC), located in Norwich, Norfolk, England, is an independent centre for research and training in plant and microbial science founded in 1910. It is a registered charity (No 223852) grant-aided by the Biotechnology and ...

in the UK using genetic modification (GM), incorporating genes from

snapdragons ''Antirrhinum'' is a genus of plants commonly known as dragon flowers, snapdragons and dog flower because of the flowers' fancied resemblance to the face of a dragon that opens and closes its mouth when laterally squeezed. They are native to r ...

to increase the anthocyanin levels in the flesh of the tomatoes. While both the conventionally-bred and the engineered varieties exhibit altered expression of the same

transcription factor In molecular biology, a transcription factor (TF) (or sequence-specific DNA-binding factor) is a protein that controls the rate of transcription of genetic information from DNA to messenger RNA, by binding to a specific DNA sequence. The f ...

of the

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gene class which controls the anthocyanin biosynthesis, the engineered variety additionally produces the pigments in the flesh of the fruit rather than just the skin. This results in almost 100-fold higher concentration of anthocyanins in the engineered fruits compared to the conventional varieties. The inventors of the GM blue tomato, Jonathan D. G. Jones and Cathie Martin of the

, founded a company called Norfolk Plant Sciences to commercialize the blue tomato. They partnered with a greenhouse farm in Canada to grow blue tomatoes from which to create new commercial products.

Difference from black cultivars

Many other tomato cultivars have names indicative of their dark color, such as

Black Krim The Black Krim (also known as Black Crimea and Noire de Crimée) is an heirloom tomato originating from Crimea. The plant is open-pollinated, indeterminate, bearing 8 ounce flattened globe fruits that are dark reddish-purple to black with gree ...

and

Cherokee purple Cherokee Purple is the name of an old variety of tomato that develops a fruit with a deep, dusky-rose color while maintaining a somewhat greenish hue near the stem when mature for eating. The deep crimson interior and clear skin combination give ...

. These colours come from an altogether different process, whereby the chlorophyll is not efficiently degraded resulting in the accumulation of the pigment

pheophytin Pheophytin or phaeophytin is a chemical compound that serves as the first electron carrier intermediate in the electron transfer pathway of Photosystem II (PS II) in plants, and the type II photosynthetic reaction center (RC P870) found in pur ...

in the fruit. This pigment combined with other

carotenoids Carotenoids (), also called tetraterpenoids, are yellow, orange, and red organic pigments that are produced by plants and algae, as well as several bacteria, and fungi. Carotenoids give the characteristic color to pumpkins, carrots, parsnips, co ...

in the fruit, including beta-carotene and

lycopene Lycopene is an organic compound classified as a tetraterpene and a carotene. Lycopene (from the neo-Latin '' Lycopersicum'', the tomato species) is a bright red carotenoid hydrocarbon found in tomatoes and other red fruits and vegetables. Occu ...

, produces a brown or black color.

Additional images

References

{{Tomatoes Tomato cultivars Genetically modified organisms in agriculture