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Bioscience in brief
Plant genetics and crop breeding
Where do our crops come from? II. Tomato
More Crops: Maize – Banana
Tomato is one of the most important crops world-wide. It belongs to the Solanaceae family, which includes >3000 species with origins in both Asia (aubergine in China and India) and in Central and South America (pepper/potato/tomato).
Wild tomatoes have a large genetic diversity, but by contrast the cultivated tomato is genetically poor: the genomes of tomato cultivars contain only about 5% of the genetic variation of their wild relatives.
This diversity is invaluable. To conserve it, thousands of related wild species have been collected and are maintained at the Tomato Genetics Resource Center in California, United States, a global resource (TGRC, http://tgrc.ucdavis.edu/).
Fruit of Solanum galapagense, Galapagos Islands. Global Crop Diversity Trust Photo H. Teppner (Creative Commons)
In wild tomatoes hair-like protrusions (called trichomes) produce a mixture of specialized chemicals that protect the plant against insects. Because cultivated tomatoes were not selected for these chemicals (nor hairs), they are more vulnerable to attack compared to their wild relatives we do not eat.
An obvious feature of the domesticated tomato plant is the massive increase in fruit size in some cultivars. Another feature is the development of a very wide range of fruit shapes. Wild tomatoes bear fruits that are almost invariably round, while cultivars available today can be round, oblate, pear-, torpedo- and bell-shaped.
Fruiting branch of Solanum carolinense. Wild tomatoes are invaluable sources of genetic resistance to pests and diseases and of important agronomic traits, even if we cannot directly eat them. The fruits of this species are poisonous.
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