Yellow, streaked or purple, enormous or tiny, round, plum or lobed 鈥� the colours, sizes and shapes of the tomato varieties traditionally grown in Europe vary greatly. But it turns out this diversity is only skin deep. Apart from the few genes controlling these obvious characteristics, these tomatoes are virtually identical genetically.
鈥淚t鈥檚 like a desert with some oases of variety,鈥� says at Valencia Polytechnic University in Spain. 鈥淭he tomatoes that you find in the supermarket nowadays, they have more diversity than the traditional [European] ones.鈥�
A handful of varieties of tomato were brought to Europe from the Americas around the 16th century, where they were grown mostly by poorer farmers in Spain and Italy. These farmers bred hundreds of varieties.
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鈥淧eople think these are natural, but they are not,鈥� says Blanca. 鈥淭hese are artificial. They are human artefacts.鈥�
The fruit became popular in the UK and North America in the 19th century, and nowadays most tomatoes grown commercially are modern varieties created by seed companies. However, seed banks and a few amateur growers around the world are trying to conserve the vintage or 鈥渉eirloom鈥� varieties.
鈥淭here are few diverse sites, but the ones that are diverse, they are very diverse,鈥� says Blanca. 鈥淭he rest, they are all the same.鈥�
This is because the European farmers selected for mutants that had an obvious effect, he says. But because all the varieties derive from just a few plants that arrived in Europe in the 16th century, they remain very similar otherwise.
The modern varieties were far more diverse, in line with previous research.聽The reason for this is that聽modern breeders crossed plants with wild varieties to reintroduce some of the variety lost during domestication. But many wild varieties are going extinct.
Having lots of diversity is really important, says Blanca. It provides the raw material for creating new varieties that can cope with evolving pests and diseases, and with a changing climate
鈥淭he future of the tomato is in our hands,鈥� says Blanca. 鈥淲e need to modify it.鈥�
Seed banks are struggling to preserve tomato varieties because of a lack of funding, says Blanca. The problem is that the seeds cannot be stored indefinitely, but need to be planted and recollected every decade or so. His findings show that seed banks need to maintain only around 200 varieties to preserve the vast majority of diversity within heirloom tomatoes.
Blanca also found that the same name has often been given to different varieties that look similar. This is the case with those labelled 鈥淢armande鈥�, for instance. The opposite is also true, with a single variety sometimes having several different names.
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