Mystery of the potato’s origins solved by genetics

The humble potato, it turns out, is the product of a tryst between an ancient tomato plant and a lesser-known South American lineage named Etuberosum.

Etuberosum plants are often described as looking like a potato plant, except for one crucial difference – they don’t produce the starch-rich tubers that have made cultivated potatoes one of the world’s most important food staples.

Sandra Knapp at the Natural History Museum in London and her colleagues studied the genetics of three groups of plants in the genus Solanum: Petota, with 107 species including cultivated potatoes (Solanum tuberosum); the tomato group, with 17 species; and Etuberosum, with three species. The three lineages shared a common ancestor around 14 million years ago.

The team looked at 450 genomes from cultivated potatoes and 56 wild potato species and found there was, in every one of them, a steady mix of tomato and Etuberosum genes.

The results suggest that the potato lineage stems from a hybridisation event between the ancestors of the tomato and Etuberosum groups, probably around 8 million years ago in what is now Chile.

Knapp says the hybridisation event allowed for new gene combinations to occur, creating innovations like the growth of tubers. “This event led to a reshuffling of genes such that the new lineage produced tubers, allowing these plants to expand into the newly created cold, dry habitats in the rising Andes,” she says.

This shows that hybridisation is a “powerful force in the evolution of diversity”, says Knapp.

“Actually the parts of the tomato and potato we eat look different but the plants themselves are quite similar,” she says. “If you by luck get a potato plant that produces fruit, it’s a green, tomato-like berry – but don’t eat it, it tastes terrible.”

Brett Summerell at the Botanic Gardens of Sydney, Australia, who wasn’t involved in the study, says the new work provides comprehensive evidence of hybridisation and subsequent species radiation – something that has been lacking for this group of plant relatives.

“The study also highlights the importance of protecting wild crop relative species in order to better understand how important crops have evolved and are likely to adapt to challenges in the future,” says Summerell.

“Many of the relatives of species like potatoes are threatened with habitat destruction and the impact of climate change.”