Today’s potatoes arose out of an unlikely mashup — with a tomato.
Until now, the potato’s origin and evolution had long been a scientific mystery. It now appears that the starchy spud emerged 9 million years ago as the Andes Mountains were forming. It came about from natural breeding events between an early tomato plant and a potato-like species.
This ancient cross gave rise to the plant’s swollen stem parts, known as tubers. Tubers eventually spread through some 180 wild species of potatoes and thousands of cultivated varieties. Scientists from around the world shared the new findings in the September 18 issue of Cell.
Digging into potatoes
The cultivated potato — Solanum tuberosum — is one of the world’s most important staple foods. Scientists knew it was related to Solanum etuberosum, a South American plant. That species looks a lot like our potato plant. It just can’t form tubers, those parts that we turn into fries, baked potatoes and chips.
Genetics had shown that potatoes are related to tomatoes. But scientists thought the two plants were like distant cousins. Instead, research now shows, species from these two lines interbred.
The team peeled back the potato’s origin by analyzing dozens of wild and cultivated varieties of potato. About half of the genes in every potato species traced to the tomato, the rest to S. etuberosum.
This suggests potatoes came from a single hybrid cross of these two groups, says Sandra Knapp. She’s a botanist at the Natural History Museum in London, England.
“In creating that hybrid offspring, various gene families came together and interacted to enable the creation of tubers,” she says.
One gene — SP6A — came from the tomato side. Previous studies had shown it works as a master switch for tuber initiation. Another gene — IT1 — is key to the growth of underground stems that form tubers. It came from S. etuberosum.
Experiments in potato plants now confirmed that without the IT1 gene, tubers are tiny. Without SP6A, tubers don’t even form.
How combining these genes in one plant “led to potatoes making potatoes isn’t fully explained in this paper,” says Salomé Prat. She’s a plant biologist who did not take part in the new study. She works at the Centre for Research in Agricultural Genomics. That’s in Barcelona, Spain. Showing that these genes came together from a natural cross does not mean tubers formed right away, she adds. “The story is much more complicated.”
A more resilient spud
How interbreeding led to tubers shows that hybrid crosses can be a powerful driver of evolution. Some new hybrids can be sterile (unable to reproduce). But tubers store water and nutrients. And if left buried, they can sprout new plants. No pollination or seeds are needed.
This likely gave the new potato lines time to regain an ability to reproduce sexually. And the new tuber structures may have given early potato plants an edge as the Andes began to form millions of years ago.
Tomatoes prefer dry, warm conditions. S. etuberosum thrives in cold, wet places. Potatoes inherited a mix of traits that allowed them to flourish even in cold, dry sites. They got “the best of both worlds,” Knapp says. And changing habitats in the Andes might have given these new species opportunities to thrive.
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Most of today’s 180 wild potato species are bitter or toxic. But many thousands of years ago, Indigenous people in the Andes found a tasty wild potato. Over time, they developed many varieties from it. Spanish explorers later brought several of them to Europe. This led to the potato’s global spread as a food staple.
More recently, scientists and farmers have crossed potato species to get traits such as high yield or pathogen resistance. Many of these lost some of the potato’s initial genetic variability. That makes today’s potatoes less adaptable — and more vulnerable — to extreme heat, flooding and other features of our changing climate.
Identifying the genes inherited from the early tomato and S. etuberosum might lead to a more resilient potato. Lost traits might be restored through traditional breeding or genetic engineering. And that, Knapp says, might lead to more adaptable varieties.