The Starset SocietyBy: Rhodilee Jean Dolor
An ancient botanical event—the hybridization of two distinct plant species—set the stage for the evolution of the modern potato and paved the way for the beloved French fries to become a global favorite.
In the new study published in the journal Cell on July 31, an international team of researchers discovered that about 9 million years ago, natural interbreeding in the wild occurred between the tomato plant and potato-like species from South America.
Study author Sanwen Huang, from the Chinese Academy of Agricultural Sciences in China, and colleagues said that this development gave rise to the modern-day potato and resulted in the most notable feature of the starchy, tuberous crop.
Tuberization of the Potato
The potato is one of the world’s most important crops. According to the Peru-based research organization International Potato Center (CIP), more than a billion people worldwide eat the culinary staple. This makes the potato the third most important food crop in the world after rice and wheat in terms of human consumption.
But while the potato is found in virtually all kitchens across the globe, scientists have long been puzzled by its origin.
The appearance of modern potato plants is almost identical to those of three potato-like species from Chile called Etuberosum, but the latter do not carry tubers—enlarged underground structures that store nutrients in plants like potatoes, yams and taros. Phylogenetic analysis also shows that potato plans are more closely related to tomatoes.
Etuberosum and tomatoes are distinct species of plants but they shared a common ancestor about 14 million years ago. These plants were also able to interbreed about 5 million years after their divergence, which gave rise to the earliest potato plants with tubers around 9 million years ago.
By analyzing 450 genomes from cultivated potatoes and 56 wild potato species, the researchers found that every species of potato has a stable, balanced mix of genetic material from both tomato plants and Etuberosum.
“Our results show that the phylogenetic conflicts detected among the three lineages are widespread across genomes in Petota and were caused by hybridization events from the ancestors of Tomato and Etuberosum,” the researchers wrote about their observations on the genetic mixtures they found in the present-day Petota potato species.
The study also suggested that the evolutionary inbreeding event triggered the formation of the tuber, a prominent feature of the modern-day potato.
In their paper, Huang and colleagues said that positively selected genes (PSGs) associated with the tuberization of potatoes were derived from both tomato and Etuberosum.
The SP6A gene that signals the growth of tubers are from the tomato’s side while the IT1 gene that regulates the growth of the tubers comes from the Etuberosum.
“Our findings show how a hybridization event between species can spark the evolution of new traits, allowing even more species to emerge,” said Huang. “We’ve finally solved the mystery of where potatoes came from.”
They added that the ability to form tubers appears to be a crucial development that enabled the petota ancestor to asexually reproduce and expand into seasonal high-elevation habitats.
“This trait, along with the sorting and recombination of hybridization-derived polymorphisms, likely triggered the explosive species diversification of Petota by enabling occupation of broader ecological niches. These findings highlight how ancient hybridization fosters key innovation and drives subsequent species radiation.”
The Role of Natural Selection
The researchers clarified that hybridization is not the sole cause of the appearance and growth of tubers. They said that natural selection also played an important part in the development and propagation of the Petota species.
“Genes involved in tuberization are expected to undergo rapid evolution, due to natural selection, with diverged alleles potentially becoming alternately fixed in the hybrid offspring lineage,” the researchers wrote.
They said that natural selection recruited alternately inherited parental genes for specific pathways that contributed to tuber formation.
Huang and colleagues said that after searching for PSGs from 17,872 homologous gene groups in a dataset of 128 genomes, they detected 229 PSGs derived from Etuberosum and 269 PSGs from tomato “which were under natural selection in the two parental lineages prior to interspecific hybridization and were alternately inherited by Petota during its origin.”
Beyond the Study
The researchers hope that understanding the evolution of the potato will allow scientists to develop innovative ways to breed new species of the dietary staple. This is crucial given the role of potatoes in global food security.
According to a 2022 report from the Food and Agriculture Organization (FAO) of the United Nations, about two-thirds of the world’s population consumes potatoes as a staple food. Nearly 50% of potatoes are also used as household food or vegetables.
“Promoting potato industry can alleviate the contradiction between the shortage of cultivated land and water resources to a
considerable extent, expand food sources, and improve the coefficient of ensuring global food security,” read the FAO report.
Huang and his team are already conducting experiments to propagate fast-breeding seed potatoes by reintroducing key tomato genes.
Potatoes reproduced by seeds could be more genetically diverse and resistant to risks that threaten modern crops including drought, environmental change, new pests and diseases.
“Evolving a tuber gave potatoes a huge advantage in harsh environments, fueling an explosion of new species and contributing to the rich diversity of potatoes we see and rely on today,” Huang said.
Meanwhile, reproducing potatoes by cutting them in pieces and planting them results in genetically identical crops that can be wiped out by new diseases.
“In addition to helping us understand potato evolution and potato tuber development, the methods used (in this study) can also help researchers
learn about other traits, such as disease and insect resistance, nutrition, drought tolerance, and many other important plant traits in potato and tomato,” said Amy Charkowski, research associate dean of Colorado State University’s College of Agricultural Sciences, who is not involved in the study.
