The next time you and your friends share some fries, impress them with some knowledge on your favorite side dish. They’ll be amazed to learn that potato is the world’s third most consumed food crop and America’s favorite vegetable (according to the US Department of Agriculture). Strangely enough though, potatoes haven’t always been a fan favorite. In fact, they weren’t largely grown or consumed until about 250 years ago. This is because they were thought to be a dangerous food, suitable only for livestock to consume. It would take many years and prominent figures to help popularize the consumption of potato. Today, it is a widely eaten crop but faces many pest and climate change related issues, such as the Colorado Beetle. Breeders are working to improve current potato varieties to have better resistance to the pest, however the crop’s complicated genetics and lack of diversity makes this a challenge. One of the ways scientists are overcoming these hurdles is by utilizing the diversity of wild potatoes to find novel genes encoding pest resistance.
The Origins of Potato
Potatoes are native to the Andes mountains and were domesticated between 8000-5000 BC. Genetic evidence and archeological records of potato consumption point to modern day Peru as the site of domestication. The potato we consume today (scientific name S. tuberosum) was likely domesticated from a hybrid cross of two wild potato species, S. stenotomum and S. sparsipilum. Native South Americans would cross the early S. tuberosum with other wild potato species to produce cultivars that fit their cultural and growing needs. For example, bitter cultivars were selected for cultivation at high altitudes because typical freeze drying storage methods would inactivate the toxicity of the bitter compounds.
Today, South American farmers continue to maintain genetic diversity of potato by allowing their cultivars to grow and cross with wild potatoes. It is estimated that there are over 200 different wild potato species across South America. These plants are a tremendous resource of genetic diversity as they contain genes for novel traits such as pest and pathogen resistance. The International Potato Center (CIP) in Peru is an organization growing over 4,000 different types of potato to preserve this diversity. Scientists all over the world can request potato varieties from the CIP for research or to use in breeding programs for developing new varieties. While potato had been a staple crop in South America for hundreds of years, it was slow to catch on in Europe.
The Growth of Potato Popularity in Europe
Potatoes were thought to have arrived in Europe around 1570 by Spanish sailors. Many Europeans were skeptical about consuming potatoes and considered them deadly since they resemble plants in the “Nightshade family,” a poisonous group of plants. Back then, it was thought that this dangerous family of plants was created by witches and devils. Potatoes were not allowed to be grown except in small gardens. This was because the agricultural infrastructure was prioritized for growing grains, the most common being wheat. Because of agricultural restrictions and unsavory opinions, potatoes were mostly used as animal feed. It wasn’t until the 1770’s when famines became more rampant and prominent figures began pushing potatoes did Europeans begin to accept them.
The French physician Antoine Parmentier was serving as a pharmacist in the army during the Seven Years War (1754-1763). While fighting, he was taken as a prisoner of war by Prussians and forced to eat nothing but potatoes. It was here that he realized how delicious the vegetable truly was. After returning to France, he began to study potatoes for their nutritional value and was credited with popularizing the crop as a staple food in Europe. Marie Antoinette was another prominent supporter of potatoes and even wore their flowers as an accessory. After the 1770s, potatoes were grown in many European countries to feed the working class. The crop was highly nutritious and required less land to grow on compared to other crops. In Ireland, many poor families relied on potatoes as their sole source of food. Ireland’s single crop dependency and the complicated genetics of potato would lead to one of the worst global famines in human history.
In 1845, Ireland had unusually cool and wet weather, allowing the fungal pathogen Phytophthora infestans to thrive. This mold caused potato blight and decimated fields of potato in Ireland which had no resistance to the pathogen. In Ireland, potatoes were clonally propagated, meaning that all plants are derived from cuttings and are genetically identical. The method of clonal propagation leads to very low genetic diversity as there is no introduction of new genetic variation by cross pollination. Without genetic diversity, potato plants did not have the genes that would allow them to withstand changing environments or other stresses. The reliance on a singular crop and the low genetic diversity of potato would ultimately lead to the Irish Potato famine.
The Genetics of Potato Are Complicated
Diploid organisms, like humans, have two sets of genes, one set from their mom and another from their dad. For breeding better varieties in diploid crops, such as cabbage and broccoli, plant breeders cross two parents together and screen the offspring who have desirable traits such as larger leaves or improved flavor. However, most cultivated potatoes are tetraploid meaning they have four sets of genes, two sets from each parent. This complicates traditional breeding as the probability of producing an individual with your desired traits becomes extremely low.
The complicated genetics of potato has hampered our ability to generate new varieties with better disease resistance or improved culinary traits. This means that we have relied on natural mutations to improve potato cultivars for us. For example, in 1872 Luther Burbank was growing potatoes when he discovered a new variety caused by a random mutation in an originally smooth skinned variety. This new variety, known as Russet Burbank, has tubers with rough skin that act as a barrier against pathogens in the soil. It also has an iconic flavor that has made it the variety of choice for McDonald’s french fries. Since the random mutation, Russet Burbank has become one of the most commonly grown varieties in the United States for the last 100 years. Our dependence on a singular variety of potato however, could be detrimental, such as the case of the Irish Potato Famine. Thankfully, scientists and breeders are looking to new scientific approaches to incorporate genetic diversity into current cultivars to improve their culinary profiles and resistance to different stresses.
A New Era for Potato
While most potatoes grown today are tetraploid, there are some that are diploid. Breeders have been working towards using more diploid potato to easily create cultivars with better traits. For example, breeders are currently looking to produce varieties with Colorado Beetle resistance. This pest is a major threat to potatoes grown in North America. To do this, breeders are analyzing the genomes of wild, South American diploid potatoes as they carry genes conferring resistance to pathogens and other stressors. One of the major issues with using these wild diploid potatoes, however, is that they are self-incompatible. This means that a plant cannot reproduce fertile offspring through self-pollination and requires outcrossing (or mating) with another plant. This outcrossing process leads to continuous reshuffling of genes, leading to losses of favorable genetic combinations in the subsequent generations. Breeders are trying to overcome this issue by using gene editing tools such as CRISPR-Cas9 to inactivate the genes that cause self-incompatibility. Using gene editing would then facilitate the introduction of new genes from wild potato into cultivated diploid potato varieties by allowing plants to self-pollinate. The self-pollination process would then maintain those favorable genetic combinations. Several varieties of potato have already benefited from gene editing including the Russet Innate varieties by JR Simplot. Gene editing was used to improve the storage capability of this variety to help reduce food waste. The variety was approved by the FDA and marks a new era for potato breeding.
These new scientific approaches enable us to generate new potato varieties with improved flavor, texture, and of course resistance to diseases and climate change. After all, we wouldn’t want to see our favorite side dish become decimated by another pathogen.
About the Author
Dionne Martin is a Ph.D. student in the Genetics Department at the University of Georgia. Their research focuses on identifying key genes involved in potato tuber development and uncovering the evolutionary origins of tuber development across plant species. Outside of the lab, they enjoy watching UGA football, hanging out with her two cats, and doing Brazilian Jiu Jitsu.
