Potato

A potato is not a root. It is the swollen tip of an underground stem, and its eyes are buds. Knock out one gene in a potato and the stems that should swell into tubers grow into branches.13

The plants that do this are a branch of the nightshades, with more than 100 wild species between the southwestern United States and southern Chile. Most records of them come from Peru, Bolivia, Argentina and Mexico. 1,3,1476

One study of 128 genomes reports that the whole branch began as a cross, 8 to 9 million years ago, between the tomato's line and a tuberless one. 7813

Wild tubers defend themselves with bitter glycoalkaloids. In one comparison their flesh held 300 to more than 1,600 mg per kilogram, against a limit of 200 thought fit to eat. 5858,3

The oldest sure sign of anyone eating potatoes is in North America. At North Creek Shelter in Utah, grinding stones from a layer 10,900 to 10,100 years old carry starch grains of the wild Four Corners potato, Solanum jamesii. Stones from 4,000 years later carry them too. 2727

That potato was never tamed, so far as anyone has shown. It still grows 150 m from the shelter, and its stands near old settlements are less varied than those farther south, as if people had carried a few tubers in. 277927,80

A still older claim comes from Monte Verde in southern Chile, where scraps of tuber lay in hearths 18,500 to 14,500 years old. They were put down to the wild potato Solanum maglia by the shape of their starch. That reading is now being checked again. 2828

Until 2005 most botanists thought the potato had been tamed several times, from several wild species. Then a study of 362 wild and farmed potatoes put every Andean landrace in one group, sprung from the wild potatoes of Peru. Genome studies now name the species: Solanum candolleanum. 1,141,2,33,13,2

The ground is less clear. At Jiskairumoko, a village site near Lake Titicaca lived in from about 3400 to 1600 BCE, grinding stones carry potato starch. The team that found it cannot say whether the potatoes were wild or farmed. 292929

The oldest tubers themselves come from middens in the Casma Valley, on the coast. The excavators dated the sites to about 2000 to 1500 BCE. A later paper gives the tubers an age of 7,800 years, which we could not trace. 303027

The first farmed potatoes had two sets of chromosomes, like their wild parent. Potatoes often make pollen and eggs with the full double set, and from such accidents came potatoes with four. They became the main potato of the Andes. 143,621,4

The crop also crossed back to the wild. A two-set potato and the frost-hardy wild Solanum acaule gave a bitter potato with three sets. That one, crossed with the four-set potato, gave another with five. A third bitter kind has a different wild parent. 4,5,64,5,144,5,14

The three stand apart from the other farmed potatoes in DNA studies, near the wild species.4,60 Botanists have sorted the whole family into 21 species, or 7, or 4, or one.4,14,81

The count of chromosomes is no sure guide. Of 89 genebank potatoes labeled as one two-set kind, 18 turned out to have three sets or four.4

Bernabé Cobo, writing in the 1600s, described the mountains as steps. On the cold step near the top no maize or wheat would grow. People there lived on potatoes, oca, ulluco, maca and quinoa, and frost often burned the fields. 2323

Each crop has its own band. Potato landraces are grown mostly between 3,000 and 4,000 m. Above that, on ground where frost can strike on 300 days of the year, the bitter potatoes go on to 4,200 m. 14,37273

A household does not bet on one field or one kind. Families studied in Huancavelica worked about five scattered potato fields a year, and one household kept as many as 160 different potatoes. 2424

Cieza de León, whose chronicle was printed in 1553, wrote that in the Collao, the cold high country of the south, potatoes were the main food and no maize grew. 3131

Chuño is a potato made to keep for years. Cobo set down the method: spread the potatoes on the ground, to the sun by day and the frost by night, for 12 to 15 days. Tread them to press the water out. Leave them 15 to 20 days more, until they are light and hard as cork. 2323

An Aymara dictionary of 1612 defines the word the same way: cured by frost at night, dried by the sun, trodden.16 The treading does more than dry. The bitter compounds dissolve in water and leave with it. 73,2914

There was a finer white kind, soaked in water for two months before the last drying.23 The calendar of the farming year drawn by Guaman Poma in 1615 gives June to digging potatoes and making chuño, and July to carrying the harvest to the storehouses. 8282

Cieza saw Spaniards grow rich selling it at the mines of Potosí.31

No document describes potatoes being carried to Europe.7,20 The first dated record outside the Americas is of a cargo: barrels of potatoes shipped from Gran Canaria to Antwerp in November 1567. 7,87 Records in Seville name them in 1573 and 1576.7

In January 1588 the botanist Carolus Clusius, in Vienna, was sent two tubers and a fruit from Mons. The sender had them from the household of a papal envoy, under the Italian name taratoufli, little truffles. German Kartoffel comes from it. 18,2018,2018,19,20 Clusius knew the plant was the papas of Peru. The Italians, he wrote, did not know where they had got it. 18,2018

In London, John Gerard grew it by 1596 and printed its picture the next year as the potato "of Virginia". It did not grow in Virginia. 202120,21

The usual story is that Europeans shunned the potato for two centuries, until rulers pressed it on them. The historian Rebecca Earle argues that this has it backward.34 Church courts were hearing disputes over tithes on cottage potatoes in Britain from the late 1600s. Lancashire had potato markets by then, and Ireland grew it as a field crop by 1668. 343420

The promoters came later. Frederick II of Prussia issued fifteen orders to grow potatoes, the first in 1746.35 In France, Parmentier won a prize in 1771 for an essay on famine foods. All seven essays sent in said the potato was already an old crop there. 2020,34

Adam Smith did the sums in 1776. An acre of potatoes, he reckoned, gave three times the food of an acre of wheat. 8383 Two economists have since put about a quarter of the Old World's growth in people and towns between 1700 and 1900 down to the potato. A review found the method sound and the figure nearer a sixth. 984

The potato reached English America by way of England. It was taken to Bermuda in 1613, and in 1621 the governor there sent some to Virginia.20 Settlers from Ireland brought it to New Hampshire in 1719.20

In Asia the early records are thin and tangled with the sweet potato. A traveler saw potatoes in the gardens of Surat in the 1670s. Dutch writers noted them in Taiwan in 1650, and a county record in Fujian describes one in 1700. 202020 In much of Africa its names still say who brought it: the white man's yam, the European root.20

New Zealand's potatoes came with French and British ships between 1769 and 1773. Māori growers took the crop up at once. By 1814 a visitor described fenced and weeded potato fields at the Bay of Islands. 3636,20 Darwin, who called there on the Beagle, wrote that it was the most essential benefit the islands had received from outside.39 Many old Māori kinds are deep-eyed and knobbly, like Andean ones.36

An Andean potato sets tubers when days are short. In the long days of a northern summer it would not.63,40 The potatoes of southern Chile were already used to long summer days. So Soviet botanists argued that Europe's potato must have come from Chile. Others held that it came from the Andes, and that Chilean stock arrived only after the blight of the 1840s. 320,8585,8

Pressed plants answered it. One marker in the DNA of old herbarium sheets showed that Andean potatoes were the rule in Europe in the 1700s, that the Chilean kind was there by 1811, and that it had taken over well before the blight. 4185,86

Whole genomes agree. Europe's potatoes of 1650 to 1750 were close kin of Andean ones, and lacked the gene variants that later let potatoes tuber in long days. Those turn up in the 1800s. 4040

Both sides were partly right. The old landraces of the Canary Islands hold both kinds.8

The disease was first reported in 1843 around the ports of New York and Philadelphia. By 1845 it had been reported from 17 states and provinces. 42,4342

In June 1845 it was seen near Courtrai in Belgium. Within weeks it was in the Netherlands and northern France. A letter of 16 August reported it on the Isle of Wight. A week later there was hardly a sound potato in Covent Garden. On 13 September it was at Dublin. 101044,4544,4544,45

The cause is Phytophthora infestans, a water mold, kin to brown algae and not a true fungus.87,47 DNA from blighted leaves pressed between 1845 and 1896 shows one strain behind the outbreaks for fifty years. 4747

Where it began is argued. One group traces it to wild potatoes in the Toluca Valley of Mexico, others to the Andes. How it crossed the Atlantic is not known either: no ship is named. 49495046

On the eve of the blight about a third of Ireland's 8.5 million people ate almost nothing but potatoes, at 4 to 5 kg a day for a grown man. 89,1111

The blight took about a third of the crop in 1845 and nearly all of it in 1846.11,10 Belgium, the Netherlands and Prussia lost about half theirs that year, and the Scottish Highlands four fifths. Nowhere else did so many depend on the one food. 1010,1111,10

About a million people died, most of fever and dysentery. About a million more left. The census of 1851 counted 6.55 million. 11,1211,1089,1011,89,10

Food left Ireland through it all. Historians agree on that, and disagree on whether keeping it would have closed the gap. 9011,90 Nothing reliable was found against the blight until the 1890s.11

A potato variety is a clone. Plant a tuber and the same plant comes up. Sow its true seed and every seedling differs, because the plant carries four unlike sets of chromosomes. 7794,95

After the blight, growers went looking for new stock. In 1851 the Rev. Chauncey Goodrich of Utica, New York, got a few South American potatoes through the consul at Panama. He sowed seed from one, Rough Purple Chili, and kept a seedling he called Garnet Chili. 93,1151,52,5351,52

From a seed ball of Garnet Chili came Early Rose, in Vermont in 1861. From a seed ball of Early Rose, found by the young Luther Burbank in his mother's garden in 1873, came the Burbank. 51,52,6951,52,54,55 And from the Burbank, with no seed at all, came Russet Burbank: a tuber whose skin had turned brown and netted. DNA confirms the two are one clone.51,55,67

Early Rose went on to parent varieties on both sides of the Atlantic. 5351,52,69

The Mexican wild potato Solanum demissum gave breeders at least eleven genes against blight. The blight overcame them quickly. The strain of the 1840s already carried the means to beat the first one. 96,9393

Other wild genes lasted better. Maris Piper, released in Britain in 1963, has its resistance to a cyst nematode, a pest of the roots, from an Andean potato. The American variety Atlantic has the wild Solanum chacoense behind one parent. Ten varieties and breeding lines, Maris Piper and Atlantic's parent Lenape among them, brought in half of all the new variation in European potatoes since 1945. 51,69,6767,6951,69,676767

Little was lost on the way: 96% of the variants in varieties from before 1945 are still in modern ones.67

The newest plan is to remake the crop. A two-set potato can be inbred, and two inbred lines crossed give uniform seed. A team reported such hybrids in 2021. 94,979895,99 And potatoes given three wild resistance genes at once stood through three seasons of trials in Uganda without spraying.100

The world grew 390 million metric tons of potatoes in 2024. China grew 24% of them and India 15%. 2222 China has been the largest grower since 1993, while Europe's harvest has shrunk. 101101 By one reckoning the potato is the third food crop of the world, after wheat and rice.101

In the United States about half of all potatoes are now eaten frozen, mostly as fries.102

The variety stayed behind. The genebank of the International Potato Center in Lima keeps about 4,700 to 4,800 traditional potatoes from 18 countries, and more than 2,500 samples of wild ones. 5656,103 In Peru's Potato Park, six Quechua communities grow some 900 native kinds and share more than 200 with the Center's scientists.25

The wild relatives are less safe. Of 73 studied, only three are well represented in genebanks. 104105