Rediscovering the potato onion

Have you ever eaten a potato onion? It’s highly likely, but you probably called it a ‘shallot’. Now researchers have studied this lesser known relative of the common bulb onion, and we may be seeing a renaissance of this venerable vegetable among green-fingered folk.

Forskare vid bland annat LiU och Stockholms universitet har tittat närmare på potatislökens ursprung.Researchers at Linköping University and Stockholm University have studied the potato onion Photo credit Matti LeinoHardly anyone has heard of the potato onion, but when Sweden and other Nordic countries began inventoring heritage plants, it became clear that it is still cultivated in many kitchen gardens. The potato onion is a close relative of the much more common bulb onion, and just as a potato grows from a set potato, which generates many new potatoes, a potato onion grows from a set potato onion. The potato onion, however, has been known in the Nordic countries for much longer than the potato, and has many familiar names in Swedish, such as ‘Johanneslök’, ‘knipplök’ and ‘krasslök’.Forskare vid bland annat LiU och Stockholms universitet har tittat närmare på potatislökens ursprung.Researchers at Linköping University and Stockholm University have studied the potato onion Photo credit Jenny Hagenblad

Researchers at Linköping University and Stockholm University have worked with several other Nordic institutions and investigated this plant – in test cultivation, through genetic analysis of its relationships with other plants, and by collecting traditional knowledge. Over 100 potato onions have been collected from kitchen gardens throughout the Nordic region, and in many cases the plant has a history that goes back many generations.Biträdande professor Jenny Hagenblad, IFMJenny Hagenblad, associate professor Photo credit Anna Nilsen

“We knew nothing about the material when we started. Was everything derived from a single ancestor, or were there many different varieties of potato onion?”, remembers Jenny Hagenblad, professor of genetics at Linköping University.

It turned out that there are many different varieties, although growers share bulbs of the most popular ones, which in this way spread through a region. The researchers found examples of the same variety being grown in Norrbotten in the north of Sweden and in Skåne, far to the south. The bulbs were highly prized, and a family that moved would take set potato onions with them.

“Another conclusion was that the vegetable that we call ‘potato onion’ is genetically indistinguishable from ‘shallots’,” says Jenny Hagenblad.

Viking onions?

“Alliums are among the plants mentioned in the oldest written sources from the Nordic region – on golden coins from the 6th century, as travelling rations on Viking trading journeys, and in medieval laws. This is surprising, since the allium species we know today, such as the bulb onion and the leek, are difficult to grow and propagate. It is much more likely that it was potato onion that was cultivated in prehistoric times in the Nordic region”, says Matti Leino from the Department of Archaeology and Classical Studies at Stockholm University.Matti Leino, Stockholms universitetMatti Leino at Stockholm University Photo credit Linda Wiking

The potato onions are now preserved in gene banks in several Nordic countries. And the plant is becoming popular in kitchen gardens in these countries. It is easy to manage, hardy, and tastes excellent. The researchers are hoping that a type of onion grown for hundreds of years only to be nearly forgotten is now making a comeback in Nordic horticulture.

The results of the study were published on 25 October in the journal Economic Botany. It was conducted with financial support from the Swedish Board of Agriculture within the framework of the National Program for Diversity of Cultivated Plants (POM).

Translation by George Farrants

The article:Patterns of Exchange of Multiplying Onion (Allium cepa L. Aggregatum-Group) in Fennoscandian Home Gardens”, Matti W. Leino, Svein Ø Solberg, Hanna Maja Tunset, Jesper Fogelholm, Else-Marie Karlsson Strese and Jenny Hagenblad, (2018), Economic Botany, published online 22 October 2018, doi: 10.1007/s12231-018-9426-2

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