Seed Banks and the Future of Food

A Human beings have eaten perhaps six thousand plant species over the course of their history. Today just nine of them supply around two-thirds of the calories consumed worldwide, and wheat, rice and maize alone account for roughly forty per cent. The narrowing happened quickly. Through the twentieth century, farmers in almost every country replaced the local landraces they had inherited, each shaped over generations to suit a particular valley or soil, with a small number of high-yielding varieties bred for uniformity. The gain in productivity was enormous and it fed a growing population. The loss was harder to see: as the landraces vanished from the fields, so did the genetic variation that plant breeders draw on when a new disease, a new pest or a drier decade arrives.

B The idea that this variation might be deliberately stored belongs largely to one man. Nikolai Vavilov, a Russian botanist, spent the 1920s and 1930s travelling through five continents, gathering seeds and mapping what he called the centres of origin, the regions where each crop showed the greatest diversity and where, he argued, it had first been domesticated. By the end of his expeditions the collection he had assembled in Leningrad was the largest in the world. Vavilov himself fell foul of Soviet agricultural politics; he was arrested in 1940 and died in prison three years later. During the wartime siege of the city, the researchers who remained in his institute guarded a store of edible seed through a winter of famine, and several of them starved to death rather than eat the collection they were protecting.

C A modern seed bank rests on a simple principle: seeds live longer when they are cold and dry. Incoming samples are cleaned, checked for disease and then dried until the moisture inside the seed falls to roughly five per cent. They are sealed into foil packets and moved into a chamber held at minus eighteen degrees Celsius. Decades of trials suggest that every one per cent of moisture removed, and every five degrees of cooling, roughly doubles the time a seed remains alive; well-stored wheat or barley may still sprout after a century. Curators withdraw samples periodically and test them, and once the proportion that germinates falls below a set threshold the sample must be regenerated, grown out into fresh plants in isolation so that it does not cross with neighbouring varieties. Regeneration is the slowest and most expensive job in the building.

D Roughly a thousand seed banks now operate around the world, and most are more fragile than they look: war, budget cuts, a failed compressor or a long power cut can undo decades of work. The Svalbard Global Seed Vault, opened in 2008 on a Norwegian island about thirteen hundred kilometres from the North Pole, was built as insurance against exactly that. A tunnel driven into a sandstone mountain leads to chambers surrounded by permafrost, which would hold the temperature down for weeks even if the refrigeration stopped. Svalbard owns nothing it stores; depositors send sealed boxes and may ask for them back at any time. The first withdrawal came in 2015, when a research centre forced out of Aleppo by the Syrian war requested its own material in order to rebuild its collection in Lebanon and Morocco. Replacement boxes were deposited two years later.

E Not every seed can be treated this way. The seeds of cocoa, avocado, mango, coconut and a great many tropical forest trees are what botanists call recalcitrant: they are shed with a high water content and are killed, rather than preserved, by drying and freezing. Crops of this kind, along with those such as banana and potato that are propagated from cuttings or tubers, must be kept as living field collections, orchards and plots that have to be weeded, watered and replanted, and that a single hurricane or new disease can destroy. The alternative is cryopreservation: shoot tips or embryos are treated with protective solutions and plunged into liquid nitrogen, where metabolism effectively stops. It works, but a reliable procedure has to be devised species by species, and for most plants nobody has done it yet.

F A seed bank is not a museum, and its worth is measured by what leaves it rather than by what it holds. In the early 1970s a virus called grassy stunt swept through the rice fields of Asia; resistance was eventually traced to a single wild population collected in India years earlier and stored in the Philippines, and the gene it carried now sits in varieties grown across millions of hectares. Stories of that kind depend on collections being catalogued, shared and, increasingly, sequenced, and on international rules governing who may take material and how any benefits return to the countries the seeds came from. None of this replaces the older method. Landraces still growing in farmers' fields keep changing as the climate around them changes, which is something no freezer can imitate, and the strongest programmes now do both at once: seeds preserved in the cold, and seeds still at work in the ground.