What Is a Seed Bank? Insurance Against Losing a Crop Entirely
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Modern agriculture grows a small number of varieties across enormous areas, which is efficient and fragile, because a disease that defeats one variety defeats it everywhere at once. Seed banks store the genetic diversity that breeding will need when that happens, in cold vaults holding hundreds of thousands of samples, most of which will never be planted and all of which must stay viable for decades.
Why the diversity matters
Crop plants have been selected for yield, uniformity and processing characteristics, which has narrowed their genetic base substantially, and the traits that will be needed in future, including resistance to a pathogen that does not yet exist and tolerance of temperatures not yet experienced, are more likely to sit in a landrace grown by a few farmers in a mountain valley than in a commercial variety. The practical demonstrations are well documented. A 1970 fungal epidemic destroyed a large share of the American maize crop because almost all of it shared a single genetic component, and resistance had to be found in stored material. Wheat breeders have repeatedly drawn resistance genes from wild relatives and old landraces to stay ahead of rust fungi that evolve to defeat each new variety. The Irish potato famine is the standard historical case, with a population dependent on a very narrow range of potato genetics meeting a pathogen it had no resistance to.
How storage works
Most seeds can be dried and frozen, and the physics of that is what makes banking possible:
- •Orthodox seeds tolerate drying to low moisture content and freezing, which slows their metabolism so far that viability extends from a few years at room temperature to decades or centuries at minus eighteen to minus twenty degrees
- •Seeds are cleaned, dried carefully to a specified moisture content, sealed in moisture-proof containers and frozen, with humidity control as important as temperature
- •Viability is tested periodically by germinating a sample, and when germination falls below a threshold the accession must be regenerated by growing it out and harvesting fresh seed, which is the most expensive and most easily neglected part of the whole operation
- •Recalcitrant seeds, including those of many tropical trees, avocado, cocoa and oak, cannot be dried or frozen without dying, so they are kept as living collections, as tissue cultures or in liquid nitrogen by cryopreservation
- •Clonally propagated crops including potato, banana and cassava cannot be stored as seed representatively at all and require field collections or cryopreserved tissue
- •Duplicate samples are held in more than one location, which is the entire logic behind a global backup facility
The global system
Around 1,700 seed banks exist worldwide, most of them national or institutional collections holding material relevant to their region, and their reliability varies enormously with funding, political stability and infrastructure. The Svalbard Global Seed Vault, opened in 2008 inside a mountain on a Norwegian island, exists as a backup to those collections rather than as a bank that lends material: depositors retain ownership, nobody else may withdraw their boxes, and the facility simply stores duplicates in permafrost with no permanent staff. Its one withdrawal to date came in 2015, when researchers evacuating an international collection from Aleppo during the Syrian civil war retrieved their duplicates to re-establish the collection elsewhere, which is precisely the scenario it was built for and a good demonstration of why backup matters. Kew's Millennium Seed Bank pursues a different objective, storing wild plant species rather than crops, with a target running to a substantial fraction of the world's flora.
The arguments
Two criticisms recur and both have force. The first is that storing seeds in freezers is conservation without evolution: a sample frozen in 1985 is genetically frozen in 1985, while the pests, pathogens and climate it would face have continued to change, which is why on-farm conservation, where farmers continue growing traditional varieties that keep adapting, is regarded as complementary rather than optional. The second concerns ownership and benefit. Material collected from farmers in one country has historically been used to breed varieties sold commercially elsewhere, with no return to the communities that developed it over centuries, which prompted the international treaty on plant genetic resources establishing a multilateral system with access rules and a benefit-sharing fund. Implementation remains contested, and the interaction with patents on genetic sequences is unresolved. The practical vulnerability is more mundane: seed banks require continuous funding to regenerate ageing accessions, and collections have been lost through war, flood, equipment failure and simple budget cuts.
The takeaway
Seed banks store crop and wild plant diversity because commercial agriculture is genetically narrow and future resistance traits are likelier to sit in old landraces and wild relatives. Orthodox seeds are dried and frozen and last decades, while recalcitrant seeds and clonal crops need living collections or cryopreservation. Svalbard is a backup holding duplicates, used once to restore a collection evacuated from Syria. Frozen seeds stop evolving, which is why farmers continuing to grow traditional varieties matters alongside them.