Seed banks are the last hope for plants that face imminent extinction but these floral vaults may be unable to save some of the most iconic and high-risk species.
More than a third of critically endangered plant species cannot be preserved in seed banks using current methods, researchers have discovered.
Seed banks use a process of drying and then deep-freezing to -20°C (-4°F) to preserve the precious items in an effort to save plants, trees and wild relatives of crops.
Important UK tree species such as oak, horse and sweet chestnuts, and global foods including avocado and cocoa could all be lost forever if current methods are not updated.
A global strategy for plant conservation has set a target to conserve 75 per cent of threatened species outside their natural habitat – or ‘ex-situ’ – by 2020.
Places such as Kew’s Millennium Seed Bank at Wakehurst Place, West Sussex and The Svalbard Global Seed Vault are trying to meet this criteria.
Seed banking in the conventional sense will not work for many at-risk plants and researchers are claiming urgent investment and research is needed to create alternatives to preserve some of the world’s most threatened plants.
A study last year by researchers from the Royal Botanic Gardens, Kew, estimated that about 8 per cent of all the world’s plants produce seeds which cannot be banked.
Research from the team at Kew suggests the problem may be worse for species that are at risk of extinction.
Researchers used four major plant lists and looked at various categories of threatened plants to see how many species are likely to be ‘bankable’.
They estimate 36 per cent of the most at risk of extinction, or critically endangered species, produce ‘recalcitrant seeds’.
This means they do not survive the drying process and cannot be frozen, making them ‘unbankable’, the study published in the journal Nature Plants said.
More than a quarter (27 per cent) of endangered species produce seeds that cannot be banked, along with 35 per cent of plants considered to be ‘vulnerable’ to extinction.
It is a particular problem for trees, with 33 per cent of all the world’s tree species producing seeds that do not survive the drying process, the study suggests.
In tropical moist forests, such as rainforests or cloud forests, as many as half the species of trees which create the canopy can be unsuitable for preserving in seed banks.
An alternative to conventional storage in seed banks could be ‘cryopreservation’.
This involves removing the embryo from the seed and using liquid nitrogen to freeze it to -196°C (-320°F), and could allow ‘unbankable’ seeds to be preserved.
John Dickie, from Kew’s Millennium Seed Bank and one of the authors of the paper, said: ‘Ex-situ conservation of plants is more critical than ever, with many threats to plant populations including climate change, habitat conversion and plant pathogens, we need to make sure we’re doing all we can to conserve the most important and threatened species.
‘As successful as seed banking is for some species, it is not suitable for all seed plants and we need to invest in other ways to safeguard recalcitrant seeds.
‘This paper shows that we need greater international effort to understand and apply alternative techniques like cryopreservation which have the potential to conserve many more species from extinction.’
Conventional wild species seed banks should play to their strengths, meanwhile, redoubling efforts to conserve species such as medicinal plants and crop wild relatives which can be banked.
The researchers also warn it may be ‘somewhat naive and dangerous’ to assume conservation outside of habitats is a valid way to protect a high proportion of tropical moist forest trees from extinction – and conserving the forest may be the only feasible tool for many plants.