Seed banks must adapt to include techniques like cryopreservation to meet target of conserving 75% of threatened plant species by 2020, a report from Kew Gardens, UK, finds.
An oak tree, one of the UK heritage trees that is not compatible with seed banking. Image: Royal Botanic Gardens, Kew.
Seed banking is currently the most commonly practiced method in the conservation of endangered plant species, with over 1,000 seed banks across the world. It is estimated that 60,000 to 10,000 plant species are vulnerable to extinction without human intervention.
However, researchers at the Royal Botanic Gardens, Kew, have found that up to 36% of ‘critically endangered’ species are not compatible with seed banking, putting the global conservation target at risk. The ‘critically endangered’ species that are unsuitable for seed banking produce recalcitrant seeds that cannot tolerate the drying process needed for the species to be ‘banked’.
The paper found that 35% of ‘vulnerable’ species, 27% of ‘endangered’ species and 33% of all tree species were unbankable despite a 2017 report that estimated only 8% of plant species produced recalcitrant seeds and were therefore incompatible.
To store a species in a seed bank, the seeds of the plant are dried and then frozen at -20oC. This kind of ex-situ conservation, when plants are conserved outside of their natural habitat, can be beneficial in several ways: seeds can be stored for long periods of time at relatively low-cost and take up minimal space, and it allows for the preservation of high levels of genetic diversity.
‘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,’ said Dr John Dickie, one of the paper’s authors and Head of Seed & Lab-based Collection at Kew’s Millennium See Bank – home to 13% of the world’s plant species.
Although seed banking is the preferred method of plant conservation, the report suggests new techniques should be adopted to improve preservation efforts. Cryopreservation is highlighted by Kew as a viable alternative to ex-situ conservation for plant species with recalcitrant seeds. This method involves the removal of a seeds embryo and then freezing the seed with liquid nitrogen at -196oC.
‘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,’ said Dr Dickie. Now, Kew are calling for a generic protocol for the banking of species with recalcitrant seeds to include cryopreservation, which includes an injection of funding to scale-up the technology.
‘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.’