BANKING THE WORLD’S SEEDS
Dr John Dickie
Head of Seeds and Lab-based collections, Wakehurst
Mankind’s footprint weighs heavily on global ecosystems with a diminution of diversity and permanent loss of both plants and animals. In detail, threats to the natural world include climate change, habitat conversion and plant pathogens.
Extinctions are nothing new in the natural world. There is a background species extinction rate of several per cent per million years. Running alongside background extinction is the co-evolution of new species with generally a net gain of species over time, giving diversity and resilience to the natural world.
In recent years the extinction rate has increased somewhat. This is most evident with the big beasts of Africa and Asia but just as prevalent, though less noticeable, in all other parts of the natural world. Of concern is the loss of plant species. With plants endangered, the stability and abundance of Earth systems is threatened. Plants are central to existence, without them, there would be little in the way of other life. A climate changing temperature rise of 2C, a very probable likelihood, will put 15-40% of current plant species at serious risk.
History reminds us of one individual who responded magnificently to a major extinction threat. The old patriarch Noah set a precedent, in the faunal department at least, of saving all animals from an extreme climate event. Kew Gardens has similarly taken up the mantle, in the plant world this time, seeking to use their expertise to ensure that threatened species are not only saved for prosperity but available for research and replanting.
The modern world challenge of species salvation is more complex than Noah’s one off, though admirable, rescue mission. Dr John Dickie travelled from his base at Wakehurst Gardens in West Sussex (see Fig.1), satellite to Kew Gardens and the base for the Millennium Seed Bank, to discuss Kew’s world beating response to the threat to global flora. John is Head of Seed and Lab-based collections, responsible for the quality of collections (which consists of living seed, DNA, microscopic slides of leaves, wood, pollen and flowers).
2. IMPORTANCE OF PLANTS
Life depends exclusively on plants because they form the base of virtually all food chains. Other important benefits also accrue from plants such as provision of medicine and materials, climate regulation, soil stability and the maintenance of natural environments. In fact, these so-called ‘ecosystem services’ are globally worth 30-40B$ per year. As H. sapiens, we may mistakenly think of ourselves as the premier species on Earth. However, we are entirely outclassed by plants. Our floral friends represent 450 GtC (giga tonnes of carbon) on the planet; animals in comparison represent only 2GtC and humans a mere 0.36GtC.
In terms of food security, three plant species (rice, maize and wheat) represent half of all food energy consumed and these are grown from an increasingly restricted range of seeds constraining the diversity of these species. The Irish Potato Famine (1845-1849) indicated the disadvantage of relying exclusively on one particular crop species. Not all countries rely on cultivated crops. In Africa generally, 75% of people rely on wild plants for food, in Tanzania particularly, 49% of vegetables consumed are wild species, reflecting the importance of non-standard, wild crops.
In the health arena, plant derivatives provide remedies for three-quarters of people requiring medication. Aspirin, for example, is derived from the willow (Salix) and digitalis, the heart drug, from the foxglove (Digitalis purpurea). New discoveries are regularly made. Until recently, in London, only 40% of children with lymphoma survived; with the use of recently discovered Rosy Periwinkle (Catharanthus rosea) derived drugs, that figure is now a much more positive 80%.
3. CHALLENGES FOR THE PLANT WORLD
As previously noted, the co-evolution of new species usually more than matches the background extinction rate with a net effect of radiating floral diversity. In recent years, the background extinction rate has increased by 1,000 times, which for any evolutionist, will set the alarm bells ringing. One in five plant species is considered to be threatened.
To protect against floral extinction, in situ preservation is the most effective and the most natural option. Where environments are threatened, ex situ preservation (i.e. away from natural habitat) is the next best alternative, by storing seeds as an insurance policy against extinction. Seed storage isn’t always a viable method. A significant proportion of species are unbankable in that they produce seeds that do not survive drying/freezing techniques used for storage (‘recalcitrant’ seeds). The rest (‘orthodox’ seeds) survive the process with relative ease. Data indicates that 35% of vulnerable species, 27% of endangered species and 33% all tree species have recalcitrant seeds suggesting that seed banking is not the panacea it may at first appear.
4. KEW’S APPROACH
Kew is not only a pleasant botanical garden for an afternoon’s stroll whilst visiting the ‘Big Smoke’ but a globally significant, world class research institute backed by over 300 scientists. As a reflection of its botanical clout, it has an inventory of 94,000 floral collections from 190 countries and 2 billion seeds, with the inventory covering some 40,700 species. 5,948 genera and 350 families of plants are found in its vaults (see Fig.2). Collections represent 95% of known plant genera and 66% of known genera of fungi (see Sherborne Science Cafe talk ‘Fungi will save the world!’ by Lee Davies, also of Kew, in March 2018).
Kew has several strategic outputs in the botanical domain, looking, for example, at plant-based solutions for environmental issues, such as water shortage, food scarcity, health, biodiversity and climate change. With the statistics of decline set against the plant kingdom, Kew established the Millennium Seed Bank (MSB) in 1996 with the aim of providing safe ex situ storage of seeds against future risks, an economical and effective way of preserving seeds for posterity. The MSB represents a revamped and re-purposed previous seed bank at Kew, which together with its seed storage facilities, is now based at Wakehurst. It is the biggest, most diverse stored seed resource in world (see Fig.3).
The UK is the first country to conserve its botanical heritage and Kew’s remit spreads across partnerships with botanical gardens in 95 countries (the MSB Partnership). Funding is provided by DEFRA, RBG Kew, philanthropic donations (e.g. Arcadia, GSK, Wellcome Institute), competitive grants, consultancy and from overseas MSB partners (e.g. Australia, Chile, USA). The importance of the MSB can perhaps be judged by Prince Charles’ comment that it is … ‘A gold reserve .... a place where this reserve currency, in this case life itself, is stored’ .
5) SEED BANKING
Seed banking is recognised as a highly effective insurance policy against future floral extinction. This type of ex situ conservation allows preservation of high levels of genetic diversity at low cost in minimal space and seeds can be kept for comparatively long periods. The involvement of other countries as partners helps those nations meet international objectives such as Global Strategy for Plant Conservation (GSPC). This is a program of the UN’s Convention on Biological Diversity, founded in 1999, which acknowledges the vital complementary role of ex situ conservation, including seed banks and living collections in botanical gardens, with a view to slowing the pace of plant extinction.
Most will be aware of the seed bank in Svalbard (opened 2008), constructed within an old Norwegian coal mine set in the permafrost on the tectonically stable island of Spitzbergen. Whilst conceptually broadly similar to the MSB, it is in detail more constrained in its ambitions. Svalbard collated existing Nordic collections and currently stores seeds from plant breeding institutions and crop species only. Kew, in contrast, extends its collection to non-crop species, carries out active research methodology and supplies seeds, as required, for continued research. For Kew, seed banking is more than static storage, with options for further uses of its collections for species reintroduction and restoration, habitat restore ration, and sustainable utilisation to improve rural livelihoods.
Seed banking is applicable to a large proportion of threatened species. It is useable for most seed-bearing species, with dried and frozen seeds lasting possibly thousands of years and is a low technology and economical solution. The process involves cleaning, air drying, packaging in containers and then placing in a freezing vault at -20C (see Fig. 3). Kew was an early adopter of this process.
Seed banking does present challenges. The process of seed preparation for banking is similar to process that occurs in natural seed aging. In consequence, the same vulnerabilities are apparent. Reactive oxygen species (ROS) cause damage to seeds by denaturing protein structures, oxidising lipids (cell membranes), and cause direct damage to cellular DNA. In consequence, vigour when sprouting, can be detrimentally affected.
Recalcitrance is a particular issue. 8% world’s plants produce recalcitrant seeds that do not survive drying/freezing techniques and threatened species tend to be more recalcitrant than others. The problem is particularly severe for tree species, especially those from moist tropical forests where half of canopy tree species are unsuitable for seed banking. In the UK, the same problem affects heritage trees such as Oak, Horse Chestnut and Sweet Chestnut. Globally, recalcitrant species include world-wide staples such as avocado, cacao and mango. In contrast to more delicate tropical seeds, seeds from species residing in arid locations are more robust and can tolerate being dried and frozen for long periods.
Fig. 4. MSBP- a partnership of 95 countries
To extend preservational advantages of seed banking, Kew have long championed cryopreservation as a more sophisticated method where the embryo is removed and the seed rapidly frozen to -196C using liquid nitrogen. This technique has potential to conserve many more species and offers potentially longer term, safe storage for recalcitrant seeds.
Collections are pulled from the vault every 10 years or so for inspection. There is a decline in viability over time. It is useful to give seeds a half-life as a measure of future viability and anticipated longevity of the collection. In some species, such as the carrot, there is a large range of half-lives. Some lowland and montane species, in comparison show shorter survival times Some collections are more than 40 years old. It is thought many seeds will remain viable for well over 1,000 years. An indication of survivability of seeds was demonstrated in the 1940’s when bomb damage to the Natural History Museum released seeds collected in the early 1700’s from China which then sprouted.
The GSPC target of ex situ preservation of 75% of world’s threatened plant by 2020 is practically impossible, even for Kew. Good judgement and discretion have to be used in deciding which plants to preserve, with a realisation that not every species can, nor will, be saved. There is a clear focus on the 3 ‘E’s’, the Endangered, the Endemic and the Economic. With that in mind, current priorities concentrate on plants in alpine, dry land, coastal and island ecosystems (Endangered) which are the most vulnerable to climate change because there is nowhere for the plant species affected to migrate. Of particular interest, too, are those found only in one particular spot and not anywhere else (Endemic) and those important to a locality such as wild plants used by people (Economic).
The Seed Bank collection team is responsible for all aspects of curation of MSB seed collections, associated data and herbarium specimens. Partners from overseas are trained in all areas of seed conservation. Germination specialists develop strategies for breaking seed dormancy and protocols for processing and storing seeds of short-lived species. Where possible, seed collections at Wakehurst are duplicated in the country or origin.
6) PROGRESS SO FAR
Britain is the first country in the world to have preserved its botanical heritage achieving its aim of storing all seeds from UK’s native plant species by 2009, apart from those which are extremely rare or whose seeds are particularly difficult to store. During the first 10 years, MSPB achieved a target of 10% of world’s seed-bearing flowers and is seeking 25% by 2020 with a long-term target of 75% of bankable plant species. The MSB is now the largest and most diverse, wild plant species genetic resource in the world, the result of contributions from a global network working across more than 95 countries (the Millennium Seed Bank Partnership), an international bench mark of excellence for which Kew, and its collaborators, can be justly proud.
Wakehurst is open to the public: Ardingly, Haywards Heath, Sussex, RH17 6TN firstname.lastname@example.org tel. 01444 894066
See: Sherborne Science Cafe talk ‘Fungi will save the world!’ by Lee Davies, also of Kew, in March 2018.