- A study by researchers at the Royal Botanic Gardens, Kew said that 36 percent of ‘critically endangered’ species produce recalcitrant seeds which means they can’t tolerate the drying process and therefore cannot be frozen, the key process they need to go through to be safely ‘banked’.
- This new data shows that there is a need for greater international effort and investment to understand and apply alternative techniques like cryopreservation which have the potential to conserve protect many more species from extinction.
- Though ex situ methods such as seed banks are “helpful”, for conservation of forest trees and plant biodiversity in general, in situ methods should remain the focus: their natural habitats must be shielded from destruction, feel experts.
India which has “great expertise” in conservation of genetic resources of crop plants through seed banking is now “rapidly” working to extend the safeguards to difficult-to-conserve (recalcitrant) seeds of wild species, threatened species, forestry and agroforestry trees.
Researchers say sophisticated techniques such as cryopreservation that complement conventional seed banking are aiding this endeavour.
“Till recent past we were working to conserve the crop plants diversity, but now rapidly we are trying to conserve wild species which have genes of interest for future crop improvement,” Anuradha Agrawal of ICAR-National Bureau of Plant Genetic Resources told Mongabay-India.
The spotlight was on crop plants that are cultivated widely and to meet the requirements of breeders who would often ask for the material to use in their breeding programmes. That is fairly well under control, said Agrawal.
“Now we intend to conserve vigorously those species which are biologically important and available as wild in nature but relatively more difficult to conserve,” Agrawal said.
There are broadly speaking two basic approaches to genetic resources conservation: ex situ (conservation outside natural habitats using approaches such as gene banks) and in situ (in natural habitats and protected areas). Currently, seed banking is the most commonly practised way of conserving plants outside of their natural habitat (ex situ conservation).
“We always talk of complementary conservation strategies. We have farmers’ fields or the forests that is in situ conservation; then we have the ex situ conservation where we remove the plants from there natural environment and bring them under controlled conditions,” said Agrawal. “These can include botanic gardens, seed gene banks, tissue culture banks and cryobanks. NBPGR has also the technology of DNA banking to conserve the genes,” she said.
Banking seeds
In seed banks, seeds are dried and frozen at -20°C, whereas cryopreservation involves removing the embryo from the seed and then using liquid nitrogen to freeze it rapidly at a much colder temperature of -196°C.
Orthodox seeds are those that survive drying and/or freezing during ex situ conservation. Eight percent of all plant life produce ‘recalcitrant’ seeds that cannot survive drying — oak, mango, avocado and cacao seeds among them.
Expanding further, Agrawal said seeds of forest trees are more difficult to collect and conserve compared to those of cultivated crops (that bear orthodox seeds) because relatively less information is available on forest trees.
“When we are talking of crops which comprise domesticated plants, a lot of information is there in terms of agronomy, reproductive biology and other factors, whereas the forest trees have been relatively less studied,” she said.
Though ex situ methods are “helpful”, for conservation of forest trees and plant biodiversity in general, their natural habitats must be shielded from destruction to maintain them in situ (conservation in natural habitats).
This is because species conserved in natural habitats equip themselves with the right tools to adapt to environmental changes, said Veena Gupta, Principal Scientist and Head, Division of Germplasm Conservation at ICAR-NBPGR.
“That natural resistance is lacking in gene banks. Because of climate change and its impacts on food crops, we are now preferring ex situ methods, especially for these kind of crops. To stop their extinction we are relying on seed banks. But there should be a balance between ex situ and in situ methods,” Gupta said.
For ex situ conservation, the major advantage is that germplasm is ready-to-use and for in situ the main advantage is that you allow nature to take its course and the plants undergo evolutionary adaptation against biotic and abiotic stresses. “So all options are complementary to each other and need to be exercised,” said Agrawal.
The need for complementary approaches
Their observations come in the wake of a study published in Nature Plants by researchers at the Royal Botanic Gardens, Kew, that detail for the first time the scale of threatened species that are unable to be conserved in seed banks.
The paper reveals that when looking at threatened species, 36 percent of ‘critically endangered’ species produce recalcitrant seeds. This means they can’t tolerate the drying process and therefore cannot be frozen, the key process they need to go through to be safely ‘banked’.
This latest research shows that the scale of plants unable to be conserved in seed banks is much higher for threatened species. The issue is particularly severe for tree species, especially those in tropical moist forests where half of the canopy tree species can be unsuitable for banking.
John Dickie, head of seed and lab-based collections at Kew’s Millennium Seed Bank and one of the authors of the paper said this new data shows that we need greater international effort and investment to understand and apply alternative techniques like cryopreservation which have the potential to conserve many more species from extinction.
The study questions “whether it may even be somewhat naïve and dangerous to assume that ex situ conservation is a valid means of safeguarding a high proportion of threatened tropical moist forest trees from extinction.”
The researchers write in the paper: “In situ conservation may be the only feasible tool in the conservation toolbox for many such plants.”
Explaining this, Dickie said while ex situ conservation in conventional seed banking is a very cost-effective backup, it is of concern to note that certain people think in situ (in natural habitats) conservation can be ignored because ex situ options exist.
“What gets a little worrying is that when politicians and businessmen think that we don’t have to worry about keeping that piece of forest (to exploit it) because we can store seeds and that species will not become extinct. That is a very dangerous thinking,” he said.
Question of balance and priorities for India
In the India context, Dickie suggests highlighting the species that are likely to be a bit more difficult to bank and to extend the existing cryopreservation facilities and research that already exist in India to these recalcitrant species.
According to Vania Azevedo, head of the genebank at ICRISAT, cryopreservation is a practical and efficient approach for long term conservation of all kind of crops, from orthodox to recalcitrant. Most of the wild species, especially trees, are recalcitrant, and so, ex situ conservation is a big challenge.
“In vitro and cryopreservation would be the best alternative, techniques which per se are big challenges. This technique has some advantages and disadvantages, as all different techniques,” Azevedo said.
For instance, the development of an adequate protocol because most of the time one unique protocol is not efficiently applicable to all accessions of the same species.
“Cryopreservation requires lot of study and tests in order to identify the right strategy to each accession. To each species, years of study may be necessary to develop the right protocols for cryopreservation of different accessions. It is necessary to build a very specific laboratory structure to maintain the material, which is expensive and requires specific scientific knowledge,” Azevedo, who was not associated with the study, said.
Given the complications and challenges associated with cryopreservation and looking at India’s vast biodiversity, chunks of which are still unexplored in northeast India and Western Ghats, Dickie emphasised that it is a question of balance and priorities.
According to Botanical Survey of India, the floral diversity in India is majorly concentrated in four biodiversity hotspots, namely Eastern Himalayas, Western Ghats (and Sri Lanka), Northeast India and Andaman Islands (Indo-Burma) and Nicobar Island (Sundaland), out of 34 biodiversity hotspots recognised in the world.
Though the geographical area cover of the country represents about 2.4 percent of the world’s total landmass, it harbours a total of 47,513 plant species out of about 400,000 hitherto known in the world — as much as 11.4 percent of world flora. About 28 percent of plants that occur in India are endemic to the country.
“Each species would be weighed on its merits and that’s another reason why we say, maybe for a large number species in wild tropical forests there may not be just enough resources to guarantee ex situ conservation methods and so in situ should always be the gold standard,” Dickie told Mongabay-India.
“We need to get an estimate of what’s bankable and what is likely to be difficult to bank at the species level so we can plan better at the global level and decide where we need to put in more effort,” he added.
The researchers also emphasised on seeking out at-risk plant species in the tropics and updating their risk status.
“India has enormous plant diversity and not everything can be conserved. We need to prioritise. Biosphere Reserves are excellent in situ conservation areas, wherein many wild species grow in natural ecosystems, thereby not only being conserved, but also evolving over time with new adaptive genes,” added Agrawal.
Not just genetic resources but conserving communities
Azevedo also averred that ex situ conservation is not a substitute to the in situ conservation. Ex situ is an alternative strategy to help in the conservation of species.
“The main objective of genebanks is not to avoid extinction, but to guarantee that the genetic resources, important to us, are well conserved, studied and accessible to be used in breeding, other research programmes and also to be reintroduced to farmers, especially in the case of landraces,” she said.
The ICRISAT Genebank serves as a world repository for the collection of germplasm of the six mandate crops: sorghum, pearl millet, chickpea, pigeonpea, groundnut, finger millet; and five small millets: foxtail millet, little millet, kodo millet, proso millet and barnyard millet.
Read the Mongabay-India article about ICRISAT’s gene bank: “Saving the seed: A bank that secures the future of agriculture.”
“Considering the knowledge, infrastructure and experience already developed over the last at least 50 years, ex situ gene banks can collaborate with the conservation of threatened species too, in the sense of collaborating to the conservation of the biodiversity, which has a much bigger scope than the conservation of genetic resources,” she said.
In situ will also be necessary and mandatory, especially if one considers other aspects as water conservation, climate, environmental and population conservation, pollinators, other insects, animals and microorganisms.
“In situ conservation is much more than conserving some threatened tree species, but is also about conserving and entire community, including us,” explained Azevedo.
In addition, Agrawal of NBPGR iterated that there is an urgent need that the whole set of germplasm of genebanks also be conserved at some distant place as “safety duplicates.”
The Svalbard Global Seed Vault, which lies deep inside a mountain on a remote island in the Svalbard archipelago, halfway between mainland Norway and the North Pole, is a long-term seed storage facility and is a ‘safety back-up’.
The Svalbard gene bank provides that extra layer of protection in cases when gene banks are at risk of losing unique accessions due to technical failures, natural or human made catastrophes, human strife, or because they lack the resources needed to ensure proper storage. It stores only orthodox seeds.
“In situ conservation should be prioritised and be the predominant means for conserving these (threatened tropical moist forest trees) species. However, ex situ conservation could add security and in some cases provide material for re-introduction of species that is lost in certain habitats,” said Asmund Asdal, Svalbard Global Seed Vault Coordinator.