Seed banking and native trees – Expert Reaction

Traditional seed banking – storing seeds at low temperatures – will fail to save a third of the world’s tree species from extinction, according to new research from one of the world’s largest seed banks.

Storing seeds ‘ex-situ’ (away from their natural habitat) serves as a conservation insurance policy in case of disaster. However, this new research shows vast numbers of trees have ‘recalcitrant seeds’ that can’t survive the most common preservation technique – drying and freezing.

Lead author Dr Sarah Wyse, who now works in New Zealand at the Bio-Protection Research Centre, says one in five native NZ trees and shrubs have recalcitrant seeds – including tōtara, rimu, tawa and swamp maire. Kauri are also affected as, while their seeds can be frozen, they don’t last beyond 10 years in storage.

The SMC asked New Zealand experts to comment on the study.

Dr Nari Williams, Forest Pathologist, Scion, and Healthy Trees, Healthy Future research programme leader, comments:

“This paper raises many valid points with regard to the role of seed banking in plant conservation and specifically the risks associated with relying on off site storage of threatened plants over in field conservation and expanded planting programmes.

“For some species, such as kauri, freezing provides a medium-term option for storing seed and maintaining genetic diversity, but there is a lot of uncertainty around the long-term viability of stored seed.

“For threats such as kauri dieback, selection for resistance presents as the most promising strategy for the long-term survival of the species with seed storage having a role in such programmes.

“There is a need for expanded research to develop off site species-specific methods and long-term strategies for plant conservation in the forest, across the diverse range of New Zealand plant species. But, these need to be supported by efforts to conserve plant species through sanctuary plantings and re-vegetation programmes.

“While there is a role for laboratory-based conservation, Wyse is right to flag the dangers of assuming that type of conservation will work as there is nothing more depressing than taking seed from the freezer to have nothing germinate.

“I support Wyse’s closing comment: ‘If we are serious about wanting to save our unique trees, we need to do everything we can to save them in their natural environment, because other methods may simply not work.'”

Conflict of interest statement: The Healthy Trees, Healthy Future research programme has commenced screening kauri for resistance to kauri dieback.

Associate Professor Bruce Burns, School of Biological Sciences, University of Auckland, comments:

“I welcome the insight of Sarah Wyse and her co-authors on the current limitations of seed banking with respect to conservation options for many of our native trees.

“Currently a suite of novel plant pathogens in New Zealand are challenging the future survival of many of our most valued native trees, e.g. kauri and pōhutukawa, and other nasties are undoubtedly heading our way.

“Although conventional seed banking is a hugely valuable tool to preserve the genetic potential of many of our plant heroes, knowing which species can’t be conserved by this technique should provide the impetus for the timely investment in development of alternatives.

“We know kauri can be propagated using tissue culture, so perhaps this could be the basis of an approach for long-term conservation of kauri.

“These alternative techniques, however, are more expensive, can’t preserve tissue for long periods (<10 years), and usually only preserve a limited gene pool. Research could seek to improve the efficacy of these existing alternative techniques or develop new innovations.

“I urge those involved in the biodiversity response to these threats to take particular note.”

Conflict of interest: I was Sarah Wyse’s supervisor for her BSc(Hons) and PhD and have coauthored several papers with her. However, I have not been involved in this work. 

Dr Phillip Wilcox, Senior Lecturer, Department of Mathematics and Statistics, University of Otago, comments:

“This research strongly indicates that ex situ seed banking alone is not sufficient to ensure survival of some of Aotearoa/NZ’s iconic native species such as kauri and tōtara.

“Such ex situ methods should only be considered as a complement and/or backup to in situ methods for a range of other reasons.

“Firstly, from a Māori perspective, a very important benefit of in situ methods is maintaining ongoing connections between indigenous peoples, indigenous flora, the environments that they naturally grow in, and the knowledge and cultural practices associated with these. Kaitiakitanga is an important practice in Te Ao Māori, but is impossible to undertake if the species exist only in ex situ collections.

“Secondly, although ex situ cryopreservation has been developed in NZ for some exotic tree species, it is expensive and slow to develop, partly because it needs to be optimised on a species-by-species basis.

“In contrast, in situ methods are cheaper and allow for a greater range of extant genetic variation to be preserved. Such variability is necessary for long-term survival of species, by providing resilience to abiotic factors such as climate change, and to biotic factors such as pests and diseases.

“Ongoing efforts should therefore be prioritised to ensure in situ methods (a) preserve the range of species and the genetic variation that occur within them, and (b) maintain and enhance the natural environments where they are found, and (c) the traditional knowledge and practices associated with these species.”

No conflicts of interest.

Craig McGill, Research Officer, Seed Science and Technology, Massey University, and Project Leader, New Zealand Indigenous Flora Seed Bank, comments:

Seed banking needs to be seen a part of a wider conservation strategy. It is not a substitute for maintaining plant populations in situ in their native habitat.

Seed banking is designed to provide insurance against loss of biodiversity in situ as a result of, for example, disease threats, such as myrtle rust. Myrtle rust is a new disease that attacks plants in the Myrtaceae family.

“For conventional banking, seeds must be able to be dried before storage at -20C. This is not possible with seeds of all species. There are examples of these seeds, termed recalcitrant, in the New Zealand flora.

Seed of all New Zealand Myrtaceae, except swamp maire can be dried.

“For swamp maire an alternative storage approach is cryopreservation. With cryopreservation, seed or parts of the seed such as the embryo, from which the new plant will develop, is stored in the vapour or liquid phase of liquid nitrogen.

“Protocols for cryopreservation of swamp maire are currently being developed as part of a Massey University PhD project that is being jointly supervised with Plant and Food Research in Palmerston North.

“Protocols will need to be developed for other recalcitrant species, including New Zealand species. For seed that does survive drying, the storage life will vary between species. For example, seed of legumes such as Clianthus (kākā beak, kōwhai ngutukākā) are expected to store much longer than for example orchid seed.

“Research is needed to determine the potential storage life of seed and to understand the factors that can limit storage life.

“Kauri is another example of where the maximum potential storage life of the seed is not certain. Early work undertaken in New Zealand by Preest, showed that at -10C, some kauri seed will remain viable for at least 12 years. Storage at -20C or in cryopreservation may be able to extend this storage time.

“In addition to conserving the biodiversity within seed in storage, the data gathered as part of the seed collection and banking process also has the potential to support other conservation strategies.”

Conflict of interest statement: I know authors Sarah Wyse and John Dickie and am a co-author with Sarah on the Sommerville et al (2018) paper mentioned in the comment paper.

Dr Kioumars Ghamkhar, Senior Scientist, AgResearch, and Director, Margot Forde Germplasm Centre comments:

“The paper makes some relevant points about the limitations of traditional seedbanks, especially as it relates to tropical or sub-tropical plant species that have more moisture in the seed.

“This has been an ongoing discussion for some years, and there is no question that a combination of traditional seed banking and use of cryopreservation techniques are needed to ensure the preservation of a broad range of species into the future.

“In New Zealand, where the Margot Forde Germplasm Centre houses more than 115,000 samples of forage and some crop species using the traditional freezing method, the tropical and sub-tropical plant species are in a very small minority. The freezing method applied at Centre is ideal for the grassland and crop species typically requiring storage in New Zealand, and including the majority of the species of the New Zealand Indigenous Flora Seed Bank (NZIFSB).

“While we know the seeds won’t last forever in these traditional banks, last year we tested seeds from one clover species that had been stored since the 1940s by the traditional method, and 70 per cent of the seed was still viable.

“The potential use of cryopreservation, for plant species where it is suitable, has been the source of ongoing discussion between Crown Research Institutes in New Zealand.

“There are more than 1200 seed banks around the world, and for many of these the economic cost of cryopreservation may be too high. Therefore more frequent regeneration of the stored seed supply – by growing to a plant to create more seed – becomes important.”

Conflict of interest: Kioumars is the director of the Margot Forde Germplasm Centre – a traditional seed bank.