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TREE SEEDS AND THE MILLENNIUM SEED BANK PROJECT24

by
Hugh W. Pritchard25 and Simon H. Linington2

INTRODUCTION

The Millennium Seed Bank Project (MSBP) is an international partnership for the conservation through seed storage of research quantities of endangered, endemic and useful, though mainly undomesticated, plant species. It was established in 1995 with a substantial grant from the UK's lottery Millennium Commission to the Royal Botanic Gardens, Kew. The Project's origins lie within Kew's seed banking effort started in the 1960s and moved in 1974 to its Wakehurst Place site. It is here that the Project's focal point, the Wellcome Trust Millennium Building (WTMB) has been built. This 5 000m2 building comprises a seed bank vault, a number of processing and research laboratories, seminar and library facilities, visitor accommodation and interactive interpretation for the public. A strong impetus for the launch of the Project was the establishment of the Convention on Biological Diversity. There was international recognition both that a great number of the world's plant species are under threat of genetic erosion leading to loss and that seed banks are a cost-effective means of countering some of this threat. Consequently, a key aim of the Project has been to draw together partner organisations from around the world with the aim of banking seeds from 24 000 species before 2010. While samples are sent to the UK for duplicate storage, a key aim of the work has been to strengthen `within country' banking through training and joint research. A major channel for data outputs from the Project is the Seed Information Database that can be found on the Project's website (access via www.rbgkew.org.uk).

SEED CONSERVATION PRACTICE

Targeting of tree (and other) species by the MSBP is led by the priorities of the partner countries. The initial aim of the Project is directed towards the conservation of inter-specific variation (one well-sampled population of each species). Inevitably, multiple population samples of many species are being conserved and these often have a wide geographical background. Apart from their conservation role, these samples can act as the basis for studies including those on seed biology (mainly carried out `in-house') and other conservation biology such as genetic analysis. The latter will in due course inform further subsequent sampling. The quantities made available for research and trialling reflect the primarily conservation role of the collections. Insufficient material is being stored for large-scale trials. With regard to distribution to users from stocks held at the WTMB, this is done under a material supply agreement that enables RBG Kew to retain rights over the material on behalf of the country from which each sample was collected. Some of the access and benefit-sharing agreements (ABSAs) signed between RBG Kew and the partner countries permit such distribution and some do not26. Consequently, each collection is tagged on the seed bank database with the conditions of its ABSA. It is anticipated that web-site access to the collections that are available for use will be available by the end of December 200227.

The field collecting effort attempts to capture a significant proportion of the alleles present within each targeted population. Collections are then returned to the local facility where part is retained and part swiftly forwarded to the Millennium Seed Bank. The Wakehurst Place facility has a permit to import into the UK material that is restricted on plant health grounds. Collections are contained and debris carefully destroyed during processing. Subsequent long-term storage of collections closely follows that used for crops (see FAO / IPGRI, 1994).

TREE SEED STORAGE

It is difficult to predict exactly how many tree species the Project and its partners will be involved with at the conservation level, but the importance of such species is well established. Deforestation affects the daily lives of millions of people, and the suggestion has been made that around 10 percent of the known tree species, i.e. about 7 000, are threatened with extinction (Oldfield et al., 1998). The starting material for reforestation is, primarily, seed and it is also the most useful material for the conservation of species (see Linington and Pritchard, 2001). Nonetheless, the driving force currently for the collection of tree seeds is essentially commercial rather than conservation. The potential benefits of tree seed conservation may have been underestimated previously, with suggestions that there was little point in storing such material unless longevity approached the life span of the species. This view is rather short-sighted, for two reasons. Firstly, short-term storage and regeneration is a valuable means of protecting some species, and is the only large scale approach available for species with desiccation intolerant, Type III seeds (i.e. recalcitrant in their storage behaviour), e.g. many dipterocarps and oaks (Pritchard, 2002). Secondly, the predictions for seed longevity in some tree species, based on extensive studies, are in the order of many decades (Tompsett, 1986; Tompsett and Kemp, 1996; Medeiros et al., 1998). For instance, the FAO base collection of land stabilisation species held at Wakehurst Place has declined very little in viability since initial storage in the mid 1980's. This confirms that seed storage is an attractive proposition for the conservation of many tree species.

However, baseline data on the storability (desiccation tolerance and longevity) of tree seeds is very limited (Hong et al., 1998; Dickie and Pritchard, 2002; Tweddle et al., 2002), as is basic information on the control of tree seed germination, including (for some species) the method by which dormancy can be alleviated. To maximise the effective use of genetic resources, we need far greater knowledge in these areas, and this is one of the primary aims of tree seed conservation research by the MSBP.

PRIORITY SPECIES FOR INVESTIGATION: THE THREE E'S

But out of the estimated 70 000 tree species globally, what should we aim to research and conserve first? In terms of mobilising a global effort to achieve this, it is probably the case that most support would be given to the preservation of trees that are classified as either Economic, Endangered or Endemic, or a combination of these categories (the three E's). Undoubtedly, the first group of species (economic) is the primary driver of much tree science and technology work, and some regions of the world have developed target lists of trees for use in plantations, sustainable management projects and large-scale conservation efforts. As an example, FAO's Panel of Experts on Forest Gene Resources produces updated lists of priority species on the basis of their actual or potential value either as taxa or populations at the global, regional and / or national level28. As another example, 27 sub-Saharan African countries have identified 62 priority species for work (including seed research), the so-called SAFORGEN list (see Sacandé et al., 2002). These species - which are of value either as edible fruits, forage, timber and amenity or craft and non-wood products - are drawn from 51 genera and 27 families, thus representing considerable biodiversity. The MSBP is currently working with the African Tree Seed Centres to develop a network approach to essential studies on the seeds of these species. This work follows on from the Project's recent work on tree seeds of economic, endemic or endangered status. Case histories are presented below.

RECENT CASE HISTORIES FOR FOUR SPECIES ACROSS FOUR FAMILIES

Hyophorbe lagenicaulis (Arecaceae)

This palm species is endemic to Round Island in the Mascarenes. It is highly prized horticulturally because of its attractive bottle-shaped trunk and because it is easy to grow. Nowadays, it is highly endangered in the wild as there are very few adult individuals. However, recent in situ conservation management efforts are helping the recovery of native populations of young individuals. As a backstop to these efforts, the MSBP has assessed, in association with the Mauritian Government, the storage potential of the seeds about which nothing was known previously. The seeds tolerated drying to an embryo moisture content of 8 percent and survived 18 months at 15°C (Wood et al., 2002). Such longevity and desiccation tolerance suggests possibilities for their ex situ conservation. Palms (Arecaceae) are one of the most highly threatened families globally (Oldfield et al., 1998) and yet there is seed storage information on only about 100 species ( < 5 percent of the family). Semina Palmarum, a five year initiative within the MSBP, aims to assess the seed conservation potential of 400 palm species.

Kigelia africana (Bignoniaceae)

This species has multiple uses: timber for construction or furniture, fruit as a dressing for sores and the bark to treat dysentery. This is a widespread species in sub-Saharan African, although it is considered to be rare in some regions. Previous indications were that the seeds could survive drying to 13 percent moisture content, which is probably not dry enough for conventional seed storage, and that they may require special pretreatment to ensure a high level of germination. The MSBP has established as part of an IPGRI-DFSC project and in collaboration with CNSF in Burkina Faso, that the seeds can tolerate desiccation to 3 percent moisture content and germinate at a warm temperature (25°C) without the need for pretreatment (Dudley et al., 2001).

Prunus africana (Rosaceae)

This species has multiple uses, providing hardwood timber and medicinal products, especially from the bark. Bark extract is used traditionally as a purgative for cattle and in the treatment of prostate-related illness (benign prostatic hyperplasia and prostate gland hypertrophy). The species is currently assessed by IUCN as "vulnerable, facing a high risk of extinction in the medium term future" (Oldfield et al., 1998) and is listed on Appendix II of CITES. However, the general trend towards greater human longevity almost certainly means that the threat of over-exploitation of this species for bark will increase. Consequently, there is an urgent need to improve the conservation prospects for the species, and we have recently assessed this at the ex situ seed conservation level. The experiments conducted so far have revealed, contrary to earlier reports, that seeds of this species can tolerate desiccation to around 5 percent moisture content as long as they are extracted from mature, purple fruits. In addition, it was noted that the seed germination capability of this species extends as low at 1°C, matching the moist highlands (up to 3 400 m) origin of this sub-Saharan African species (Sacandé et al., 2002). This work was facilitated by KEFRI, Kenya and future studies will assess seed longevity under dry, cool conditions.

Salix hybrids (Salicaceae)

This group of species is being assessed for use in agroforestry, especially for their potential as biomass producers. Many of these trials involve species crosses and only a small quantity of the resulting seeds can be used in any one breeding season. Storing seeds is an obvious way of supporting such breeding efforts, but willow seeds are reputed to be inherently short-lived. Our research, with the Institute of Arable Crops Research, Long Ashton, UK, has revealed that seeds of two hybrids are tolerant of dehydration, that drying increases their longevity in a manner similar to that of crops, e.g. barley, and that ultra-low temperature storage (i.e. cryopreservation in liquid nitrogen) of the seeds is possible (Wood et al., 2002).

CONCLUSIONS

The MSBP is a long-term project that complements efforts such as those by IPGRI and DFSC to study seed conservation and at the same time assist national institutes in seed storage. The Project formally comprises institutes in 14 countries with informal links to those in many others. Its key aim is to conserve population samples of 24 000 species by 2010 of which perhaps 10-25 percent are likely to be trees.

REFERENCES

Dickie, J.B. & Pritchard, HW. 2002. Systematic and evolutionary aspects of desiccation tolerance in seeds. Pp 239-259 In: Desiccation and survival in plants: drying without dying. M Black and HW Pritchard (eds). CABI Publishing, UK.

Dudley, A., Wood, C.B. and Pritchard HW. 2001. Quantification of dryland tree seed storage behaviour. Kigelia africana. The Project on Handling and Storage of Recalcitrant and Intermediate Tropical Forest Tree Seeds, Newsletter No. 9, 6-11. Published by IPGRI/DFSC.

FAO / IPGRI (1994). Genebank Standards. Food & Agriculture Organisation of the United Nations / International Plant Genetic Resources Institute, Rome.

Hong, T.D., Linington, S.H. and Ellis, R.H. 1998. Compendium of Information on Seed Storage Behaviour. Volumes 1&2. Royal Botanic Gardens Kew, UK.

Linington, S.H. and Pritchard, H.W. 2001. Genebanks. p 165-181. In: Encyclopaedia of biodiversity. Volume 3. S Levin (editor-in-chief ). Academic Press.

Medeiros, A.C.S., Probert, R.J., Sader, R. and Smith, R.D. 1998. The moisture relations of longevity in Astronium urundeuva (Fr. All.) Engl. Seed Science and Technology 26, 289-298.

Oldfield, S., Lusty, C. and MacKinven, A. 1998. The World List of Threatened Trees. World Conservation Press, Cambridge, UK. 650 pp.

Pritchard, H.W. 2002 (in press). Classification of seed storage `types' for ex situ conservation in relation to temperature and moisture. E. Guerrant, K Havens, M. Maunder (eds). Island Press, USA

Sacandé, M., Pritchard, H.W. and Dudley, A.E. 2002 (in press). Germination and storage characteristics of Prunus africana seeds. New Forests.

Sacandé, M., Pritchard, H.W., Ouedraogo, L.G. & Dulloo, E.M. 2002 (in press). An agenda for seed research on Sub-Saharan African Forest Genetic Resources (SAFORGEN) listed tropical trees: a critical role for the African Tree Seed Centres and the seed science community. Plant Genetic Resources Newsletter.

Tompsett, P.B. 1986. The effect of temperature and moisture content on the longevity of seed of Ulmus carpinifolia and Terminalia brassii. Annals of Botany 57: 875-883.

Tompsett, P.B. and Kemp, R. 1996. Database of tropical tree seed research (DABATTS). Database contents and user manual. Royal Botanic Gardens Kew, UK.

Tweddle, J.C., Turner, R.M. and Dickie, J.B. 2002. Seed Information Database (Release 2.0, Jan. 2002). http://www.rbgkew.org.uk/data/sid

Wood, C.B. and Pritchard, H.W. 2002 (in press). Germination characteristics of fresh and dried Hyophorbe lagenicaulis seeds. Palms.

Wood, C.B., Pritchard, H.W. & Lindegaard K. 2002 (in press). Seed cryopreservation and longevity of two Salix hybrids. CryoLetters.


24 Received June 2002. Original language: English.
25 Seed Conservation Department, Royal Botanic Gardens Kew, Wakehurst Place, Ardingly, West Sussex RH17 6TN, United Kingdom E-mail: h.pritchard@rbgkew.org.uk e-mail: s.linington@rbgkew.org.uk
26 The principles to which RBG Kew adheres on access to genetic resources and benefit-sharing can be found at: www.rbgkew.org.uk/conservation/principles.html
27 Access will be by free subscription to bona fide users via the RBG Kew website http://www.rbgkew.org.uk
28
For more information see the FAO website: http://www.fao.org/forestry/FOR/FORM/FOGENRES/GENEPANE/general/FGRframe-e.stm


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