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Seed Conservation at the National Botanic Garden of Belgium

Volume 2 Number 9 - December 1997

I. T. Vanderborght

The seeds manipulated in the seed bank of the National Botanic Garden of Belgium are collected either in the living collections or from wild plants spontaneous in Belgium. The first are mainly used for our own sowing programme and/or exchange with other gardens or scientific institutions. They are conserved on a short-term basis. Every year, a seed catalogue is published offering about 900 different species, and 4,000 seed samples are distributed to more than 300 institutions. The seeds from wild Belgian species are not distributed but conserved on a long-term basis. This ex situ conservation is considered to contribute to a global strategy of nature conservation.

For appropriate orthodox seed conservation, the seed bank is equipped with a cold room (50 m Sq) where the temperature and relative humidity are maintained respectively at 15ºC and 10%. These conditions are quite suitable for short-term storage (10 years), the seeds being conserved in open glass or paper containers placed on shelves. For long-term storage, seeds dried at 5% moisture content are packed in sealed plastic-aluminium laminated bags and placed in deepfreeze units at -20ºC.

About 2,500 accessions are stored in the seed bank. For each of those accessions, an action (Table 1) is decided upon, based on several criteria. Action 01 is attributed to each accession to be cultivated in the living collections. This action can be combined with actions 02, 03 or 05 (Table 2), according to a global value attributed to the taxon (e.g. rarity, vulnerability, taxonomic value, horticultural value, human utilisation), the quality of the data on the provenance of the accession and the verification level of the plant material in cultivation. The action for an accession is never definitive.

This system of action(s) has implications for the daily activities in the seed bank, e.g. the seed harvest in the living collections, the setting-up of security seed samples or the compilation of the annual seed catalogue.

The harvest of seed samples in the living collections strongly depends on the action attributed to the accession (Table 3). Action 01 (accession useful for the living collections) or 02 (accession to be kept in the current and future seed catalogues) used alone or in combination with another action, implies the absolute necessity to collect those accessions. Accessions to which a single action 03, 04, 05, 06 or 07 is given do not have to be harvested. Action 08 is used for accessions producing recalcitrant seeds or seeds rapidly losing their viability. These ones are therefore only harvested on request, just before dispatching or utilisation. As for the accessions to be harvested, a higher priority is attributed to annual plants than to perennials which must not be planted every year. A list is compiled every year and used as a guide by the collectors.

Seed harvesting is extremely time-consuming, particularly for annuals, which have to be verified every year. The seed bank is testing a system of security seed samples in order to reduce those activities and to respond to an eventual complete destruction of the accession in cultivation and to avoid the whole seed stock being distributed. The system consists of the preparation of a certain number of seed samples harvested during one year from verified plants, each of them being sufficient for one sowing. For annuals, one seed sample is conserved on a long-term basis and six others on a short-term basis. Five of the short-term seed samples provide sowing material for five consecutive years without requiring any verification work. The sixth short-term seed sample is used as a starting point of a new seed multiplication (with plant verification), while the sample conserved on a long-term basis constitutes a strategic reserve. For perennials, only one seed sample is conserved on a long-term basis. This system of security seed samples is completed by one reference seed sample and by one long-term stored sample with seeds of origin. It is applied to all the accessions with action 01 used alone or in combination with other actions.

The National Botanic Garden has participated in the International Seed Exchange Scheme for botanic gardens for a long time. A list of seeds is compiled every year and mailed to about 600 correspondents. The system of actions has been applied to the compilation of the seed catalogue since 1995 and is partly the result of an in-depth analysis of the contents of previous Index Seminum and their corresponding demands. Accessions of very common species with no data on origin were eliminated. Other seeds that were removed are, for example, seeds harvested on out-crossing species cultivated with related taxa in the same area, seeds characterised by a short viability, seeds harvested from plants with doubtful or incomplete identification. Efforts are made to increase the number of accessions from interesting species with high-quality data on provenance (although it is not a criterion for being selected by the correspondents of the Garden) and with recent verification information. In terms of actions, only the accessions with an action 02 or 03 are now included in the seed catalogue, that is 900 instead of the 1,600 before this analysis and the use of actions. We also try to offer numerous accessions harvested in the greenhouses, by far the the most requested items of the seed catalogue. As most of the species cultivated in the greenhouses are characterised by short-lived seeds, we created the action 08 (harvested on demand). A list of species, based on experience and phenological observations, is compiled and offered for exchange.

The 'Seed Bank Management' module of LIVCOL, the multi-user relational database application developed by the National Botanic Garden of Belgium using the software PROGRESS, allows to process all information about seeds, including date of harvest, actions, security samples and reference samples and type of storage. The module is very useful for the establishment of accession lists to be collected or be verified. It also allows the compilation of the annual seed catalogue and facilitates the seed dispatching. Statistics related to seed supply and offer are provided, too.