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The establishment and implementation of ex situ conservation priorities include five steps:

1. Review ex situ conservation gaps.
2. Formulation of the ex situ collecting programme.
3. Germplasm field collection.
4. Genebank seed processing.
5. Post-storage seed care and monitoring.

1. Review of ex situ conservation gaps

Ex situ conservation gaps at individual CWR taxon as well as at ecogeographic, genetic and trait levels should be reviewed in order to establish priorities for the ex situ collection programme.

2. Formulation of the ex situ collecting programme

The formulation of an ex situ collecting programme involves selecting target CWR populations and collecting sites, and planning when and how the collection will be undertaken. The selection of target CWR populations and sites is likely to result from the combination of ex situ conservation gap analyses (at individual CWR taxon, ecogeographic, genetic and/or trait diversity levels and, for instance, using a ‘hotspot’ or a complementarity approach, see here) and climate change analysis. Priority is likely to be assigned to:

• Individual CWR that are not conserved ex situ or in situ.
• CWR populations (within a single taxon) that are under-represented at ecogeographic, genetic or trait diversity levels as identified by the ex situ analysis.
• CWR taxa and populations most likely to be negatively affected by climate change (Magos Brehm et al. 2016).

The ex situ collecting programme should also include information about the number of sites sampled. Generally, collectors should aim to sample the maximum number of sites possible with the resources available. However, the species’ breeding system, seed dispersal mechanism, the ecogeographic characterization of the species and the predicted impact of climate change on its distribution may also be used to determine the number of sites to be sampled.

3. Germplasm field collection

CWR should be collected from natural or semi-natural habitats, and the following five factors should be considered when sampling from the field:

• Distribution of sites within the target area: using either the cluster approach where selected sites are close together to pick up micro-habitat associated genetic diversity, or the transect approach where selected sites are along a line to pick up diverse ecosystem associated genetic diversity.
• Delineation of a site: site boundaries should be related to the size of the interbreeding unit. a site may also be delineated by changes in dominant habitat.
• Distribution of the plants sampled at a site: sampling could be carried out randomly throughout the site or, if there are distinct habitats, using a stratified random sampling method that encourages sampling from each habitat type. Collection of off-types or interesting material should be carried out selectively.
• Number of plants sampled per site: Recommendations suggest the collection of at least 2,500 seeds sampled from 40–50 plants, but ideally 5,000 seeds from 100 individuals. These numbers also depend on the species’ breeding system and seed dispersal mechanism.
• Indigenous knowledge held by local communities: field collectors should note any knowledge held by local people on the CWR found in their area, this knowledge may relate to population locations, threats, habitat associations and uses.

Each of these factors may vary depending on the nature of the target CWR being sampled and also assumes that it is possible to apply the ideal sampling strategy. For instance, many CWR are found as individual plants or small clumps of plants, not dense stands. Furthermore, ripening is not uniform so not all of the potential fruit produced by a population will be available during one sampling visit. Another important point to consider is that germplasm is virtually worthless unless it has detailed passport data associated with the collection location. Therefore, these data must be collected in the field (including GPS location), placed in a database and made available to the user community. With CWR collections it is also advisable to collect voucher specimens so the accessions’ taxonomic identification can be checked post-collection.

Note that all CWR collections should be undertaken legally with the appropriate national permission and ensuring the collection is not counter to international conventions (e.g. CITES). Collectors are also referred to the FAO International Code of Conduct for Plant Germplasm Collecting and Transfer for further guidance.

4. Genebank seed processing

Following collection, the sample arrives at the genebank and is processed according to standard practice. This includes:

• Seed cleaning (to separate chaff and fruit debris from the seed and to ensure the accession is a sample from a single species).
• Seed health evaluation (inspection for seed-borne diseases and pests).
• Dehydration (normally to around 5–6% relative humidity).
• Packaging (usually in glass vials, metal cans or laminated aluminium foil packets).
• Registration (entering an associated record in the genebank management system and making the accession available to users).
• Storage (usually in a -18°C cold room).
• Seed safety duplication.

When a seed sample arrives at the genebank but is not considered large enough to be banked directly (e.g. due to a small in situ population size or if the collection was made outside of the peak collecting season for that particular species), there may need to be a seed multiplication cycle before the seed can be processed and incorporated into the genebank or there may need to be further visits to the same population to collect more seed. For detailed genebank methodologies, click here.

5. Post-storage seed care and monitoring

Once seeds are incorporated into the genebank, their viability will gradually decrease over time. Viability is usually determined via germination tests before the seeds are packed and placed into storage, and subsequently at regular intervals during storage (at approximately 10-year intervals). It is a measure of how many seeds are alive and have the potential to develop into normal plants. Usually expressed as ‘percentage germination’, a level of viability above 75% is acceptable. When germination falls below 75% the accessions require regeneration. The aim of regeneration is to increase the quantity of seed in an accession, but while doing so it is very important to ensure that the original genetic characteristics of the accession are retained as far as possible. Each multiplication/regeneration cycle has the potential to compromise the genetic integrity of an accession through: (a) contamination from foreign pollen during fertilization, (b) contamination through seed adulteration during harvesting, threshing and packaging, (c) changes due to gene mutation, (d) genetic drift due to random loss of alleles, particularly when regenerating from small numbers of individuals, and (e) genetic shift due to unconscious natural or artificial selection (related to diverse environmental conditions during regeneration) (Sackville-Hamilton and Chorlton 1997). The risks involved with regeneration will vary considerably according to the species. Regardless, it is a costly operation and so the most efficient and cost effective way of maintaining genetic integrity is to keep the frequency of regeneration to an absolute minimum.