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CWR prioritization can be carried out at different geographical (i.e. global, regional, national, subnational) and taxonomic (e.g. crop genus) scales and can be simple or complex and time-consuming depending on a number of factors such as the scale, methodology, and criteria used, the number of taxa in the CWR checklist and the available resources. Both criteria and methodology should be defined by the national agency or researcher that is prioritizing CWR and should, ideally, involve major stakeholders that play a role in CWR conservation and use (see Magos Brehm et al. 2016).

In terms of the method, the starting point for prioritization is the CWR checklist. Whatever the approach, floristic or monographic, prioritization essentially consists of three main steps:

  1. Define the prioritization criteria to be applied.
  2. Define the prioritization methodology.
  3. Apply both the criteria and prioritization methodology to the CWR checklist.

Associated with these steps there will also be a need to consider how many priority CWR will be flagged for immediate conservation action.

1. Define the prioritization criteria

There are three main criteria that are generally used in CWR prioritization:

  • Socio-economic value of the related crop: the primary application of a CWR is in the genetic improvement of existing crop varieties or the creation of new ones. The economic importance of the related crop species is thus a good indicator of the value of their wild relatives. The selection of priority crops will vary according to the scale of prioritization (i.e. global, regional, national or local) and may even vary according to the implementing agency. However, the highest priority crops are likely to be food crops (important for food security and nutrition), crops with high economic value and crops with multiple use values. It should be noted that a single genus may contain more than one crop (e.g. Solanum tuberosum L. – potato, and Solanum melongena L. – aubergine). Several sub‐criteria concerning the national economic value of the related crop can be taken into consideration, such as: production value, quantity produced and/or surface area cultivated over a specific time period, number of varieties grown at national level, value to local populations or regions of the target country and the importance of the crop as an energy source e.g. average annual contribution of dietary energy (kilocalories) per capita per day. In addition, these sub-criteria can be considered at national, regional, continental and/or global scales, and by considering some or all of these different levels it will help to build a clearer picture of the relative importance of crop wild relatives at these different scales. See how this criterion has been used in China and South Africa.
  • Utilization potential for crop improvement: wild taxa belonging to a single crop gene pool are genetically related to one another, and some are more closely related to the crop than others. To determine the degree of relatedness between a crop and its CWR and therefore the utilization potential of the wild relatives, where genetic information is available, CWR taxa can be classified using the Gene Pool concept. For some crops, the Gene Pool concept has already been defined (see here), however, if genetic data are not available and the Gene Pool concept has not been previously defined, the Taxon Group concept, which provides a proxy for taxon genetic relatedness, can be applied. In general, the closest wild relatives in GP1B and GP2 or TG1B and TG2 are given priority. In addition, wild relatives in GP3 or TG3 and TG4, that have already been used as gene donors or have shown promise for crop improvement, should also be assigned high priority. If neither the Gene Pool nor the Taxon Group concept can be applied, then the available information on genetic and/or taxonomic distance should be analyzed to make reasoned assumptions about the most closely related taxa. For other crops, a literature survey will be required in order to ascertain if Gene Pool or Taxon Group concepts have already been established, or, if taxonomic classifications are available to establish new Taxon Group concepts and determine the degree of relatedness of each wild relative to its associated crop (see here for more materials on this subject.
Collation of CWR threat assessments
  • Threat status: relative threat is commonly used to prioritize taxa for conservation, i.e. the more threatened—for example with an increased likelihood of genetic erosion or actual extinction of the species—the greater the conservation priority. Using this criterion involves the collation of existing threat assessments in a three stage process: (i) identify potential sources of CWR threat assessments, (ii) identify whether CWR have been Red List assessed and (iii) collate threat assessments (at national, regional and global levels). For CWR lacking threat assessments, the following steps can be taken: (i) gather the necessary data and undertake a novel Red List assessment, (ii) use an indicator to determine threat (e.g. endemism, distribution, inferences from known threats to taxa/loss of habitats/land use types) or (iii) consider not using threat status as a prioritization criterion. Existing threat assessments can be gathered from national Red Lists and Red Books published based on the IUCN Red List Categories and Criteria (IUCN 2001)―the most commonly applied means of assessing threat to wild taxa—or from other national threat assessment systems, the IUCN Red List of Threatened Species (for global Red List assessments), or peer-reviewed papers and reports and expert knowledge. Threat assessments can be carried out at different geographical scales (i.e. global, regional, national), and all scales should be taken into account in the prioritization process. However, as the implications of threat status depend on the scale of the assessment, this should also be taken into account when applying the criterion of relative threat.

2. Define the prioritization methodology

Prioritization schemes often include rule‐based and scoring systems, with or without weighting of the criteria, and using different combinations of criteria. Prioritization may be carried out either in parallel or in series. Prioritization in parallel (i.e. scoring systems) is where the selected criteria are scored against all taxa first, then the scores are summed and the taxa with the higher scores are the prioritized taxa. Prioritization in series is where the criteria are scored in a sequence using one criterion at a time and only the high scoring taxa for the first criterion is scored for the second criterion and so on, until finally the remaining taxa at the end of the process are the prioritized taxa. While the prioritization in parallel may include some irrelevant/distantly related CWR, the prioritization in series may miss important CWR. The choice of the method is up to the researcher/country’ stakeholders doing the prioritization and care should be taken in making this decision.

3. Apply both the criteria and prioritization methodology to the CWR checklist

Once the criteria and the method have been defined, they will need to be applied to the CWR checklist. If a scoring system has been defined as the prioritization method, then scores for each criterion need to be assigned to each CWR in the checklist. The scores are then summed, and the taxa with the highest total scores are prioritized. The minimum total score required for prioritization is subjective and may depend on the financial resources available to conserve priority CWR. If a serial prioritization is to be carried out, then CWR may be filtered based on the first prioritization criterion, then the second criterion, and so on. After applying all criteria, the prioritized taxa are those that remain. Regardless of the method used, it will culminate in a list of priority CWR.

The Interactive Toolkit for Crop Wild Relative Conservation Planning was developed within the framework of the SADC CWR project www.cropwildrelatives.org/sadc-cwr-project (2014-2016),
which was co-funded by the European Union and implemented through ACP-EU Co-operation Programme in Science and Technology (S&T II) by the African, Caribbean and Pacific (ACP) Group of States.
Grant agreement no FED/2013/330-210.