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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:

Define the prioritization criteria to be applied.
Define the prioritization methodology.
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.

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.

TOOLKIT MENU FLOWCHART

Other prioritization criteria
Other prioritization criteria

Other prioritization criteria

Three criteria are generally used when prioritizing CWR: economic value of the related crop, utilization potential for crop improvement and threat status. Nevertheless, there are many other criteria that have been used and can be considered when prioritizing CWR:
Status of occurrence: whether the CWR is native to the country, introduced¹, and if it is known to be invasive.
Conservation status: whether sufficient genetic diversity is already conserved in situ and/or ex situ. Additional conservation efforts may not be justified for those CWR already efficiently conserved, and resources should focus on those species that are not conserved.
Ex situ: careful attention to the information obtained from current ex situ conservation holdings should be paid because: the material held in genebanks might be incorrectly determined, dead, in poor condition or unavailable to potential users, the number of accessions might be misleading because of duplicates, and/or the ex situ accessions might not be representative of the overall genetic diversity of a species.
In situ: two types of in situ conservation can be distinguished: passive, when a species occurs within a protected area but it is not being monitored and managed, and active conservation, when species and genetic diversity is afforded long-term monitoring and management. Therefore, a species that is found in a protected area is not necessarily adequately conserved. Higher conservation priority can then be assigned to CWR that do not occur within existing protected areas, then to those that are passively protected and lastly to those that are actively protected in at least part of its native range.
Legislation: if the taxon is under any kind of regional, national or local legislative protection it will automatically require conservation attention because national governments are under a legal obligation to protect them. It is important to note however that these species may already be afforded some level of conservation action due to their legislative protection status.
Species distribution: in general, priority increases inversely to geographic range, such that species with a more restricted distribution (e.g. national endemics) should be given higher priority than species occurring worldwide. The reason that relative distribution may be used for prioritization is that geographically restricted species are potentially more adversely impact by localized threats and extinction events and loss of any single population or group of populations may impact the entire viability of the species. When deciding priorities on the basis of the geographical range of taxa, a degree of objectivity is required since there is no clear dividing line between a taxon with a limited, and therefore threatened, range and one with a limited range but not in immediate need of conservation action.
Global distribution: the distribution of the taxon worldwide. Species endemic to a country or that occur in only a few countries are likely to be prioritized above those that occur in several countries (see Ford-Lloyd et al. 2008, 2009). However, it should be noted that a species can occur in several countries and still be of priority at national level because of its nationally restricted range or based on other prioritization criteria. Also, the size of the countries (i.e. Russia versus Lesotho) that the species occurs in must be taken into account, as well as the extent of the species’ distribution within those countries.
National distribution: the distribution of the taxon within the country (e.g. the number of provinces/districts/states where each taxon occurs, extent of occurrence). It may be considered as an indicator of rarity or threat; a species occurring in few regions within the country is considered rarer than a species occurring throughout the country.
Other criteria: these may include population data, genetic diversity information, relative costs of conservation, selection of wild relatives of crops in centres of crop origin when prioritization is being carried out in countries located in centres of crop origin etc.
_{¹ According to Kornas (1990), an introduced species can be roughly classified according to its approximate date of introduction: archaeophyte (before 1500s) or neophyte (after 1500s) and diaphyte (established in a non-permanent way).}
How to deal with missing information when prioritizing CWR for conservation
How to deal with missing information when prioritizing CWR for conservation

How to deal with missing information when prioritizing CWR for conservation

When gathering information to prioritize CWR for conservation action, we often face the problem of missing information—for example, not all CWR have been Red Listed and the genetic relationships between crops and their wild relatives are not known for all crop gene pools. Missing information is a general problem in all steps of conservation planning and we need to make use of the available information in the best way possible, as well as taking into account that some information is missing.

Regarding the three main prioritization criteria: economic value of the related crop, utilization potential for crop improvement and threat status, missing information may include:
Socio-economic value data for all relevant crops.
Known or potential uses of the wild relative in crop improvement.
Gene Pool or Taxon Group concepts for the wild relative.
Threat status of the wild relative.
Options to help compensate or nullify the impact of the different types of missing information when prioritizing CWR:
Socio-economic value data missing for all relevant crops. This situation is very common as only major crops or crop groups usually have this type of information. Rather than using socio-economic data, any indicator of economic value can be used instead, e.g. knowledge of the local, national or regional socio-economic value of crops (e.g. for particular nutritional qualities, local market value or cultural importance), the number of varieties of a crop cultivated in a country or region, the number of accessions of crops held in national or regional genebanks to give an indication of how important those crops are for the country/region. However, not only do these indicators introduce a degree of subjectivity to the analysis, practitioners should be careful when ranking their importance with respect to other crops since direct comparisons cannot be made using different indicators (Kell et al. submitted). For instance, socio-economic data are often combined into crop groups (e.g. FAOSTAT presents data for millets, a crop group that includes Echinochloa, Eleusine, Eragrostis, Panicum, Pennisetum, Setaria crops). In this particular case, all crop genera within the crop group can be given the same socio-economic value.
Known or potential uses of the wild relative in crop improvement. When the uses of a wild relative are unknown, the Gene Pool concept can be used as a proxy for the potential of the wild relative for crop improvement, as it reflects its genetic proximity to the crop. If the Gene Pool concept is also missing, the Taxon Group concept can be applied instead to determine the taxonomic proximity of the wild relative to the crop.
Gene Pool or Taxon Group concepts for the wild relative. If these data is not readily available in the current main sources (the Harlan and de Wet inventory and GRIN Taxonomy for Plants), ideally literature searches should be undertaken. If this information is still missing and if you are using a scoring system, the score for missing information should distinguish between situations where there is no information on the potential utilization for crop improvement and cases where the wild relative is not of potential use for crop improvement, i.e. rather than scoring a ‘0’, a ‘not applicable’ would be more suitable. On the other hand, if you are using a serial system then you might consider either prioritizing only those species which have potential utilization for crop improvement information (Gene Pool or Taxon Group concepts and known and potential uses in crop improvement) or using the generic concept (or the TG4 definition, i.e. that all wild species in the same genus as the crop are CWR) and prioritize all species within the same genus of a crop.
Threat status of the wild relative. If the extinction risk of a particular CWR has not been assessed either using the IUCN Categories and Criteria (IUCN 2001) or another (national) threat assessment system, then we can categorize these taxa as NE (Not Evaluated). If you are using a scoring system the score for NE should take into account that the species is a priority for Red List assessment and not necessarily a low priority for conservation action. In this way, there is no implication in terms of conservation planning. If you are using a serial system you could prioritize first based on the criteria for which you have data and then add to the prioritized list those CWR that have information on threat status and that are threatened (as suggested by Kell et al. submitted).
Other suggestions include:
If a scoring system is being applied to prioritize the CWR checklist, calculate an 'index of scoring precision' per species in order to estimate the number of criteria that contributed to the score obtained for that particular CWR. It can be estimated by counting the number of criteria used in the scoring of that species, divided by the total number of criteria (Magos Brehm et al. 2012). This is only applicable when a scoring system with more than five criteria is used for prioritizing CWR, and it implies that all criteria are equally valuable, which is unlikely to be the case. How to use this information to obtain the final list of priority species or to assign different levels of conservation priority is the responsibility of the researcher undertaking the task.
To decide not to use the criteria for which information for the majority of the CWR is missing in a scoring system. For instance, if only four species out of a few hundred have been Red Listed, it is not advisable to use 'threat status' as a prioritization criterion. It is suggested that for any prioritization criterion, if more than two thirds of the data for the taxa being prioritized is missing then that criterion should not be used.
Finally, it should be highlighted that CWR taxa that lack any of the data listed above should be tagged as 'high priority to obtain the missing information'.

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.

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Other prioritization criteria

How to deal with missing information when prioritizing CWR for conservation