Threats affecting CWR
Genetic erosion is a key problem for CWR. What is genetic erosion?
Genetic erosion is a fundamental problem for CWR and has been referred to in the literature as the permanent reduction in richness (total number of alleles) or evenness (spread of allelic diversity) of common local alleles, or the loss of combinations of alleles over time in a defined area. Genetic erosion can affect wild populations but can also affect populations conserved in situ and accessions conserved in ex situ collections (i.e. when the ex situ collection goes through the regeneration process and accessions are inadvertently selected to suit the regeneration site). It is important to distinguish between genetic changes that are detrimental to populations and the ‘normal’ background levels of change. Any loss of diversity through genetic erosion means the individual is less likely to be able to adapt to a changing environment and means that potentially useful traits will be unavailable to the breeder.
Why are CWR threatened?
There are numerous factors that negatively impact wild plant populations (including CWR) resulting in genetic erosion, and potentially the eventual loss (extinction) of taxa (varieties, subspecies and species). The main factors that contribute to the genetic erosion of CWR diversity include:
- Expansion of the human population (which leads to the unequal and unsustainable use of natural resources, and is the basis of all other threats).
- Habitat destruction, degradation, homogenization and fragmentation.
- Changes in agricultural practices, soil and land use.
- Use of pesticides and herbicides.
- Over-exploitation (excessive extraction from the wild of timber, fuel wood, medicinal and horticultural plants, overgrazing, excessive tourism etc.).
- Introduction of exotic species (weeds, pests and diseases that compete with, hybridize with, cause physical or biological damage to, or kill native species).
- Natural calamities (floods, landslides, soil erosion etc.).
- Climate change (which is expected to directly affect phenology and lead to extinction of wild plant species, particularly in drier regions where certain CWR may already be at the edge of their distribution) (e.g. see Parmesan and Yohe 2003, Root et al. 2003, Thuiller et al. 2005, Jarvis et al. 2008, Lenoir et al. 2008).
- Lack of education and awareness of the importance of CWR and the need to conserve them.
- War and political instability.
- Lack of knowledge regarding CWR breadth, location and real use potential.
- Lack of conservation action for CWR. For instance, CWR are often associated with disturbed habitats such as field margins, forest edges and roadsides, and these populations are not being adequately conserved by ecosystem conservation agencies.
- Environmental mismanagement.
What are the concrete consequences of CWR genetic erosion?
- A decline in the short- to medium-term viability of individuals and populations.
- A reduction in the evolutionary potential of populations and species.
- Loss of genetic diversity which implies inability to adapt to changing environmental conditions.
- A decrease in the availability of genes and alleles that may confer microhabitat adaptation, disease and pest resistance, yield enhancement traits etc., for crop improvement (e.g. to develop better or newly adapted varieties), which will restrict breeder’s options and have a fundamental impact on future food security.
Threat assessment of CWR diversity—current status
Threat assessment of CWR diversity—current status
Significant progress has been made in assessing the loss of botanical diversity, particularly in regions where the flora is well known. It has been estimated that about 268,000 flowering plant taxa exist globally and, of these, 19,206 were assessed as part of the IUCN Red List by 2015 with 10,551 of them classified as threatened. At European level, there are over 20,000 flowering plants (Euro+Med Plantbase 2006–2011), of which 11,117 were assessed for the IUCN Red List by 2015.
CWR are intrinsically no different to other wild plant species, and, like them, many are currently threatened with loss of diversity and/or extinction (Maxted et al. 1997b, Stolton et al. 2006). A review of Red List assessments using the current and most detailed IUCN Red List Categories and Criteria (IUCN 2001) showed that, of the 25,000 CWR species present in Europe, less than 1% had been assessed by 2008 (Kell et al. 2008). Further, Maxted and Kell (2009) reviewed whether the CWR within 14 global priority crop gene pools had been threat assessed and found that only one, Solanum, had been partially assessed using the 2001 IUCN Red List Categories and Criteria.
Even though there is currently no comprehensive global review of CWR threat assessment, if, as shown by Kell et al. (2008), the majority of wild plant species may be considered CWR—as there is at least one crop in the majority of genera—then a Global Red List of plants would be indicative of the threat facing CWR. Therefore, because the Sampled Red List Index for Plants project (Brummitt and Bachman 2010) recently found that 20% of all plants are currently threatened with extinction, it can be implied that a similar proportion of CWR are also likely to be threatened. More specifically, for European CWR, an IUCN Red List assessment was recently undertaken for 591 European CWR species representing 25 crop gene pools/groups (Bilz et al. 2011). It found that 11.5% (66) of the 591 species are considered to be threatened, with 3.3% (19) Critically Endangered, 4.4% (22) Endangered and 3.8% (25) Vulnerable—a further 4.5% (26) of the species are classified as Near Threatened.
Outside of Europe, as part of the UNEP/GEF-supported project ‘In situ conservation of crop wild relatives through enhanced information management and field application’, Bolivian CWR were prioritized. Ecogeographic data for 36 CWR genera and over 310 CWR species were then collated and threat assessments undertaken. It was found that 14.6% (45) of the species are considered threatened, with 2.3% (7) Critically Endangered, 7.1% (22) Endangered and 5.2% (16) Vulnerable—a further 6.5% (20) of the species are classified as Near Threatened (Mora et al. 2009). It is anticipated that these initiatives will act as a catalyst for more countries and regions to follow suit.
CWR and climate change
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.