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Threats affecting CWR

Genetic erosion is a key problem for CWR. What is genetic erosion?

Habitat of Vicia bithynica (L.) L., a tertiary wild relative of faba bean and potential gene source for rust resistance and other diseases, being invaded by Carpobrotus edulis ((L.) N.E.Br. in Ericeira, Portugal. (Photo: Joana Magos Brehm)

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:

Major threats that affect European CWR (source: Kell et al. 2012)
  • 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.

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