Crop Genetic Diversity

Crop genetic diversity describes the genetic diversity within or between plant species that are either directly useful to humans in the context of food and agriculture or are relatives of such species.

This genetic diversity can be assessed at different taxonomic levels, such as families, genera, species, subspecies, varieties, or landraces. Genetic diversity can be measured by different methods, ranging from the more traditional phenotypic approaches—in which the plant's physical appearance is assessed through field or greenhouse observations—to modern methods that assess genetic diversity at the molecular level.

To increase the genetic diversity of U.S. corn, the Germplasm Enhancement for Maize project seeks to combine exotic germplasm, such as this unusually colored and shaped maize from Latin America, with domestic corn lines.

Source: Keith Weller/ARS/USDA.

Crops are thought to harbor less genetic diversity than their wild relatives, since selection by humans during domestication causes a loss in genetic diversity—a process also known as a domestication bottleneck. Modern breeding efforts often lead to a further decrease in genetic diversity because of very strong selection pressures and the development of phenotypically uniform lines or varieties for commercial production. However, crop-breeding programs rely heavily on genetic diversity among different cultivars and crop wild relatives as a “genetic resource” for improvement. Also, the cultivation of a diverse array of varieties can be a promising preemptive strategy for disease management. Enhancing crop genetic diversity in agricultural production systems through the cultivation of a wide range of crops and varieties is increasingly recognized as a sustainable way to achieve food security, especially in areas with frequently fluctuating environmental conditions (see photo). However, as agriculture in most countries is being increasingly intensified using relatively few high-yielding and uniform varieties, crop genetic diversity is in decline, and much has already been lost. Increase of this decline in genetic diversity has been termed genetic erosion and is also caused by several other factors, including environmental and socioeconomic changes.

Genetic resource conservation programs exist that aim to counteract the loss of crop genetic diversity through in situ or ex situ approaches. In situ efforts attempt to protect habitats of crop wild relatives or encourage farmers to grow and evaluate a great diversity of crops and varieties. Ex situ conservation efforts consist of national gene banks or botanical gardens, as well as international collections such as the gene banks of the Consultative Group on International Agricultural Research (CGIAR) or international backup collections such as the Svalbard Global Seed Vault.

Since crop genetic diversity is geographically unequally distributed around the globe, there is a considerable interdependence among nations and across generations for these genetic resources. As a result, the International Treaty on Plant Genetic Resources for Food and Agriculture (ITPGRFA) has been set up to govern international exchange of genetic diversity of many major crops, as well as ensure fair and equitable benefit sharing. Since humans exert much of the selection pressures that determine the amount of genetic diversity present within a crop's gene pool and genome, traditional knowledge of crop diversity and production systems is an important source of information and [Page 627]as such needs to be considered in efforts that aim to conserve crop genetic diversity.

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