1-global challenges and crop origins

Domestication

• Genome modification through ‘Artificial’ selection

  • Chooses specific traits and behaviour

• Animals = genes that modify behaviour/growth rate

• Plants = genes that determine

  • Morphology = seed/size/dispersion

  • Physiology = timing of seed germination/flowering

Crop domestication

• Cultivating plants instead of gathering them from the wild

  • Leads to selection of alleles

    • Gradual change over many years

Domestication results in genetic bottlenecks

• Small population sizes

• Results in genetic drift = allele loss

• Genes for desirable phenotypes experience a more drastic loss of diversity than neutral genes

Commonly selected traits of crops

• Higher yield

• Non-dispersal

• Reduced dormancy

• Colour variation

• Seedlessness (parthenocarpy)

• Greater stress tolerance

  • Abiotic = drought, extreme temperatures, salinity, nutrients

  • Biotic = viruses, bacteria, fungi, pests

• Longer storage for harvested crop

Pros of cross-breeding

• New trait is added to genetic background of existing ‘elite’ variety by recombination

• Useful (elite) genes are not loss

• Trait enhancement

• Increased genetic variety

• Environmental adaptability

• Improved efficiency

Cons of cross-breeding

• Relatively slow - multiple backcross generations

• Linkage drag = hard to remove undesirable genes physically linked to the gene of interest

• Loss of purebred traits