The Genetics of Wheat

1
The Genetics of Wheat

• Crop Clinics 2000
• Jochum Wiersma

2
Outline

• Genetics of Wheat
• Variety Development
• Consequences for You as Producer

3
Genetics of Wheat

• Spontaneous hybridization events between the
  ancestors let to rise of durum and bread wheat
• Common ancestors have been partly lost or have
  evolved themselves
• The allopolyploid can be recreated by crossing
  the current, closest ancestors.

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The Genus Triticum

• Triticum monococcum (2n2x14, AA)
• Triticum turgidum (2n4x28, AABB)
• Dicoccum - emmer (hulled)
• Durum -durum
• Triticum aestivum - wheat (2n6x42, AABBDD)
• Compactum - club
• Spelta - spelt (hulled)
• Aestivum - common

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Origin of Wheat
6
Origin of Wheat

• Vavilov developed the concept of Centers of
  Diversity in the 1920s.
• These Centers of Diversity are generally
  regarded as the place of origin and the place
  where early domestication took place for those
  species.
• The Center of Diversity for wheat, barley, oats
  and rye is the middle east region stretching from
  Ethiopia, North Africa through Turkey all the way
  to Pakistan.

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Center of Diversity
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Characteristics of Wild Wheat

• Cool season annual
• High temperature dormancy
• Vernalization requirement
• Day-length sensitivity
• Ability to tiller
• Survival mechanism for arid conditions.
• Reproductive System
• Self pollinating species with perfect flowers
• No fertility regulating mechanisms
• Self seeding (brittle rachis and shattering)

9
Characteristics of Modern Wheat

• Seed characteristics
• Less/ no shattering
• Hull-less seed
• High temperature dormancy decreased.
• Growth habit
• Spring and winter types
• Day-length insensitivity
• Introduction of dwarfing genes.

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Classes of Wheat

• In the US six classes - Soft Red Winter, Hard Red
  Winter , Hard Red Spring, Hard White Winter
  Wheat (Hard White Spring), Soft White and Durum
  wheat
• The Chicken and the Egg questions
• 1) Are the classes of wheat historical accidents
  because of regional difference in growing
  conditions or a concerted effort to define
  quality?
• 2) Did we select the different classes for
  different end-use qualities or did it just happen
  to work the best with a specific class of wheat?

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Variety Development

• Wheat cultivar is
• True breeding or homozygous - the offspring will
  have exactly the same genetic make-up as the
  parent plant from which the seed was harvested
• A mixture of a few different genotypes and was
  selected from a group of plants that looked very
  alike.
• If a breeder wants to create a new cultivar he or
  she will have to cross two different plants by
  hand and harvest that seed
• It then takes at least 7 generations after the
  initial cross to approach homozygosity
• It takes at least 7 years after the initial cross
  to release a new cultivar

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Segregation of Genotypes
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Genetic Make-Up
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Variety Protection

• No legal protection
• PVPA (20 years of protection)
• Regular
• Title V
• Utility patents
• Genetics protection
• F1 hybrid seed production
• TPS systems (Terminator technology)

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Function

• PhenotypeGenotypeGE Interaction Environment

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GE Interaction

• Phenotypic expression of a genetic trait as a
  function of the environment.

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GE Interaction
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Consequences for a Producer

• Varieties or cultivars do not change
  genetically over generations, unless
• Seed mixtures occur
• Cross pollination occur (very small percentage)
• Mutations occur (even more rare).
• Varieties will respond differently to the
  production environment if
• A-biotic conditions change (GE interaction)
• Mutations occur in biotic stresses (insects or
  disease become virulent)

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Consequences for a Producer

• In other words Varieties dont wear out
• But
• Change varieties if chances for biotic stresses
  increase and current cultivars dont offer
  genetic protection.
• Change varieties if genetics yield potential of
  new cultivars is higher.