Triticum aestivum, wheat

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Taxonomy

cellular organisms - Eukaryota - Viridiplantae - Streptophyta - Streptophytina - Embryophyta - Tracheophyta - Euphyllophyta - Spermatophyta - Magnoliophyta - Liliopsida - commelinids - Poales - Poaceae - BEP clade - Pooideae - Triticeae - Triticum - Triticum aestivum

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Brief facts

• Wheat is a cereal grass that is cultivated worldwide and is one of the most important food grain along with maize and rice.
• In comparison with other domesticated cereal species wheat genetics is quite complicated because some wheat species occur as stable polyploids (having more than two sets of diploid chromosomes), which makes genome mapping and QTL (quantitative trait loci) tracking quite difficult. Each wheat genome is an order of magnitude larger than the genomes of other model plants such as Arabidopsis thaliana and rice. Indirect evidence suggests that in the wheat genomes there may be gene-rich islands (gene insulae) separated by gene-poor or gene-empty regions.
• T. aestivum (bread wheat) is a hexaploid species that is most widely cultivated. It is very good model to study polyploidy, a driving force for plant genome evolution.

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Developmental stages (life cycle)

Life Cycle Stages

The development and growth of cereal grains have been translated into several numeric scales to quantify development for scientific and management purposes. The most commonly used scales are the Feekes, Zadoks and Haun. The most widely used scale in the United States is the Feekes scale. Completion of development from germination to maturity takes 280-359 days for winter wheat and 120-145 days for spring wheat.

• Seeds MeSH
  • dormant seed dry seed
  • germination MeSH Zadok stages 00-09; this stage includes imbibition, emergence of radicle and emergence of coleoptile
• vegetative
  • seedling MeSH Zadok stages 10-19; Feekes stage 1; first five leaves are unfolding on the main shoot
  • tillering growth of shoots (tillers) that sprout from the base of a grass; Zadok stages 20-29; Feekes stage 2-3
  • stem elongation also called jointing; most tillers have been formed by this stage, and the secondary root system is developing; winter wheats, which may have a prostrate growth habit during the development of vegetative parts, begin to grow erect; stem elongation stage continues from start of pseudo stem erection until flag leaf becomes fully visible; Zadok stages 30-39; Feekes stages 4-9
• reproductive
  • booting at this stage, the head is fully developed and can be easily seen in the swollen section of the leaf sheath below the flag leaf; Zadok stages 40-49; Feekes stage 10.0-10.1
  • heading emergence of inflorescence; Zadok stages 50-59; Feekes stages 10.2-10.5
  • flowering also called anthesis; Zadok stages 60-69; Feekes stages 10.5.1-10.5.3
• ripening Zadok stages 90-99; Feekes stages 11.1-11.3
  • watery ripe Feekes sage 10.5.4
  • mealy ripe Feekes stage 11.1
  • kernel hard Feekes stage 11.3
• ripe plant reached physiological maturity and is harvest ready; Feekes stage 11.4

Wheat inflorescence anatomy

Plant Compoments

• spike a type of monocot inflorescence that does not have branches and pedicels; the spikelets, are attached directly to the central axis, or rachis of the stem; examples of crops that have this type of inflorescence would be wheat, barley, ryegrass, and wheatgrass
• rachis the central axis of the inflorescence to which spiklets are attached
• spikelet the individual flowering units in the spike; grass inflorescence flower cluster; it consists of two glumes and one or more individual florets
  • glume the glumes are a pair of empty scale-like bracts that are located at the base of the grass spikelet
  • floret MeSH a small flower; there are one or more florets contained in the spikelet
    • lemma and palea two bracts enclosing the floret
      • lemma the outer bract that usually
        encloses or partially encloses a
        flower in the spikelet of the grasses
        • awn an extension of the vein
          or mid- rib of the lemma
      • palea the inner and usually smaller of
        two scaly bracts immediately
        subtending the grass flower
        in a spikelet
    • pistil the entire female reproductive system
      • ovary reproductive structure that
        contains one or more ovules
        that upon fertilization will
        develop into the seed or seeds
      • style the stalk-like portion of the
        pistil that connects the
        stigma and the ovary
      • stigma the organ in which the pollen
        adheres and germinates
    • lodicle lodicles are two small structures
      located at the base of the pistil that
      function to open the floret during the
      time of pollination and fertilization
    • stamen the male reproductive system
      • anther the enlarged terminal portion
        of the stamen; the structure
        that contains the pollen
        • pollen
      • filament the stalk-like portion of the stamen,
        which bears the anther at its tip
        
  • rachilla an axis of a spikelet that bears the florets

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References

Websites

• Wheat: the big picture
• Growth and Development Guide for Spring Wheat

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