Role of Genes in Modern Bread Wheat
Wheat was originally a very tall plant, as seen in "The Corn Harvesters" painted by Pieter Bruegel the Elder in 1565. That shows wheat growing up to the heads of the men harvesting it with scythes. After the discovery of shorter in Japan, wheat breeders transferred selected height reducing (Rht) genes from different landraces to create the shorter but higher yielding wheat varieties more suited to modern farming. Most modern combines are unable to harvest tall cereals with long straw due to blockage problems.
The picture on the left shows the wheat variety "Mercia" with a control and four lines with different Rht genes.
The rht (Control), without height reducing genes, is used as the control for height comparison.
Rht-1 (Rht-B1b) and Rht-2 (Rht-D1b) typically produce semi-dwarf plants, about two-thirds the height of the control. Rht-3 (Rht-B1c), Rht-10 (Rht-D1c) and Rht-12 typically produce dwarf plants one-third the height of the control.
Plants with the Rht-12 gene also have awns on the ears. The awn and Rht genes are believed to be located very close together on the same chromosome and wheat geneticists have been unable to separate the two genes.
Most wheat varieties now include height reducing genes, usually Rht-1 or Rht-2 to control the height of the plants.
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