Wheat Facts

Stylized image of wheat

The History of Wheat Production
Wheat (Triticum sp.) is one of the oldest and most extensively grown of all crops. It was first cultivated for use as food between 10,000 – 8000 B.C. Modern bread wheat is a hexaploid and originated from at least two hybridization events between different species however the botanical origin of wheat is still largely unknown and hotly debated. There is little doubt that wheat cultivation mirrored or supported the rise of civilizations in Europe and the Middle East. It was introduced to Mexico by the Spanish (1700s) and to Virginia by English Colonists (1800s). Wheat is being harvested somewhere in the world in any given month. It has been adaptable to a range of geographical regions and is grown in all but tropical climates.

Wheat Grain Structure
Wheat grain is actually a fruit called a caryopsis. Baked goods made from the entire caryopsis or wholegrain contain the starchy endosperm, bran and embryo. In contrast bread made of refined flour has the germ and bran removed and contains only the endosperm.

Images taken from “Professional Pasta” from Italy

BRAN: This is the pericarp or the outer coat surrounding the fruit and it is made up of several layers that serve to protect the embryo. The bran is rich in B vitamins and minerals and contributes significantly to the fibre content in wholegrain flour.

GERM: What is commonly called the germ is the embryo. If placed in the right conditions the embryo will germinate into a new plant. The embryo is a rich source of B vitamins, oil, vitamin E and natural plant fat. It is often removed during milling because the fat causes rancidity during flour storage. However because the Wheat germ is nutritionally valuable it is often sold separately or added to other products.

ENDOSPERM: This is the primary site of starch and protein storage and the fraction of the grain that when the grain is milled, gives rise to white flour. The endosperm is typically 60 – 80% starch and 5 – 15% protein with some lipids and minerals associated with these compounds.

Wheat Use
The flour extracted from wheat grain is unique. It is the only cereal flour which will produce a leavened or light baked product, thus wheat flours can be used for croissants, pastries and light cakes, foods not easily produced using corn flour for example. Further, the proteins associated with starch granules makes wheat ideal for pasta production. The higher protein content of pasta wheat gives them the highly desirable al dente texture. Wheat’s fortune as a food may have waned in recent times with the popularity of the Atkins diet and the heightened awareness of gluten allergies.

Wheat as a Research Organism
Most bread wheat is hexaploid—it has six copies of each gene, where most organisms have two. Much of the wheat used for pasta is tetraploid with four copies of each gene. The DNA content of bread wheat is enormous containing 16 billion base pairs of DNA. This is 40 times as much as rice, six times as much as maize and five times as much as humans. This complicates efforts to improve the crop using modern genetic techniques, however in some cases it is an advantage. Notable features of wheat which influences its use as a research organism:

Wheat

  • Large genome size (16 Mb).
  • Hexaploid.
  • Genetic transformation is possible even though the efficiency is very low.
  • The genome has large intergenic spaces filled with retrotransposons.
  • Mutant phenotypes are not easily detected in visual screens.
  • Wheat is a good organism to study polyploidy.
  • Mutational breeding can be facilitated because deleterious gene changes may be buffered by the presence of a normal gene(s) on another chromosome(s).
  • Wheat is an inbreeding species.
  • Performing genetic crosses is simple.
  • Wheat has a short life cycle and is amenable to greenhouse cultivation.
  • Extensive cytogenetic stocks are available. http://www.k-state.edu/wgrc/Germplasm/Stocks/stocks.html
  • Karyotyping is advanced. http://www.k-state.edu/wgrc/Extras/cbands.html
  • Research efforts are highly co-operative. http://maswheat.ucdavis.edu/
  • Its widespread use as a food means that improvement by scientific research is critical.
  • There are traits unique to wheat that can only be understood by studying this organism.

Sources:

  1. “Ears of plenty – The story of wheat” The Economist. December 2005.
  2. Wheat Chemistry and Technology (1988) ed. Y. Pomeranz. American Association of Cereal Chemists.