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Triticum (wheat genus)

Life > eukaryotes > Archaeoplastida > Chloroplastida > Charophyta > Streptophytina > Plantae (land plants) > Tracheophyta (vascular plants) > Euphyllophyta > Lignophyta (woody plants) > Spermatophyta (seed plants) > Angiospermae (flowering plants) > Monocotyledons > Order: Poales > Family: Poaceae

Triticum (wheat genus) Triticum (wheat genus)

Triticum aestivum under cultivation in Vienna Botanical Gardens, Austria. [photos H.G. Robertson, Iziko ]

The two main types of wheat used these days are Durum wheat Triticum turgidum and bread wheat Triticum aestivum. Durum wheat is a variety of Emma wheat, the latter of which was the first type of wheat to be domesticated, about 9000 years ago. Bread wheat is derived from the hybridization of Emma wheat with the wild grass Aegilops squarrosa, which happened about 6700 years ago. Wheat is now the world's major crop in terms of food production.

Wheat is the World's major crop in terms of food production. Of the total food produced by the World's top 30 crops (based on dry matter), about 23.4% comes from wheat, followed by maize (21.5%) and rice (16.5%) (Harlan 1995). 

The objectives of wheat domestication

  1. To produce 'non-shattering' varieties that have seeds that are not lost by breaking off the plant before harvest. Wild grasses are adapted to dispersing their seeds by releasing them once ripe but grasses under cultivation, such as wheat, need to have seeds that are retained and only break off during the threshing process. Selection of non-shattering varieties would have occurred quickly once cultivation started, as it was only these plants that would have been successfully harvested.
  2. To produce large, plump seeds
  3. To produce more seeds per plant by increasing the number of fertile flowers (termed florets in grasses).
  4. To produce 'free-threshing' or 'naked' varieties where the husk round the seed comes off during threshing. All's that needs to be done after threshing is for the grain to be winnowed so that the empty husks (i.e. chaff) are blown away from the seeds. Wild varieties of wheat are hulled - i.e. the seeds are covered by a tough husk that stays round the seed once it has been threshed. To get this husk off the seed, it has to be pounded in some way which is more laborious than winnowing the husks away and means the grain is broken and less suitable for storing.
  5. To produce seeds that germinate together. Wild forms are adapted to delay germination until there are suitable conditions and to vary the timing of germination so that seeds do not grow up and die altogether during a season of erratic and poor rainfall. 

There are four species in the wheat genus:

  1. Triticum monococcum (Einkorn Wheat).Has two sets of chromosomes (i.e. diploid). Most varieties produce only one grain per spikelet, hence its latin and common names. It was domesticated from wild forms in the Near East about 9000 years ago to produce plants with plumper seeds that did not break off the plant before harvest. Einkorn Wheat was grown extensively during the Neolithic period but from the Bronze Age on, its importance wained in favour of the Emmer and Bread wheat varieties. It is now a relic crop, grown in the Balkans (i.e. countries between the Adriatic and Aegean Seas - Yugoslavia, Albania, Rumania, Bulgaria, Greece and western Turkey), Germany, Switzerland, Spain and Caucasia.

  2. Triticum turgidum (Emmer and Durum Wheat). Has four sets of chromosomes (i.e. tetraploid). Emmer Wheat is hulled (see above) and was selected and cultivated from wild forms. Durum Wheat is the predominant variety that was selected from Emmer Wheat and has free-threshing grain.

  3. Triticum timopheevi (Timopheev's Wheat). Like T. turgidum it is also tetraploid. Wild and cultivated Timopheev's Wheat is only known from a small region in Georgia (between the Black and Caspian seas) and has never gained prominance in World agriculture.

  4. Triticum aestivum (Bread Wheat). Has six sets of chromosomes (i.e. hexaploid). Bread Wheat was produced under cultivation by the hybridisation of Triticum turgidum with the wild grass Aegilops squarrosa, about 4700 BC. The first variety formed from this hybridisation is termed Spelta Wheat and has hulled seeds. Later on, free-threshing varieties were formed.

A number of other species names have been used in the past to refer to various varieties within the above four types but these names are usually no longer used in modern species classifications of wheat.

History of Wheat domestication

Event Year
People were collecting and eating wild Emmer Wheat in the Near East (as well as barley). Evidence for this comes from the finding of wild Emmer Wheat seeds in an archaeological site on the shores of the Sea of Galilee in Israel. c 17000 BC
People were collecting and eating wild Einkorn Wheat in the Near East and were probably doing so well before this. Evidence from this stems from the finding of carbonised remains of wild Einkorn Wheat seeds in archaeological sites in northern Syria. Seeds of the wild forms can be distinguised from the domesticated forms because they are thinner in appearance. c10000 BC
People had domesticated hulled Emmer Wheat through selection of plants with plumper seeds than wild forms which were non-brittle so they were retained during harvesting and only shed through the threshing process. Evidence for this comes from the occurrence of plump Emmer Wheat seeds at an archaeological site near Damascus in Israel. Emmer Wheat was the main cereal crop in the Near East from the very beginnings of agriculture in this region. It also came to be cultivated further afield in the Aegean region (e.g. Greece), on the Balkan Peninsula and in central Europe and remained the main cereal crop through the Neolithic period and into the Bronze Age although Einkorn Wheat was often grown as well.  c 7800 BC
Einkorn Wheat had been domesticated through selection and propagation of plants with plumper seeds than wild forms. Evidence for this domestication comes from finding these plumper seeds at archaeological sites in Syria, Turkey and Iran. With time Einkorn Wheat becomes a major crop in the near East in the Neolithic period. It spread further than this in the Neolithic period to Cyprus, Greece, the Balkan Peninsula, Europe and the Caucasus. For instance, domesticated Einkorn has been found in in Greek agricultural settlements dating back to 6000-6500 BC. c7000 BC
Selection of free-threshing, naked, forms of Emmer Wheat has been successful although hulled Emmer and Einkorn continue to be grown. However, by the Late Bronze Age, growing of naked wheats predominated in the Mediterranean and Near East regions. Durum Wheat is derived from these naked wheat types. 6000-7000 BC
Earliest record of people using Bread Wheat (the hulled Spelta variety). This occurred in the Caucasus region between the Black and Caspian Seas which makes sense because this is within the main geographical distribution of Aegilops squarrosa which is the grass that at some stage formed a fertile hybrid with cultivated Emmer Wheat to form Bread Wheat. Free-threshing, naked, Bread Wheat is thought to have developed soon afterwards (before 4000 BC). 4700 BC

References

  • Harlan, J.R. 1995. The living fields - our agricultural heritage. Cambridge University Press, Cambridge.

  • Sauer, J.D. 1993. Historical geography of crop plants - a select roster. CRC Press, Boca Raton, Florida.

  • Zohary, D. & Hopf, M. 1993. Domestication of plants in the old World - The origin and spread of cultivated plants in West Asia, Europe, and the Nile Valley. Clarendon Press, Oxford.

Text by Hamish Robertson


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