Editing Wheat (section)

== Evolution ==

=== Phylogeny ===

[[File:Polyploid wheat origins.svg|thumb|upright=2.5|Wheat origins by repeated [[Hybrid (biology)|hybridization]] and [[polyploidy]].<ref name="Golovnina-2007"/> Not all species are shown.]]

Some wheat species are [[diploid]], with two sets of [[chromosome]]s, but many are stable [[polyploidy|polyploids]], with four sets of chromosomes ([[tetraploid]]) or six ([[hexaploid]]).<ref name="Golovnina-2007"/> [[Einkorn]] wheat (''Triticum monococcum'') is diploid (AA, two complements of seven chromosomes, 2n=14).<ref name="Belderok-2000"/> Most tetraploid wheats (e.g. [[emmer]] and [[durum]] wheat) are derived from [[Emmer#Wild emmer|wild emmer]], ''T. dicoccoides''. Wild emmer is itself the result of a hybridization between two diploid wild grasses, ''[[Triticum urartu|T. urartu]]'' and a wild goatgrass such as ''[[Aegilops speltoides|Ae. speltoides]]''.<ref>{{cite journal |last1=Friebe |first1=B. |last2=Qi |first2=L.L. |last3=Nasuda |first3=S. |last4=Zhang |first4=P. |last5=Tuleen |first5=N.A. |last6=Gill |first6=B.S. |s2cid=13010134 |title=Development of a complete set of ''Triticum aestivum''-''Aegilops speltoides'' chromosome addition lines |journal=[[Theoretical and Applied Genetics]] |date=July 2000 |volume=101 |issue=1 |pages=51–58 |doi=10.1007/s001220051448}}</ref> The hybridization that formed wild emmer (AABB, four complements of seven chromosomes in two groups, 4n=28) occurred in the wild, long before domestication, and was driven by [[natural selection]]. Hexaploid wheats evolved in farmers' fields as wild emmer hybridized with another goatgrass, ''[[Aegilops squarrosa|Ae. squarrosa]]'' or ''[[Aegilops tauschii|Ae. tauschii]]'', to make the [[hexaploid]] wheats including [[common wheat|bread wheat]].<ref name="Golovnina-2007"/><ref name="Dvorak-2012">{{Cite journal |last1=Dvorak |first1=Jan |last2=Deal |first2=Karin R. |last3=Luo |first3=Ming-Cheng |last4=You |first4=Frank M. |last5=von Borstel |first5=Keith |last6=Dehghani |first6=Hamid |date=2012-05-01 |title=The Origin of Spelt and Free-Threshing Hexaploid Wheat |journal=[[Journal of Heredity]] |volume=103 |issue=3 |pages=426–441 |doi=10.1093/jhered/esr152 |pmid=22378960 |doi-access=free}}</ref>

A 2007 [[Molecular phylogenetics|molecular phylogeny]] of the wheats gives the following not fully-resolved [[cladogram]] of major cultivated species; the large amount of hybridisation makes resolution difficult. Markings like "6N" indicate the degree of [[polyploidy]] of each species:<ref name="Golovnina-2007">{{cite journal |last1=Golovnina |first1=K. A. |last2=Glushkov |first2=S. A. |last3=Blinov |first3=A. G. |last4=Mayorov |first4=V. I. |last5=Adkison |first5=L. R. |last6=Goncharov |first6=N. P. |title=Molecular phylogeny of the genus Triticum L |journal=Plant Systematics and Evolution |publisher=Springer |volume=264 |issue=3–4 |date=2007-02-12 |doi=10.1007/s00606-006-0478-x |pages=195–216|bibcode=2007PSyEv.264..195G |s2cid=39102602 }}</ref>

{{clade
|label1=[[Triticeae]]
|1={{clade
   |1=[[Barley]] 2N, [[rye]] 2N/4N, and other cereals
   |label2='''Wheats'''
   |2={{clade
      |1={{clade
         |1=''Triticum monococcum'' ([[Einkorn wheat|einkorn]]) 2N
         |2=''[[× Aegilotriticum]]'' hybrids (''[[Aegilops]]'' x ''Triticum'') 6N
         }}
      |2={{clade
         |1= ''[[Triticum timopheevii]]'' (zanduri wheat) and others 4N
         |2={{clade
            |1=''Triticum aestivum'' ([[Common wheat|common or bread wheat]]) 6N
            |2=''Triticum durum/turgidum'' ([[durum]] wheat) 4N
            |3=''Triticum spelta'' ([[spelt]]) 6N
            |4=''Triticum turanicum'' ([[khorasan wheat]]) 4N
            |5=''Triticum dicoccum'' ([[emmer]]) 4N
            |6= many other species
            }}
         }}
      }}
   }}
}}

=== Taxonomy ===

{{main|Taxonomy of wheat}}

During 10,000 years of cultivation, numerous forms of wheat, many of them [[hybrid (biology)|hybrids]], have developed under a combination of [[artificial selection|artificial]] and [[natural selection]]. This complexity and diversity of status has led to much confusion in the naming of wheats.<ref>{{Cite journal |last=Shewry |first=P. R. |date=2009-04-01 |title=Wheat |journal=[[Journal of Experimental Botany]] |volume=60 |issue=6 |pages=1537–1553 |doi=10.1093/jxb/erp058 |pmid=19386614 |issn=0022-0957 |doi-access=free}}</ref><ref>{{Citation |last1=Fuller |first1=Dorian Q. |last2=Lucas |first2=Leilani |title=Wheats: Origins and Development |date=2014 |encyclopedia=Encyclopedia of Global Archaeology |pages=7812–7817 |publisher=[[Springer New York]] |doi=10.1007/978-1-4419-0465-2_2192 |isbn=9781441904263 |s2cid=129138746 }}</ref>

==== Major species ====

Hexaploid species (6N)

* [[Common wheat]] or bread wheat (''T. aestivum'')&nbsp;– The most widely cultivated species in the world.<ref name="Yang-2022">{{Cite journal |last1=Yang |first1=Fan |last2=Zhang |first2=Jingjuan |last3=Liu |first3=Qier |last4=Liu |first4=Hang |last5=Zhou |first5=Yonghong |last6=Yang |first6=Wuyun |last7=Ma |first7=Wujun |display-authors=3 |date=2022-02-17 |title=Improvement and Re-Evolution of Tetraploid Wheat for Global Environmental Challenge and Diversity Consumption Demand |journal=[[International Journal of Molecular Sciences]]|volume=23 |issue=4 |pages=2206 |doi=10.3390/ijms23042206 |pmc=8878472 |pmid=35216323|doi-access=free }}</ref>
* [[Spelt]] (''T. spelta'')&nbsp;– Another species largely replaced by bread wheat, but in the 21st century grown, often organically, for [[Artisanal food|artisanal]] bread and pasta.<ref>{{cite news |last=Smithers |first=Rebecca |title=Spelt flour 'wonder grain' set for a price hike as supplies run low |newspaper=[[The Guardian]] |date=15 May 2014 |url=https://www.theguardian.com/money/2014/may/15/spelt-grain-supplies-under-pressure-high-demand }}</ref>

Tetraploid species (4N)

* [[Durum]] (''T. durum'')&nbsp;– A wheat widely used today, and the second most widely cultivated wheat.<ref name="Yang-2022" />
* [[Emmer]] (''T. turgidum'' subsp. ''dicoccum'' and ''T. t.'' conv. ''durum'') – A species cultivated in [[Ancient history|ancient times]], derived from wild emmer, ''T. dicoccoides'', but no longer in widespread use.<ref name="USDA_ARS">{{GRIN |''Triticum turgidum'' subsp. ''dicoccon'' |314587 |access-date=11 December 2017}}</ref>
* [[Khorasan wheat|Khorasan or Kamut]] (''T. turgidum ssp. turanicum'', also called ''T. turanicum'') is an ancient grain type; Khorasan is a historical region in modern-day Afghanistan and the northeast of Iran. The grain is twice the size of modern wheat and has a rich nutty flavor.<ref name="Khlestkina-2006">{{cite journal |last1=Khlestkina |first1=Elena K. |last2=Röder |first2=Marion S. |last3=Grausgruber |first3=Heinrich |last4=Börner |first4=Andreas |year=2006 |title=A DNA fingerprinting-based taxonomic allocation of Kamut wheat |journal=Plant Genetic Resources |volume=4 |issue=3 |pages=172–180 |doi=10.1079/PGR2006120 |s2cid=86510231 }}</ref>

Diploid species (2N)

* [[Einkorn]] (''T. monococcum''). Domesticated from wild einkorn, ''T. boeoticum'', at the same time as emmer wheat.<ref>{{ Cite book |last=Anderson |first=Patricia C. |year=1991 |chapter=Harvesting of Wild Cereals During the Natufian as seen from Experimental Cultivation and Harvest of Wild Einkorn Wheat and Microwear Analysis of Stone Tools|title=Natufian Culture in the Levant |editor-first=Ofer |editor-last=Bar-Yosef |location=Ann Arbor, Michigan |series=International Monographs in Prehistory |page=523 |publisher=Berghahn Books}}</ref>

==== Hulled versus free-threshing species ====

[[File:Naked and hulled wheat.jpg|thumb|Hulled wheat and [[einkorn]]. Note how the einkorn ear breaks down into intact spikelets.]]

The wild species of wheat, along with the domesticated varieties [[einkorn]],<ref name="Potts-1996">{{cite book |last=Potts |first=D.T. |year=1996 |title=Mesopotamia Civilization: The Material Foundations |publisher=[[Cornell University Press]] |page=62 |isbn=0-8014-3339-8}}</ref> emmer<ref>{{cite book |last=Nevo |first=E. |title=Evolution of Wild Emmer and Wheat Improvement |publisher=Springer Science & Business Media |publication-place=Berlin ; New York |date=2002-01-29 |isbn=3-540-41750-8 |page=8}}</ref> and [[spelt]],<ref>{{cite book |last1=Vaughan |first1=J.G. |last2=Judd |first2=P.A. |year=2003 |title=The Oxford Book of Health Foods |publisher=[[Oxford University Press]] |page=35 |isbn=0-19-850459-4}}</ref> have hulls. This more primitive morphology (in evolutionary terms) consists of toughened glumes that tightly enclose the grains, and (in domesticated wheats) a semi-brittle rachis that breaks easily on threshing. The result is that when threshed, the wheat ear breaks up into spikelets. To obtain the grain, further processing, such as milling or pounding, is needed to remove the hulls or husks. Hulled wheats are often stored as spikelets because the toughened glumes give good protection against pests of stored grain.<ref name="Potts-1996"/> In free-threshing (or naked) forms, such as durum wheat and common wheat, the glumes are fragile and the rachis tough. On threshing, the [[chaff]] breaks up, releasing the grains.<ref>{{cite web |title=Field Crop Information |publisher=College of Agriculture and Bioresources, University of Saskatchewan |url=https://agbio.usask.ca/cdc/field-crop-information.php |access-date=10 July 2023 |archive-date=18 October 2023 |archive-url=https://web.archive.org/web/20231018003729/https://agbio.usask.ca/cdc/field-crop-information.php |url-status=dead }}</ref>