Common wheat (Triticum aestivum), also known asbread wheat, is a cultivatedwheat species.[1][2][3][4][5] About 95% of wheat produced worldwide is this species;[6] it is the most widely planted of all crops by area (as of 2009) and thecereal with the highest monetary yield.[citation needed]
Numerous forms of wheat have evolved under human selection. This diversity has led to confusion in the naming of wheats, with names based on both genetic and morphological characteristics.
Bread wheat is anallohexaploid – a combination of six sets of chromosomes from different species. Of the six sets of chromosomes, four come fromemmer (Triticum turgidum, itself atetraploid) and two fromAegilops tauschii (a wilddiploid goatgrass). Wild emmer arose from an even earlier ploidy event, a tetraploidy between two diploids, wildeinkorn (T. urartu) andA. speltoides (another wild goatgrass).[8][6][9][10][11]
Free-threshingwheat is closely related tospelt. As with spelt, genes contributed fromAegilops tauschii give bread wheat greater cold hardiness than most wheats, and it is cultivated throughout the world's temperate regions.[citation needed]
Common wheat was first domesticated inWest Asia during the earlyHolocene, and spread from there to North Africa, Europe and East Asia in the prehistoric period.[citation needed] Naked wheats (includingTriticum aestivum,T. durum, andT. turgidum) were found in Roman burial sites ranging from 100 BCE to 300 CE.[12]
Wheat first reachedNorth America with Spanish missions in the 16th century, but North America's role as a major exporter of grain dates from the colonization of theprairies in the 1870s. As grain exports from Russia ceased duringWorld War I, grain production inKansas doubled.[citation needed]
Worldwide, bread wheat has proved well adapted to modern industrialbaking, and has displaced many of the other wheat,barley, andrye species that were once commonly used forbread making, particularly in Europe.[citation needed]
Modern wheat varieties have been selected for short stems, the result of RHt dwarfing genes[13] that reduce the plant's sensitivity togibberellic acid, a plant hormone that lengthens cells. RHt genes were introduced to modern wheat varieties in the 1960s byNorman Borlaug fromNorin 10 cultivars of wheat grown inJapan. Short stems are important because the application of high levels of chemical fertilizers would otherwise cause the stems to grow too high, resulting in lodging (collapse of the stems). Stem heights are also even, which is important for modern harvesting techniques.[citation needed]
Compact wheats (e.g., club wheatTriticum compactum, but in IndiaT. sphaerococcum) are closely related to common wheat, but have a much more compact ear. Their shorter rachis segments lead to spikelets packed closer together. Compact wheats are often regarded as subspecies rather than species in their own right (thusT. aestivum subsp.compactum).[citation needed]
^Bonjean, Alain P. and William J. Angus, ed. (2001).The world wheat book: a history of wheat breeding.Andover, Massachusetts, US: Intercept. p. 1131.ISBN978-1-898298-72-4. Excellent resource for 20th century plant breeding.
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