Hexaploid Wheat: Evolution, Domestication, Dissemination, US Commercialization, and Molecular Characterization

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Hexaploid Wheat: Evolution, Domestication, Dissemination, US commercialization, and Molecular characterization

Wheat is one of the major food crops in the world, which provides 532 kcal/capita/day (http://faostat.fao.org). World production of wheat is about 670 M tonnes, which is only behind maize (872 M tonnes) and rice (720 M tonnes) (http://faostat.fao.org) whereas the US is the third largest wheat producer in the world (http://faostat.fao.org). Wheat group comprise of 13 diploid and 18 allopolyploid species (12 tetra and 6 hexa) (Feldman et al. 2012), where hexaploid wheat is the most cultivated class throughout the world (Faris 2014). Hexaploid wheat (bread wheat) is known as the allohexaploid (2n=6x=42, BBAADD), because it is
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The first event took place between T.uratu (AA) (Br13Aq5A) (Dvorak et al. 1993) and Ae. Speltoides ssp.lingustica (SS) (Br13S Tg22Sq5S) around 0.5 MYA ago. This event led to the formation of T.turgidium ssp. dicoccoides (AABB) (Br13ABr13BTg22Bq5A q5B), which evolved to T.turgidium (br13Abr13Btg22BQ5A q5B), the free threshing tetraploid (Faris 2014). The progenitor of T.turgidium is uncertain .It either belongs to the dicoccum or parvicoccum subspecies but there are lots of factors that lead to this uncertainty, including brittle rachis, the waxiness gene (Faris 2014).

The second amphiploidization event between T.turgdium (AABB) and Ae. Tauschii (DD) led to the formation of the hexaploid wheat (Dvork et al. 1998; Lelley et al. 2000; Faris 2014) T.aestivum ssp spelta (Asian or Asian like), which has hulled seeds due to the presence of Tg1 from the Ae. Tauschii. The B, G, S genomes diverged from Ae.spletoides (SS), but still have some common features (Zhang et al. 2002; Kilian et al. 2006; Faris 2014). Further evolution of T.aestivum ssp spelta led to the formation of the free threshing T.aestivum ssp aestivum (br13Abr13Bbr13Dbr23Dtg22Btg12DQ5A q5B q5D) about 8000 YA. Other hexaploid wheat varieties, T.aestivum ssp spelta (European), T.aestivum ssp macha, T.zhukovskyi (AmAmAAGG), are not ancestors of the modern free threshing wheat. The spp. macha and spelta both originated by the hybridization between

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