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Illustrated by Cindy Roché, Hana Pazdírková, and Christine Roberts
ŠUtah State University

Illustrated by Cindy Roché, Hana Pazdírková, and Christine Roberts
ŠUtah State University

Distribution of species, compiled from regional floras

Genomic constitution

All the species of Triticum include the A genome. The additional chromosomes in the polyploids are one or more of the B, D, and G genomes all of which derived from species of Aegilops.

Distinguishing features

Annual plants with keeled glumes and  lemmas.

Description

Plants annual. Culms 14-180 cm tall; internode below the inflorescence usually solid for at least 1 cm, even if hollow lower down.

Auricles present, often deciduous at maturity; blades 4-20 mm wide, flat.

Inflorescences spikelike, 4-18 cm long, with solitary spikelets; middle internodes (0.5)1.4-8 mm long; disarticulation in the rachis, the spikelet usually falling with the internode below attached (wedge disarticulation), sometimes with the internode above (barrel disarticulation), cultivated taxa not disarticulating or disarticulating only under pressure.

Spikelets 10-25(40) mm long, usually 1-3 times the length of the adjacent internode, appressed to ascending, with 2-9 florets, the distal florets often reduced and sterile. Glumes subequal, chartaceous to coriaceous with one prominen keel, at least distally, keels often winged and ending in a tooth or awn, a second keel or prominent lateral vein evident in some species. Lemmas keeled, chartaceous to leathery, at least the two lowest florets usually awned, awns of lowest florets 30-230 mm long, scabrous. Anthers 3.

Caryopses often falling enclosed by the glumes, not adhering to the lemma and palea.

Size

The number of species recognized varies widely, depending primarily on the treatment of the cultivated and artificial hybrids. Those involved in wheat breeding argue that having a binomial associated with genetically distinct entities, whether or not these exist in the wild, helps those maintaining the world's genebanks ensure that the genetic diversity of Triticum is maintained. In at least some instances, the entitites these scientists have shown that species may resemble each other in a morphological feature, such as the presence of an awn but that the genes each uses to control awn development are on different chromosomes and in different genomes.

Distribution

Triticum is native to western and central Asia but its cultivars are grown almost throughout the world.

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Miscellaneous comments

Taxa of Triticum have been cultivated for about 10,000 years. Nowadays, the most frequently cultivated species is bread wheat, T. aestivum which is an ABD hexaploid as is spelt., T. spelta. The two differ in their gluten content, but the amount varies in the different cultivars. Durum wheat, T. durum, is an AB tetraploid.

In 2005, Drs.Shafqat Farooq and Farooq Azam of the Pakistan National Institute of Agriculture described an octoploid hybrid derived from natural chromosome doubling in an artificial hybrid between Triticum durum and A. geniculatum, i.e., an ABMU octoploid. In their field trials, it demonstrated superior tolerance to drought and salinity to T. aestivum.

Zhang et al. 92008) have also synthesized an octoploid wheat, but its genomic constitution is ABD(A+D), the fourth set of chromosomes being derived from both the . A and D chromosomes. It has not been field tested.

Alternative interpretations

Triticum is sometimes interpreted as including Aegilops and Amblyopyrum

Type species

Triticum aestivumL.

Known problems

The main problem is that most wheat cultivars are susceptible to a strain of stem rust that was first noticed in Uganda in 1999, from which it gets its name, Ug99. This stem rust has a devastating effect on crop yields. It has now reached western Asia.

References

Farooq, S., and F. Azam. 2005. In vivo conservation of agro-biodiversity: A selective but practical approach for its sustainable utilization. Czech Journal of  Genetics and Plant Breeding 41(Special Issue): 134-139. http://utc.usu.edu/Triticeae/Trit5/CJGPB%202005%20Spec%20134_140.pdf

Farooq, S. and  Azam F. 2007. A new allopolyploid wheat for stressed lands and poverty alleviation. Field Crops Research 100, 369-73. Contact: Farooq, Shafqat ; NIAB, POB 128,Jhang Rd, Faisalabad 38000, Pakistan.

Morrison, L.A. 2007. Triticum. Pp. 268-277 in Barkworth et al., Flora of North America north of Mexico, vol. 24. Oxford University Press, New York.

Zhang, Lianquan, Dengcai Liu, Xiujin Lan, Youliang Zheng, and Zehong Yan. 2008. A  synthetic wheat with 56 chromosomes derived from Triticum turgidum and Aegilops tauschii. Journal of Applied Genetics 49: 41-44. http://jag.igr.poznan.pl/2008-Volume-49/1/pdf/2008_Volume_49_1-41-44.pdf

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