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The Origins of Triticum Domestication

Explore the domestication traits and glutenin loci study of Triticum species. Understand the implications of allele distributions and phylogenetic relationships. Referenced by notable experts in the field.

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The Origins of Triticum Domestication

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  1. The Origins of Triticum Domestication Ben Grady Dept. of Botany UW-Madison

  2. The genus Triticum • Poaceae • Highly inconsistent taxonomy • Triticum and Aegilops separate genera • Triticum sensu lato • Includes Aegilops • Triticum sensu stricto ~ 10 species • Native to Mediterranean area • Base n = 7

  3. Domesticated Wheats • Triticum monococcum L. (cultivated einkorn) • T. boeoticum (wild einkorn) • Diploid - AA • Triticum dicoccum Schübl. (emmer wheat) • T. dicoccoides (wild emmer) • Tetraploid – AABB • Triticum aestivum L. (bread or common wheat) • Hexaploid - AABBDD • T. dicoccoides (AABB) + Aegilops tauschii (DD)

  4. Domestication Traits • “As soon as one begins to plant seed in a seed-bed on a yearly basis and save seed for the following season, selection pressures are automatically set in motion, leading toward domestication” –J.R. Harlan • Non-shattering rachis (two independent recessive loci) (Davies and Hillman, 1992) • Seed dormancy periods • Uniform ripening of seeds • Seed size

  5. Traits of Domestication Salamini et al., 2002

  6. Glutenin Loci Study • HMW glutenin loci: Glu-1-1 & Glu-1-2 • 9 alleles of the B chromosome Glu- B1-1 (Glu-D1-1 outgroup) • Wild and domesticated emmers • Two well-supported clades a & b; divergence dated to 1.4-2.0 MYA • Multiple domestication events? • Domestication of mixed populations? • Introgression?

  7. NJ tree from Glu-B1-1 alleles in T. aestivum a (black) b (white) from Brown et al., 2006

  8. a & b Glu-B1-1 frequencies in wild emmers • a – black • b - white From Brown et al., 2006

  9. Glu-B1-1 subclades in cult. emmers Figure 9.2 (from Brown et al., 2006) Proportion of α (black) & β (white) alleles

  10. Implications of Glu-B1-1 allele distributions • a alleles more common than b alleles • a alleles present in all accessions sampled • b alleles present in Turkey and NW, through Europe • Do a alleles confer a selective advantage? – probably not • Independent introductions of emmer into Europe? – probably

  11. Allele expansion in Europe Higher % of A alleles Higher % of B alleles

  12. Origins of Glu-B1-1 allele subclades • Multiple domestications of emmer wheat? • probably not • Single domestication of diverse wild population? • not bloody likely • New alleles introduced after domestication via introgression with wild relatives? • Yeah (supported by rDNA evidence)

  13. Phylogenetic Relationships…Peterson et al., 2006 • Hybridization history of T. aestivum (allohexaploid) • DD (A. tauschii) + AABB (T. dicoccoides) • T. dicoccoides = AuAu (T. urartu) + BB (A. speltoides

  14. Wild Triticum species www.icarda.org

  15. Strict consensus tree from 8 equally parsimonious trees, sequences from two nuclear genes, DMC1 & EF-G, and plastid gene ndhF (Peterson et al., 2006) • Triticum polyphyletic • Aegilops polyphyletic

  16. Selected References • Harlan, J.R. 1992. “Origins and Processes of Domestication”. In Grass Evolution and Domestication. Ed: G.P. Chapman. Cambridge U. Press, pgs: 159-166. • Brown, T.A., S. Lindsay, & R.G. Allaby. 2006. “Using Modern Landraces of Wheat to study the Origins of European Agriculture”. In Darwin’s Harvest. Eds: T.J. Motley, N. Zerega, & H. Cross. Columbia U. Press, pgs: 197-212. • Peterson, G., O. Seberg, M. Yde, & K. Berthelsen. 2006. Phylogenetic relationships of Triticum and Aegilops and evidence for the origin of the A, B, and D genomes of common wheat (Triticum aestivum). Molecular Phylogenetics and Evolution 39: 70-82 • Salamini, F., H. Ozkan, A. Brandolini, R. Schafer-Pregl, & W. Martin. 2002. Genetics and geography of wild cereal domestication in the Near East. Nature Reviews Genetics Vol. 3 June 2002 429-441.

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