The Origins of Triticum Domestication Ben Grady Dept. of Botany UW-Madison.
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Transcript of The Origins of Triticum Domestication Ben Grady Dept. of Botany UW-Madison.
The Origins of Triticum Domestication
Ben Grady Dept. of Botany UW-Madison
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
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)
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
Traits of Domestication
Salamini et al., 2002
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?
NJ tree from Glu-B1-1 alleles in T. aestivum
a (black)
b (white)
from Brown et al., 2006
a & b Glu-B1-1 frequencies in wild emmers
• a – black
• b - white
From Brown et al., 2006
Glu-B1-1 subclades in cult. emmers
Figure 9.2 (from Brown et al., 2006) Proportion of α (black) & β (white) alleles
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
Allele expansion in Europe
Higher % of A alleles
Higher % of B alleles
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)
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
Wild Triticum species
www.icarda.org
• 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
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.