Transcript Slide 1
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 seedbed 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.