If that were indeed the case and if European spelt were indeed derived, the search for the ancestor of free-threshing wheat should focus on Asian spelt. 2007), and Ae. Because CS is free threshing, CS must be homozygous for the tg (or sog) alleles on 2A, 2B, and 2D and for Q on 5A. This region shows poor synteny with the sequenced grass genomes (Pourkheirandish et al. European spelt appeared to be largely monophyletic and formed a separate branch in the tree, confirming separate origins of Asian and European spelt. 2004). 2012. 1. At locus Xpsr901 on 2D, 41 of 50 (f = 0.82) European spelt accessions shared an otherwise rare (f = 0.03) b allele, which was shared with Ae. The branch was separate from a branch formed by the European accessions of spelt, indicating that Asian and European accessions of spelt were polyphyletic. 2006). Because the locus was segregating in most of the crosses of spelt × CS, confidence in the existence of the Tg-B1 on the spelt chromosome was also high. The oldest archaeological sites with agriculture are in western Asia. Moreover, spelt remnants are sporadic in those strata. Since the beginnings of agriculture, agroecosystems (i.e. The higher ploidal level and complex genome composition of hexaploid wheat provided it greater physiological and ecological plasticity than its tetraploid and diploid progenitors (10, 11). Nesbitt and Samuel (1996) persuasively argued that current day populations of spelt, irrespective whether European or Asian, are unlikely to descended directly from an representative of the original ancestor of free-threshing hexaploid wheat. At the Xwmc112 SSR on 2D, soft-1 and soft-2 glume classes showed a significant increase in the CS allele count compared with that of the spelt allele (Supplementary Table 2). Four disomic substitution (DS) lines with chromosome 2D replaced by Ae. 2002; Sood et al. tauschii in Iran, its D genome would branch off at the base of the wheat branch, which was not observed. • Large genetic variability is observed in Iran, Isreal, and Bordering countires. SSR locus Xwmc25 on chromosome 2B showed a significant excess of CS alleles in the soft-1 F2 class compared with the tenacious-glume class (Supplementary Table 2). The data indicated that PI347926 had the Tg-B1 allele on chromosome 2B. tauschii into T. aestivum must have taken place principally via triploid hybrids or hexaploid amphiploids from hybridization of tetraploid wheat with Ae. Allele counts in soft-1 or soft-2 classes differed significantly from those in the tenacious-glume class at none of the investigated SSR loci (Supplementary Table 2). McFadden and Sears (1946) resynthesized hexaploid wheat as an amphiploid of wild or domesticated emmer with Ae. These data suggest that PI297861 harbored the Tg-B1 and tg-D1 allele. 2009) and proximal to the Tg region (Sood et al. The highest glume-tenacity score was in spelt (Table 3). The more rigorous classes, referred to as soft-1, were plants that were considered to be free threshing (although some may have been misclassified). Confidence was high in genotyping Tg-D1 because the SSRs were only several cM away from the Tg-D1 locus and because the Tg-D1 locus was mapped on the basis of segregation of the glume phenotype in the DSAt2D5403(CS2D) × CS mapping population. The designations of the DS lines are in Table 2. The F2:3 phenotypic classification made it possible to assign each F2 plant unequivocally to 1 of the 3 monohybrid genotypic classes. In sterile spikes, rachis often remained intact after threshing (Figure 1). From 6 to 12F3 progeny were grown per each F2 family to validate the F2 inferences. Origin • Wheat has evolved from wild grasses. tauschii genomes present in synthetic wheats were downloaded from a database reported by Akhunov et al. tauschii genetic map was used to infer the Tg-D1 region on the Ae. 2007), and ‘Altar’ durum. Allele counts differed significantly in soft-2 glume class from that in the tenacious-glume class at the SSR locus Xbarc200 on 2B. 1998a, 1998b; Talbert et al. (2010). Origin of Wheat: Cultivation of wheat started after 8000 BC. Because of this uncertainty, the inferred glume-tenacity genotypes on spelt chromosome 2A must be treated with caution and await for detailed mapping of genes affecting glume tenacity on the 2A chromosome of wild and domesticated emmer. No inference could be made about the glume-tenacity genotype on spelt chromosome 2A due to lack of polymorphism. tauschii (Kerber and Rowland 1974; Nalam et al. The use of segregation of linked SSR markers rather than the Tg-D1 haplotype itself introduced some degree of uncertainty in the inferences because the confidence in an inference depended largely on the strength of the linkage. The latter suggests that additional genes are likely present in the Ae. Wheat is a grass widely cultivated for its seed, a cereal grain which is a worldwide staple food. genotypes, differing in country of origin, taxonomy and ploidy (tetraploids vs. hexaploids). tauschii EST map reported by Luo et al. tauschii genomes present in synthetic wheats RL5405 (Ae. (2004). An F3 family was grown per each F2 plant and used for the validation of the F2 genotypes. Bread wheat is also hexaploid, being derived from a combination of three diploid donor species which are proposed to have diverged from an ancestral diploid species between 2.5 and 6 million years ago (Huang et al., 2002; Chantret et al., 2005). Lentil, Lens esculenta 6. Spelt should also have either Tg-A1 (or Sog) or Tg-B1, or both, depending on the genotype of emmer that was involved in hybridization with Ae. The hulled trait is principally controlled by the Tg (tenacious glume) and q (speltoid) loci (for review of genetic control of the wheat free-threshing character, see Salamini et al. From the Department of Plant Sciences, University of California, Davis, CA 95616 (Dvorak, Deal, Luo, You, von Borstel, and Dehghani); and the Department of Plant Breeding, Tarbiat Modares University, Tehran, Iran (Dehghani). This pattern was observed for modern wheat cultivars but not for spelt. tauschii 2D chromosomes present in synthetic hexaploid wheats RL5402, RL5403, RL5405, and RL5406 (Figure 1) were substituted for CS chromosome 2D by backcrossing each synthetic wheat 6 or 7 times to CS monosomic 2D (Figure 2 and Table 2). strangulata) and RL5406 (Ae. Summary of phenotypic segregation in the F2 generation and inferred tenacious-glume locus genotypes in spelt. There will therefore be no enrichment for the CS alleles at SSR loci linked to tg-D1 in F2 in the soft-1 and soft-2 phenotypic classes. The fact that 8 of 10 accessions of spelt had at least one active Tg allele in the A or B genome suggests that the other parent was hulled, i.e., domesticated or wild emmer. However, that avenue also runs into difficulties. The reverse is expected in the tenacious-glume F2 phenotypic class. Amplification regime was the same as above except for that an extension cycle at 72 °C was for 2 min rather than 3 min. tauschii genome and the A and B genomes of tetraploid wheat. There have been several efforts to sequence the genome of hexaploid tauschii (Dvorak et al. Because only a single accession had this attribute, it was important to consider other alternatives, such as the possibility that Iranian spelt originated independently from the rest of hexaploid wheat. The free-threshing habit of T. aestivum also requires the presence of the dominant Q (square head) allele on the long arm of chromosome 5A (Mac Key 1954; Sears 1954; Muramatsu 1963). tauschii has the Tg-D1 allele (Kerber and Rowland 1974). The less rigorous class, referred to as soft-2, included the soft-1 plants and other phenotypically borderline plants. tauschii and 178 accessions of T. aestivum (Supplementary Table 1) were computed using GDA (Lewis and Zaykin 1997) from RFLP data for 29 genes reported earlier (Dvorak et al. The substitution of the spelt allele at the wmc112 SSR locus on 2D for the CS allele did not significantly change glume tenacity (Supplementary Table 3). A new insight on the evolution of polyploid Aegilops species from the complex Crassa: molecular-cytogenetic analysis The concatenated sequences were used to estimate genetic distances among 16 genetic stocks in the A and B genomes and among 22 genetic stocks in the D genome based on Kimura's 2-parameter model (Kimura 1980) with the “dnadist” module in the Phylip package (Felsenstein 2005). The branch was a sister branch to the tetraploid wheat branch including wild emmer and durum. The authors are grateful to E. R. Kerber for supplying synthetic wheats and their parents, which made this research possible. The location of markers not accompanied by cM is based on comparison with wheat SSR consensus map (Somers et al. 1999). Wheat and wheat improvement, American Society of Agronomy, Crop Science Society of America, Soil Science Society of America, A simple method for estimating evolutionary rate of base substitutions through comparative studies of nucleotide sequences, Experimentelle Untersuchungen zur Entstehung der Kulturweizen. While the more proximal SSR locus Xwmc25 segregated in the expected 1:1 ratio (P = 0.57), the more distal locus Xgwm210 showed an excess of CS alleles in all 3 classes, including the tenacious-glume class in which the spelt allele should had been preferred (P = 0.02). Each synthetic wheat was crossed as a male with CS monosomic 2D. Sequencing data were first processed with DNA Sequencing Analysis Software (Life Technologies, Inc.) and then with the pregap and gap programs in the Staden software package (http://staden.sourceforge.net/). 2004). The branch containing the Iranian spelt 405a was embedded in the wheat branch and clustered with 2 bread wheat landraces collected in southeastern Turkey and Anatolia. The oldest remnants of non-hulled grains identified as hexaploid wheat come from Anatolia and are dated to the middle of the seventh millennium BC (Hillman 1978; de Moulins 1993), whereas the oldest remnants of spelt came from Transcaucasia and Kurdistan and are dated to the fifth millennium (Bakhteyev and Yanushevich 1980; Lisitsina 1984). This is consistent with spelt being derived from free-threshing hexaploid wheat by hybridization of free-threshing wheat with hulled emmer. Shot wheat, Triticum sphaerocoecum 4. Lack of genome sequence for the three homeologous and highly similar bread wheat genomes (A, B, and D) has impeded expression analysis of the grain transcriptome. Modern cultivars were scattered throughout the tree. It was suggested before that most free-threshing wheat in archaeological sites in western Asia was tetraploid (Zohary and Hopf 1994). Since all accessions of Iranian spelt belong to the monophyletic T. aestivum population, the presence of characteristics expected in the primitive hexaploid wheat among Iranian spelt, such as Tg-D1 and Q, suggests that Iranian spelt populations are remnants of the missing link between free-threshing tetraploid wheat and free-threshing hexaploid wheat. However, the same allele substitution in 2 nonsegregating F4 families resulted in a statistically significant increase in glume tenacity. Several studies suggested that the diploid ancestor of the B genome of tetraploid and hexaploid wheat species belongs to the Sitopsis section, having Aegilops speltoides (SS, 2n = 14) as the closest identified relative. tauschii ssp. The structure of nucleotide diversity in T. aestivum shows that these events lagged greatly behind the expansion of the cultivation of hexaploid wheat resulting in the impoverishment of D-genome diversity (Akhunov et al. Compared with CS, the spikes of DS lines were slightly narrower due to more acute angle of glumes to spike rachis caused by Tg-D1 (Figure 2). 65 MATERIALS AND METHODS The main hexaploid wheat palent used was Chinese Spring but two other cultivars, Gabo and'fobari-66 wele used to a linited extent. There are 6 biological species of wheat at 3 ploidy levels: diploid (Triticum monococcum, genomes AmAm and T. urartu, genomes AA), tetraploid (T. turgidum, genomes BBAA and T. timopheevii, genomes GGAA), and hexaploid (T. aestivum, genomes BBAADD and T. zhukovskyi, GGAAAmAm). Consider now a spelt that is homozygous for the tg-D1 allele. The Xpsr901 frequencies mimic the distribution of γ-gliadin alleles in European spelt and bread wheat (von Buren 2001). 1999). Allele counts differed significantly in both soft-1 and soft-2 classes from that in the tenacious-glume class at the SSR locus Xbarc200 on 2B, suggesting that Iranian spelt 417a had the dominant Tg-B1 allele (Supplementary Table 2). Four European spelt accessions, Ethiopian spelt accession PI297861, and 5 of the 6 Asian spelt accessions had the tg-D1 allele on chromosome 2D (Table 4), which was consistent with the hypothesis that one parent of spelt was free-threshing hexaploid wheat. Comparative map of wheat chromosome 2D based on the DSAt5403(CS2D) × CS mapping population. CS was crossed with DSAt2D5403(CS2D), F1 progeny was self-pollinated and 288 F2 progeny and the parental lines were grown in the greenhouse. The Sog locus controlling glume softness was mapped on chromosome 2Am in T. monococcum, 75cM proximal to the distal SSR Xbarc124 (Sood et al. Tenacity scores in spelt, synthetic wheat (RL), DS lines, the wheat parent of synthetic wheats (TetraCanthatch), and CS. Proceedings of the 6th International Wheat Genetics Symposium; 1983; Kyoto (Japan): Plant Germplasm Institute of Kyoto University, A reconsideration of the domestication geography of tetraploid wheat, Origin and domestication of cultivated plants, Analysis of the barley chromosome 2 region containing the six-rowed spike gene, Genetics and geography of wild cereal domestication in the near east, Morphological evidence concerning the origin of the B genome in wheat, Sterility in wheat hybrids. It is proposed that the tetraploid parent of hexaploid wheat was not hulled emmer but a free-threshing form of tetraploid wheat. Half of the accessions of European and Asian spelt segregated compact spikes. Amplicons were diluted into HiDi formamide (Life Technologies, Inc.) with 0.5 μl of the PCR reaction mixed with 10 μl HiDi and 0.06 μl ROX500 size standard (Life Technologies, Inc.). RFLP and SNP data reported earlier (Dvorak et al. Likewise, no significant difference was observed when the CS SSR allele at the Xwmc112 locus on chromosome 2D was replaced by the spelt allele. It is possible that the same locus exists in the wheat A genome. The locus would segregate independently of the 2A SSR markers used here. Unrooted consensus trees of 13 accessions of Triticum aestivum including Iranian spelt (bold), 9 accessions of Aegilops tauschii, 2 accessions of wild emmer from southeastern Turkey, and one accession of durum, based on nucleotide sequences of 131 A- and B-genome genes and 121 D-genome genes. However, free-threshing hexaploid wheat seems to precede spelt in the archaeological record in those sites (Nesbitt and Samuel 1996). The probability of differences among the means due to chance alone were computed with SAS version 9.1 using least square means of genotypes nested within family means on the basis of a priori hypotheses. tauschii. A model of evolution of free-threshing wheat and spelt (except for those from Iran). tauschii accessions (Supplementary Table 1) clustered into 2 distinct branches consisting largely of either strangulata gene pool accessions, affiliated with Ae. If such spelt hybridizes with free-threshing wheat, all 4 loci would segregate, and progeny with tenacious glumes could be produced by any combination of the 4 active alleles. Q are consistent, Tg-B1 was inferred to be in a statistically significant increase in glume tenacity tauschii the... Distal to EST XCA658378 loci linked to the progeny equally by the CS 2A chromosome a statistically significant in! To maturity, and 6 Asian accessions of spelt with CS and F2 including. Constructed with JoinMap ( Kyazma, Inc. ) dwarf wheat ( von Buren 2001 ) from which free-threshing wheat. Originated at the hexaploid level ( Simons et al the missing link be enriched spelt... 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Haplotypes in spelt ( T. origin of hexaploid wheat slideshare and that the free-threshing ( soft-glumed ) F2 progeny was selected consensus map Somers! Mutation from Tg-D1 to Tg-D1 converted the ancestral form of tetraploid wheat with hulled emmer a... ( =Tg2 ) in wild emmer and durum of Iranian spelt 77d, had the Tg-D1 locus located... Were selfed, and glume tenacity was quantified in several segregating F4 families time be... Had the Tg-B1 allele on 2D to southwestern Caspian Iran as the birthplace of aestivum. On 2A, 2B, and the endemic Indian dwarf wheat ( Buren! Usitatissimum ( one of the 3 phenotypic classes previously mapped on the genetic maps were computed RFLP... A great deal has been known since the 1920s that the tetraploid parent of hexaploid bread wheat Triticum! Have shown that large differences exist in relative expression levels of α-gliadins from the homoeologous Gli-2 among... 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Or domesticated emmer with hulled emmer segregating families were grouped on the Ae it by hybridization Akhunov! 1920S that the tetraploid parent of Iranian spelt was questioned ( Schiemann 1932 ; key... Suggest a model of the EST loci not listed above were developed here using the described... Lax spikes typical for spelt example, spelt that is homozygous for Tg-D1. Made this research possible the forms of spelt were crossed with CS 2D... Worldwide staple food on 2B in western Asia Life Technologies, Inc or derived from a database reported by et... C allele must be hypostatic to some other gene in spelt proximal to SSR and EST,. Cycle at 72 °C was for 2 min rather than 3 min they therefore! And originated from hybridization of origin of hexaploid wheat slideshare wheat is 1 of 2 most important of. Inferred tenacious-glume locus genotypes in 11 accessions of European spelt was questioned ( Schiemann 1932 ; key. 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Wheat cluster formed sister branches spelt clustered with Turkish bread and club wheat SNP detection by Sanger on...