Chromosomal Changes over the Course of Polyploid Wheat Evolution and Domestication

Abstract

Polyploid wheats are represented by two evolutionary lineages – Emmer and Timopheevi. It was reported that the species of these groups differentiated by species-specific translocations; they showed distinct karyotype structures, i.e., the amount and the distribution of heterochromatin. Analysis of more than 1,500 accessions representing 21 wild and cultivated polyploid wheat species using C-banding revealed that intra- and interspecific divergence within these two groups was accompanied by chromosomal rearrangements. Intraspecific diversity was the highest for wild species, followed by landraces and commercial cultivars. Chromosomal rearrangements were more frequent in T. araraticum than in T. dicoccoides (55.7 % and 35.3 % correspondingly). Altogether, 2 pericentric inversions, 28 single translocations, 13 double translocations, and five multiple translocations were identified in 150 of 270 T. araraticum accessions. Sixty types of chromosomal rearrangements (4 inversions, 37 single translocations, 11 double and 6 triple translocations, and two unclassified rearrangements) were found in T. dicoccoides (143 of 400 accessions). The range of karyotype diversity decreased in cultivated Emmer: 25 single translocations, 4 pericentric inversions, 6 double and 3 multiple translocations were detected in 119 of 470 accessions (24.5 %). The translocation T5B:7A significantly dominated over other variants; alone or in combination with other translocations, being identified in 51 lines of T. dicoccum (Schrank) Schubler, preferentially from Western Europe and Mediterranean countries. Chromosomal rearrangements were also found in common wheat, the translocations T5B:7B and wheat-rye T1RS:1BL being the most frequent (25 and 29 cultivars respectively). In addition to them, 24 variants of chromosomal rearrangements, including inversions, single and multiple translocations and wheat-alien translocations and substitutions were discovered in 112 of 295 cultivars we studied.