Aegilops tauschii, the D-genome donor of Triticum and the geographic origin of hexaploid wheat

Abstract

The place of origin of alloploid hexaploid wheat is directly connected with the distribution area of its parent species. One of them is wild plant Aegilops tauschii, the donor of D-genome. The distribution area of Ae. tauschii is stretched extensively from the western Transcaucasus (Georgia) to Central Asia, Pakistan and China. However, it is known that Ae. tauschii diverged into subsp. tauschii and subsp. strangulata at the very beginning of its existence as a species and each of its two subspecies - subsp. tauschii and subsp. strangulata - originated in the Caucasus. Studies of Aegilops tauschii provide evidence that common wheat (T. aestivum) was derived from single or limited number of accessions of Ae. tauschii and Ae. tauschii subsp. strangulata populations from its birthplace (the western Transcaucasus) were involved in the formation of common wheat, which originated in the Transcaucasus ca. 8000 BP. Natural diversity of wheat and archaeological excavations of the Neolithic sites of Georgia dated back to 8,000 BP provide evidence that the Transcaucasia is the most probable place of origin of common wheat, because: a) agriculture had been already developed and represented by all founder crops in Georgia; b) AABB-genome containing domesticated hulled and free-trashing tetraploid wheat species (T. dicoccum, T. palaeocolchicum, T. carthlicum and T. durum) had already existed in Georgia; c) hexaploid wheat species: T. spelta, T. spaerococcum, T. compactum, and T. aestivum were also present here. These three archaeological findings provide sufficient ground to propose that Ae. tauschii subsp. strangulata cross with a tetraploid wheat species could had happened here by 8000 BP.