Fig. 4

Scientific insights gained from plant aDNA, as exemplified by wheat. Top: The geological periods are indicated at the top (orange arrow) above the associated temperature profiles (blue curve showing the variation of temperature at constant elevation (y-axis) over thousands of years before present (x-axis), modified from Cuffey and Clow [168]) and key climatic changes. Center: The known historical routes of wheat migration from the site of origin (Fertile Crescent) are indicated by green arrows: westwards via an inland route (through the Balkans to Central Europe) or along a coastal path (via Anatolia to the Mahgreb and Iberian peninsula); or eastwards via routes to the north and along the Inner Asian Mountain Corridor. Major migration phases are shown in different colors on the time scale. Diploid, tetraploid, and hexaploid wheats are depicted as colored circles (green, red, and blue colors) with mixed colors reflecting hybridization events. Bottom: Illustration of the hexaploid bread wheat paleohistory from progenitors (with some possibly extinct) A (green circles), B (red circles), and D (blue circles) shown at the left, along the time scale expressed in million years (left) at the bottom. Subgenomes (A, B, and D) are illustrated with circles so that hybridization events are highlighted with mixed color within circles (similar to the central panel). Modern (diploid, tetraploid, and hexaploid) species are illustrated at the right of the figure. Wheat aDNA offers the opportunity to investigate the impact of migration, translocation, extinction, and hybridization events in shaping the modern genetic diversity and in driving adaptation to environmental constraints (temperature variation) over 10,000 years of domestication and cultivation