Origin and evolution of wheat and related triticeae species

The origin and evolution of the wheat group (the genera Aegilops, Amblyopyrum, and Triticum) in the wild and under cultivation is reviewed. The diploid species diverged from a common ancestor, about 2–4 million years ago, presumably in the marginal Mediterranean region of Southwest Asia. Speciation resulted in distinct genomes, specialized dispersal unit, and unique eco-geographical environments that are described here. In contrast to the diploids, the allopolyploid species have undergone convergent evolution, exhibiting a wider variation, larger distribution areas and a broader range of ecological conditions. Recent molecular studies show reprograming of gene expression in the allopolyploids and the interactions between genomes. The process of allopolyploidization generates a genetic shock that triggers a variety of cardinal genetic and epigenetic changes leading to cytological and genetic diploidization, enabling various gene dosage effects to take place and providing tolerance to hybridization and introgression.