22The evolution of bread wheat (Triticum aestivum) is distinctive in that 23 domestication, natural hybridization, and allopolyploid speciation have all had 24 significant effects on the diversification of its genome. Wheat was spread around 25 the world by humans and has been cultivated in China for ~4,600 years. Here, 26we report a comprehensive assessment of the evolution of wheat based on the 27 genome-wide resequencing of 120 representative landraces and elite wheat 28 accessions from China and other representative regions. We found substantially 29 higher genetic diversity in the A and B subgenomes than in the D subgenome. 30 Notably, the A and B subgenomes of the modern Chinese elite cultivars were 31 mainly derived from European landraces, while Chinese landraces had a greater 32 contribution to their D subgenomes. The duplicated copies of homoeologous 33 genes from the A, B, and D subgenomes were commonly found to be under 34 different levels of selection. Our genome-wide assessment of the genetic changes 35 associated with wheat breeding in China provides new strategies and practical 36 targets for future breeding. 37 38 Main 39 Bread wheat (Triticum aestivum) differs from other major grain crops, such as maize 40 (Zea mays), rice (Oryza sativa), and barley (Hordeum vulgare), by having an 41 allohexaploid genome with six sets of chromosomes, two sets each from three closely 42 related ancestral species that formed the A, B, and D subgenomes. Archaeological and 43 genetic evidence indicated that wheat underwent two polyploidization events during 44 its domestication. The first occurred ~0.82 million years ago between two diploid 45 species, T. urartu (AA) and an unknown close relative of Aegilops speltoides (SS), 46 which produced the allotetraploid T. turgidum (AABB). The second polyploidization 47 occurred during cultivation around 8,000-10,000 years ago, when T. turgidum 48 crossed with another diploid grass, Ae. tauschii (DD), to form the ancestral bread 49 wheat (T. aestivum, AABBDD) 1-4 . In addition, a recent genome analysis suggested 50 that Ae. tauschii originated from a more ancient homoploid hybridization event 51 between the A and B lineage ancestors 5 . The A, B, and D subgenomes comprise the 52 ~17-Gb allohexaploid bread wheat genome. Enormous genome sequencing efforts 53 have resulted in the recent publication of a reference genome sequence for wheat 4,6-9 , 54 which has greatly enhanced our understanding of the genome of this vital crop. 55After its evolution in the Middle East and Mediterranean regions, bread wheat 56 gradually spread to the rest of the world and was domesticated for human use 10 . China 57 3 has been cultivating bread wheat for ~4,600 years 11,12 , and has been the largest wheat-58 producing country for more than two decades. Wheat has been under continuous 59 artificial selection in the diverse ecological zones of China for thousands of years 11,13 ; 60 thus, the domestication and breeding of bread wheat in this country provides unique 61 evolutionary insights into h...