The Genetic Diversity And Genomic Divergence Between Annual Wild And Cultivated Barley From Four Different Regions

Barley(Hordeum vulgare L.)is one of the oldest food, feed and brewing crop in the world,and it possesses such traits as early-maturing, barren resistance and wide adapting, thus it has a large range of cultivation. Barley is the fourth gramineous food crop in China followed after maize, rice and wheat. Barley who has seven pairs of chromosomes(2n=14) is the only one self-pollinated diploid crop, and it has diverse variations on morphology, genetics and physiology. In the main, barley is an ideal model for studying plant genetics and plant physiology.Wild barley(Hordeum spontaneum) is the ancestor of cultivated barley(Hordeum vulgare), Fertile Crescent in the western Asia and Qing-Tibet Plateau in China are two major original centers of cultivated barley. Wild barely has many types of variations with diversified features of pre-mature, disease resistance and stress tolerance. The rich germplasm resources of wild barley worldwide have great potential value on the study about genetic domestication and breeding development.Nature selection was the major power which forced wild species changing to cultivated types, annual wild barley was subjected to diverse selected pressures including positive and balancing selection in the domestication process. All the selected pressure forced wild genotype and phenotype changing to the expectations of humans. In the process of barley domestication, wild barley happened big changes on the morphology and physiology such as the traits of row-type(Vrs1 gene), brittle rachis(Btr gene), hulled and naked caryopsis(Nud gene), seed dormancy(SD gene) and vernalization(Sgh gene) which induced the reduction of genetic diversity on cultivated barley. Difference of genetic diversity between annual wild barley and cultivated barley could reveal the effect of natural selection on different chromosomal regions; and some molecular markers, like SSR markers, were useful methods for barley domesticated study.Here we analyzed and compared the chromosomal genetic diversity among four annual barley populations(Western Asian wild barley population, Central Asian wild barley population, Tibetan wild barley population and Chinese cultivated barley population) by SSR molecular markers, with the purpose of finding genetic divergence among barley chromosomes and examining the effect of selected pressure on different barley chromosomal regions in the process of barley domestication.The main results were summarized as follows:1. The genetic diversity of western Asian annual wild barley was higher than the other three barley populations. In terms of a single chromosome, western Asian annual wild barley population had the highest genetic diversity; in terms of a single geographic population, the chromosome 2H of western Asian and central Asian annual wild barley populations had the highest diversity among theirs seven chromosomes, the chromosome 1H of Chinese annual barley populations had the highest diversity among theirs seven chromosomes.2. Compared with Tibetan wild barley, chromosomes 2H and 6H of Chinese cultivated barley may contain some elite loci, which may be the potential resources for molecular study and breeding development. The chromosome 6H had the biggest genetic divergence among three annual wild barley populations. Some chromosomal gene loci may control adapted traits of different environments, but we need to do further study.3. The average genetic divergence was 28.07% between wild and cultivated barley populations, and chromosome 5H had the biggest divergence of 35.29%, then followed by 3H, 7H, 4H, 2H, 6H and 1H.4. The chromosomal domesticated and non-domesticated regions were divided on 1H, 2H, 3H, 4H, 5H and 7H based on AMOVA method between wild and cultivated barley. Chromosomal domesticated regions of six chromosomes included 18 SSR molecular markers. The results of molecular variable ratio showed that the genetic divergence of chromosomal domesticated regions on 5H 1H and 7H was higher than theirs corresponding non-domesticated regions, and genetic divergence of domesticated regions on 2H and 4H was almost equal with theirs corresponding non-domesticated regions, while it was lower than non-domesticated region on the chromosome 3H. The average genetic divergence of these chromosomal domesticated regions was 33.73%, which was higher than the non-domesticated regions of 27.56%.5. Based on the genetic distance(c M), chromosomal domesticated regions narrowed to a small range, which could reflect the effect of nature selection on the domesticated loci. The divergence of most artificial domesticated regions was higher than theirs corresponding artificial non-domesticated regions. In addition the domesticated region of 5H-I had the biggest divergence.6. Phylogenetic results also showed that western Asian annual wild barley population had a higher genetic diversity, the genetic relationships of different barley accessions were closely related to theirs geographic distribution. Western Asian annual wild barley accessions had a close genetic relationship with central Asian annual wild barley accessions, and Chinese barley accessions could be divided to one cluster. The phylogenetic result of domesticated markers showed that all the accessions could be divided to many small clusters with almost equal genetic distance. Thus, we inferred that the chromosomal domesticated regions suffered a distinct selection pressure in which contained some effect of important genes in the process of barley domestication, and diverse microenvironmental selection may be the reason of genetic divergence on these domesticated regions.