Association mapping is a method to test the association between molecular markers and quantitative trait loci (QTL) based on linkage disequilibrium (LD). In this study, the collection of 108 wheat germplasm accessions form China were evaluated for their plant heights, spike length, spikelets per spike, grains per spike, thousand kernel weight and spikelets density in 3 years at three locations. And they were genotyped with 85 SSR markers and 40 EST-SSR markers. The population structure was inferred on the basis of unlinked 48 SSR markers and 40 EST-SSR markers. The extent of LD on chromosome 2A was 2.3 cM. Association of 37 SSR loci on chromosomes 2A with six agronomic traits was analysed with a mixed linear model. A total of 14 SSR loci were significantly associated with agronomic traits. Some of the associated markers were located in the QTL region detected in previous linkage mapping analysis. Our results demonstrated that association mapping can enhance QTL information and achieves higher resolution with short LD extent.

1201 published maize QTLs conferring for 68 traits were collected and imported into local CMap software to construct an integrated QTL map, which can be used for marker-mining, QTL localization, gene cloning and marker-assisted selection. The maize integrated QTL map showed that maize QTLs for various traits usually clustered in all chromosomes. 22 plant height QTLs of maize were co-linear with 64 plant height QTLs of rice, 43 grain yield QTLs of maize were co-liner with 7 grain yield QTLs of rice. 127 plant height QTLs of maize were refined by means of "overview" analysis. At last, 40 "real" QTLs were identifed. A substantial number of candidate quantitative trait genes for plant height of maize were found. These results established an important bioinformatics platform for extracting most of maize QTL information.Since the first publication of quantitative trait locus (QTL) localization using molecular markers [1] , a large number of QTLs have been identified in different genetic backgrounds and environments. Affected by many factors, such as marker sets, experimental design, mapping populations, and statistical methods, the locations of QTLs varied in different studies, even if QTLs for the same trait were screened in the same population. So the comparative QTL analysis has attracted huge attention: (1) In one given species, do the locations of QTLs for the same trait identified in one population correspond to those in another? (2) Using comparative genomics methods, can the locations of QTLs for the same trait in one species guide the cloning of related quantitative trait gene (QTG) in another? 181 maize QTLs relevant to drought tolerance were integrated and 15 "universal drought tolerance QTL" and linked markers were identified [2] . Allelic QTLs were found between cultivated tomato and other two wild relatives [3] . Correspondences between QTLs affecting height and /or flowering were also found across sorghum, maize, rice, wheat and barley populations [4] . Homologues of the maize rust resistance gene Rp1-D are genetically associated with a major rust resistant QTL in sorghum [5] . It was observed that there were extensive conserved relationships of QTLs affecting important agronomic traits between maize and rice, and co-linear QTLs usually clustered. These studies help to map, isolate and clone QTL in grass genomes, such as maize, using rice genome information, and to understand the evolutionary force that structured the organization of the grass genomes [6] .Thomson and coworkers [7] indicated that the validity of locations of integrated QTLs generated only by maps comparison was hard to be ensured, and that there were biases when these integrated QTLs were explored by comparative analysis. Fortunately, meta-analysis can narrow down the confidence interval of integrated QTLs to increase their precision and validity by using mathematical model to refine integrated QTLs [8] .Meta-analysis, denominated by psychologist Glass in 1976 [9] , is a statistical analysis combining data from different sources in a sin...

Association mapping is a powerful approach to identify associations between traits of interest and genetic markers. In this study, 103 wheat germplasm accessions from China were genotyped using 76 SSR markers and 40 EST-SSR markers. The phenotyping of plant height, spike length, spikelets per spike, spikelets density, grains per spike and thousand-kernel weight were carried out in three locations for three years. Six subpopulations were identified among these accessions by population structure analysis based on 49 SSR and 40 EST-SSR markers. Linkage disequilibrium (LD) on chromosome 4A extended up to ~3 cM with r 2 =0.054. Based on the mixed linear model considering population structure and relative kinship, a total of 10 SSR markers (p<0.01) on chromosome 4A were significantly associated with six agronomic traits, and six of them were associated with multiple traits. Some of the associated markers were in agreement with previous quantitative trait loci (QTL) analysis. This study demonstrated that association mapping can be successfully applied in wheat breeding context for detection of marker-traits associations. Furthermore, association mapping can enhance previous QTL information and provide additional QTL information for marker-assisted selection.

No abstract

No abstract

Duck (Anas platyrhynchos) is one of the most important domestic avian species in the world. In the present research, fifteen polymorphic microsatellite markers were used to evaluate the diversity and population structure of 26 Chinese indigenous duck breeds across the country. The Chinese breeds showed high variation with the observed heterozygosity (Ho) ranging from 0.401 (Jinding) to 0.615 (Enshi), and the expected heterozygosity (He) ranging from 0.498 (Jinding) to 0.707 (Jingjiang). In all of the breeds, the values of Ho were significantly lower than those of He, suggesting high selection pressure on these local breeds. AMOVA and Bayesian clustering analysis showed that some breeds had mixed together. The F ST value for all breeds was 0.155, indicating medium differentiation of the Chinese indigenous breeds. The F ST value also indicated the short domestication history of most of Chinese indigenous ducks and the admixture of these breeds after domestication. Understanding the genetic relationship and structure of these breeds will provide valuable information for further conservation and utilization of the genetic resources in ducks.

No abstract

No abstract