| Bread wheat is a major food crop in China and increasing the yield has been pursued by breeders with the increasing of human population worldwide. Wheat yield is determined by three main components:Panicle Number, Kernel Numbers Per Ear and Thousand Grain Weight. Increasing the grain weight is one of the major approaches that have attributed to yield. And how to use the genomic theory and methods to improve yield is very important for increasing the grain weight at the Genome-Level. With the development of molecular biology and plant genomics, a bunch of markers have been developed in the major crops. Mark/traits association analysis has been widely adopted in dissecting complex traits recently. This also makes it possible for us to analyze and locate thousand grain weight (TGW) loci in wheat by association mapping.Based on wheat whole genome scanning with SSR markers using a natural populaiton, 27 loci and theirs alleles associated with grain weight have been identified in our group. In thist study, we detected above-mentioned 27 loci and alleles by mark/trait association analysis in the shijiazhuang 8 and shi 4185 derived breeding population using two-year phenotyping data, in order to further validate the effectiveness of associated SSR loci detected in the natural population. The cfd78 locus on the 5DS was found significantest associated with TGW. And, more markers were selected flanking this locus to make association analysis more pricesely. Three markers, cfd78, cfd67 and cfd40 were decided and formed an important chromosomal region related with TGW. Then we used cfd78 and cfd67 which are tightly linked SSR markers significantly associated thousand grain weight to screen the BAC library of Aegilops tauschii (D). Major results of this study are as following.1. In the 27 loci,7 have polymorphism between shijiazhuang 8 and shi4185. Effects of 7 were redetected in the breeding population with mark/traits association analysis. cfd78265 (shijiazhuang 8 type) has the positive effects on thousand grain weight, with increase of 3.48g and 3.63g in 2008 year and 2009 year, respectively.2. More loci near cfd78 were verified and the major QTL flanked by cfd78-cfd67-cfd40 with genetic distance 2.94 cM was found after marker/trait association mapping. Results of thousand grain weight indicated that the cfd672o5 and cfd40187 also have the positive effect on TGW, with TGW increase 3.09g and 3.17g for cfd67205 well as 3.46g and 3.49g for cfd40187 in 2008 and 2009, respectively.3. TGW comparison analysis of various alleles between cfd67205, cfd78265, cfd40187 (shijiazhuang 8 type) and cfd672o3, cfd78259, cfd40190 (shijiazhuang 4185 type) indicated that TGW difference of these two types of alleles was at the significant level (P<0.001) on three loci.4. Association analysis using two-year’s phenotyping data showed that the significant amount of cfd78 could arrive at 7.9 (-Log value) in 2008 and 4.9 in 2009, accordingly, 8.5 in 2008 and 4.8 in 2009 for the cfd67 and 7.2 in 2008 and 4 in 2009 for the cfd405. The C20 and H8 positive clones were obtained scussefully after screening Ae. tauschii BAC library by cfd78 and cfd67. Moreover, two and four candidate genes were predicted in C20 and H8 clones, respectively. Gene diversity and haplotype analysis of these genes will be our next work. |
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