Genome-Wide Association Mapping Of Oil Content Trait In Rapeseed(Brassica Napus L.)

Rapeseed is one of the most important oil crops with significant economic value. Rapeseed oil is belived to be rich in nutrition for containing several unsaturated fatty acids and vitamins which could be absorbed easily by human body. On the other hand, due to the similar unsaturated fatty acides component with diesel oil, oilseed is considered to be an important solution to the lack of petroleum. With the development of biotechnology, we could alter the composition of rapeseed oil by genetic methodologies to fulfill the industry requirment. Hence, breaders always devote themselves to improve the oil content in unit area. Based on the natural population consisting of189rapeseed inbreds from the main rapeseed growing countries, we combined the21348SNP genotypes and oil content phenotype in two years to analyse the population structure, relative kinship and linkage disequilibrium of B. napus genome. Finally,7loci which significantly associated with the oil content trait have been detected by the method of genome wide association study. These results lay the foundation of the high oil breeding in rapeseed and the studies of other important agronomic traits. The main results are listed:Analysis of population structure and relative kinship:The natural population is divided into two groups P1and P2, and different rapeseed lines belonged to the same group tend to be gathered together. P1group contained44rapeseed lines (23.28%), and145rapeseed lines (76.72%) are grouped into P2group. P1group could be further departed into three sub-groups, named G1, G2and G3. Gl is constituted by synthsis lines, and rapeseed lines in G2and G3are mainly from Europe, Canada and Australian. P2group could also be futher divied into two sub-groups, G4and G5, of which are mainly from China. In the association panel, almost80%kinship between any two lines is below0.05, about56%kinship between any two lines is0, and about22%is bettwen0-0.05. These results indicate that influence by the population structure is little due to the weak relationship among189rapeseed lines. The broad-sense heritability is0.8800calculated by the Two-way ANOVA, indicate that the oil content is mostly influenced by the genotype, and the heredity is stable.Linkage disequilibrium:By calculating the r2value of pairwise markers in the same chromosome, we simulate the trend lines of LD found that r2value declined rapidly while the genetic distance increased. When the cut off value of r2was setted to0.2, it was found that the decay of the LD in A genome is about1.6cM, and approximately1.9cM in C genome.Association mapping of oil content trait in rapeseed:By comparing the results in Q model、K model and Q+K model, we found that Q+K model is the best model which would efficiently control the false positive caused by population structure and relative kinship. In Q+K model,7loci were detected significantly associated with oil content trait which located in Al, A3and C1chromosomes respectively. These loci are reliable and stable and could explained the phenotype variation from0.1126(mk676) to0.1791(mk10434).