| Brassica napus is one of the most important oil crops in the world.It is of great significance to study yield traits and stress tolerance of Brassica napus.The present study explored the locus controlling seed-related traits and water-logging tolerance using SNP technology and QTL mapping to mined related QTLs.The main results were as follows:1.QTL mapping of seed weight and shape:Based on the high-density SNP map,QTL mapping of thousand seed weight（TSW）was carried out with 189 recombinant inbred lines.A total of 25 QTLs controlling TSW were detected in five different environments,with each QTL accounting for 4.33%-10.45%of the phenotypic variation.In the present study,seed shape was firstly decomposed into seed length（SL）,seed width（SW）,length-width ratio（LW）,seed cross-section area（SA）,seed circumference（SC）,seed diameter（SD）and seed roundness（SR）to mine QTLs of seed shape.A total of 152 QTLs controlling seed shape were detected in five environments.QTLs for the same trait with overlapping confidence intervals were integrated.149 QTLs controlling seed weight and shape were obtained.Of these,a QTL cqSC.C7-3,which controlling seed circumference,explained 12.54%,13.14%and 5.11%of the phenotypic variation in 14NJ 15NJ and 16NJ,respectively.QTL cqSC.C7-3 was considered as a major QTL.QTLs controlling different traits but with overlapping confidence intervals were further integrated into 69 QTLs.Among them,34 QTLs controlled at least two different traits.The unique QTL uqC2-1 affected all eight seed-related traits and explained 6.60%-7.57%of the phenotypic variation.2.QTL linkage mapping of water-logging tolerance:Based on the high-density SNP map,the linkage analysis of water-logging tolerance（WT）was performed with 189 recombinant inbred lines.As a result,a total of 8 QTLs of water-logging tolerance were detected in two environments.These QTLs were integrated into 7 consensus QTLs by meta-analysis.Among them,a QTL cqWT.C3-2 could be repeatedly detected in two environments and explain 10.3%and 23.3%of the phenotypic variation,respectively.QTL cqWT.C3-2 was the major QTL of water-logging tolerance detected in this study.Correlation analysis among water-logging tolerance and seed-related traits showed that WT had highly significant positive correlations with TSW and SR,but had a significant negative correlation with LW.QTLs controlling seed-related traits were further integrated.A QTL uqC3-4 controlling WT,LW and SR were obtained.This pleiotropic QTL could explain the highly significant correlations between WT and seed shape-traits at the QTL level.3.Genome-wide association study of water-logging tolerance:Based on the 60K Brassica SNP array,genome-wide association study of water-logging tolerance was conducted with a natural population of 530 brassica napus varieties.Using mixed linear model（MLM）,17 and 15 significantly related SNP loci were obtained in the two environments of illumination incubator and natural conditions,respectively.One locus on C3 chromosome（Bn-scaff172981-p679830）was detected in two experiments.Comparing the results of linkage and association analysis,two SNPs（bn-a05-p6405415 and bn-a05-p6539730）detected by association analysis and QTLs（cqWT.A5-1 and cqWT.A5-2）were located on A5 chromosome.The locations of the SNPs were close to the confidence interval of the QTLs. |
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