Abstract: In order to study the genetic mechanism of oil content and yield-related traits in B. napus， an immortalized F2 （designated as IF2） population （134 crosses） was generated by randomly permutated intermating of SG-DH lines. Phenotypic data were collected from four environments. Using updated SG-map and QTL Network 20 mapping program， the QTL analysis for oil content （OIL）， 1000-seed weight （SW） and seeds per silique （SP） were conducted. The genetic effects including additive， dominant and all related digenic epistasis were estimated. The results showed that in total eight major QTL for three traits were identified in seven linkage groups. Except qSWC6 and qSPA2，one QTL for OIL， four for SW and one for SP were all located in the overlapped confidence intervals with that revealed by SG\|DH population，showing similar additive effect and same effect direction. In the loci of qOILA7 and three of SW qSWA7，qSWC2，qSWC4， significant additive without dominant effects were found. While for qSWC6 and qSWC8， both additive and negative dominant effects were detected. However， two major QTL for SP （qSPA2 and qSPA6） showed positive dominant effects beside additive effects. Of eight loci corresponding to four pairs of digenic interactions， seven were marker loci without additive effects involved. The QTL-based selection for increasing oil content by flanking markers of qOILA7 and seed weight through linked markers with qSWA7/qSWC8 was discussed. The results showed that predominant additive effects were observed for QTL of oil content and 1000-seed weight， predicting no heterosis of these two traits in F1 generation. Therefore， to increase the oil content and 1000-seed weight in rapeseed hybrids， the strategy was to breed two parents with high oil content and large seed size first. However， since seeds per silique demonstrated both additive and positively dominant effects， the performance which was better than two parents could be expected in hybrids and might contribute to yield heterosis of F1 hybrids.

Key words: Brassica napus L., immortalized F2 population, QTL, oil content, 1000\|seed weight, seeds per silique