| Rapaseed is not only an important source of edible oil, but also important materials of bioenergy. Therefore, it is very important to improve the yield and oil content of rapeseed. As a complex quantitative trait, the genetic mechanism of oil content in oilseed is still unclear. To study the genetic mechanism, QTL mapping was used to locate the QTL for seed oil content, and to find the closely linked marker for molecular assisted breeding.M201 and M202 have high and low seed oil content, respectively. A recombinant inbred lines (RILs) population was constructed using these two Brassica napus lines. Then, QTL mapping analysis and epistatic interaction detection controlling seed oil content were done using WinQTLcart 2.5 and QTLNetwork 2.0. On this basis, this study constructed a near isogenic lines (NILs) population of major QTL on A10, verified the location and effect of major QTL, and found molecular markers which are tightly linked to seed oil content trait for assisting high-oil content breeding. The main results are as follows:1. Under natural conditions, RILF6 population was plant in Wuhan and Yichang in 2009, respectively; RILF7 population was plant in Wuhan in 2010. Transgressive segregation of seed oil content was found in three environments. And, oil content was found to be one high heritability trait and environmental factors can be ignored in this population.2. QTL for seed oil content was detected based on the whole genome analysis of RILF4. Five QTLs were detected on A10. qOC09WF4-A10-1 and qOC09YF4-A10-1; qOC09WF4-A10-2, qOC09YF4-A10-2 and qOC10WF4-A10 were detected in the same confidence intervals, respectively. Using BioMercator 2.1, QTLs for seed oil content on A10, which were discovered in different environments, were integrated into two major QTLs. Then they were renamed as qOCF4-A10-1 and qOCF4-A10-2, respectively. Because they could be detected repeatedly in two or more different environments, suggesting that these QTLs were stable against the environmental impact. In addition, an interacting loci pair between non-QTLs, with additive by additive effect and no environmental effect, was detected on A6 and A9 using QTLNetwork 2.0.3. The genetic linkage map of A9 and A10 was re-constructed based on the RILF6 population, respectively. The LGs of A9 covered 108.1 cM with an average interval of 1.93 cM, including 56 SSR loci; the length of A10 was 91.67 cM, including 44 SSR loci, and the average distance between markers was 2.08 cM. Based on the new genetic linkage map of A9 and A10,3 QTLs for seed oil content were detected on A10 by CIM. Of which, qOC09YF6-A10-1 and qOC10WF6-A10 were detected in the same confidence region, then it is renamed qOCF6-A10. Using QTLNetwork 2.0, an interacting loci pair between two QTLs, with additive by additive effect, was detected on A9 (BrGMS 1056b～BrGMS25) and A10 (BrGMS902～BnGMS9), but epistatic effect of which is very small. Furthermore, we found that the markers of qOCF6-A10 share the markers of qOCF4-A10-1 and qOCF4-A10-2, indirectly indicating that these three QTLs were the same QTL, so it was renamed as qOC-A10.4. According to the preliminary mapping results and the genotypes of F4, the A10-NILs population consisting of 210 lines was generated using the strategy of recombinant inbred marker heterozygosity, it was renamed as MH-A10-NILs. Its seed oil content showed a continuous distribution, and skewed toward the parent M201 of high-oil content.5. Two QTLs were detected based in the MH-A10-NILs, qOCNIL-1 and qOCNIL-2. The markers of qOCNIL-1 are BnGMS15N, BnGMS9 and sORH13, the markers of qOCNIL-2 are BoGMS197, BoGMS731 and BnEMS965, which are consistent with the markers of qOC-A10, these also confirmed the existence of the QTL for seed oil content on A10. In addition, the molecular markers of target QTL can be used for assisting high-oil content varieties of rapaseed breeding. |
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