In a previous study, Radoev (2007) was investigating a DH population derived from a cross of Express617 and the resynthesized line R53. Radoev (2007) identified one major QTL for glucosinolate content on linkage group N19 (C09) explaining 23.5% of the phenotypic variance.
Co-located in the same marker interval of this QTL, a minor QTL for oil content was detected. To confirm these results and to compare QTL positions of the Express617 x R53 population (ExR) to the SGEDH population, QTL of the ExR population were recalculated using a set of 725 DArT markers mapped in a GABI-OIL project (data provided by Dr. W. Ecke, Universität Göttingen, Göttingen, Germany). QTL were calculated applying composite interval mapping of QTLNetwork.
QTL results from recalculated data (Table 5.6) showed a reduced number of QTL for all traits.
While original data showed between two to nine QTL per trait, the recalculation only identified one to four QTL. Besides, linkage groups of detected QTL in some cases differed from previous results. Since R53 has medium erucic acid content, one QTL for erucic acid is expected within the ExR population, representing one of the erucic acid genes. Radoev (2007) identified a major QTL for erucic acid on N08 (A08), while with recalculated data a major QTL was found on N13 (C03).
Nevertheless, as previously reported a major QTL for glucosinolate content ExR_GSL-3 was detected on N19 (C09) explaining 62.4% of the phenotypic variance, but a co-located QTL for oil content was not detected anymore. Physical mapping for the ExR_GSL-3 was conducted using the closest marker to the QTL peak (34.3cM), brPb660902 at 31.6cM. The physical position of the marker was identified at 1958690bp on B. napus Darmor-bzh reference genome, and a region from 1.9 to 2.5Mbp was scanned for glucosinolate candidate gene matches, resulting in no suitable matches. In comparison, within the SGEDH population the major QTL GSL-5 on C09 which was detected stable in Europe and in China, was found at position 116.7cM (confidence interval 113.7 - 116.7cM). As closest marker to the QTL peak the SNP Bn-A09-p2730673 of position 117.5cM was identified. The physical position of this marker was found at 2894200bp.
Due to a striking marker disorder comparing genetic and physical marker positions on C09 a region from 2.5 to 3.1Mbp around Bn-A09-p2730673 was scanned for glucosinolate candidate gene matches. This screen identified 115 A. thaliana protein matches including four matches involved in the regulation of the glucosinolate biosynthetic process. 32.7kbp apart from Bn-A09-p2730673, AT1G18570.1 the myb domain protein 51 (MYB51; 2926900-2927542bp) and AT5G60890.1 the myb domain protein 34 (MYB34; 2926900 - 2927977bp) were found, which overlapped the B. napus gene prediction BnaC09g05060D alias GSBRNA2T00146117001. About 205kbp apart from Bn-A09-p2730673 in the region from 3099235-3100634bp, AT5G07700.1 the myb domain protein 76 (MYB76) and AT5G61420.2 the myb domain protein 28 (MYB28)
were identified, overlapping gene predictions BnaC09g05290D alias GSBRNA2T00146147001 and BnaC09g05300D alias GSBRNA2T00146148001, respectively.
Most of the increasing alleles for oil content in the SGEDH population are contributed by SGDH14 which was derived from a cross between the German cultivar Sollux and the Chinese cultivar Gaoyou both showing high oil contents, but also high erucic acid and glucosinolate contents (Zhao et al. 2005). Five out of seven QTL for oil content in EU trials and five out of six QTL in Chinese trials identified SGDH14 to contribute the increasing alleles for oil content. In the Sollux x Gaoyou DH population Zhao et al. (2005) previously detected eight oil-QTL on A01, A07, A09, C01, C02, C04, C08 and C09. Comparison of these oil-QTL to those of the SGEDH population showed the detection of oil-QTL on A07 and C04 (cf. section 5.2) in both populations. QTL positions on these linkage groups were supposed to be the same, although no common marker or sequence information was available to prove this assumption. Since no more oil-QTL were detected on common linkage groups, it was suggested that alleles of Express617 and SGDH14 showed equal effects at the other QTL positions previously detected in the Sollux x Gaoyou DH population, thus detecting no significant differences at these positions anymore in the SGEDH population. But Zhao et al. (2006) not only investigated the genetic basis of oil content, but also evaluated the genetic interrelationship between oil content and phenological traits, specifically begin of flowering and flowering period, by applying conditional mapping. Results of the evaluation of a possible genetic relation between oil content and phenological traits indicated that although begin of flowering and flowering period still showed significant genetic correlations to oil content, only three of the eight oil-QTL of the Sollux x Gaoyou DH population failed to show significant effects after conditioning on phenological traits, but these QTL showed the smallest effects. Therefore, it was assumed, that most of the variation in oil content occurred independent from the variation in phenological traits (Zhao et al. 2006). Nevertheless, in the SGEDH population significant positive correlations between oil content and begin of flowering (rs = 0.2**), end of flowering (rs = 0.3**), as well as plant height at end of flowering (rs = 0.5**
EU/ rs = 0.4** China) were observed. Furthermore, in EU experiments the oil-QTL E_Oil-3 on C05, which explained 13.8% of the phenotypic variance for oil content, was found co-located with QTL for phenological traits with same sign for the additive effects, however indicating a genetic interrelation of oil content and phenological traits.
Table 5.6: QTL detected for contents of seed oil (%), protein (%), glucosinolates (GSL in μmol/g) and erucic acid (%), and for thousand kernel weight (TKW in g) and plant height at end of flowering (PH_EOF) in the Express617 x R53 population (ExR) LinkagePositionConfidence QTL Group[cM]Interval [cM] Aa R2b V(A)/V(P)c V(I)/V(P)d V(G)/V(P)e ExR_Oil-1 C0290.388.4-94.50.489.936.4- 36.4 ExR_Oil-2 C034.00.0-10.0-0.8518.1 ExR_Oil-3 C03124.4109.4-138.30.517.4 ExR_Protein-1A0250.038.6-67.60.309.19.1- 9.1 ExR_GSL-1 A0248.036.6-58.62.435.469.66.375.9 ExR_GSL-2 C0288.888.6-90.3-2.798.4 ExR_GSL-3 C0934.330.3-38.3-12.0062.4 ExR_NIRS22:1-1C034.00.0-7.0-8.6367.867.8- 67.8 ExR_TKW-1A0532.028.7-55.10.075.733.0- 33.0 ExR_TKW-2A0789.079.3-96.3-0.108.5 ExR_TKW-3C0189.487.2-89.50.109.5 ExR_TKW-4C0281.079.7-88.4-0.1010.7 ExR_PH_EOF-1C03137.9137.9-137.93.0612.219.9- 19.9 ExR_PH_EOF-2C0526.016.0-33.42.447.7 a additive effect; positive additive effect indicating that the alleles increasing the trait were derived from SGDH14 b percentage of phenotypic variation explained by each QTL c variance of additive effects/phenotypic variance – total contribution of additive effect QTL in % d variance of epistatic effects/phenotypic variance in % e variance of genetic main effects/phenotypic variance in %