| Brassica napus is one of the main oil crops, especially an important economic oil crop in our country. In one side, the oleic acid and linoleic acid contained in the high quality seed oil are favorable to human health. Further more, they are more advantageous than animal oil to our body without the component of cholesterin,So, seed oil is a good choice for edible oil. On the other side, the carbochain length of fatty acid in seed oil is near to diesel fuel, thus seed oil can be a good material for biodiesel. As the fact of petroleum crisis nowadays, increasing seed yield and seed oil content becomes strategically important. How to improve seed oil content has long been a hotspot to scientists all over the world, and breeding elite double low variety is the goal for breeders in a long time. Oil content of rapeseed is an important trait controlled by quantitative trait locus (QTL). A segregating Fl-derived double haploid population (Tapidor x Ningyou7) of 202 individuals had been developed from across between a European winter variety Tapidor and a Chinese semi-winter cultivar Ningyou7. Then a high density linkage map with 786 molecular markers was constructed based on the TNDH population. The TNDH population and its parents were planted in 12 natural environments. Dozens of QTL had been detected for oil content and the main-effective QTL located on linkage group A08. Twenty-one QTL related with oil content were discovered and then integrated into 4 unredundant QTL with the highest contribution about 14.46% of the genotype variance grounded on the overlapped confidential intervals with the highest. The four integrated QTL were nominated as a QTL cluster for oil content. At the same time, main-effective QTL for erucic acid were also detected on linkage group A08 and overlapped with the oil content QTL. FAE1, a key gene for erucic acid biosynthesis, had been mapped in the confidential interval region of these QTL and even interestingly this gene lay on the peak of erucic acid QTL and near another peak of oil content QTL. Following the classical route of QTL mapping and cloning, some BC4F2 populations with 199 plants in total were developed. The markers closely linked with the major QTL were validated by the result of single marker analysis, which were used to develop 6 NILs arid 2 segregation populations thereafter. Finally, those seed oil content QTLs on A8 were successfully sort into two types based on the relationship with erucic acid QTL:Qoc8-1 which were related with erucic acid and Qoc8-2 which were not. They are respectively at two sides of a centromeric marker on A8 linkage group. The phenotype and genotype of these populations were further analyzed, which indicated that:there are at least two or more seed oil content QTLs in A8 in TN DH population, and one is regulated by erucic acid content which has been popular recognized and another is independent to erucic acid content but responds to environment factors. In order to study the relationship between seed oil QTLs and erucic acid QTL, genetic drag analysis were carried out, and we found that:the genotype of one parent of TN DH population Tapidor in QTL confidence interval are the same with Liho which is the origin of low erucic acid. So we believe that the inferior seed oil content gene in A8 came from Liho. During the breed process of choosing low erucic acid gene, the inferior seed oil content gene was dragged in at the same time.With the aim to investigate whether the genetic drag is a widespread phenomenon or not in this region,101 cultivars were collected from about 10 countries. Erucic acid seed content of these cultivars were measured by gas chromatograph and the genotype of 7 markers in the QTL region were analyzed. The result demonstrated that:22 in 60 low erucic acid content cultivars had genetic drag phenomenon in JICB1088-HAU65 region, which fully proved the significance of our research. From our study, we notice that in the long range of breeding, breeders attached importance merely to the way of hybridization but neglect the molecular detection, which lead to the drag-in of some inferior genes in offspring Brassica napus varieties and finally reduce seed oil content. If much attention had been paid to the phenomenon, it can be eliminated in the early generation with closely linked markers, which is a both good and simple way to increase seed oil content in Brassica napus.In the discussion part, whether another major erucic acid QTL (in C3 lingkage) and seed oil content QTL have genetic drag or not was posed out. Moreover, erucic acid QTL in A8 linkage may be also dragged with other traits, which can be a new research area.
|
PDF Full Text Request