Inheritance And QTL Identification Of Oil Content In Rapeseed (Brassica Napus L.)

Oilseed rape is one of the most important oil crops in the world. It's also a main source of edible oils in China. After several decades of hard work, rapeseed area in China has been significantly expanded, and the unit area yield markedly increased. China has been largest rapeseed producer in the word. However, rapeseed in our contry was lower in oil content than the imported. In our contry, the average oil content in rapeseed was about 40%, while the imported rapesed contains an oil content of up to 43%-45%. At the same time, with China's growing demand for vegetable oils, we need to import large quantities of oil seeds or vegetable oils to meet the gap for a long time. So, it is very important to increase the oil content in the rapeseed in our contry. In this study, the genetic models of oil content in rapeseed (Brassica napus L.) were analysized with six genetic populations (P1, P2, F1, B1, B2 and F2) of the cross CG38 (high oil content)×B25 (low oil content) by a mixed genetic model of major gene plus polygenes. In addition, using BC1 as amapping population, SSR,RAPD and SRAP were used to construct a molecular linkage map. Finally, we used QTL Icimapping v2.2 to identificate the QTL of oil content. The main results from the research were as follows:1. NIR Systems-5000 was used to test the six generations'oil content. The results showed that the average oil content of high oil content parent CG38 was 41.67%, and low oil content parent B25 was 30.02%, they have a difference of 11.65%, and showed significant difference in the traits of oil content. The oil content of F1 was 37.04% for average, it's higher than P2, lower than P1, and it's even higher that the midparent value 35.85%, skewed towards the high oil content parents P1. From that, we can see high oil content has some dominance effects with low oil content. Three separate generations of B1, B2, F2 showed a continuous distribution of the oil content, the mean of oil content in B1 was higher that that in B2.which indicated that the gene which controled the oil content have additive effects. In this research, none of the six generations showed the phenomenon of surplus.2. The genetic models of oil content in rapeseed (Brassica napus L.) were analysized with six genetic populations (P1, P2, F1,B1, B2 and F2)of the cross CG38XB25 by a mixed genetic model of major gene plus polygenes. The results showed that oil content in Brassica napus L. was controlled by one pair of additive-dominant major gene plus additive-dominant-epistatic polygenes (D-0). The genetic and environmental variances accounted for 75.84% and 24.16% of the phenotypic variance, respectively. It was indicated that both genetic and environmental factors played important roles in oil content in Brassica napus L. On an average, the inheritabilities of major gene and polygenes were 46.04% and 29.79%, respectively. It was demonstrated that oil content in Brassica napus L. was controled by both major gene and polygenes, and that the major gene played a greater role.3. In this study,218 plants from BC1 were used as a mapping population, and three kinds of molecular markers SSR,RAPD and SRAP were used to construct a genetic linkage map of Brassica napus L.. This genetic linkage map contained 20 linkage groups,136 marker loci including 67 SRAP,48 SSR and 21 RAPD loci. The total length of the genetic linkage map was 1725.00 cM, and the average distance between markers was 15.97cM.4. The QTL's of oil content in Brassica napus L. were analyzed by QTL Icimapping v2.2. In the experimental materials, we identified two QTLs associated with oil content. qOCl was located on linkage group LG10, and the marker interval was SSRRa2-E03～EM15ME14. qOCl could explain 4.43% of the phenotypic variation of oil content Brassica napus L.. And the positive additive effect indicated qOC1 could increase the oil content. qOC2 was located on linkage group LG15, and the marker interval was EM5ME11b～EM12ME14. qOC2 could explain 18.68% of the phenotypic variation of oil content Brassica napus L.. And the negative additive effect indicated qOC2 could reduce the oil content.5. Genetic analysis showed a high heritability of oil content in rapeseed, so, in the breeding process, the high oil content traits selection in early generation was effective. And in this study, oil content was controlled by the major gene plus polygenes, the heritability of the major gene was 46.04% by average, additive effect was 2.3120, indicated that the parent of high oil content have a synergistic effect on the oil content. The oil content of B1, B2 and F2 were higher than the low oil content parent, and the mean of oil content of Bl(38.61%)was higher than that of B2(34.46), so during the high oil content breeding, the use of the major gene effect should be first considered. Therefore, in high oil content breeding, we should choose high oil content parents, and take the conventional breeding methods of hybrid and recurrent selection, combined with the methods of QTL localization to increase the frequency of allele to improve oil content trait in oil rape.