Studies On Creating Novel Type Of Brassica Napus Through Hybridization Between Brassica Juncea And Brassica Napus

Brassica napus（AACC,2n=38）and Brassica juncea（AABB,2n=36）are two important allotetraploid Brassica species.Brassica napus has the characteristics of high yield and good quality.It is the largest type of rape in China and plays an important role in production.Brassica juncea has the characteristics of drought resistance,insect resistance,barrenness resistance and yellow seed.Some conventional species of Brassica napus in China have narrow genetic basis due to long-term artificial selection and crossing,and through distant hybridization,new germplasm resources with good traits can be created.In this study,the novel type of Brassica napus with excellent genetic characteristics were created by crossing Brassica juncea with Brassica napus.The genetic basis of Brassica napus was broadened.At the same time,molecular cytogenetic analysis was carried out on the offsprings of hybrid.The main results were as follows.1.Hybrid compatibility analysis of Brassica juncea and Brassica napus:The compatible index of Brassica juncea×Brassica napus was between 2.91and 7.54,and that of Brassica napus×Brassica juncea was between 0.04 and 0.09,which indicated that the hybrid compatibility of Brassica juncea as female parent was better than that of Brassica juncea as female parent.The number of orthogonal pollen tubes extending into ovaries was similar to that of reciprocal cross,and the recognition of pollen and stigma was not the main reason for the difference of reciprocal and orthogonal compatibility.Fifteen days after fertilization,all orthogonal combinations of embryos had grown into cotyledon-shaped embryos and continued to develop normally,while reverse-crossing embryos had stopped growing from fifteen days to present as heart-shaped embryos,torpedo-shaped embryos,or degenerated into heart-shaped embryos,and eventually brown and apoptotic,suggesting that serious post-fertilization obstacles exist in reverse-crossing,possibly because endosperm can not provide nutrition for developing embryos.2.Obtainment of hybrid F₁ and cytological and morphological observation of hybrid offspring:With Brassica juncea and Brassica napus as parents,the chromosome composition of both orthogonal and reciprocal crosses were AABC,2n=37.The main separation mode of orthogonal and reciprocal crosses was 18:19,and the plant morphology was between in two parents.Most of the plants in F₂ population were morphologically similar to Brassica napus with mostly 38 chromosomes.The average dyeability of F₁-F₆ pollen increased from 32.68%to more than 90%.The pollen fertility of F₁-F₆ increased gradually with the generation increasing.By F₅ generation,the pollen fertility had returned to normal.3.The genetic introgression analysis of donor Brassica juncea in offsprings:The results of SSR molecular markers showed that the average genetic introgression rates of A genome of Brassica juncea from F₁ to F₆ were 29.99%,23.44%,20.33%,12.72%,12.49%and 11.86%,respectively.The average genetic introgression rates of B genome from Brassica juncea were 42.43%,31.94%,18.06%,8.09%,7.08%and 4.17%,respectively.AFLP molecular marker analysis showed that the average genetic introgression rates of A genome in Brassica juncea were 20.93%,15.19%,11.14%,4.45%,3.46%,3.15%,respectively.The average penetration rates of B genome genetic material were 28.83%,21.28%,13.76%,4.43%,3.38%and3.07%,respectively.The results of SSR and AFLP molecular markers showed that the genetic introgression from Brassica juncea decreased with the increasing of generations.In F₂,BC₁ and F₃ generations,the genetic introgression of Brassica juncea varied greatly among individual plants.When F₄,F₅ and F₆generations were reached,the genetic introgression rates of individual plants tended to be stable.The genetic material in B genome of Brassica juncea was lost quickly,and the genetic material in B4,B5,B7 and B8 genome was first found to be lost.4.Damaged by flea beetle and agronomic traits of new Brassica napus obtained from hybridization Brassica juncea were investigated and analyzed:The average damage index of novel type Brassica napus was lower than Qingyou 14,among which four novel type Brassica napus had significant difference compared with Qingyou 14.Variance analysis of agronomic traits showed that the number of primary branches and kernels per pod of the novel type Brassica napus variety Strain 1 were significantly higher than that of Qingyou 14.The number of secondary branches and the length of main sequence of material Strain 5 and Strain 2were significantly higher than those of Qingyou 14.The number of main fruit in Strain 1 and Strain 2 was significantly higher than that in Qingyou 14.The average1000-grain weight of material Strain 3 was 4.12g,which was significantly higher than that of Qingyou 14.The pod length of all materials was significantly lower than Qingyou 14,and there was no significant difference in yield per plant and plot between novel type Brassica napus and Qingyou 14.The correlation analysis and principal component analysis among agronomic traits showed that the main traits affecting the yield of novel type Brassica napus were the number of pods per plant,plant height and number of main ordinal fruits.The selection of these traits should be synthesized in later breeding application.