Heterosis Analysis And QTL Mapping Of Intersubgenomic Hybrids Of Brassica Napus

Brassica napus（rapeseed）,as one of the most significant oil crops all around the world,has been planted in many countries around the world,but its genetic basis is limited.It is expected to improve the heterosis of Brassica napus by enlarging the genetic base and increasing the genetic distance between the parents.In this study,we crossed conventional B.napus with new-type B.napus lines with introgressed genomic components from B.carinata and B.rapa.All parental and F₁ hybrid lines were analyzed for heterosis and combining ability,so that the parents and hybrids with high combining ability and heterosis potential as well as elite agronomic traits were selected.This would provide a basis for the subsequent analysis of intergenomic heterosis.Meanwhile,a F_2:3 family mapping population was constructed by crossing a new-type B.napus line SV_A2C2 with a conventional B.napus cultivar Express 617.A large number of molecular markers were obtained by whole-genome resequencing and genotyping.Then,we constructed a high-density genetic linkage map using different types of markers to detect QTLs for yield and related agronomic traits.The main results are as follows:1)We performed the yield experiment of 135 F₁hybrid lines crossed by new-type and conventional B.napus according to a completely randomized block design.The results showed that the mid-parent heterosis of 67%F₁ lines were positive in both two environments and the high parent heterosis was up to 61.49%.The results of combining ability analysis showed that male lines 12,13 and 14,and female lines 1 and 19 exhibited high general combining ability in both two environments.At least 68 hybrid combinations with positive special combining ability were selected in both environments,and most of the combinations exceeded the yield of commercial hybrid cultivars.The results above indicated the strong heterosis potential exists among subgenomes of B.napus on the one hand,and provided reference for further screening of superior combinations and good parents.2)Total 3,546,419 polymorphic markers were obtained by SNP calling using Express617 reference genome sequencing data following the whole-genome resequencing of F_2:3familial and parental lines.All detected markers were divided into three types:NORMAL,PAV,and HEMI.27,337 NORMAL bin markers and 1500 PAV bin markers were obtained for genetic map construction following filtering.The genetic map F_2:3 mapV1 constructed by NORMAL markers contained 1991 genetic loci,and the genetic map mapV2 constructed by NORMAL and PAV markers contained 2374 genetic loci.Map V1 and mapV2 were complementary to each other.PAV markers can fill part of the gaps in mapV1,which could provide more abundant genetic information.3)QTLs for seven traits were mapped by composite interval mapping method based on the BLUP values of phenotypic data of F2:3 families in 2019WH environment and mapV1 and mapV2.Eleven and ten QTLs for seven traits were mapped by mapV1 and mapV2,respectively,of which phenotypic contribution rates were 4.80%-28.41%.The phenotypic contribution rates of two seed glucosinolate QTLs on A03 were both over 20%.A thousand seed weight-related QTL,of which confidence interval was located in a PAV marker region,were mapped on C07.This implied that a potential structural variation have occurred in this region,which led to that structural variations possibly have an impact on traits of new-type B.napus.These genetic information will lay a foundation for us to further analyze the genetic mechanism of subgenomic hybrid dominance.