Construction And Genetic Analysis Of Double Haploid Mapping Populations For New-type Brassica Napus

Brassica napus is not only an important oil crop in China,but also widely cultivated in the world.It is a young allotetraploid formed from interspecific cross between the dipoid progenitors of B.rapa and B.oleracea and genetic resources are relatively narrow.To broaden the genetic basis of B.napus,our research group has massively introduced the A^r genome of B.rapa and the C^c genome of B.carinata into B.napus.A new-type B.napus with exogenous introgression components close to the genome constitution of A^rA^rC^cC^c was established.Previous molecular marker analysis shows that there is a significant genetic difference between new-type B.napus and traditional B.napus,and there are a large number of new genetic variations in the genome of the new-type B.napus.However,the detailed characteristics of these variations,as well as their position and distribution within the genome,and the effect on the improvement of the trait,has not yet known.In order to further explore the new variation and genetic effects of exogenous introgressions and interspecific hybridizations on new-type B.napus genome,we propose to screen elite new-type B.napus homozygous lines for hybridization with sequenced B.napus to develop mapping populaitons and construct high-density genetic map to identify the genetic variation introduced by different exotic subgenomes in new-type B.napus.This study aims to provide mapping populations and lay the foundation for further analysis of the genome structure characteristics of the new-type B.napus.In this study,to screen elite parents for construct genetic mapping populaitons,we selected a total of 110 diverse lines from the third generation of new-type B.napus gene pool and crossed them with two sequenced cultivars to evaluate potential heterosis.One was a Chinese semi-winter rapeseed Ningyou 7,and the other one was a European winter rapeseed cultivar,Tapidor.These hybrid F₁ and their parents were planted in Xining and Wuhan for a primary evulation.According to the preliminary observations of growth traits at seedling stage and the seed yield,the optimal three pairs of hybrid F₁ between new-type B.napus with Ningyou7 and Tapidor were identified.The buds of these 6 F₁ were used for microspore cultivation and doubled by colchicine.Finally,approximately a total of 3680seedlings and the seeds of 1165 plants seeds with normal pollen sterility were obtained for the six populations.We tested the ploidy of seedlings for one of the mapping populations by flow cytometry.A total of 275 double haploid lines were finally obtained,and recorded as NG3-1 DH population.The agronomic traits and seed quality traits of NG3-1 DH population were recorded.The SNP Calling was performed using the Brassica napus genome of Darmor-bzh v4.1as a reference genome.The obtained 340,000 original markers were subjected to rigorous quality control.A total of 8,422 bin markers were obtained?Each bin includes several genotype-consistent polymorphic markers,a total of 33032 high-quality representative markers?.The 8422 bin markers were analyzed and genetic maps were constructed by using MSTMap and Joinmap4.0 software.Finally,a high-density genetic linkage map containing2727 markers,covering a length of 2664.01 cM and containing 17 linkage groups was obtained.The linkage groups of A02 and C02 were not constructed,because one of the parents was new-type B.napus which contained exogenous introgression from other species.The chromosomal structure of A02 and C02 is more complex and would be further explored after this study.The three pairs of DH mapping populations developed in this study,as well as the high-density genetic map of the NG3-1 DH population,will provide genetic resource for the subsequent genomic analysis of new-type B.napus and would also help to identify some of the structural variations among different mapping parents.