Construction Of NILs With A Main Flowering Time QTL And High-Density Genetic Map In Spring Rape

Flowering time is a complex quantitative trait controlled by multiple genes.A large number of studies have shown that flowering time affects important agronomic traits such as environmental adaptability,plant-type,stress resistance and yield,and it significantly correlates with maturity.The breeding and application of early maturing varieties is one of the hotspots in rapeseed breeding.It is an important goal of spring rape breeding in China to cultivate early maturing varieties of Brassica rapa L.and Brassica napus L.which can be cultivated in high altitude areas.For these reasons,the study on flowering time trais of spring rape and the construction of high-density genetic map of spring rapeseed has important theoretical guidance for early flowering gene pyramiding and the selection of new early spring rapeseed varieties.Previous studies used NN DH population to locate the main effect QTL cqDTFA2a on the A2chromosome within 1.7 Mb.This study was based on the previous results,we developed molecular markers closely linked to flowering time and the MAS backcross method was used to construct the NILs with a main flowering time QTL cqDTFA2a;in addition,203 individual plants of a F₂ population of B.rapa were used as the mapping population,and the high-density genetic map was constructed by using Reduced-Representation Genome Sequencing.The main research results are as follows:1.Development of foreground selection primers and background selection primers for molecular marker-assisted breeding.Based on previous results,10 pairs of InDel markers were designed on both sides of the candidate interval,and 3 pairs of markers closely related to flowering time were obtained by screening the polymorphism between parents,including 1 pair of dominant markers and 2 pairs of codominant markers;25 pairs of AFLP primers were randomly selected,and the genetic background polymorphism of the parents was analyzed,and 8 pairs of AFLP markers were selected.2.Development of NILs with a main flowering time QTL cqDTFA2a by using molecular marker-assisted backcross breeding method.The F₁ population derived from the cross between one DH line containing the target locus in the NN DH population and the late flowering parent No.5246,and NILs were constructed by using No.5246 as recurrent parent.According to the result of foreground selection in BC₁F₁ and BC₂F₁ population,34 and 87 heterozygous genotypes were obtained respectively.Using 8 pairs of AFLP primers to detect the background of BC₂F₁generation materials,and the results showed that the average background recovery rate of this generation was 83.9%.3.The high-density genetic linkage map of B.rapa was developed by using Reduced-Representation Genome Sequencing.Two parents and 203 individual plants of one F₂ population were sequenced by using GBS technology and Illumina HiSeq sequencing platform.The GBS sequencing library was successfully constructed and a total of 99.26Gb Raw data was generated.After data filtering,98.10Gb Clean data was obtained,and the average Raw data of filial generation was about 488.940Mb.A high-density genetic linkage map of B.rapa was constructed using 11,451 developed SNP markers.The genetic distance of this map is 6224.3cM,covering 10 linkage groups,and the average genetic distance between genetic markers was 0.54cM.