Inheritance Of Flowering Time And QTL Mapping Of Plant Height And Flowering Time In Brassica Napus L.

Brassica napus L.is an important oil crop in China and the main source of edible vegetable oil in China.Plant height and flowering time are two important traits of current rapeseed breeding.Appropriate reduction of plant height and shortening of flowering time are of strategic significance for improving the lodging resistance and early maturity of rapeseed,promoting mechanized harvesting of rapeseed and promoting the development of rapeseed industry.Since 2015,our research team has conducted in-depth research on the plant height and flowering time of Brassica napus L.,using two high-quality inbred lines of high-generation Brassica napus YG-1?high pole late ripening?and 72-27-1-2?dwarf pole precocity?was used as the parent,and the inheritance of plant height traits was studied by its six generations.The genetic map of plant height and flowering time of Brassica napus L.was preliminarily constructed by SSR markers,the QTL of plant height and flowering time was preliminarily located.?Liu Xia 2018?.Based on the previous research,this study continued the quantitative genetic analysis of flowering time and related traits.On the other hand,the F₂ population was sequenced by SLAF-seq technology to construct high-density genetic maps of plant height and flowering time.The plant height and flowering time QTLs were located and predicted candidate genes,in order to provide theoretical and technical basis for rape dwarf and early maturity breeding.The main results of this study are as follows:1.Genetic analysis of"main gene+polygene"in flowering timeThe constructed six-generation genetic population was planted at Yangling and Sanyuan,investigate its squaring time?ST?,bolting time?BT?and flowering time?FT?,genetic analysis of flowering time and related traits was carried out using the genetic model of major gene+polygene of plant quantitative traits.The results show that both locations ST are in line with the C-0?PG-ADI?model;the Yangling point BT and FT are in line with the E-0?MX2-ADI-ADI?model.the Sanyuan point BT and FT are in line with the E-1?MX2-ADI-AD?model.ST is controlled by multiple genes,BT and FT are controlled by two pairs of major genes,and there is a micro-effect multi-gene interaction effect.The major gene heritability of BT and FT in Yangling was 59.29%and 67.64%,the polygenic heritability was24.28%and 22.63%and the major gene heritability of BT and FT was 65.29%and 54.38%,the polygenic heritability was 13.76%and 22.59%in Sanyuan.the heritability of the major gene is greater than that of the corresponding generation.Therefore,the line with suitable flowering time can be selected in the early generation.2.Phenotypic statistics and correlation analysis of plant height and flowering timeTo investigate the agronomic traits associated with plant height and flowering time in the F2 population:plant height?PH?,main inflorescence length?MIL?,first valid branch height?VBH?,the numbers of valid branch?BN?,the nsecondary valid branch number?SBN?,internodal length?IL?,squarying time?ST?,bolting time?BT?,flowering time?FT?,correlation analysis.Correlation analysis between plant height traits and flowering time traits showed that PH and VBH,MIL,BN,and SBN showed extremely significant positive correlations,and the correlation coefficients were 0.476,0.492,0.384,and 0.301,respectively;FT was significantly positively correlated with ST and BT,with correlation coefficients of 0.761 and 0.763,respectively;PH and ST.There was a significant positive correlation with FT performance,and a significant positive correlation with BT performance.The correlation coefficients were 0.312,0.385 and 0.260,respectively,indicating that the higher the plant height of rape,the later the bud,twitch and flowering time.3.Construction of genetic map of Brassica napus L.based on SLAF-seq technologySNP markers were developed by parental resequencing,SLAF simplified sequencing was performed in F₂ population,and aa/bb type markers were selected for SNPs developed by parents.The marker typing of F2 population was analyzed,and cabbage type was constructed by composite interval mapping?CIM?.The genetic map finally obtained a genetic map of cabbage with a total map distance of 2,195.02 cM.The map contained 3,161SNP markers covering 19 linkage groups?A01-A10,C01-C09?with an average density of0.70 cM.Compared with the previous map of the laboratory,the total length increased by1294.39 cM,and the average distance between markers was shortened by 7.8 cM.4.QTL mapping of plant height and flowering time traits?1?The QTLs of plant height and flowering time were detected by MapQTL6.0combined with the genetic map constructed above.A total of 15 QTLs were detected,mainly distributed on A02,A04,A05,A07,A09,C04 and C06 chromosomes.Among them,8 QTLs are related to plant height traits,5 of them's phenotypic variation rate of more 10%,which are qPH-2,qVBH-2,qBN,qMIL,qIL,and the phenotypic variation rate of qVBH-2 and qBN exceeds 20%.They were 27.227%and 20.689%respectively;7QTLs were related to flowering time traits,and their phenotypic variation rates were all above 10%,of which qST had the highest phenotypic variation rate of 65.949%.?2?Using the ST and BT data of the F₂ population surveyed by Yangling in 2017 and measuring the plant height and flowering-related physiological indexes of the F₂ family by SPAD,reducing sugar?RS?and soluble protein?SP?in 2018.A total of 19 QTLs were detected in the genetic map constructed by Liu Xia?2018?,mainly distributed on chromosome A01-A09.The phenotypic variation rate above 10%are qSPADYL-2,qSPADYL-3,qRSYL-8,qSPYL-1,qST-2,qST-17 and qFT-5,of which the soluble protein qSPYL-1 has the highest phenotypic variation rate that up to 30.376%?3?Integrating 20 QTLs located by Liu Xia?2018?,this study used the SSR genetic map to detect 39 QTLs,and compared the 15 QTLs detected by their SNP genetic maps on the rapeseed genome.The physical location,finally obtained 5 pairs of QTLs with overlapping regions,A02?qMILSY-1 and qPH-1?,A03?qBNYL-12 and qFT-1?,A04?qRSYL-8 and qBN?,A07?qFT-16 with qPH-2?and A09?qFT-5 and qSBN?.5.Candidate gene prediction and analysisReferring to the Brassica napus database,the plant height and flowering time-related15QTLs regions of SLAF simplified sequencing were screened,and a total of 642 genes were obtained from all the localization intervals.Compare with SwissPort,NR,COG,GO,KEGG database blast to obtain functional annotations of each gene,and screen 139 plant height and flowering-related genes.2 of which were in the SLAF simplified sequencing location with a contribution rate greater than 20%of QTLs and SNP differences between parents,and the other 2 genes were in 5 overlapping QTLs and there are SNP differences between the parents.The expression analysis of the 4 genes in the roots,stems and leaves of the parents was carried out,and two candidate genes BnaA02g23350D and BnaC06g19740D were identified.Among them,BnaA02g23350D was associated with biological process photomorphogenesis?GO:0009640?,BnaC06g19740Dandbiologicalprocesslight.Morphogenesis?GO:0009640?is associated with floral developmental regulation?GO:0009909?.