Construction Of High-density Genetic Map And QTL Mapping For Tiller Number And Spike Number In Wheat

Tiller number and spike number are important biological characters of wheat.It is essential for wheat breeding programs to elucidate the genetic mechanisms and explore the QTL and molecular markers associated with tiller number,spike number and related traits.In the present study,a set of 371 recombinant inbred lines derived from Coordination-type wheat cultivar CN18 and wheat line T1208 were used to construct a high-density genetic map using the Wheat 55 K SNP array and to perform QTL analysis for tiller number,spike number,spike formation rate,kernel-related traits and grain yield.It is expected to explicate the genetic mechanisms controlling tillering at QTL level,to provide a theoretical basis of wheat breeding in the Southwestern wheat region,to further increase the grain yield potential and breeding efficiency,and to break through the ecological spike number limited in Sichuan Province.In addition,it is laid the foundation of marker-assisted selection and map-based cloning of genes that controlling tiller number and spike number.The main results are as follows:1.QTL mapping for spike formation rate have been performed by using SSR markers.The mechanism of spike formation rate at QTL level was clarified,and it was proved that spike formation rate is a quantitative rate controlling by a few major genes and several minor genes,and it was susceptible to the environment.We found a major QTL controlling spike formation rate(QSFR.sicau-4D-SSR),which was repeatedly detected in two years,and the performance was stable,which could explain 24.48% and 18.24% of the observed phenotypic variation,respectively.In addition,the QTL was pleiotropic that controlling TNPW and MTN.The QTL was closely linked to SSR marker Xcfd23.2.A set of 371 recombinant inbred lines derived from Coordination-type wheat cultivar CN18 and wheat line T1208 were used to construct a high-density genetic map by using the Wheat 55 K SNP array and SSR markers,both parental lines are carrying 1BL/1RS translocation.The genetic map was covering the whole genome except chromosome 1BS,consisting of 11583 SNP markers and 59 SSR markers spanning 4,513.95 c M,and the average marker density of the genetic map was 0.39 c M.The number of markers mapped to A,B,and D genome was 3296,4705,and 3641,accounting for the proportion of 28.31%,40.41%,and 31.28%,respectively.These 11642 markers had 2001 patterns of segregation in the RIL population,and hence,2001 markers with the lowest missing rate in each bin were chosen to represent the corresponding Bin and were shown in the genetic map.The number of markers in each Bin ranged from 1–989,the average Bin density of the genetic map was 2.26 c M.3.The TNES,TNPW,MTN,SN,SFR,TKW,KL,KW,KNPS,and GY of the RIL population were determined.All traits showed a normal distribution and were suitable for QTL mapping.All traits showed transgressive segregations,which can provide great germplasm resources for breeding in Southwestern wheat region.The correlation analysis showed that statistically significant positive correlation among various tiller number and related trait,which include TNES,TNPW,MTN,and SN were observed.There is a negative correlation among tiller number related traits and kernel related traits.In the “three elements of yield”,SN,TKW,and KNPS were all significantly positively correlated with GY.4.A total of 26 additive QTL of TNES,TNPW,MTN,SN,and SFR were detected by using ICIM-ADD method of QTL Ici Mapping V4.1.These QTL mapped to chromosome 1A,2B,2D,3A,4A,4D,5A,5D,6D,and 7D,respectively.Each QTL explained 0.74%–18.10% of the observed phenotypic variation.12 QTL related to kernel traits were detected and distributed on chromosome 1D,2A,3A,3D,4A,4B,5D,and 6D,respectively.Each QTL explained 2.19%–16.24% of the observed phenotypic variation.2 QTL related KNPS were detected and mapped to chromosome 2D and 7D,QKNPS.sicau-7D explained 37.84% of observed phenotypic variation.2 QTL controlling GY were detected on chromosomes 4B and 7D,explaining 8.61% and 7.32% of the observed phenotypic variation,respectively.The chromosomal location of all QTL showed 9 QTL clusters mapped to 2D,4A,4B,4D,5A,5D,and 6D,respectively.There is a QTL cluster controlling tiller number,spike number,and related traits on chromosome 2DS,QTL in this region showed pleiotropic and co-localization in this study.TNES,TNPW,MTN,and SN have some correlativity,and the genes controlling the related traits were more likely to form the genetic aggregation region,which had a certain value in polymerization breeding.5.The combined QTL analysis of TNES,TNPW,MTN,and SN growth stages were performed by using MET function of QTL Ici Mapping V4.1.A total of 9 QTL of tiller number were detected,which is consistent with single environment QTL analysis and distributed on chromosome 2B,2D,4A,4D,5A,5D,and 7D,respectively.Among these QTL,c QTN.sicau-2D.2 could be detected in the four tiller growth stages,explaining 4.92%,6.90%,13.62%,and 17.16% of the observed phenotypic variation,respectively.By comparing the flanking markers to the physical locations,this QTL spanned 13.71 Mb(2D:82189047–95895626),and the candidate genes prediction showed 136 contigs in this region of chromosome 2D,this region might include candidate genes controlling tiller number and spike number.6.Using ICIM-EPI method of QTL Ici Mapping V4.1 to perform additive×additive epistatic QTL analysis,a total of 17 pairs of epistatic QTL were detected.Among these,1 pair of epistatic QTL was detected between 2 additive QTL,8 pairs of epistatic QTL were detected between additive QTL and random site,8 pairs of epistatic QTL between 2 random sites were detected.QTNES.sicau-2B and QTNES.sicau-5A.1 was a pair of epistatic QTL between 2 additive QTL,the LOD value was 6.59 and explained 3.81% of observed phenotypic variation,and the epistatic effect was greater than additive effect.7.To evaluate the practicability and validity of the molecular markers associated with tiller number and spike number in wheat,utilizing 6 SSR markers to analyze the correlations between PCR amplification patterns and the phenotypic values.The result showed that SSR markers Xgwm264 and Xwmc169 could be used in screening tiller number and spike number in breeding programs in the Southwestern wheat region;Xwmc215,Xgwm437,and Xcfd23 could be used in screening tiller number;Xbarc232 was not suitable for screening tiller number and spike number.