Genetic Analysis For The Formation Basis Of Spike Morphology And Grain Size In Bread Wheat(Triticum Aestivum L.)

Bread wheat(Triticum aestivum L.)is one of the most important stable foods in the world,providing an important source of calories and protein for about 35-40%world’s population.China is the largest country in the production and consumption of wheat.Thus,cultivating high-yield wheat varieties is an important measure to continuously increase wheat production and ensure food security.Wheat yield is a complex trait affected by genetic and environmental factors and constituted of three major components,i.e.,thousand grain weight(TGW),grain number per spike(GNS),and spike number per unit area.The GNS is mainly determined by spike morphology,and the TGW is mainly determined by grain shape.Therefore,mining and verifying the major QTL for spike morphology-related and grain size-related traits,and developing molecular markers that are closely linked to them,are important for utilizing the molecular breeding methods to regulate wheat spike morphology and grain size,and thereby increase wheat yield.In this study,multiple bi-parental segregating populations were developed using wheat varieties with significant differences in spike morphology and grain size.Around these genetic populations,the genetic analysis and molecular mapping of spike morphology-related and grain size-related traits,including total spikelet number per spike(TSN),fertile spikelet number per spike(FSN),spike length(SL),spike compactness(SC),TGW,grain width(GW)and grain length(GL),were performed.The following main results were obtained:1.Genetic analysis for the formation basis of TSN and FSN in wheatA high-density genetic map was constructed using the Wheat 55K SNP array in the Kechengmai 1(K1)×Chuanmai 42(CM42)doubled haploid(DH)population(CK1,187 lines).The genetic linkage map contains 13,068 SNPs distributed in 2406 Bins with a total length of 3091.39 cM and an average interval distance of 0.24 cM/marker and 1.28 cM/bin,respectively.A comparison between the genetic and physical maps indicated high consistence of the marker orders.CM42 and K1 have significant differences in the TSN and FSN,and K1 shows more TSN and FSN than CM42.Based on the phenotypic data in five environments,a total of 27 QTLs associated with TSN and FSN were detected in the CK1 population.Among them,five QTLs were detected in multiple environments and the best linear unbiased prediction(BLUP)datasets,explaining the phenotypic variance ranging from 3.64%to 23.28%.QTsn/Fsn.cib-3D was a major QTL for TSN and FSN,explaining 5.97-23.28%of the phenotypic variation.Comparison analysis showed that QTsn/Fsn.cib-3D is probably a novel major QTL for TSN and FSN.Effect analysis showed QTsn/Fsn.cib-3D had a significant effect on GNS,and no effect on TGW,GW,GL,plant height(PH),and SL.Additionally,QTsn/Fsn.cib-3D was further verified in two populations with different genetic backgrounds by using a closely linked Kompetitive Allele Specific PCR(KASP)molecular marker.Additionally,two genes,TraesCS3D02G443900 and TraesCS3D02G445400,within the interval of QTsn/Fsn.cib-3D probably related to spikelet development were identified.These results provide theoretical foundation for future fine mapping and cloning of QTsn/Fsn.cib-3D,and the developed KASP marker could be utilized in molecular breeding for increasing the grain yield in wheat.2.Genetic analysis for the formation basis of SL and SC in wheatTwo bi-parental populations with CM42 as a common parent were used for QTL mapping,one of which was the CK1 population,and the other was a recombinant inbred line(RIL)population derived from the cross of CM42×CN16(CC,120 F10 lines).A total of 34 QTLs were detected,and six major QTLs of them were repeatedly detected in more than four environments and the BLUP datasets,explaining 7.13-33.6%of phenotypic variation.These major QTLs were co-located in two genomic regions on chromosome 5A and 6A,namely QSc/Sl.cib-5A and QSc/Sl.cib-6A,respectively.By developing KASP markers that linked to them,the two loci were validated in different genetic backgrounds,and their interactions were also analyzed.Comparison analysis showed that QSc/Sl.cib-5A is not the Vrn-Al and Q,and QSc/Sl.cib-6A is likely a new locus for SC and SL.Both QSc/Sl.cib-5A and QSc/Sl.cib-6A had pleiotropic effects on other yield-related traits,including PH,TGW,and GL.Additionally,significant effects on SL and SC were detected in the near-isogenic lines(NIL).Furthermore,TraesCS5A01G301400 and TraesCS6A01G090300 were considered as potential candidates for QSc/Sl.cib-5A and QSc/Sl.cib-6A,respectively.These results provided valuable information for fine mapping and cloning of the two loci in the future,and these major QTL combined with developed KASP markers could be utilized in marker-assisted selection(MAS)in breeding programs.3.Genetic analysis for the the formation basis of grain size in wheatSix major QTLs,QGw.cib-4B.2,QGl.cib-4A,QGl.cib-5A.l,QGl.cib-6A,QTgw.cib-4B,and QTgw.cib-5A,were consistently identified in at least three individual environments and the BLUP datasets in the CK1 population,explaining 5.65-34.06%of the phenotypic variation.Of them,QGw.cib-4B.2,QTgw.cib-4B,QGl.cib-5A.l,and QGl.cib-6A showed no effect on GNS.In addition to QGl.cib-4A,the other major QTLs were further validated using KASP markers in different genetic backgrounds.Moreover,significant interactions for three major GL QTLs and two major TGW QTLs were observed.Comparison analysis showed that QGl.cib-5A.l and QGl.cib-6A are likely new loci.Notably,QGw.cib-4B.2 and QTgw.cib-4B were co-located on chromosome 4B and improved TGW by exclusively increasing GW,which is different from nearby or overlapped loci reported previously.Similarly,significant effects on TGW and GW were detected in the NIL population.Additionally,three genes,TraesCS4B01G318500,TraCS4B01G320400,and TraesCS4B01G317400,are probably associated with grain development within the interval of QGw.cib-4B.2/QTgw.cib-4B were observed by sequence similarity,spatial expression patterns,and orthologous search.Overall,these major QTLs and KASP markers will be useful for elucidating the genetic architecture of grain size and weight and developing new wheat varieties with high and stable yield.