A High-density Genetic Map And QTLs For Yield Related Traits In Wheat (Triticum Aestivum L.)

A high genetic map was constructed of wheat (Triticum aestivumL.) and QTL analysis foryield traits was conducted using a population of176recombinant inbred lines (RILs) derivedfrom “Shannong0431×Lumai21”(F7in2010). The main results are as follows:A total of74500molecular markers were used to screen the polymorphism of RILs andtheir parents. A number of7955polymorphic loci (6237DArTs,1519SNPs and199SSRs)were identified and used to construct the genetic map. A genetic map with5916loci wasfinally constructed covering all the21chromosomes. In which,4530loci were unique loci,including3605DArTs,850SNP and75SSR loci; and the other1386loci showedco-segregation with other markers. The final map spanned a total length of2929.96cM across42linkage groups, with an average chromosome length of139.5cM. The largest chromosomewas3B (201.95cM), and the shortest was3D (31.15cM). The total number of mapped lociper chromosome ranged from30(3D) to447(3B) with an average of215.71loci perchromosome. The density ranged from0.31(6A) to2.18(1D) cM/marker with an averagedensity of0.65. The map length and locus number was unequally divided among the threegenomes:1065.36cM (36.4%),1072.95cM (36.6%) and791.65cM (27.0%) in lengths; and1591(35.1%),2278(50.3%) and661(14.6%) loci for the A, B and D genomes, respectively.The seven homologous groups also varied in locus number and map length: group7containedthe most loci and length (899loci covering471.16cM); whereas group4had the smallest lociand length (402loci covering245.25cM).The parents of the RILs displayed remarkable differences for the investigated traits in theeight environments and their average value (AV). For the RILs, the variance for genotypesand environments of all of the14investigated traits were significant at the P≤0.001level,indicating that the environments and genetic background were both important in explainingthe overall phenotypic variations. The for the investigated traits ranged from28.10(GY) to76.90%(GL), which were over50%for PH, TGW, SL, GL, GW, GLW, BSSS, TSSS andTSS; whereas lower than50%for GY, FSS, SN, FFD and GNS. The coefficients of variation(CVs) ranged from3.38%for GW in E4to197.53%for TSSS in E2. Transgressivesegregation was observed for all of the traits in the eight environments and AV.The Pearson correlation coefficients for PH appeared significant positive correlations with SN, TGW, GY, SL, BSSS, TSSS and GW; and negative correlation with GNS. The yieldcomponent traits, SN, GNS and TGW, showed extremely significant negative correlation. Thesignificant positive correlations were obtained between GY and SN/GNS. For spike traits, thestrong positive correlations were simultaneously obtained between SL, TSS and FSS. BSSSappeared significant positive correlations with TSS, and negative correlation with FSS.Significant negative correlations were found between TSSS and FSS. Some correlationcoefficients were significant between GNS/TGW/GY and spike traits. For the grain size traits,the significant positive correlations were obtained between the GL and GLW, and significantnegative correlations between the GLW and FFD. Some correlation coefficients weresignificant between yield traits and grain size traits.A total of204additive QTLs (370QTLs for trait-environment combinations) weredetected on20chromosomes except for3D for all of the investigated traits in the eightenvironments and their AV. An individual QTL in different environments explained3.84-33.31%of the phenotypic variations. Of which,123QTLs showed positive additiveeffects with Shannong0431increasing the effects of QTLs, whereas81QTLs were negativeeffects with Lumai21increasing the QTL effects. The highest LOD value for a single QTL inthe different environments was17.03for PH in E4. Fifty-six QTLs were identified for yieldcomponent on20chromosomes except for3D,4B and6D. An individual QTL in differentenvironments explained5.26-20.15%of the phenotypic variations. Eight-two QTLs wereidentified for PH and spike triats on20chromosomes except for3D. An individual QTL indifferent environments explained4.65-33.31%of the phenotypic variations. Sixty-six QTLswere identified for PH and spike triats on19chromosomes except for3D and6D. Anindividual QTL in different environments explained3.84-24.36%of the phenotypicvariations.Nineteen relatively high-frequency (RHF) or relatively stable QTLs (9.27%) expressing inmore than four environments and/or in AV were located, including eight traits (PH, TGW, SL,BSSS, TSS, GL, GLW and FFD) with the average contributions ranging from6.59%to24.05%. Of which, all the RHF-QTLs except for QPh-2B, QTss-6A and QBsss.2-6A showedpositive additive effects with Shannong0431increasing the effects of QTLs. SevenRHF-QTLs (QPh-4D, QSl.2-1A, QTss-6A, QBsss.2-6A, QFfd-5B, QGl.2-5B and QGlw-5B)were stably main effect QTLs with explaining more than10%of phenotypic variations.A number of21QTL clusters (C1-C21) with more than three traits were mapped on10chromosomes:1A,1B,1D,2B,2D,3A,3B,4D,5B and6A, which were related to all of theinvestigated traits and involved84QTLs (84/204×100%=41.18%) and15RHF-QTLs (16/19×100%=84.21%). Cluster C2, C8, C10, C11, C15, C16, C17, C18, C20and C21detected in at least one RHF-QTL and over nine trait-environments combinations, which wereconsidered the most important QTL clusters, and these QTL cluster interval should be usefulfor marker-assisted selection (MAS).