Construction Of Genetic Linkage Maps&Quantitative Trait Loci And Genetic Analysis For Branch Traits In Cut Chrysanthemum

Chrysanthemum,Dendranthema morifolium Ramat.(Syn.D.grandiflorum(Ramat.)Kitam)(Compositae,Anthemideae),is one of the most important floricultural crop in the cut flower,flowering potted plant,and herbaceous perennial markets of the world.Its diversity with respect to growth habit and inflorescence form and color have ensured its ecomomic importance.There is little information reported as to the genetic pattern of some ornamental traits in cut chrysanthemum and its breeding strategy so far.In this research,the analysis of heterosis and major gene plus polygene mixed model were carried out on branch traits through a two-year data in 2011?2012 of a F1 progeny derived from the cross between two cut chrysanthemum cultivars 'QX-145' and 'Nannongyinshan',both of which widely contrast for their branch traits.This F1 progeny was used as the mapping population to construct genetic maps for cut chrysanthemum in accordance with "double pseudo-testcross mapping strategy" and quantitative trait loci(QTL)mapping analyses on four branch traits of cut chrysanthemum were put into effect by using WinQTLCartographer v2.5 software with composite interval mapping(CIM)method and LOD threshold of 2.5.The main research results were as follows:1.Genetic analysis for branch traits in cut chrysanthemumThe 4 branch traits,including primary branch number,branch height,primary branch length and branch angle,segregated widely in F1 pogeny with coefficient of variation(CV)at a range of 14.60%to 38.89%.The phenoma of hybridization heterosis and extra-parent segregation existed generally in F1 population.Compared with mid-parent value(MPV),the heterosis value of mid-parent(Hm)of 4 branch traits investigated demonstrated a remarkable difference degree at 0.01 level except primary branch length,and the ratio of heterosis value of Hm for the three traits were-2.35%,-23.27%,and-3.69%,respectively.The mixed genetic analysis suggested that primary branch length and branch angle were fitted to A-0 model and no major gene was detected.The primary branch number and branch height are accorded with A-4 model with a negative complete dominant effect with major gene heritability of 51.45%and 53.92%.2.Constrction of genetic linkage maps for cut chrysanthemumA initiatory genetic linkage map of cut chrysanthemum was constructed by genotyping 92 F1 progeny of the bi-parental cross 'QX-145' and 'Nannongyinshan' with SRAP and SSR markers through a double pseudo-testcross mapping strategy.A total of 407 polymorphic markers,consisting of 239 SRAPs and 168 SSRs,were validated by the Chi-square test to determine whether the genotypic frequencies differed significantly from the expected segregation ratio.Most of the loci fit 1:1and 3:1 segregation ratio with chi-square value ranging from 0.00 to 3.82 with?25%of segregation distortion.234 testcross markers were mapped on the two parental maps,leaving behind 92 markers unlinked.In the'QX-145' linkage map,109 testcross markers were distributed into 25 linkage groups,spanning 1465.6 cM with an average distance of 13.4 cM between adjacent markers.In'Nannongyinshan' linkage map,125 testcross markers were distributed into 21 linkage groups,with genome coverage of 1452.1 cM and the average distance between two adjacent markers was 11.6 cM.The two genetic linkage maps covered 68%and 73%of the estimated genome size,respectively.3.QTL detection controlling branch traits in cut chrysanthemumThe phenotypic data of 4 branch traits including primary branch number,branch height,primary branch length and branch angle in 2011 and 2012 croping seasons had no remarkable difference,and the average of four traits in F1 population was between that of both parent,although there were some extra-parent progenies;all traits abiding by normal distribution were demonstrated for quantitatively controlled traits which were appropriate for the further QTL analysis.The QTL mapping for four branch traits based on SRAPand SSR-based maps of cut chrysanthemum showed that a total of 20 QTL were identified in 2011 and 2012,which mainly distributed on the 5 linkage groups of 'QX-145' genetic map and the 6 linkage groups of 'Nannongyinshan' genetic map with a single QTL accounting for the phenotypic variation of 6.87?24.38%.Four QTL at the same or adjacent mapping area on the same linkage map were detected both in two different environments,respectively.That the contribution ratios of PbnE1N4(PbnE2N4),BhE1N11(BhE2N11),PblElQ1(PblE2Ql)and PblElN15(PblE2N15)to phenotypic variation were above 10%suggested that these QTLs identified both in 2011 and 2012 were major effect QTL little affected by environment factors.