Combining Ability And Major Gene Analyses And QTL Mapping For Branching Traits Of Cut Chrysanthemum Under Different Planting Densities

Cut chrysanthemum,especially spary cut chrysanthemum,its cultivation pattern,production cost and ornamental quality all depend on its branch trait,which makes the branch trait a main target trait in breeding work.However,the genetic mechanism governing branching trait in chrysanthemum is rarely investigated,which negatively impact the breeding targeting plant architecture.In this research,seven branching traits,i.e.,total lateral bud number,up-part primary branch number,primary branch length,primary branch angle,total secondary branch number,secondary branch length,and secondary branch angle of the twelve F1 progenies derived from a 4 × 3 diallel design(NCII)are investigated in two successive years to dissect the combining ability effects;and the segregating‘Nannongxuefeng' × 'Monalisa'F1 population are used to identify the major gene effect by major gene plus polygene inheritance model and to unravel the QTL responsible for branching traits of cut chrysanthemum.The main results are as follows:1.Combining ability analysis for branch traits of spary cut chrysanthemumCombining ability analysis shows total lateral bud number is controlled by non-additive gene action;and The up-part primary branch number,total secondary branch number,primary branch length and secondary branch length by both additive and non-additive genes;and the primary branch angle and secondary branch angle by additive genes.‘Monalisa' exhibits positive GCA for most branching traits,and‘Qx-021'and‘Qx-096'show negative GCA for most branching traits,thus the latter two cutlivars may be elite parents in crossbreeding targeting for cut chrysanthemum of compact type.The crosses‘Qx-021'בQx-098'and‘Qx-081'בQx-098'shows high total combining ability(TCA)for primary and secondary branch number but negative TCA for the other five branching traits,so it is likely to develop new cut chrysanthemum of compact type from these crosses.In addition,a high level of broad-sense heritability ranging in 73.81%?94.41%is calculated for the seven branching traits,and a moderate high narrow-sense heritability larger than 60%is estimated for all the investigated branching traits except total lateral bud number(1.88%)?2.Mixed genetic analysis for branch traits of spary cut chrysanthemumThe seven branching traits,i.e.,total lateral bud number,up-part primary branch number,primary branch length,primary branch angle,total secondary branch number,secondary branch length,and secondary branch angle of the segregating 'Nannongxuefeng'× 'Monalisa' F1 population are investigated in two successive years of 2015 and 2016,and the major gene effects are analyzed using major gene plus polygene inheritance model for each branch traits.All the investigated branch traits show continuous variations,with the coefficient of variation ranging from 12.89%to 61.55%.The phenoma of mid-paraent heterosis and extra-parent individuals exist generally for every branching trait,but transgressive heterosis is not yet to take shape in the F1 population,and the mid-paraent heterosis is relatively large for total lateral bud number,up-part primary branch number,primer branch angle and total secondary branch number,with the ratio of mid-parent heterosis calculated respectively at-9.69%?-9.10%?12.99%and 25.51%.The mixed genetic analysis indicates that the inheritances of total lateral bud number,primary branch angle and secondary branch angle fit to the A-0 model with no major genes;the up primary branch number and total secondary branch number fit to the B-2 model,governed by two pairs of major genes showing additive-dominant effect;the secondary branch length accords with the A-1 model,controlled by a pair of major gene displaying additivity and part dominance or super-domimance effect;and the secondary branch length is in accordance with the B-1 model with the presence of two pairs of major genes expressing additivity-dominance-epistasis effect.The heritability of major genes for the up-part primary branch number,primary branch length,total secondary branch number and secondary branch length were calculated at,respectively,0.74,0.46,0.72 and 0.50.3.QTL detection for branch traits of spary cut chrysanthemum under different planting densitiesBased on the genetic linkage maps of cut chrysanthemum cultivars 'Nannongxuefeng'and 'Monalisa',QTL mapping identified a total of 84 QTL underlying the seven branching traits under two planting densities over tow years,in the F1 population derived form the two cultivars.Of the 84 QTL,13 QTL are identified for total lateral bud number,8 for up primary branch number,13 for primary branch length,12 for primary branch angle,18 for total secondary branch number,11 for secondary branch length,and 9 for secondary branch angle,with individually explained phenotypic variation varying from 5.36%to 16.59%at a LOD threshold of 2.5 to 5.1.Twenty of the 84 QTL are regarded as major QTL for their contribution ratio larger than 10%.In addition,eleven of the 84 QTL are predicted in more than one environment:four specific to low planting density,five specific to high planting density,and two for both planting densities.