Evaluation And Genetic Variation For Branching Traits Of Standard Cut-Chrysanthemum

Chrysanthemum(Chrysanthemum morifolium Ramat.)has diversiform flower patterns and long vase life and is one of the four most popular cut flowers over the world.According to the cultivation characteristics,cut-chrysanthemum can be divided into standard cut-chrysanthemum(disbud cut-chrysanthemum)and spray cut-chrysanthemum.In the production of standard cut-chrysanthemum,removing lateral buds artificially is required and has high production costs,while it is easy to hurt the main bud and affect the quality of flowers.Therefore,it is an effective way to reduce the production cost and improve the quality of cut flowers by clarifying the genetic characteristics of branching traits and cultivating the standard cut-chrysanthemum cultivars with fewer lateral buds.In this study,we evaluated the budding ability and branching ability of standard cut-chrysanthemum cultivars,analyzed the alleles associated with branching traits in standard cut-chrysanthemum using association analysis and SNP markers,and explored the heterosis and major gene effects of branching traits in different F1 populations.This study has screened out standard cut-chrysanthemum cultivars with fewer lateral buds and branches and preliminarily defined the genetic variation mechanism of branching traits,which laid an important foundation for the standard cut-chrysanthemum production and breeding of cultivars with fewer lateral buds and branches.The main conclusions are as follows:1.Evaluation of branching ability and budding ability were carried out in 127 standard cut-chrysanthemum cultivars using principal component analysis and subordinate function value method.Seven branching traits and three budding traits of standard cut-chrysanthemum cultivars were measured,including total number of lateral buds,number of upper primary branches,total number of secondary branches,primary branch diameter,primary branch angle,primary branch length,total number of lateral buds/number of leaf nodes,disbudding times,total disbudding number and total disbudding number/number of leaf nodes.Cultivars were divided into 5 grades from weak to strong branching ability,including 13,26,47,30,and 11 cultivars in turn.And cultivars were also divided into 5 grades from weak to strong budding ability,including 8,12,51,32,and 24 cultivars in turn.According to the result,we had screened standard cut-chrysanthemum cultivars with fewer lateral buds and branches such as ’Sei No Issei’,’QD3-143’,’QD3-144’ and ’QD3-149’that could be used as dominant production cultivars or parent materials for further breeding.2.Eleven branching traits,including plant height,number of leaf nodes,stem diameter,total number of lateral buds,number of upper primary branches,number of lateral flower buds,total number of secondary branches,primary branch diameter,primary branch angle,primary branch length and total number of lateral buds/number of leaf nodes,were measured for 156 standard cut-chrysanthemum cultivars.A set of 416,730 SNPs were used for association analysis of branching traits in two planting environments(E1 and E2).The result indicated that 101 and 82 SNPs were associated with branching traits in El and E2,and phenotypic variation explanation was 8.94%-30.53%and 6.20%-43.40%,respectively.In E2,three markers were detected simultaneously in more than one trait.Moreover,we identified twelve favorable alleles associated with fewer lateral buds and branches trait based on phenotypic effects.3.Inheritance of six branching traits,including total number of lateral buds,number of upper primary branches,primary branch diameter,primary branch angle,primary branch length and total number of lateral buds/number of leaf nodes were examined by major gene plus polygene mixed genetic model analysis for two F1 populations of ’QD3-7’ × ’Sei No Issei’(1)and ’Qinhuaichunxue’X ’ Jinba’(Ⅱ).The results indicated that branching traits of the two combinations had various degrees of mid-parent heterosis,and the phenomenon of over-parent individuals widely existed.Partial maternal inheritance was observed for total number of lateral buds and number of upper primary branches in the two combinations.The mixed inheritance analysis indicated that the major gene effects of standard cut-chrysanthemum branching traits were different in different genetic backgrounds.In cross combination 1,total number of lateral buds/number of leaf nodes was fitting B-3 model with additive effect of two pairs of major gene,and the heritability of major gene was 98.84%.In cross combination Ⅱ,number of upper primary branches was fitting B-1 model with additive-dominant-epistatic effect of two pairs of major gene,and the heritability of major gene was 93.04%.Meanwhile,primary branch length and total number of lateral buds/number of leaf nodes in cross combination Ⅱ were fitting A-1 model with additive-dominant effect of one pair of major gene,and the heritability of major gene was 36.84%and 52.11%,respectively.However,total number of lateral buds was fitting A-1 model with additive-dominant effect of one pair of major gene in two combinations,and the heritability of major gene was 57.39%and 46.73%,respectively.Primary branch diameter and primary branch angle were fitting A-0 model in two combinations with no major gene detected.