Evaluation And Genetic Analysis For Flower Opening Angles Of Spray Cut Chrysanthemum At Full-Bloom Stage

Chrysanthemum（Chrysanthemum morifolium Ramat.）originates from China with a long cultivation history and abundant germplasm resources,which is one of the ten famous traditional flowers in China and of the four leading cut-flowers in the world.It is an important prerequisite for development and utilization of high-quality resources and breeding new cultivars to evaluate the traits of variety resources and clear their genetic characteristics.In this study,the flower opening angle was quantified by image processing method,and we investigated the genetic diversity of flower opening angle of spray cut chrysanthemums natural population at full-bloom stage.Additionally,we explored the heterosis and the major gene effects of the flower opening angle in two F₁crosses.According to the size of the flower opening angle,the petal firmness and the petal texture,some superior progeny lines were selected from F₁populations.The findings of this research has important theoretical and practical significance for the development and utilization of the variety resources as well as the breeding of spray cut chrysanthemum.The main results are as follows:1.Based on 203 representative spray cut chrysanthemum varieties,the flower opening angle of spray cut chrysanthemum was quantitatively measured by image processing at full-bloom stage and 11 flower opening angle related traits such as leaf petiole angle and inflorescence diameter were investigated.The results indicated that there was abundant variation in flower opening angle of spray cut chrysanthemum,and the coefficient of variation was 22.87%.‘Nannong Xiufengche’has the smallest opening angle（62.12°）,while‘Q1-79’has the largest opening angle（218.29°）.The flower opening angle was significantly negatively correlated with the corolla tube length（-0.46）,the corolla tube merged degree（-0.45）and ray floret length（-0.21）,whereas it was significantly positively correlated with the number of ray florets whorls（0.39）,ray floret width（0.35）and center disc flower diameter（0.31）.Principal component analysis integrated the investigated 12 traits into five principal component factors,including ray floral related traits,inflorescence size and leaf angle etc,and the cumulative contribution rate was 89.07%.According to phenotypic clustering,203 spray cut chrysanthemum varieties were divided into 4 groups,and the flower opening angle of different groups were significantly different.2.Two hybrid combinations of‘Q1-52’בDublin’（crossⅠ）and‘Q1-24’בDublin’（crossⅡ）were made with large flower opening angle of spray cut chrysanthemum as female parent and small flower opening angle as male parent.The variation coefficient of flower opening angle in two F₁populations was 16.23%and 16.92%,respectively,and other traits were between 10.66%and 119.44%.There were positive and negative heterosis in 12 traits for two crosses.The heterosis value of mid-parent（H_m）of flower opening angle showed a significant difference degree at 0.01 level and it was14.95 in crossⅠ,while-3.64 in crossⅡ.The mixed genetic analysis suggested that the optimal genetic models of the same trait were different in different crosses.Flower opening angle fitted A-0 model in crossⅠand no major gene was detected,while it fitted B-1 model in crossⅡwith additive-dominant-epitasis effect,the heritability of major gene was96.32%.3.The relationship among flower opening angle,vase life and petal firmness and texture was investigated in F₁progeny derived from two spray cut chrysanthemum cross combinations‘Q1-52’בDublin’and‘Q1-24’בDublin’.It was found that there was no significant correlation among flower opening angle,vase life and petal firmness and texture,the correlation coefficients were-0.03,0.11 and-0.02,respectively.According to the size of flower opening angle,petal firmness and petal texture,we preliminary screened the F₁progeny,and 32superior lines were obtained.