| Chrysanthemum（Chrysanthemum morifolium）is a traditional and famous flower in China.It plays an important role in landscaping and urban beautification,and has high ornamental and economic value.With the improvement of people’s life,more and more attention has been paid to spiritual consumption and people have a deeper understanding and appreciation of flowers,so it is particularly important to create new chrysanthemum varieties to meet market demand.Hybridization is the most direct and effective method in chrysanthemum breeding.Understanding the genetic and evolutionary mechanism of main ornamental traits is of great significance for the cultivation of new varieties of chrysanthemum.Artificial selection can accumulate genetic variation and makes an impact in crop genetic improvement.Although many reports are documented regarding the genetics of chrysanthemum,the mechanism of chrysanthemum in response to artificial selection remains unclear yet.Plant height is an imporant trait for cut chrysanthemum.In the current study,the inheritance of plant height in reciprocal F1 populations were investigated;Artificial directional selection was used to create F1 and F2 lines of different plant height（high,low and random group）,and the genetic variation and synergistic evolutionary mechanism of plant height in response to artificial selection were explored;and finally the genetic structure of selected population were examined using SSR markers.Results of this study will preliminarily clarify the genetic mechanism of chrysanthemum’response to artificial selection for plant height,and enrich the theory of chrysanthemum hybrid breeding.The main results include:1.Seven traits of cut chrysanthemum F1 population,such as plant height,internode length,internode number,leaf length,leaf width,deepest depth of notch and number of notches,were found to be superparent in both reciprocal crosses.The variation coefficients of internode length and deepest notch depth varied greatly among different traits.The variation coefficients of internode length and deepest notch depth in orthogonal cross were 35.28%and 32.71%respectively,and those of internode length and deepest notch depth in backcross were 31.24%and 31.58%,respectively.The coefficient of variation of internode number was the smallest.The coefficients of variation of orthogonal cross and backcross were 17.30%and 13.37%,respectively.The coefficients of variation of the other four traits were in the middle.There were significant differences in the phenotypic values of the progenies of reciprocal crosses with leaf width,deepest notch depth,plant height,internode length,and internode number.There might be maternal genetic effects.There was no significant difference between the progenies of orthogonal cross and backcross with leaf length and number of notches.In orthogonal cross,the leaf length conformed to B-1 model,the deepest depth of notch and the number of notches conformed to A-1 model,and the heritability of major genes were 96.58%,56.03%and 56.68%respectively;in backcross,plant height conformed to B-1 model,the deepest depth of notch and the length of internode conformed to B-3 model,and the number of notches conformed to B-4 model,with the heritability of major genes 97.17%,97.85%,97.34%,and 89.23%respectively.The number of intervals and other traits fitted A-0 model with no major gene identified.2.The cut flowers chrysanthemums‘Q1-81’and‘Q2-1’were used as materials to created F1 and F2 lines with contrasting plant height（high,low,and random group）by the group selection method.We analyzcd genetic response of plant height and other six traits in two-progeny population.The results showed that the average plant height increased from 91.82 cm in F1 generation to 101.12 cm in F2 generation for high group,and decreased from 68.91 cm in F1 generation to 47.79 cm in F2 generation for low group.After two generations of artificial directional selection,the height of high group tends to develop higher,and the height of low group decreases gradually.The phenotypic analysis showed that for high group the performance of the investigated trais of F2 generation was higher than that of F1 generation after two generations of artificial selection for the other five traits,except internode length;for low group,the average performance of F2 generation was lower than that of F1 generation,except neck diameter.Pearson correlation analysis suggested that there was no correlation between plant height and other traits for high group,but plant height was positively correlated with internode number in low and random groups.Results from regression analysis showed that there were certain correlations between plant height and the other five traits in the artificial groups of F1 and F2 progenies,among which plant height had the highest correlation with internode number,internode length,and flower neck diameter,indicating that three traits may co-evoluted with plant height.3.The genetic diversity of 64 F1 and F2 progenies with different plant height by artificial directional selection in cut chrysanthemum‘Q1-81’and‘Q2-1’were analyzed by SSR markers.The results showed that 54 clear bands were obtained from 11 pairs of primers,of which 51 were polymorphic,and the percentage of polymorphic loci was 96%.Cluster analysis showed that there were 34 plants（52%）in the first and female parent together with‘Q1-81’,and 30 plants（48%）in the second and male parent‘Q2-1’.The results of phenotypic traits showed that after two generations of artificial selection,the high group,the low group and the random group in the two generations were not clustered into one group.The variation range of genetic similarity coefficient was 0.14-1.00,and the average genetic similarity coefficient was 0.57 for the offspring of‘Q1-81’and‘Q2-1’.The genetic similarity coefficient between hybrid progeny and maternal parent ranged from 0.44 to 0.84 and between 0.40 and 0.81.From F1 to F2 generation,we can see that the genetic basis of hybrid offspring is narrower or more homogeneous. |
PDF Full Text Request