Creation Of New Drought-Tolerant And Creeping Germplasms By Crossing Chrysanthemum Japonese And Chrysanthemum Indicum

Chrysanthemum（Chrysanthemum morifolium Ramat.）is a perennial herb of the genus Compositae.It is one of the top ten traditional famous flowers in China and one of the four major cut flowers in the world,possessing high ornamental and economic value.Drought is a major abiotic stress factor that negatively affects the growth,development,yield and quality of chrysanthemum.Most chrysanthemum cultivars have poor drought tolerance,while the wild relatives of chrysanthemum have formed strong drought tolerance through evolution and adaptation in the long-term natural environment.Discovery and effectively utilization of the excellent drought resistance genes of these wild relatives will open up a new way to improve chrysanthemum’s drought tolerance.In addition,with the acceleration of urbanization and the increasing demand for landscaping,creating creeping type chrysanthemum varieties has important practical significance.In this study,wild relatives of C.japonese were used as female parent,C.indicum（Shanxi）and C.indicum（Japan）were used as male parents to produce two sets of interspecific F₁populations,and genetic variation of the main flower and leaf traits and drought tolerance were investigated and finaly some elite hybrids with strong drought tolerance and creeping type were screened for future breeding use.The main results are as follows:1.The main morphological traits segregated widely and heterosis is common in both C.japonese×C.indicum F₁populations,and a significant mid-parent heterosis were observed for the investigated traits.In C.japonese×C.indicum（Shanxi）F₁population,the coefficient of variation ranged in 13.18%～43.79%,the genetic trend of the lowest first-level crack depth is generally increasing,and a dominant genetic effect was observed for leaf length,leaf width,terminal lobe length and leaf area.In C.Japonese×C.indicum（Japan）F₁population,the coefficient of variation varied in a range of 13.36%～39.21%,and the heterosis showed an upward trend.Correlation analysis revealed a largest correlation coefficient between leaf area and leaf width across of the two F₁populations,with 0.95 and0.96,respectively.Principal component analysis extracted two principal components in C.japonese×C.indicum（Shanxi）F₁population and three principal components in C.japonese×C.indicum（Japan）F₁population,with the cumulative contribution rate of73.53%and 78.48%,respectively.The first principal component is determined by leaf length,leaf width and leaf area,and the second principal component by flower diameter,ray floret length and ray floret width,and the third principal component by number of sawtoot and lowest first-level crack depth.The findings preliminarily clarified the genetic variation of the main morphological traits in C.japonese×C.indicum F₁populations,and provided a theoretical basis for the future innovative utilization of chrysanthemum related species.2.The drought tolerance of C.japonese,C.indicum（Shanxi）,C.indicum（Japan）and the two F₁populations were investigated.The results showed that there was no significant difference in the two drought test results.The morphological indicators under drought condition showed significant changes compared with the control（P<0.01）.A significant difference were observed for drought tolerance-related traits across the different gentypes,and the underground fresh weight and plant height stress index showed an extremely large and low level of variation,respectively.Correlation analysis identified a significant correlation with different degrees between most drought tolerance indicators across the two two F₁populations.Two principal components were extracted using principal component analysis,with the cumulative contribution rates reaching 64.55%and 67.32%,respectively,in C.japonese×C.indicum（Shanxi）and C.japonese×C.indicum（Japan）F₁populations.Combined with the analysis of the average membership function value,the two F₁generations are divided into five types,i.e.,high drought tolerance,drought tolerance,low drought tolerance,no drought tolerance and drought sensitive.The C.Japonese×C.indicum（Shanxi）F₁population contains 4,21,38,35,and 28 hybrid lines,and C.japonese×C.indicum（Japan）F₁population contains 3,12,35,14 and 8 strains of the five drought tolerance types,respectively.The hybrid lines with high drought tolerance can be potentially used as important parent materials for genetic improvement of chrysanthemum’s drought tolerance.3.A total of 31 and 8 hybrid lines of creeping type were identified from C.japonese×C.indicum（Shanxi）,and C.japonese×C.indicum（Japan）F₁populations,with the proportions of 15.66%and 11.43%,respectively.A large magnitude of coefficient of variation were observed for plant type-related traits,i.e.,plant height,crown width and primary branches,with primary branches showing the largest coefficient of variation47.69%and 69.32%across both F₁populations,respectively.Correlation analysis suggested that plant type correlated significantly and negatively with plant height（P<0.01）,significantly and positively with crown width,but no correlation with primary branches,and crown width has a strongest correlation with primary branches.Combined with the drought tolerance analysis,four creeping hybrids,i.e.,YS249,YS9 and YR32 with strong drought tolerance（Average membership function value>0.45）were screened,which provide important parent materials for the development of new varieties of creeping-type ground-cover chrysanthemums with strong drought tolerance.