Comparison Of The Cold Hardiness Of 15 Ground Cover Chrysanthemum Species

Low temperature is a hazard frequently encountered in the process of plant growth.In order to screen out cold-tolerant varieties of ground cover chrysanthemum and provide plant materials for landscape construction in autumn and winter seasons in Linzhi city,this experiment was conducted under conventional cultivation conditions with 15 ground cover chrysanthemum varieties as experimental materials by observing leaf cold phenotypes,measuring chlorophyll fluorescence,determining photosynthetic parameters,as well as relative conductivity,malondialdehyde（MDA）,peroxide dismutase（SOD）activity,peroxidase（POD）activity and soluble protein were determined,and the comparative study on the cold tolerance of different ground cover chrysanthemums under the standing conditions in Bayi Town,Bayi District,Linzhi City,Tibet was conducted as follows:1.The cold damage phenotypic observations of leaves of 15 ground cover varieties showed that the cold damage indexes of ground cover varieties differed significantly from each other;among them,two ground cover varieties,’Pavement Light Pink’and’Cold Dew Red’,had the strongest cold tolerance,and good single plant 1 and good single plant 2 The cold hardiness of the two varieties of ground cover chrysanthemum’Pavement Pink’and’Cold Dew Red’is the strongest,while the cold hardiness of the good single plant 1 and good single plant 2 is weak.2.The results of photosynthetic and chlorophyll fluorescence parameters of the 15 ground cover varieties showed that transpiration rate（Pr）,stomatal conductance（Gs）and net photosynthetic rate（Pn）of the 15 ground cover varieties decreased significantly with the gradual decrease of temperature,and intercellular CO₂continued to increase;and’Cold dew red’and The initial fluorescence（F0）and maximum fluorescence yield（Fm）increased the least,which indicated that the transpiration rate,net photosynthetic rate and stomatal conductance of’Chilly Red’and’Pavement Pink’varieties decreased the least,and the intercellular CO₂increased the least.The initial fluorescence（F0）and the maximum fluorescence yield（Fm）increased the least,indicating that the two ground cover varieties’Cold Dew Red’and’Pavement Pink’were the most cold-tolerant.3.With the continuation of low temperature stress,the SOD and POD activities and soluble protein contents of the 15 ground cover varieties showed an overall tendency to decrease,while the relative conductivity and MDA contents tended to increase,indicating that the 15 ground cover varieties have the ability to regulate low temperature stress within a certain range.Among them,two varieties of ground cover chrysanthemum,’Cold Dew Red’and’Pavement Light Pink’,showed a significantly lower decreasing trend of all physiological indexes with the decrease of temperature than other varieties.The results showed that the cold damage index,photosynthetic index,chlorophyll fluorescence index and physiological index of the two varieties of ground cover chrysanthemum’Cold Dew Red’and’Pavement Pink’were better than the other varieties in the evaluation of the cold tolerance of 15 ground cover chrysanthemum varieties using the affiliation function method.The results showed that the cold tolerance index,photosynthetic index,chlorophyll fluorescence index and physiological index of the two varieties of ground cover chrysanthemum were better than other varieties of ground cover chrysanthemum.