Study On The Selection Of Heat-resistant Varieties Of Ornamental Chrysanthemum And Its Heat-resistant Mechanism

In order to select heat-resistant ornamental chrysanthemum varieties and explore its heat-resistant mechanism,to provide a scientific basis for regulating the flowering period and out-of-season cultivation.In this experiment,five ornamental autumn chrysanthemum varieties 'Jinlong Tengyun'(early),'Hongxianju'(middle),'waterfall liubing'(middle),'Qianshou Guanyin'(middle)and 'Guohua Yuqing'(late)were used as materials,the relative conductivity and LT50 were studied at 18 ?(CK),30 ?,35 ?,40 ?,45 ?,50 ?,55 ?,60 ? and 65 ? for 1 hour.Its physiological and biochemical indexes were studied and its heat-resistant ability was evaluated at different temperatures: 18 ?(CK),30 ?,35 ?,40 ?,45 ? and50 ? for 4 hours.Two Autumn Chrysanthemum cultivars,'Jinlong Tengyun' and'Guohua Yuqing',were treated at 18?(CK),30 ? and 40 ? for 0,6,12,24 and 48 H,respectively,the physiological and biochemical indexes,photosynthetic characteristics,chlorophyll fluorescence parameters and Fatty acid desaturase gene expression were studied.The main results were as follows:(1)After high temperature stress,the relative conductivity curves of 5 ornamental chrysanthemum varieties were "S" shape and were in accordance with Logistic equation.Therefore,it was effective to estimate the heat tolerance of 5 varieties by calculating the semi-lethal temperature at high temperature.The semi-lethal temperatures of the five ornamental chrysanthemum varieties were: 'Jinlong Tengyun'(53.6 ?),'Pushui Liubing'(51.0 ?),'Qianshou Guanyin'(49.7 °c),'Hong Xianju'(49.5 °c)and 'Guohua Yuqing'(48.3 °c).The order of heat resistance obtained by the synthesis of osmotic regulators,antioxidant enzymes and other physiological indexes was basically the same as that obtained by high-temperature semi-lethal temperature.Therefore,the 'Jinlong Tengyun'(early)has the strongest heat resistance,followed by the 'Hong Xianju'(middle),the 'Pushui Liubing'(middle)and the 'Qianshou Guanyin'(middle),and the 'Guohua Yuqing'(late)has the worst heat resistance,its heat tolerance was consistent with the florescence of various varieties of autumn chrysanthemum.(2)In response to high temperature stress,the membrane defense system and anti-oxidation defense system of 'Jinlong Tengyun' will play a significant role in reducing the damage caused by high temperature,and 'Guohua Yuqing' will rely mainly on the role of osmotic adjustment system.Under 30 ? and 24 hours before40 ? treatment,the decrease of Pn of 'Jinlong Tengyun' was mainly caused by stomatal factors,which led to stomatal closure and affected the net photosynthetic rate of plants,the decrease of PN was mainly caused by non-stomatal factors,because the continuous high temperature affected the activities of enzymes related to photosynthesis.The decrease of Pn of 'Guohua Yuqing' was caused by stomatal limitation factor in the first 6 hours at 30 ?,and then by non-stomatal factor.(3)Under high temperature stress,the total chlorophyll content of two cultivars of ornamental chrysanthemum decreased significantly,and the change trend of chlorophyll fluorescence basic parameters was basically consistent.At 30 ?,the photosynthetic pathway of two ornamental chrysanthemum varieties was not destroyed.At 40 ?,there was no significant change in 'Jinlong Tengyun',but there was some fluctuation in 'Guohua Yuqing' in the early stage of stress,it shows that the high temperature stress in this stage has a low impact on 'Jinlong Tengyun',while'Guohua Yuqing' is affected to some extent and then returns to normal.This change is due to the decrease of the electron transfer rate(TRO/RC and ETO/RC)and the increase of the thermal dissipation(DIO/RC).With the increase of temperature,the osmotic substances(SS,SP and Pro)were mainly used for respiration to maintain the life activity of plants,and the net photosynthetic rate decreased to negative value gradually.(4)Under high temperature stress,the expression of Cm SAD?Cm FAD2 and Cm FAD7 genes was up-regulated by many factors,such as translation level,modification and the activity of final-generating enzymes,at 40 °c,the expression was higher than that at 30 ?.The up-regulation of gene expression can effectively increase the unsaturation of thylakoid membrane lipids,enhance the stability of thylakoid membrane,and reduce the damage of plant under high temperature stress.This study simulated the high temperature environment of chrysanthemum growing in summer,and set light and heavy stress intensity,short,medium and long-term stress time,the physiological and biochemical characteristics,photosynthetic characteristics,chlorophyll fluorescence parameters and relative gene expression of ornamental autumn chrysanthemum were studied.The heat-resistant varieties were selected to explore their heat-resistant mechanism,it provides scientific basis for growth regulation,heat-resistant breeding,flowering regulation and out-of-season cultivation of ornamental chrysanthemum under high temperature.