Evaluation Of High Temperature Resistance Of Spray Cut Chrysanthemum And Mechanism Of Exogenous 1-MCP To Improve High Temperature Resistance

High temperature stress in summer has a serious impact on the production of spray cut chrysanthemum,and the heat resistance of spray cut chrysanthemum has become an important factor for its popularization and application.In this study,12 spray cut chrysanthemum cultivars such as ’DLD’,’KSH’,and ’VNS’were used as the research objects,and high temperature stress experiments were carried out.Varieties with strong heat resistance;heat-resistant varieties,medium heat-resistant varieties and heat-sensitive varieties were selected as test materials to study the differences in photochemical activity and energy distribution of different heat-sensitive spray cut chrysanthemum varieties under high temperature stress;Varieties were used as materials to explore the alleviation effect of exogenous1-methylcyclopropene(1-MCP)on high temperature stress.The main results are as follows:1.The cell damage rate of the leaves of 12 spray cut chrysanthemum varieties showed an "S"-shaped curve with the increase of temperature.Under high temperature stress,relative electrical conductivity(REC),malondialdehyde(MDA)content,peroxidase(POD)activity,soluble sugar(SS)content and proline(Pro)content increased with the intensification of high temperature,while photosynthetic pigment content decreased.2.Through cluster analysis,the 12 spray cut chrysanthemum varieties are divided into 4 groups,the heat-resistant varieties include ’WNS’ and ’CSH’;the more heat-resistant varieties include ’KD’,’RB’,’ZJL’,’BJ’,’YY’ and ’LJL’;less heat-labile varieties include ’JMC’,’NXC’ and ’DLD’;heat-labile varieties include ’KSH’.3.Under high temperature stress,the net photosynthetic rate(Pn)of 12 spray cut chrysanthemum cultivars showed a decreasing trend with the increase of temperature.High temperature(≦40℃)can inhibit the activity of some Oxygen-evolving complex(OEC)and photosystem II(Photosystem II,PSII)reaction centers,reduce the energy connectivity between PSII photosynthetic units and the overall photosynthetic activity of PSII,has no significant effect on the energy dissipation and the electron transport chain between the two photosystems.High temperature of 45°C severely damaged PSII and PSI activities.The heat-sensitive plant ’KSH’ basically lost its photosynthetic activity,while the heat-resistant plant ’WNS’ suffered the least impact on the photosynthetic ability.4.Under high temperature stress,1-MCP significantly improved the maximum photochemical efficiency of Pn and PSII(Fv/Fm),the relative activity of PSI(△I/Io),and the photosynthetic performance index(PItotal)and other indicators,the light energy absorption(ABS/RC)and thermal energy dissipation(DIo/RC)of the unit reaction center decreased.The expression levels of photosynthesis-related genes(Cmrbc L,Cmpsb A,Cmpsa B and Cmpsa A)were higher in the spray cut chrysanthemum treated with 1-MCP under high temperature stress.Exogenous1-MCP can effectively protect the OEC of spray cut chrysanthemum,promote smooth electron transfer,and help maintain high photosynthetic capacity.In this study,an evaluation system for heat resistance of spray cut chrysanthemum was established,and the tested cultivars were divided into four groups.’WNS’ and ’KSH’ had the strongest heat resistance;high temperature seriously damaged PSII and PSI activities,and 1-MCP could alleviate the heat resistance.The damage caused by high temperature stress maintains high photochemical activity.The results have certain guiding significance for the summer production of spray cut chrysanthemum.