Effects Of Exogenous ALA And DA-6 On The Appearance Quality Of Chrysanthemum Under Low Temperature And Low Light During Flowering Period And Its Evaluatio

Low temperature and weak light are the main environmental factor limiting the growth and quality of chrysanthemum in facilities.However,the influence mechanism of ALA and DA-6 on the appearance quality of chrysanthemum under low temperature and weak light at flowering stage and the evaluation model of appearance quality have not been reported at home and abroad.In this study,the environmental control experiment was carried out in Venlo Greenhouse of Nanjing University of Information Science and Technology from September2020 to January 2022.The L₁₆（2¹×4²）orthogonal experiment was designed with chrysanthemum’Hongmian’as the test material.Four levels of low temperature design（13℃（day temperature）/3℃（night temperature）,16℃/6℃,19℃/9℃and 22℃/12℃）,two levels of weak light design(200μmol·m^-2 s^-1 and 400μmol·m^-2 s^-1),and the duration was set at 3d,6d,9d and 12d.28℃/18℃,800μmol·m^-2 s^-1 as control（CK）;Moderate low temperature and weak light(19℃（day temperature）/9℃（night temperature）,light intensity 400μmol·m^-2·s^-1,duration6 day)and severe low temperature and weak light(13℃（day temperature）/3℃（night temperature）,light intensity 200μmol·m^-2·s^-1,duration 12 day)were selected and sprayed with5-aminolevulinic acid（ALA）and N,N-diethylaminoethanol acetate（DA-6）at different concentrations to determine photosynthetic characteristics and senescence characteristics of chrysanthemum leaves and appearance quality parameters,etc.,to determine the influence mechanism of ALA and DA-6 on chrysanthemum’Hongmian’quality under low temperature and weak light stress at flowering stage.Fuzzy comprehensive evaluation was used.In order to provide a theoretical reference for the prevention of meteorological disasters,a prediction model of ALA and DA-6 in chrysanthemums under low temperature and weak light at flowering stage was established.The main conclusions of this study are as follows:（1）With the decrease of temperature and light and the extension of stress days,Stomatal conductance（G_s）,stomatal limit value（L_s）,transpiration rate（T_r）,water utilization rate（WUE）,maximum net photosynthetic rate(P_n-max),light saturation point（LSP）,PSII The maximum quantum efficiency（F_v/F_m）,antenna conversion efficiency（F_v′/F_m′）,photochemical quenching coefficient（q P）and actual photochemical efficiency of PSII(Φ_PSII)decreased,while the intercellular carbon dioxide concentration（C_i）,light compensation point（LCP）,dark respiration rate（R_d）and non-photochemical quenching coefficient（NPQ）increased continuously.Under moderate and severe low temperature and weak light conditions,spraying ALA showed that the maximum values of G_S、P_n-max、F_v/F_m increased by 88.24%,64.29%,16.67%,and 240%,116.16%,64.29%,respectively,compared to moderate and severe stress treatments,the minimum values of C_i、R_d、NPQ decreased by 13.15%,36.63%,20.09%,and19.19%,29.80%,27.39%,respectively.Under this stress,spraying DA-6 showed that the maximum values of G_S、P_n-max、F_v/F_m increased by 70.59%,62.82%,19.44%,and 260%,112.60%,47.62%,respectively,compared to moderate and severe stress treatments,the minimum values of C_i、R_d、NPQ decreased by 11.50%,37.62%,15.24%,and 17.17%,24.75%,26.90%,respectively.（2）With the decrease of temperature and the extension of stress days,the contents of chlorophyll a（Chl_a）,chlorophyll b（Chl_b）and carotenoid（Car）decreased,the activity of superoxide dismutase（SOD）and the content of soluble protein（SP）increased,the activities of peroxidase（POD）and catalase（CAT）and the content of malondialdehyde（MDA）increased first and then decreased.With the decrease of light,the activity of SOD、POD、CAT and the content of Car、MDA、SP increased.Under moderate and severe low temperature and weak light conditions,spraying ALA showed that the maximum values of Chl_a、Chl_b、SOD increased by 33.81%,16.30%,18.06%,and 57.55%,34.90%,50.46%,respectively,compared to moderate and severe stress treatments,the minimum values of MDA decreased by 22.59%and 39.83%,respectively,compared to moderate and severe stress treatments.Under this stress,spraying DA-6 revealed that the maximum values of Chl_a、Chl_b、SOD increased by 27.35%,9.05%,15.03%,and 55.26%,13.95%,55.55%,respectively,compared to moderate and severe stress treatments,the minimum values of MDA decreased by 23.27%and 50.84%,respectively,compared to moderate and severe stress treatments.（3）As the temperature decreases and the stress days extend,the flower diameter and branch length decrease,while the abnormal flower rate and anthocyanins increase.As the light decreases,the flower diameter and branch length increase,while the rate of abnormal flowers and anthocyanins show a downward trend.Under moderate and severe low temperature and weak light conditions,spraying ALA showed that the maximum values of the flower diameter,branch length,anthocyanin content increased by 14.67%,32.69%,36.44%,and 27.56%,11.21%,71.46%,respectively,compared to medium and heavy stress treatments.The minimum abnormal flower rate decreased by 41.07%and 40.89%,respectively,compared to moderate and severe stress treatments.Under this stress,spraying DA-6 showed that the maximum values of flower diameter,branch length,anthocyanins increased by 10.04%,18.15%,21.52%,and23.11%,6.90%,86.86%,respectively,compared to moderate and severe stress treatments,the minimum values of abnormal flower rate decreased by 31.89%and 37.50%,respectively,compared to moderate and severe stress treatments.The abnormal flower rate is most affected by F_v/F_m,the flower diameter is most affected by WUE,the flower branch length is most affected by AQE,and the correlation between anthocyanin content and P_n-max is highest.（4）Three models were constructed by multivariate nonlinear regression in the temperature（T）3～12℃,light（P）200～400μmol·m^-2·s^-1,duration（D）3～12d,ALA concentration（C₁）0～200mg/L and DA-6 concentration（C₂）0～80mg/L.Model 1:The comprehensive appearance quality score of chrysanthemum,temperature,light and duration;Model 2:The comprehensive appearance quality score of chrysanthemum,temperature,light,duration and ALA concentration;Model 3:The comprehensive appearance quality score of chrysanthemum,temperature,light,duration,DA-6 concentration.The determination coefficients R² of the simulated values and the measured values of the three models were 0.93,0.92 and 0.83,respectively.The root mean square errors（RMSE）of the simulation of the comprehensive appearance evaluation value of chrysanthemum were 0.03,0.06 and 0.05,and the relative errors（RE）were 6.48%,9.77%and 7.98%,respectively,indicating that the simulation accuracy of the model was high.It has strong practicability and lays a foundation for quantitative evaluation of the effect of low temperature and weak light weather events on the appearance quality of chrysanthemum.