| Dahlia pinnata Cav.is a perennial bulbous flower of the family Dahlia.It has a wide variety of flowers,a variety of colors,and a beautiful flower posture.It is widely introduced and cultivated as one of the world's famous flowers.However,in the southern provinces of China,the high temperature conditions in the summer have seriously affected the growth and ornamental value of Dahlia.Therefore,the research on the cultivation technology of mitigation of high temperature stress on Dahlia has important theoretical value and practical significance for the application of Dali Garden.In our previous studies,our laboratory has confirmed that salicylic acid?SA?spraying on leaves has a certain regulatory effect on the heat resistance of Dahlia,and its suitable concentration is 0.5 mmol·L-1.Based on previous reports and preliminary experiments,the paper further selected plant growth retarders such as paclobutrazol and uniconazole,osmotic regulators such as betaine and proline,and brassinosteroid?BR?as exogenous chemicals.The potted seedlings of dahlia?variety'single-petal yellow'?were the main test materials.The application of clear water?HT group?and leaf application of 0.5 mmol·L-1SA?foliar spray group?was used as a control group.The effects of different exogenous substances on the growth and physiological indexes of dahlia under high temperature stress were as follows.1.Explore the effect of root-applied 0.1-2.0 mmol·L-11 SA of the growth and physiological index in dahlia under high temperature stress.The results showed that were significant differences in the regulation effect of different concentration SA on the heat resistance of Dahlia.Among them,the treatment with 1.0 mmol·L-1SA had the best effect,but its regulation was not as significant as that of the leaf application SA group.Compared with the control group HT,the leaves of heat damage index and wilting index decreased,chlorophyll and soluble protein content increased,activity of protective enzymes SOD,POD and CAT increased,MDA and proline content decreased,and all reached the level of significant difference?p<0.05?under high temperature stress.Compared with before high temperature stress,the MDA content,soluble protein content and proline content of Dahlia rose first and then decreased,the activity of SOD and POD showed an upward trend,and the chlorophyll content and CAT activity showed a trend of decreasing first and then increasing which after 2 days of high temperature stress and 1 day of normal temperature recovery.2.The effects of paclobutrazol(PP333)on the growth and physiological indexes of dahlia were studied by two methods:leaf application and root application.The results showed that there were significant differences in the regulation effect of PP333at different concentrations on the heat resistance of Dahlia.The control effect was 100-200mg·L-1leaf application and 100 mg·L-1root application were better within the range of100-400 mg·L-1of leaf application and 50-125 mg·L-1of root application,and the effect of leaf application was better than root application,similar to the SA application group.Compared with the water control group HT,the leaf heat damage index and wilting index decreased under the high temperature stress after application of appropriate concentration of PP333,and the physiological and biochemical indexes were similar to the root application SA group,but the chlorophyll content trend of the leaf application PP333group has slightly different.3.The effects of uniconazole?S-3307?on the growth and physiological indexes of dahlia were studied by the two methods:leaf application and root application.The results showed that there were significant differences in the regulation effect of S-3307 at different concentrations on the heat resistance of Dahlia.In the concentration range of10-40 mg·L-1leaf application and 10-40 mg·L-11 root application,the effect of 20-30mg·L-1was better both of leaf application and root application,and the effect of leaf application was better than root application,similar to the SA application group.Compared with the control group HT,the leaf heat damage index and wilting index decreased under the high temperature stress after the appropriate concentration of S-3307,and the trend of physiological and biochemical indexes were similar to those of the root SA group.4.The effects of exogenous betaine and proline on the growth and physiological indexes of dahlia were investigated by leaf application method.The results showed that the regulation effects of different concentrations of betaine and proline on the heat resistance of dahlia were different.In the concentration range of 0.2-2.0 mmol·L-1betaine and 1.0-6.0 mmol·L-1proline of foliar application,the effect of betaine 0.5mmol·L-1and proline 2.0 mmol·L-1were better,and exogenous proline was better than betaine,but it was not as effective as foliar application of SA.Compared with the control group HT,the leaf heat damage index and wilting index decreased under the high temperature stress after suitable concentration of proline,and the physiological and biochemical indexes were similar to that of the root SA group.5.Explore the effect of foliar-spray 0.1-2.0 mmol·L-11 exogenous brassinolide?BR?of the growth and physiological index in dahlia under high temperature stress.The results showed that different concentrations of BR have different heat resistance on dahlias.Among them,the concentration of 1.0-2.0 mmol·L-1was better,but it was not as effective as the application of SA.Compared with the control group HT,the leaf heat injury index and wilting index decreased under the high temperature stress after suitable concentrations of BR.The trend of physiological and biochemical indexes were similar to that of the root SA group.6.Based on the above experimental results and the characteristics of different types of exogenous regulatory substances,we further selected three exogenous chemicals:0.5mmol·L-1SA,100 mg·L-1PP333,and 25 mg·L-1S-3307.We used 5 dahlia species cultivated in open field as test materials.Dahlia plants in blooming stage were treated with foliar spraying under natural high temperature stress conditions in summer.The results showed that three exogenous substances could significantly improve the heat resistance of dahlias in open field.Compared with the control group HT,the heat damage index and wilting index of leaves under high temperature stress decreased;the content of chlorophyll and soluble protein increased,and MDA and proline contents increased.The activity of protective enzymes such as SOD,POD and CAT increased,the net photosynthetic rate?Pn?,stomatal conductance?Gs?and transpiration rate?Tr?increased,while the intercellular carbon dioxide concentration?Ci?decreased.In this study,we systematically investigated and analyzed the effects of various exogenous chemical substances and different application methods on the growth and physiological indexes of dahlia under high temperature stress.The results provide a new experimental basis for elucidating the physiological mechanism of response to high temperature stress in Dahlia.At the same time,it also provides a theoretical basis for the construction of Dahlia heat-resistance control technology. |
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