Evaluation And Early Warning Of Cucumber Chilling Injury In Solar Greenhouse

Cucumber（Cucumis sativus L.）is one of the important vegetable crops in facility horticultural production in my country.There are long-term low temperature and short-term critical low temperature in the cultivation of cucumber in winter and spring in northern my country.Therefore,timely early warning and prevention of low temperature and chilling injury of cucumber in facility production,improving cucumber resistance to low temperature,and alleviating low temperature injury in facility cultivation are of great significance to the practice of facility cucumber production.In this study,focusing on the early warning of low temperature and cold damage of cucumber in facilities,the related research on the characteristics of low temperature and cold damage and its cold tolerance of cucumber was carried out,and the critical point of low temperature stress damage of cucumber was identified.In order to provide a basis for the establishment of a non-destructive monitoring technology system for the occurrence of low-temperature chilling injury in cucumbers.The main results of this research are as follows:1.Evaluation of low temperature damage of cucumber in solar greenhouse（1）Effects of low temperature stress on the growth and development of cucumber seedlingsUnder low temperature stress,the growth and development of cucumber seedlings was inhibited to a certain extent,especially when the temperature deficit≥792℃,the growth of cucumber was significantly inhibited,and the morphological indicators such as plant height and leaf area were significantly lower than those of the control group;When the temperature reached 1056℃,the true leaves and leaves of some cucumber seedlings showed obvious irreversible damage;when 1320℃<temperature deficit≤1584℃,the roots of cucumber seedlings appeared necrotic.After 7 days of rewarming,the dry weight and fresh weight of the cucumber seedlings treated at low temperature were still lower than those of the control group;when the temperature deficit was≥792℃,the plant height,stem diameter,root length and number of lateral roots of cucumber seedlings were significantly reduced.Metrics could not be restored to control levels.At the same time,for the cucumber seedlings transplanted into the greenhouse,the growth and development speed of the cucumber plants treated at low temperature was slow,and the plant height reached a level similar to that of the control group after 52 days of transplanting,and the flowering time and fruit setting time were later than those of the control group.The number of flowerings,fruit set and fruit in the control group were also significantly lower than those in the control group.（2）Effects of low temperature stress on physiological characteristics of Cucumber SeedlingsUnder low temperature stress,the relative conductivity of cucumber seedling leaves increased significantly;but after rewarming for 7 days,the relative conductivity of all treatments had no significant difference compared with the control group,and had no significant correlation with temperature deficiency.It can be seen that the change of relative conductivity is not suitable for measuring the degree of low temperature stress.Under low temperature stress,O₂·^-accumulation in cucumber seedling leaves was significant.The activities of SOD and cat increased significantly,and the activity of pod increased sharply in the later stage.After warming for 7 days,the activities of SOD and cat recovered smoothly,while pod began to play a great role in this period.The chlorophyll content of cucumber seedlings decreased significantly under low temperature stress.After rewarming for 7 days,the chlorophyll content of cucumber leaves with temperature deficit≤528℃could return to the normal level;when the temperature deficit was≥792℃,the chlorophyll content of cucumber leaves was always lower than the normal level.At the same time,the net photosynthetic rate and transpiration rate of cucumber leaves decreased significantly under low temperature stress.After 7 days of rewarming,the net photosynthetic rate and transpiration rate of each low temperature treatment still failed to return to the normal level.During low temperature stress,root length,Fv/Fm value,SOD enzyme activity and temperature deficit of cucumber seedlings were significantly negatively correlated;Root shoot ratio,chlorophyll content and temperature deficit were significantly negatively correlated;There was a significant positive correlation between MDA content,cat enzyme activity and temperature deficiency.During the rewarming recovery period,the correlation between plant height and Fv/Fm value and temperature deficit was very significant,and the activity of SOD enzyme was significantly negatively correlated with temperature deficit,indicating that the Fv/Fm value of chlorophyll fluorescence can be used to evaluate the degree of Cucumber under low temperature stress.2.Research on early warning technology of low temperature injury of cucumber in solar greenhouseInfrared thermal imaging technology was used to monitor the changes of cucumber leaf temperature under low temperature stress.The results showed that low temperature stress caused the leaf temperature of cucumber to decrease,and the leaf temperature of cucumber seedlings treated with low temperature was about 5℃lower than that of the normal control when there was light.Chlorophyll fluorescence imager was used to study the changes of cucumber leaf fluorescence parameters under low temperature stress and the relationship between the recovery level and low temperature chilling injury.The results showed that under normal growth conditions,the chlorophyll fluorescence Fv/Fm value of cucumber seedling leaves was around0.7～0.8,and with the extension of time,the Fv/Fm value did not change significantly;but when cucumber seedlings were under low temperature stress,the Fv/Fm value continued to decrease,indicating that this parameter can be used to measure the degree of low temperature stress in cucumber seedlings.