Effect Of Different Rootstocks On Tolerance Of Grafted Cucumber To Low Temperature, Weak Light And Salt Stress

Cucumber ( Cucumis sativus L.) is one of the warm season fruit vegetables, which has a large greenhouse cultivation area in north China. Low temperature and weak light are main factors to restrict the high yield and high efficiency of cucumber. Meanwhile, the soil salinization has been more and more serious year by year. The soil salinization inhibited the cucumber growth and development and decreased the yield and quality. To conquer the chilling injury and soil salinization are the major problems to solve in cucumber production in greenhouse urgently. Using low temperature and weak light, salt tolerance rootstock to graft cucumber is an efficient path to improve the cold resistance of cucumber and the yield.This experiment had collected 15 lines of cucumber rootstock and identified their low temperatures, weak light and salt tolerance. On this basis, we selected several different tolerance rootstocks to graft cucumber, and researched the physiological responses of grafting cucumber under the low temperature (5℃) , weak light (100μmol·m^-2·s^-1) and NaCl (100 mmol·L^-1) conditions, in order to explore the difference mechanism of different rootstocks grafted cucumber to futher enrich vegetable grafting theory; and provided theoretical basis for selecting the suitable rootstocks, reducing the sress obstacle in greenhouse and promoting the quality and yield of cucumber. The results are as follows:1. The rootstock seedlings were treated at low temperature, weak light and researched the changes of seedlings growth and physiological indexes. Through establish the value of subordinate function and analysis the principal component regression, we obtained the regression equation: y=1.976 x₁(the function date of chilling injury index)+1.958 x₂(the function date of leaf area relative increasing)+1.943 x₃(the function date of leaf electrolyte leakage rate)+0.176. The y value determines the low temperature, weak light tolerance of different rootstocks. The results showed that'Figleaf gourd','Tielizhen'are highest tolerance to low temperature, weak light stress, follows by'Shintosa','Kurotane','Qingyanrootstock NO.1';'Shintosa-improved NO.1','Tetukabuto','Shiasuto'and'Huitailang','Eibulu'are medium low temperature, weak light tolerance;'Huofenghuang','Shielba'are low temperature, weak light higher sensitive rootstocks;'gulipu','tokiwapa','kilameki'are low temperature, weak light highest sensitive rootstocks. 2. The rootstock seedlings were treated at NaCl and researched the changes of seedlings growth and physiological indexes. Through establish the value of subordinate function and analysis the principal component regression, we obtained the regression equation: y=1.853 x₁(the function date of salt injury index)+2.116 x₂(the function date of height relative increasing)+1.907 x₃(the function date of leaf area relative increasing)+0.076. The y value determines the salt tolerance of different rootstocks. The results showed that'Figleaf gourd','Kurotane','Tielizhen','Shintosa','Qingyanrootstock NO.1'are highest resistance to salt stress;'Tetukabuto','Shintosa-improved NO.1'are higher resistance to salt stress;'Shiasuto','Eibulu','tokiwapa','gulipu','kilameki'are are higher sensitive to salt stress;'Huofenghuang','Shielba'are highest sensitive to salt stress.3.'Kilameki','Huofenghuang','Tielizhen'and'Figleaf gourd'which have different low temperature, weak light tolerance were selected as rootstocks to graft'Xintaimici', and the own-rooted seedlings being used as the control. To investigate the differences in growth and physiological responses of grafting cucumber, which were treated at 5℃,light intensity 100 umol·m^-2·s^-1. The results showed that grafting seedlings have significantly lower inhibition in plant height, leaf area and dry weight than the self-rooted seedlings. The electrolyte leakage and MDA content of rootstock-grafting seedlings are significantly lower than self-rooted seedling. The proline content, Pn and activities of POD, SOD, CAT and APX are significantly higher than self-rooted seedlings.4. The change of relative mRNA expression of the Cu/Zn-SOD, Mn-SOD and CAT genes coincided with the change of activities of Cu/Zn-SOD, Mn-SOD and CAT. The relative expression of genes of grafting seedlings are higher than self-rooted seedlings', and the grafting seedlings of'Figleaf gourd'and'Tielizhen'has a higher expression level. The change of relative mRNA expression of APX gene do not coincide with APX activity. It means that there are some other factors involved in the regulation of APX activity. However, the relative mRNA expression of APX gene in grafting seedlings is always higher than in self-rooted seedlings.5.'Shielba','Shintosa','Tielizhen'and'Figleaf gourd'which have different resistibility were selected as rootstocks to graft'Xintaimici', and the own-rooted seedlings being used as the control; which were treated under 100 mmol·L^-1 NaCl. In order to investigate the differences in growth and physiological responses of grafted cucumber. The results showed that grafting seedlings have significantly lower inhibition in plant height, leaf area and dry weight than the self-rooted seedlings under the stress of NaCl. The electrolyte leakage and MDA content of rootstock-grafting seedlings are significantly lower than self-rooted seedling, and seedlings grafted on'Figleaf gourd'showed the lowest, followed by'Tielizhen','Shintosa'and'Shielba'; The proline and soluble sugar content and activities of POD, SOD, CAT and APX are significantly higher than self-rooted seedlings. The activities of POD, SOD, CAT, APX are highest in'Figleaf gourd', and lowest in'Shielba', but there is no significant difference between'Tielizhen'and'Shintosa'; The Na⁺ concentration in leaves of grafted seedlings ranked as'Figleaf gourd'<'Tielizhen'<'Shintosa'<'Shielba'+ content among'Figleaf gourd','Tielizhen'and'Shintosa', which are significantly higher than that of'Shielba', and the self-rooted cucumber is the lowest. The Na⁺/K⁺ in grafted seedlings are significantly lower than that in self-rooted ones, and'Figleaf gourd'is the lowest.6. The relative expression of the Cu/Zn-SOD, Mn-SOD and CAT genes and the corresponding activities of these enzymes in grafting seedlings are higher than self-rooted seedlings, seedlings grafted on'Figleaf gourd'shows the highest, and'Shielba'shows the lowest. The increasing relative mRNA expression of Mn-SOD and APX genes cause high enzyme activities in the leaves of grafting seedlings. However, the relative mRNA expression of Cu/Zn-SOD and CAT mRNA reduced in both grafting seedlings and self-rooted seedlings with the lengthening of NaCl stress. It is different with the corresponding enzyme activities. The change of relative mRNA expression of the Cu/Zn-SOD and CAT genes do not coincide with the change of activities of Cu/Zn-SOD and CAT in the grafting seedling of'Figleaf gourd'and'Tielizhen'. It means that there are some other factors involved in the regulation of SOD and CAT activities.