Effects Of Mineral Nutrients (Cu, Fe, Ca, Zn) On The Occurrence Of Cucumber Powdery Mildew And The Physiological And Biochemical Characteristics Of The Host

Jinyan No.4 was used in this experiment. Under hydroponic cultivation, effects of nutrient deficiency and addition of single mineral nutrien(Cu,Fe,Ca,Zn) by foliage spray experiments on the occurrence and the physiological and biochemical characteristics of cucumber powdery mildew were studied.(1)The studies on the occurrence of cucumber powdery mildew.The plants were grown in single nutrient (Cu,Fe,Ca,Zn) deficient solution and complete nutrient solution (control group), and were inoculated till 3-true leaf stage.The plants in copper-deficient treatment group and iron-deficient treatment group became diseased after inoculated for 4 days. Diseased plants were found in all treatments after inoculated for 5 days, and the disease severity presented an obviously aggravating tendency with the passage of time.During the investigation, the disease severity in nutrient-deficient treatment group were more severe than that in control group, where the disease indexes in copper-deficient were the highest and 1.20～1.45 fold compared to the control group, and the disease severity in iron-deficient group took second place. However, there was no significant difference in disease severity between Zinc-deficient treatment group and control group in most cases. The results indicated that deficiency of single mineral nutrient (Cu,Fe,Ca) was beneficial to the occurrence of cucumber powdery mildew in different degree, while the effect of Zinc-deficient was not obvious.Meanwhile, when the plants grown in complete nutrient solution were in 3 leaf period, spraying the solution of CuSO₄, FeSO₄, ZnSO₄and Ca(NO₃)₂ on the leaves, and inoculated with Sphaerotheca fuliginea 60 hours later. The plants in control group (spraying with aseptic water) and the groups spraying with the solution of ZnSO₄, Ca(NO₃)₂ became diseased in different degree after inoculated for 5 days, while diseased plants started to appear in the groups spraying with the solution of CuSO₄, FeSO₄ after inoculated for 6 days. After this, the disease indexes in the groups spraying with the solution of CuSO₄, FeSO₄, Ca(NO₃)₂ increased slowly. The disease index in the control group had reached to 6.89 already and was 3.51, 2.05 and 1.32 fold compared to the groups spraying with the solution of CuSO₄ (1.963), FeSO₄ (3.365), Ca(NO₃)₂(5.214) after inoculated for 10 days, showing the very significant difference (P<0.01).The results indicated that the occurrence of cucumber powdery mildew was decreased effectively by foliage spray of CuSO₄; then by foliage spray of FeSO₄and Ca (NO₃)₂, while there was no significant difference on disease severity between the group spraying with the solution of ZnSO₄and the control group.(2)The studies on effects of nutrient deficiency and addition of single mineral nutrient (Cu,Fe,Ca,Zn) by foliage spray experiments on the physiological and biochemical characteristics of cucumber powdery mildew, including the activities of PPO,PAL,POD,SOD, the contents of lignin, the contents of soluble sugar, and the injury degree:After inoculated with Sphaerotheca fuliginea, the activities of PPO,PAL and the contents of lignin were decreased significantly in copper-deficient treatment, compared to control group and the other nutrient-deficient treatment groups. The electrolyte leakage outclasses that in the other groups, after inoculated for one day, while the contents of soluble sugar always had a high level.; After spraying with the solution of CuSO₄, the activities of PPO,PAL and the contents of lignin were improved and the contents of soluble sugar were decreased significantly(P<0.05).The electrolyte leakage increased in early stage, but had been already less than control group several days later.The activity of POD in the iron-deficient group was lower than that in control group and the other nutrient-deficient treatment groups except the activity peak, which appeared after inoculated for 48 hours and was higher than that in the calcium-deficient and the copper-deficient group. The decrease range of it was also greater than that in the other groups. Additionally, the activity of SOD was lower significantly than that in the other groups and the lignin synthesis was inhibited in early period of pathogen infection,while the electrolyte leakage decreased; Meanwhile, The activity of POD was increased after spraying with the solution of FeSO₄, and the activity of SOD was increased significantly after inoculated, while the contents of soluble sugar were always at a lower level. The electrolyte leakage was enhanced by spraying with the solution of FeSO₄, but could recover to normal level with the passage of time.After grown in the calcium-deficient solution, the enzymatic activities were decreased in different degree, the contents of lignin was lower than that in control group, and the electrolyte leakage was enhanced; the activity of PAL was improved obviously and the activity of POD were increased in certain degree, while there was also a certain function on the electrolyte leakage balance.After grown in the Zinc-deficient solution, the enzymatic activities were decreased in different degree, but the decrease range was less than that in the other nutrient-deficient treatment groups. The contents of soluble sugar were decreased in certain degree. After spraying with the solution of ZnSO₄, the activity of SOD was improved in certain degree while the contents of soluble sugar were in a higher level.(3) The effects of CuSO₄, FeSO₄, Ca(NO₃)₂, and ZnSO₄ on spore germinationThe results showed that CuSO₄, FeSO₄could inhibit spore germination significantly, with the inhibition rate of 75% and 74.1%; while the inhibition rate in ZnSO₄ treatment was 53.2%.The effect of Ca(NO3) 2 was least with the inhibition rate of 28.7%.