Effects Of Pyropheophorbide-Alpha On Diease Resistance And Physiogical Charateristics Of Cucumber

The control of cucumber diseases is one of the important problems in the current agricultural production,and at present,the control of cucumber diseases is mainly chemical control.Pyropheophorbide-alpha（PPa）is a photosensitive drug with low toxicity and easy degradation,and various photosensitizers with similar properties have been proved to have better anti-disease,anti-cancer and anti-bacterial abilities.To investigate the effect of PPa on the physiological characteristics of cucumber and its ability to control different diseases,this study was conducted to determine the effect of photosensitizer PPa on the normal physiological characteristics of cucumber and its effect on the control of powdery mildew,wilt and bacterial angular spot disease using"periwinkle"cucumber as plant material.Firstly,PPa was sprayed on cucumber at normal four-leaf stage with different concentrations,light intensity and light duration to investigate the effect of PPa on normal physiological activities of cucumber,and then,the effect of PPa on Fusarium oxysporium f.sp.cucumerinum（FOC）and Pseudomonas syringae pv.Lachrymans（Psl）was measured in vitro.Cucumber at the four-leaf stage was inoculated with different pathogens and sprayed with PPa solution treated with different conditions,and the degree of disease susceptibility of the materials and the corresponding physiological indicators were determined to investigate the disease resistance effect of PPa in cucumber.The results were as follows:（1）PPa can affect the normal physiological characteristics of cucumber and improve cucumber resistance.After spraying PPa solution with different concentrations as well as being treated with different light intensities and light durations on the non-inoculated pathogenic material,it was found that PPa solution could increase the content of plant proline（Pro）and malondialdehyde（MDA）,and the corresponding antioxidant enzyme activities（SOD,POD,CAT）were gradually increased.At the same time,PPa spraying also increased the content of hydrogen peroxide（H₂O₂）in the material and caused the accumulation of superoxide anion（O₂^-）in cucumber,but this change in reactive oxygen species（ROS）content did not cause significant damage to the plant,indicating that its own reactive oxygen species（ROS）balance was not disrupted.This shows that PPa can effectively regulate the physiological properties of the plant and enhance the resistance of cucumber.（2）In the in vitro experiments,PPa showed significant resistance to the cucumber wilt causal agent FOC.Under the dark condition,PPa could effectively inhibit the growth of FOC,and its inhibition rate increased with the increase of PPa concentration,and the inhibition rate of each concentration treatment group was significantly higher than that of the control group（CK）.2 g·L^-1 concentration had the best inhibition effect on FOC,and the inhibition rate was nearly 75%.Under the same conditions,PPa did not have a significant inhibitory effect on Psl,and its inhibition rate was extremely low,and there was no significant difference in relation to PPa concentration,indicating that PPa had no direct inhibitory effect on Psl.（3）PPa was able to influence the degree of susceptibility of cucumber,which was influenced by PPa concentration,light intensity,and light duration.2 g·L^-1concentration minimized the susceptible area of cucumber leaves inoculated with different pathogens,and there was a positive correlation between the susceptible area of leaves and PPa concentration.6 000 Lux,24 h of light resulted in relatively low levels of powdery mildew infection.For wilt,the materials were least susceptible under 4 000 Lux,48 h light conditions.In addition,PPa treatment also alleviated the damage caused by bacterial keratosis to some extent,and the material was least susceptible under 10 000 Lux,96 h light conditions.Thus,it can be seen that PPa can alleviate the degree of disease susceptibility of cucumber,while different light conditions can affect its disease resistance.（4）PPa improved the physiological activity of disease-susceptible cucumber and enhanced its disease resistance.After PPa treatment,the MDA content,Pro content of the susceptible material was significantly increased,while PPa also caused changes in ROS in the plant,and the corresponding changes fit with the changes in the activities of three antioxidant enzymes,thus maintaining its original ROS balance stable,and this ability was inseparable from PPa concentration,light intensity and light duration.In addition,the disease resistance of PPa varied in different susceptible materials,and under the same treatment conditions,PPa was the most effective in the control of powdery mildew and better in the control of wilt,while the effect was not significant in the control of bacterial keratosis,but still better than the control（p<0.05）.In summary,PPa can improve disease resistance in cucumber,indicating that PPa may have the effect of inducing a SAR-like disease resistance response in cucumber.In addition,PPa could directly inhibit the growth of wilt pathogenic bacteria,and had good control effects on cucumber powdery mildew,wilt disease and bacterial horn spot disease,among which,the best effect on powdery mildew control was followed by wilt disease,while the effect was weaker in the control of bacterial horn spot disease.