Effect Of Melatonin And Selenium On Sclerotinia Sclerotiorum And Its Regulatory Mechanism

Selenium（Se）,as a beneficial element that can not only help plant growth,but also enhance plant stress resistance,has been widely used in plant disease and insect pest control.Melatonin（MT）has also been proved to be a plant endogenous hormone,which plays a very good role in regulating plant biological or abiotic stress,and has been widely used as a new regulator in stress resistance research.However,sclerotinia sclerotiorum has been a problem in oil production for a long time,and can even cause serious economic loss.Therefore,in order to explore a scientific and green method to prevent sclerotinia sclerotiorum,this study mainly took"Qinyou No.2"as the experimental material,and treated rape seeds with a series of concentration gradient exogenous melatonin and selenium.After germination,the seed germination rate was measured,and the effect of melatonin and selenium on promoting the germination and growth of rape seeds was studied.Pot experiment was conducted to explore the effects of exogenous melatonin and selenium on the induced resistance of rape leaves before and after inoculation with rhizoctonia sclerosus.At the same time,the effects of exogenous melatonin and selenium on the endogenous melatonin content and selenium enrichment effect of rape were investigated.The main research results are as follows:1.MT and Se can significantly inhibit the growth of rhizoctonia in vitro:within the concentration range of 0-100 mg/L,the inhibition effect of Se on Rhizoctonia nucleoctonia increases with the increase of the concentration,and the optimal concentration of Se is 100mg/L,with the inhibition rate reaching 78.44%.When the concentration was 50 mg/L,the inhibition rate reached 53.06%.For MT,the inhibition effect of MT was enhanced with the increase of MT concentration in the range of 0-100 mmol/L,and the optimal inhibition concentration was 100 mmol/L,and the inhibition rate reached 75.62%.When the concentration was 50 mmol/L,the inhibition rate was 55.68%.2.Appropriate concentrations of MT and Se can promote seed germination of rape:three rape varieties were tested in the immersion experiment,namely"Qinyou No.2","pink rape"and"red rape".MT and Se were prepared into a certain concentration gradient and soaked seeds for 24 h,respectively.The results showed that the three rapeseed varieties had the same trend of high germination rate when MT concentration was 12.5 mmol/L or Se concentration was 10 mg/L,and all of them were the optimal concentration for promoting germination,that is,there was no significant difference in germination rate between the three varieties at this concentration.At the same time,when the optimal concentration of 12.5 mmol/L MT and 10 mg/L Se were combined,the germination rates of the three varieties were 83.33%,82.00%and 85.30%,respectively.The germination effect was significantly higher than that of the separate treatments,indicating that there was some synergistic mechanism between MT and Se,which could promote each other.As for the growth of seedlings,the growth of the three varieties treated with 12.5mmol/L MT was significantly different at the 4th to 6th day,but there was no significant difference at the 8th day.The growth trend of the three cultivars treated with 12.5 mmol/L MT and 10mg/L Se was roughly the same as that treated with MT alone,indicating that exogenous MT and Se had no significant difference on the growth of different cultivars of rape seedlings,including the chlorophyll content of seedlings.3.Pot experiments were conducted with 50 mmol/L MT and 50 mg/L Se as the test variety"Qinyou No.2",to explore the induced resistance effects of MT and Se on rape leaves before and after inoculation with pitomyces nucleatus.The results showed that MT and Se could inhibit the onset of sclerotinia sclerotinia in rape,and MT+Se had the most significant effect,with the incidence decreased by 11.62%compared with the control group.The spread of the lesion was also reduced,and the effect of leaf spray MT was superior.The chlorophyll content was not affected by MT and Se treatments.MT and Se can improve the activities of defense enzymes such as peroxidase（POD）,superoxide dismutase（SOD）,catalase（CAT）,polyphenol oxidase（PPO）,inhibit the production of H₂O₂,NO and malondialdehyde,promote the production of glutathione（GSH）,and relatively increase the total phenol content of rape leaves before and after inoculation with rhizopteris nuclei.Thus reducing the occurrence of sclerotium disease.The results showed that the expressions of NPR1 and PAL genes in the MT treatment group were lower than those in the control group,while the expressions of NPR1 and PAL in the MT and Se co-treatment group were significantly increased but PAL was not significantly increased.The results further confirmed that the synergistic effect of MT and Se on the related mechanism of rape disease resistance is significant.4.The contents of endogenous melatonin and selenium in leaves and stems of potted rapeseed were determined according to different treatments.The results showed that MT and Se could improve the endogenous melatonin content of rapeseed,and MT spraying on stem and leaf was better but second only to M+S treatment group,MT spraying on leaf roots was better but second only to M+S treatment group.MT and Se can also enhance the selenium enrichment effect of rape.For the stalks and leaves of rape,the selenium content of the three treatment groups co-treated by MT and Se is the most significant increase compared with the MT treatment group,and the M+S treatment group is the most obvious.Therefore,both MT and Se can increase the contents of endogenous melatonin and selenium in rape,and the synergistic effect is the most obvious.