Studies Of Exogenous Salicylic Acid On Inducing Apple Resistance To Apple Ring Rot Disease

The apple ring rot is an serious fruit disease. Recent researches are merely around the biological character of pathogeny and the chemical prevention to the apple ring rot, while induced resistance to apple has not been covered. With salicylic acid (SA) as the induced factor, the fruit of Red Fuji apple as the experimental material, the paper studied the resistance induced by SA to apple ring rot. Through the toxicity test, it was filtrated the range of salicylic acid, on the basis of which were designed two treatments including inducement and challenge inoculation after inducement. Meanwhile the lasting period of resistance and the physiological mechanism induced by SA was studied. The results were as follows:1. The experiment indicated high concentrations of SA treatments have the obvious toxicity to the pathogens, and that each SA treatments of 0~0.2 mmol/L had not the significant difference, which showed the resistance induced by 0-0.2 mmol/L SA was not trough the direct toxicity, but by inducing the expression of the resistance gene.2. It was interval three days from SA treatment at 0.2 mmol/L to challenge inoculation that apple could obtain the biggest induced effect, which increased 22.2% than comparing with CK. With the delaying of the treatment, the resistance to apple ring rot induced by SA declined gradually, the induced effect of the treatment that 15 days and 20 days dropped to 13.6% and 4.5%, respectively. From the change of the induced effect: the resistances induced by SA could last 15-20 days, the optimum induced time was 3 days.3. The study on physiological mechanism of resistance to apple ring rot induced by SA showed that the activities of peroxidase, polyphenol oxidase, Superoxide Distmuase and phenylalanine amonnia lyase and solubility protein of the treatment of challenge inoculation increased significantly compared with SA treatment, content of malonaldehyde, Superoxide radical of the treatment of challenge inoculation decreased significantly compared with SA treatment, peroxidase, polyphenol oxidase, phenylalanine amonnia lyase, Superoxide Distmuase, and solubility protein had the same trend with the resistance of apple. Content of malonaldehyde and Superoxide radical had the opposite trend with the resistance of apple. It was also observed the change extent of the physiological indexes showed similar change with the induced concentration, 0.2 mmol/L SA was the best, next was 0.02 mmol/L, and then was 0.002 mmol/L.4. Treating fruit of Red Fuji apple with different concentrations (0.002 mmol/L, 0.02 mmol/L, 0.2 mmol/L) of SA solution could important in the induced resistance at different degrees. 0.2 mmol/L SA had the prominent effect on elevating the solubility protein content, enhancing the activity of Superoxide Distmuase, peroxidase, polyphenol oxidase, phenylalanine amonnia lyase, reducing the superoxide radical, content of malonaldehyde. It can dalay plant cell death, and prevent or release fruit disease.5. With the increase of the concentration of SA, it showed that the resistance of apple heightened accordingly, 0.2 mmol/L SA had the best effect. SA at 0.002 mmol/L had the higher infection index than CK, Which indicated that SA at the lower concentration can not induce the resistance of apple.