| Kiwifruit had been widely planted around the world under the reputation of "the king of fruit" for its high Vitamin C content, rich nutrition and a unique flavor. In recent years, with the continuous enlargement of the planting areas on kiwifruit, disease species and damage degree are also increasing, which brings serious threat to the kiwifruit production. Among which, Kiwifruit canker was one of the most devastating diseases in the production of kiwifruit and restricts the sustainable development of the kiwifruit industry, not only influencing the yield of fruits seriously,but reducing the quality of the fruits greatly. The prevention and control effects of sulfur on kiwifruit canker and its safety to kiwifruit were determinated after treating by different concentrations of sulfur. As well as the induced resistance mechanism of sulfur involved in the defensive enzymes activities, antioxidant enzymes activities and resistant substances were evaluated. The purpose of this study was to provide a theoretical basis for production using mineral elements to prevent and control or reduce the kiwifruit canker. The main results were as follows:(1) The diseased branches of kiwifruit canker from kiwifruit orchards of Xiuwen county of Guizhou province was separated using the grinding dilute separation method. A high frequency and representative bacterial strain was obtained, which blast 16 S r DNA sequence with NCBI databases on Pseudomonas syringae pv. Actinidiae had the highest similar and the homology was99%. Phylogenetic analysis based on 16 S r DNA sequences showed that the relationships of the bacterial strain and Pseudomonas syringae pv. Actinidiae was close. Combining with the pathogenic detection results which the test strain was inoculated on the host sample of kiwifruit,the bacterial strain was identified as Pseudomonas syringae pv. Actinidiae.(2) The toxicity of sulfur against Pseudomonas syringae pv. Actinidiae were respectively detected by turbidimetric method and bacteriostatic circle method. The results showed that thesulfur suppressed mainly the logarithmic growth of the Pseudomonas syringae pv. Actinidiae,which means that the division growth of Pseudomonas syringae pv. Actinidiae was inhibited. But the toxicity was weak, with the EC50 values of 1247.0835 mg/L and 1326.9897 mg/L, respectively.The test kiwifruit canker was inoculated on the branch of potted kiwifruit treated by sulfur and organic fertilizer. The results were observed that the treatment of sulfur content 1.5 kg/m3 had the lowest incidence of kiwifruit canker. Compared with control group, the prevention and control effect was up to 73.34%. In December 2014, different concentrations gradient sulfur powder and organic fertilizer were applied on perennial kiwifruit plants by parallel groove in the field. And the occurrence conditions of kiwifruit canker in the experimental field were investigated in 2015 and2016, respectively. The results showed that the treatment of sulfur content 2.5 kg/m3 had the lowest incidence of kiwifruit canker and the prevention and control effect was up to 76.67% in2016, compared to the control. This showed that the application appropriate concentrations of sulfur in kiwifruit production can effectively reduce incidence of kiwifruit canker and improve the control effects.(3) The effects of sulfur on physiological and biochemical indices of kiwifruit were studied by ultraviolet spectrophotometric method. All pot experiment and field experiment results showed that in the range of 1.0-2.5 kg/m3, sulfur treatment could increase soluble protein contents,improve the activities of PAL, SOD, CAT, POD and PPO, and reduce MDA contents in kiwifruit leaves, which enhanced the resistance of kiwifruit plant to a certain extent. While in the pot experiment results showed that the activities of PAL, SOD, CAT, POD and PPO were the strongest,the soluble protein content was the highest, the MDA content was the lowest, and the plant disease resistance was the strongest in kiwifruit leaves after treating with sulfur content 1.5 kg/m3,compared to other treatment groups. And the field experiment results showed that the corresponding biochemistry indicators of the kiwifruit leaves after treating with sulfur content 2.0kg/m3 were the best among all treatments. The results demonstrated that it was the important physiological and biochemical mechanism to enhance the disease resistance in kiwifruit that sulfur treatment could improved the activities of defensive enzyme and antioxidant enzyme, increase the soluble protein content and reduce MDA content in kiwifruit leaves.(4) The effects of different sulfur levels on kiwifruit growth were regular observed. The results showed that the kiwifruit plant grew well, the new shoots were longer and thicker, theleaves were larger and deep green, and phenological phases were ahead of schedule after treating with the concentrations of sulfur in the range of 0.5-2.0 kg/m3. But the kiwifruit grew weakly, the new shoots were shorter, the leaves were smaller, curly and yellow, and phenological phases were delayed when the treatment concentration was higher than the level 2.0 kg/m3. So the concentrations of sulfur treatment should be controlled in the range of 0.5-2.0 kg/m3 in order to ensure the kiwifruit regular growing in the kiwifruit production process.(5) The field experiment was carried out to study the effects of sulfur on quality of kiwifruit.The results showed that after treating with the concentration of sulfur in the range of 0.5-3.0 kg/m3,the total sulfur contents in kiwifruit were ranged between 0.12% and 0.26%, which belonged to the safety range of 0.1%-1.5% to the total sulfur contents in crop. And after treating with sulfur under the level 2.0 kg/m3, the fruit shape index of kiwifruit had no significant effect. But the fruit hardness, the contents of soluble solids, Vc, soluble sugar, soluble protein and chlorophyll significantly increased in treatment kiwifruits, which improved the quality of kiwifruit. Compared with the without sulfur treatment, the values of above quality indicators were increased by32.65%?5.22%?9.17%?11.76%?25.00% and 79.15%, respectively.Overall, it can promote the growth of the kiwifruit, improve the quality of kiwifruit, increase the physiology and biochemistry activities of defensive enzyme and antioxidant enzyme that kiwifruit plant was treated with sulfur concentration in the range of 1.5-2.0 kg/m3 in the process of kiwifruit production, which effectively reduce the incidence of kiwifruit canker and improve the prevention and control effects. Therefore, sulfur can induce resistance to kiwifruit canker and has a good prospect in the efficient and safe production of kiwifruit industry. |
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