| Kiwifruit bacterial canke has become the most serious problem for the development of the global kiwifruit industry,and there is still a lack of effective control agents at present.Under the condition that other prevention and control technologies have reached the bottleneck,the use of the disease resistance of host plants may become an important breakthrough in the prevention and control of canker.By previous pot and field experiments,the researchers had found that sulfur fertilizer application not only significantly promoted the growth and development of kiwifruit and the quality of fruit,but also induced kiwifruit resistance to canker.However,the mechanism of sulfur on the kiwifruit resistance to canker is not clear yet.In this study,the orchards with serious kiwifruit canker were selected.Sulfur powder and organic fertilizer were used as base fertilizer to conduct ring groove fertilization on kiwifruit in winter,and the effects of different sulfur concentrations on soil rhizosphere microbial characteristics and fertility in kiwifruit orchards were studied.The physiological effects of sulfur-induced kiwifruit resistance to canker were studied by means of electron microscopy and ultraviolet spectrophotometry.The histochemical staining method was used to observe the tissue defense response to sulfur-induced canker resistance in kiwifruit.Meanwhile,the signal transduction pathway of sulfur-induced resistance was preliminarily explored by liquid chromatography.The results will preliminarily speculate the possible mechanism of sulfur-induced kiwifruit resistance to canker and explore a new effective way to prevent and treat kiwifruit canker.The main findings are as follows:1.The effects of sulfur on microbial characteristics and fertility of kiwifruit rhizosphere soil were studied by plate dilution and physicochemical analysis.The results showed that the number of bacteria and were increased,the enzymatic activities of soil urease,acid phosphatase,sucrase,catalase and peroxidase were raised,the physical and chemical characteristics of kiwifruit soil were improved when the application concentration of sulfur was in the range of 0.5～1.5 kg/m~3,thereby improving soil fertility.The results of redundancy analysis indicated that bacteria were the key microorganisms affecting soil environmental factors,which were positive correlation with the enzymatic activities of soil total potassium,urease,sucrase and acid phosphatase.At the same time,the catalase(P<0.01),peroxidase(P<0.05),sucrose enzyme(P<0.05)and cellulase(P<0.01)were the key indicators affecting the physical and chemical characteristics of kiwifruit soil.2.The physiological effects of sulfur-induced kiwifruit resistance to canker were studied by electron microscopy and ultraviolet spectrophotometry.The results showed that stomata of kiwifruit leaves and the opening of lenticels and morphological characteristics of kiwifruit stalk were in the best state,and the secretion substances at the lenticels of kiwifruit stalk were increased significantly when the application concentration of sulfur was 1.5 kg/m~3.When the sulfur concentration was in the range of 0.5 kg/m~3～2.0 kg/m~3,the chloroplast and mitochondria in branches with serious kiwifruit canker could be gradually restored to spindle type,the number of starch grains in organelle was raised,the growth of villi on kiwifruit stalk could be promoted,and the thickness of cell wall was increased by application of sulfur.At the same time,the enzyme activities of phenylalanine ammonia-lyase(PAL)and ascorbate peroxidase(APX)in the kiwifruit leaves were also significantly increased.The photosynthetic characteristics of kiwifruit leaves was improved,the accumulation of photosynthates was promoted,the quality of kiwifruit and the yield of kiwifruit were improved when the sulfur concentration was in the range of 0.5～1.5 kg/m~3,among which,the treatment with sulfur concentration of 1.5 kg/m~3had the best effect.Compared with the control without sulfur application,the fruit longitudinal diameter,transverse diameter,lateral diameter,single fruit volume,single fruit weight and yield per mu increased by 5.80%,6.76%,1.11%,14.20%,21.86%and 285.33%respectively,and the vitamin C,soluble solids,total soluble sugar,soluble protein and sugar-acid ratio increased by 47.06%,13.26%,13.83%,6.25%and 17.91%respectively.The correlation analysis was adopted and it was found that the activities of defensive enzymes in kiwifruit leaves were significantly correlated with the intrinsic quality of kiwifruit,and there was a positive correlation between phenylalanine ammonia-lyase(PAL)and ascorbate peroxidase(APX)and soluble solids,total soluble sugar,dry matter,soluble protein and acid-sugar ratio.The distribution of nutrients in different parts of kiwifruit was significantly different(N,P,K:leaf>stem>root;sulfur:leaf>root>stem),and there was a certain correlation among nutrient elements in the different parts.3.The content,distribution and deposition characteristics of lignin in young and old stems of kiwifruit were determined and observed by ultraviolet spectrophotometry and tissue staining.The results indicated that the content and distribution of lignin in kiwifruit stalk were improved,and the lignin deposition of kiwifruit stalk was promoted when the suitable sulfur concentration was 0.5～2.0 kg/m~3.Compared with that without sulfur application,the young and old stems of kiwifruit had the highest lignin content with the sulfur concentration of 2.0 kg/m~3and 1.5 kg/m~3respectively,the content of lignin increased by 113.40%and 150.96%respectively,and the difference was significant(P<0.05).It indicated that lignin might play a key role in physical barrier defense of kiwifruit against sulfur-induced canker resistance.4.The contents of salicylic acid(SA)and jasmonic acid(JA)in kiwifruit leaves were detected by liquid chromatography-mass spectrometry(LC-MS).The results revealed that SA content in kiwifruit leaves was increased by sulfur treatment,the effect of sulfur concentration with 1.5 kg/m~3were the best after 1 and 2 years,SA content increased by 24.78%and 31.51%respectively compared with no sulfur application(significant difference at P<0.05,the same below).However,the JA content in kiwifruit leaves fluctuated slightly and relatively stable by treatments with different sulfur concentration,and there were no significant difference compared with the control without sulfur application.It preliminarily was indicated that SA might be the main signal pathway of sulfur-induced canker resistance in kiwifruit,while JA signal pathway might not respond to the mechanism of sulfur stress. |
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