The Function And Application Of Sorbitol On The Resistance To Apple Ring Rot

In recent years,Apple ring rot has become a serious threat to the development of the apple industry.Traditional methods of preventing and treating the disease of apple ring rot not only cause injury to apple trees,but also cause serious environmental pollution.Therefore,how to safely and effectively improve the resistance to Botryosphaeria dothidea in apples is an important issue to be addressed for apple breeding and cultivation.These days,improving disease resistance in plants by using their own metabolites has become a hot research topic in the field of plant disease resistance.In order to clarify the mechanism of resistance to Apple ring rot and obtain high-quality and high resistance apple germplasm,194 F₁ hybrid seedlings were obtained from the cross between the resistant cultivar‘Golden Delicious’and the susceptible cultivar‘Fuji’.The role of the metabolite sorbitol in the resistance to B.dothidea in apples was determined via combining proteomics sequencing technology and apple calli transformation technology,and the optimal concentration of sorbitol was selected to improve the resistance to B.dothidea in apples.It provides an important theoretical basis and practical method for the development of anti-disease agents for fruit trees using its own metabolites.The specific research results are as follows:（1）By analyzing the incidence of Apple ring rot in F₁ generation,the hybrid F₁generation was divided into 5 grades.Field investigation was carried out on F₁ generation plants of‘Golden Delicious’and‘Fuji‘Nagafu No.2’’,and 194 F₁ hybrid plants were divided into 5 grades of immune,high resistant,medium resistant,medium susceptible and high susceptible according to their resistance level to B.dothidea.It was found that the content of pathogenic bacteria increased significantly with the decrease of resistance level of F₁ plants.（2）By using proteomic sequencing,hierarchical clustering and weighted correlation network analysis（WGCNA）association analysis,the molecular mechanism of resistance to Apple ring rot was preliminarily identified.The results of quantitative proteomic sequencing,hierarchical analysis and WGCNA showed that photosynthesis may be an important biological process affecting the resistance to B.dothidea in apples.The results of chlorophyll fluorescence intensity of F₁ generation leaves with different disease resistance grades showed that the intensity of photosynthesis was significantly positively correlated with the resistance to B.dothidea in apples.In order to further explore the mechanism of resistance to B.dothidea in apples,calli of F₁ generation of highly susceptible plants and immune plants were tested for disease resistance,and it was found that the area of disease spot of highly susceptible calli was significantly larger than that of immune calli.Transmission electron microscopy（TEM）showed that more starch granules were deposited in calli with high sensitivity than in immune calli.Further studies showed that the content of sorbitol increased significantly with the improvement of F₁ generation plant resistance grade.（3）Via the transformation technology of apple calli,the important role of sorbitol in the resistance to B.dothidea in apples was elucidated.In order to investigate the effect of sorbitol on resistance to B.dothidea in apples,calli with overexpression and silencing of MdS6PDH1,which is Sorbitol-6-phosphate dehydrogenase,were obtained.The content of sorbitol in calli overexpressing MdS6PDH1 increased,whereas it decreased in calli silencing MdS6PDH1.The results of disease resistance analysis showed that the calli with overexpression of MdS6PDH1 were significantly more resistant to B.dothidea than wild-type calli,while the calli with silencing of MdS6PDH1 were less resistant to B.dothidea than wild-type calli.Via detecting the expression levels of genes related to SA signaling pathway and SA synthesis in different calli,it was found that the expression levels of SA-related genes in calli overexpressed MdS6PDH1 were significantly up-regulated compared with the control group,while the expression levels of SA-related genes in calli silenced MdS6PDH1 were significantly down-regulated.Meanwhile,exogenous sorbitol treatment could significantly improve the resistance of MdS6PDH1 silenced calli to B.dothidea.（4）The effect of external application of sorbitol on the disease resistance of apple leaves and fruits was proved via analyzing the disease resistance of apple leaves and fruits after external application of sorbitol,and the optimum concentration of sorbitol was selected to improve the resistance to B.dothidea in apple fruit.In order to explore whether external application of sorbitol can improve the resistance to B.dothidea in apples,the expression levels of genes related to SA synthesis and signal transduction in functional leaves of field apple tree were detected after exogenous sorbitol treatment.The results showed that exogenous sorbitol treatment significantly improved the expression levels of SA-related genes.In order to investigate the effect of external application of sorbitol on the resistance to B.dothidea in apple fruit,the disease resistance of‘Golden Delicious’,‘Fuji’,‘Starking Red’and‘Gala’were treated with different concentrations of external application of sorbitol were analyzed.The results showed that external application of sorbitol could significantly improve the resistance of apple fruit to B.dothidea,and the optimal concentration was 200 m M.