Identification Of Pathogen Causing Blueberry Stem Brown Spot And Indoor Screening Of Fungicides

Blueberry is a small perennial shrub of the genus Vaccinium spp.,Ericaceae.With the continuous development of blueberry industry in China,the occurrence of blueberry diseases has become one of the main factors that hinder the development of the industry.In this study,the causing agent of blueberry stem brown spot disease in Changchun,Jilin Province,has been studied to provide a theoretical and technical support for the identify and control of the disease.The research includes five aspects:（1）Diseased symptoms and disease rate were investigated and recorded in the Lianhua Mountain blueberry base,Changchun city;（2）Using tissue isolation method and single spore isolation method to isolation and purified the pathogens.Morphological and molecular method was used to identified the pathogen;（3）The pathogenicity of the fungus was determined by Koch’s rule,and in order to further understand the mechanism of pathogenic infestation on blueberry stems,scanning electron microscopy combined with paraffin sectioning was used to monitor the infestation process of pathogenic infestation on blueberry stem tissues;（4）To further clarify the biological characteristics of the pathogen,effects of temperature,light,p H and nutrients on the mycelial growth rate of the pathogen were examined by setting a single variable;（5）Different fungicides and different concentrations of the same fungicide were compared for their inhibitory effects on pathogen using the growth inhibition method,and the relevant virulence regression equations and EC₅₀ were calculated based on the results obtained.Main results:1,Morphology combined with molecular biology showed that the pathogen causing blueberry stem brown spot disease in Lianhua Mountain blueberry base was identified as Alternaria tenuissima.2,Alternaria tenuissima can only affect caulicle through wounds,and has no pathogenic effect on old stems.Mycelium invaded into the stem tissue only along the epidermis and cortical tissue cells of blueberry stems to expand forward,but not the cells within the cortical layer.3,The optimum growth temperature of A.tenuissima was 30°C,the most suitable p H value was 5,and the most suitable was blueberry stem infusion juice agar medium and potato dextrose agar medium.But there was no significant difference in the growth rate of the mycelium under different light conditions.4,Ten fungicides used in the test on A.tenuissima have inhibitory effect.Among them,fluazinam had the strongest inhibitory activity,followed by prochloraz and difenoconazole.The other seven fungicides in order of inhibitory activity are:iprodione>flusilazole>pyraclostrobine>kresoxim-methly-boscalid>propiconazole>polyoxin>carbendazim.Conclusion:The disease infection progress of stem brown necrotic pathogen in Lianhuashan of Changchun city was caused by A.tenuissima.Which only infests blueberry caulicle through wounds and is weakly parasitic on blueberry stems.fluazinam,prochloraz and difenoconazole had better inhibition effect on mycelium.