Development Of Compound Microbial Agent Against Apple Valsa Canker

Apple canker is a kind of disease caused by black rot fungus,which exists widely in our country and seriously hinders the development of apple industry.Although traditional chemical fungicides can effectively inhibit apple canker,a series of problems such as pesticide residues,environmental pollution and food safety cannot be ignored.More and more attention has been paid to the problem of health and environmental protection.The advantages of biological control have been gradually shown in the control of apple canker.Fulvic acid,a broad-spectrum plant growth regulator,has stable and reliable stress resistance.Chitosan oligosaccharide which has good broad-spectrum antibacterial activity,has a good application prospect in biomedicine and disease control of agriculture.The antagonistic bacteria of apple canker were screened out from the soil by using the biological control model and soil dilution method.Strain XW5 was identified by combing the morphology,culture characteristics,physiological and biochemical characteristics and genetic characteristics.The application value of antagonistic bacteria was explored by solid-state fermentation.Different concentrations of potassium fulvic acid,chitosan oligosaccharide and the antagonistic combination were selected to inhibit apple tree canker by single factor experiment,and the formula of compound control agent was preliminarily determined.The main research results are as follows:（1）Six antagonistic strains of Apple Valsa Canker were screened out from the soil by using the biological control model and soil dilution method.A strain XW5 with 50.41%inhibition rate and no hemolysis was selected by tablet confrontation and cell safety experiment and was used in the subsequent study.（2）Establish a field ecological simulation model to simulate whether the antagonistic strain XW5 has inhibition effect on apple canker in the ecological environment.The results showed that the growth of Apple Valsa Canker was inhibited in the ecological simulation model of inoculated strain XW5.（3）The antagonistic strain XW5 was identified as Streptomyces according to the characteristics of culture,physiology,biochemistry and heredity,and inferred that strain XW5is a new species of Streptomyces.（4）When the antagonistic strain XW5 was fermented in solid state,loaded in triangle flask and edible fungus culture bag,at 28℃,p H7.2 and 60%humidity for 7 days,the number of viable strains reached 1.011 billion/g and 1.036 billion/g respectively.（5）Different concentrations of potassium fulvic acid,chitosan oligosaccharide and antagonistic suspension have different inhibition effects on apple canker.The formula was preliminarily determined by orthogonal test.The inhibition rate of compound fungicide is99.88%.Compound fungicide is consist of 0.23%potassium fulvic acid,0.13%chitosan oligosaccharide and actinomycete dilutions 8.33×10^-4mg/ml,respectively,which was similar to the inhibition effect of single factor of 0.9%potassium fulvic acid and 0.4%chitosan oligosaccharide,with low concentration,low cost and good economic effect.