Pathogenicity And Control Of Extracellular Polysaccharide From Walnut Black Spot Disease

In this paper,the pathogenic strain of Xanthomonas campestris pv.Juglandis?Pierce Dowson?was used as the tested strain,and the effects of nutrients and culture conditions on the production of extracellular polysaccharides were studied.The chemical constituents and pathogenic effects of extracellular polysaccharides were determined to investigate the effects of their effects on the physiological metabolism of walnut.At the same time,13common fungicides were used to determine the indoor virulence of walnut black spot and the outdoor pot experiment.The main findings are as follows:1.Fermentation condition optimization resultThe optimal fermentation medium and fermentation conditions were screened by single factor test:5%sucrose,0.2%ammonium sulphate,0.025%glutamic acid,0.3%calcium carbonate,0.1%magnesium sulfate,0.05%ferrous sulfate,dipotassium hydrogen phosphate.0.3%,inoculation amount 5%,liquid volume 50 mL/250 mL,pH 7,temperature30?.The optimized extracellular polysaccharide yield was 17.325 g/L,which was 22.58%higher than that before optimization.2.Chemical composition and pathogenicity of extracellular polysaccharidesThe results showed that the total sugar content,protein content,total uronic acid content,reducing sugar content and solubility of the crude polysaccharide were 78%,0.32%,9.42%,11.6%and 0.451 g/100 mL H₂O₂,respectively.Different concentrations of extracellular crude polysaccharides were applied to isolated walnut leaves and cultured for observation.The results showed that the extracellular crude polysaccharide was pathogenic and could induce the onset of healthy plants,and the degree of onset was positively correlated with the concentration of extracellular crude polysaccharide.3.Physiological metabolismThe extracellular polysaccharide solution can cause typical black spot symptoms in walnuts,significantly increasing cell membrane permeability and malondialdehyde content.In a certain concentration range,the extracellular polysaccharide of walnut was positively correlated with free proline content and defensive enzyme activity;when the concentration was higher,extracellular polysaccharide was negatively correlated with free proline content and defensive enzyme activity,indicating high The concentration of extracellular polysaccharide solution can destroy the body structure of walnut,which proves that extracellular polysaccharide plays an important role in the pathogenesis of walnut by Xanthomonas.4.Sieving of fungicides in laboratory of control Walnut black spotThe results of indoor chemical control showed that there were five fungicides that could inhibit the black spot disease of walnut to some extent in the design of different concentrations of chemicals.The pathogenic bacteria were affected by the inhibition of the five kinds of agents,and the best inhibitory effect on the pathogen of walnut black spot disease was tetramycin with a concentration of 0.3%,and the EC50 was 12.764 ug/mL.The inhibitory effect of streptomycin,80%allicin and 12%phytohormone was relatively strong,and the EC50 was 35.318 ug/mL,296.483 ug/mL and 350.752 ug/mL,respectively.The inhibition effect of 2%Chunremycin was the worst,and the EC50 value was 1399.59ug/mL.5.Outdoor pot experimentContinuous spraying 3 times,each interval 7d,concentration of 0.3%tetracycline 500times liquid agent has the best control effect on walnut black spot pathogen,the average control effect is 74.6%,streptomycin against walnut black spot The control effect of pathogens was second,and the average control effect was 71.69%.The difference between the two was not obvious.The control effect of 2%Chunremycin was the worst,and the average control effect was 39.38%.The results showed that 0.4%tetramycin was a highly effective fungicide for controlling black spot of walnut,and streptomycin could be used as an alternative fungicide.