Screening And Biocontrol Mechanism Of Antagonistic Microorganism Against The Pathogen Of Tobacco Black Shank

Tobacco black shank is one of the serious diseases on tobacco,causing huge economic losses every year.Phytophthora nicotianae is the pathogen of causing tobacco black shank,so screening biocontrol microorganism with high antagonism against Phytophthora nicotianae is of great significance for the prevention and control of tobacco black shank and effective control of losses caused by disease.In this dissertation,the screening of the antagonistic microorganism,the determination of the antibacterial activity,the identification of strains,the determination of the inhibitory spectrum,the optimization of the fermentation conditions,and the biocontrol experiment were studied.The main results are as follows :1.Screening of antagonistic microorganism and determination of antimicrobial activity.16 antagonistic bacterias and 13 antagonistic actinomycetes were screened out from tobacco roots by dilute spread plate method and plate confrontation method.Among them,F-7 strain had the best inhibitory effect on Phytophthora nicotianae,and its antimicrobial rate reached 75.00%.By inhibition of mycelial growth rate method,the inhibitory activity of 29 strains of antagonistic fermentative metabolites on Phytophthora nicotianae was measured.The antimicrobial activity of F-7 was highest,reaching 81.41%.2.The F-7 strain was identified.Combined with morphological characteristics,culture characteristics,physiological and biochemical characteristics and 16 S rDNA sequence analysis,preliminary identification of this strain belongs to the genus Streptomyces sp.3.Determination of antimicrobial spectrum.By plate confrontation method between the F-7 strain and 17 test plant pathogen strains,the experimental results showed that the strain F-7 had good antimicrobial activity against 6 strains of the tested strains,and the antimicrobial rate reached over 60.00%.The F-7 strain had high antagonistic activity against Phytophthora spp.,and had the highest antagonistic activity against Phytophthora nicotianae,The other 11 strains had less and no inhibitory effect.4.The study of F-7 strain fermentation conditions.Through the control of six single-factor variables,the best optimum fermentation conditions for the F-7 strain were as follows: the culture medium is potato dextrose broth,the inoculum size is 1 mL,the initial pH is 6.0,the culture temperature is 28°C,the shaker speed is 180 r /min,and culture time is 5d.5.The heat stability and pH tolerance of the fermentation metabolites were studied.The results showed that the inhibitory effect was the most stable at 30°C.When the temperature exceeded 70°C,the antimicrobial activity of the fermentation broth decreased obviously to zero;When pH of the fermentation broth is between 6 and 10,the inhibition rate changes little and the tolerance is better.6.The pot biocontrol experiment was conducted.The results showed that F-7 strain fermentation broth had no obvious biocontrol effect on 3-5 leaf stage,and it had better control effect on 8-10 leaf stage plants.