Screening Of Antagonistic Actinomycetes Against Phytophthora Nicotianae And Colonization In Tobacco Rhizosphere

Tobacco black shank disease is one of the important diseases in tobacco production.The outbreak of the disease every year cause serious economic losses to tobacco farmers,and the chemical control that can quickly control the disease bring a series of problems,such as pesticide residues,environmental pollution,fungicide resistance and so on.It is urgent to find a biological control method with low toxicity,no pollution to the environment and not easy to produce fungicide resistance.The pathogen of tobacco black shank is Phytophthora nicotianae and screening of antagonistic actinomycetes with high inhibition rate on the mycelial growth of P.nicotianae is great significance for the prevention and control of tobacco black shank.In this paper,the screening of highly effective antagonistic actinomycetes,determination of antibacterial activity,strain identification,tobacco rhizosphere soil colonization test and field control effect of P.nicotianae were studied.The main results were as follows:1.Fifteen strains of actinomycetes with antagonistic effect on the mycelium growth of P.nicotianae were screened from the soil by dilute spread plate method and plate confrontation method,of which the inhibition rate of antagonistic strain H-3 reached 81.90%,and the antagonistic effect was the best.2.The inhibitory activity of H-3 fermentation metabolic liquid on P.nicotianae mycelium growth were tested.The result showed that the inhibition rate of H-3fermentation metabolic liquid to P.nicotianae was also gradually increased,and finally the inhibition rate stabilized at about 86.77%.3.The 16S rDNA of antagonistic strain H-3 was sequenced,constructed a phylogenetic tree,and preliminarily identified that the strain belonged to Streptomyces sp.4.The natural resistance of H-3 to ten fungicides was determined.It was found that the natural resistance to mancozeb was the lowest and the lowest inhibitory concentration was 15mg/L.The mutant HR-3 with stable resistance to mancozeb in 105mg/L was obtained by fungicide resistance mutagenesis.5.Mancozeb labeled antagonistic strain HR-3 were colonized in tobacco rhizosphere soil,and the content of labeled antagonistic strain in tobacco rhizosphere soil was measured every other time,then the growth and decline dynamics of HR-3 in tobacco rhizosphere soil within 90 days were obtained.The isolation of labeled antagonistic strain in tobacco roots indicated that HR-3 could colonize in tobacco and its rhizosphere soil.6.Investigation on the control effect of HR-3 in the field.The field experiment on the control effect of antagonistic strain was carried out in Meitan and Zhengan tobacco fields in Guizhou province.The results showed that antagonistic strain HR-3 had obvious control effect on tobacco black shank.7.After field application,the amount of tobacco black shank pathogen in the diseased soil was detected by fluorescence quantitative analysis and it was found that the amount of tobacco black shank pathogen in the diseased soil treated with antagonistic strain HR-3 was lower than that in the soil without antagonistic strain HR-3.