Isolation And Identification Of Antagonistic Bacteria Against Potato Scab,Optimization Of Fermentation Formula,and Their Effects On Potato Rhizosphere Microorganisms

Potato scab is an important soil borne disease of potatoes with serious harm.With the continuous expansion of potato planting area and long-term continuous cropping,potato scab has become increasingly serious,seriously affecting the yield and quality of potatoes.At present,the management of potato scab usually adopts measures such as chemical management,cultivation of disease-resistant varieties,rotation,and biological control.Using antagonistic bacteria represented by Bacillus to control soil borne diseases is non-toxic to humans and animals,environmentally friendly,and effectively improve the microbial community structure of plant roots.It is easy to ferment and does not require high environmental conditions,making it an important biological control strategy.This study used Streptomyces griseus as the target.A highly efficient antagonistic strain was screened with the plate confrontation method.The strain was identified,and the fermentation medium for producing antibacterial active substances was optimized.The properties of the antibacterial active substances were analyzed,and study the effects of the strain and antibacterial active substances on potato growth,rhizosphere soil microbial diversity,and community structure.We hope to provide theoretical basis and technical support for the prevention and control of potato scab and the development of specialized microbial agents for potatoes.The main results are as follows:(1)Seven good antagonistic effects against the pathogen of potato scab strains were screened,among which JT-1 strain had the most prominent antibacterial effect and was identified as Bacillus subtilis.(2)Established the bioassay method for the potency of JT-1 strain fermentation broth,and optimize the fermentation medium formula for producing antibacterial substances.The optimized medium formula was: maltose 2%,peptone 2.317%,potassium dihydrogen phosphate 0.089%;The optimal fermentation conditions include 6 hours of seed age,3 days of cultivation time,4% of inoculation amount,50 m L/250 m L of liquid,220 rap/min of rotation speed,and 30℃ of fermentation temperature.After optimization,the potency of the fermentation broth reached 11402.38 μg/m L,which was 249.61% higher than the basic culture medium.(3)The antibacterial active substances produced by JT-1 strain are more sensitive to heat,strong alkali,and ultraviolet radiation,partially sensitive to organic solvent chloroform,stable to protease K;The MIC and MBC of potato scab pathogen were 125 μg/m L and 250 μg/m L,respectively.(4)Inoculation of JT-1 strain and application of 500 μg/m L antibacterial active substances can significantly increase potato tuber yield,significantly reduce the incidence rate of potato scab,and significantly increase soil alkaline nitrogen content,soil invertase activity and soil urease activity.Inoculation of JT-1 strain significantly reduced the relative abundance of harmful bacteria such as Neocosmospora,and the application of 500 μg/m L antibacterial active substances could significantly increase the relative abundance of beneficial bacteria such as sphingosine,Nocardioides,Marmoricola,Massilia,Exophiala,and significantly reduce the relative abundance of harmful bacteria such as Streptomyces and Neocosmospora.