Study On The Control Effect Of Bacillus Velezensis NT35 Strain On Ginseng Rust Rot

Jilin Province is the main planting area of ginseng,and the incidence of ginseng rust rot is serious.The deterioration of soil microenvironment and pesticide residues caused by the use of chemical pesticides have a great impact on the quality of ginseng.The use of pesticides is very harmful to humans and the environment.Biological control is an environmentally friendly and safe control measure.In this experiment,the antibacterial effect and biocontrol effect of biocontrol bacteria NT35 on rust rot were studied in order to clarify its biocontrol mechanism.The results were as follows:（1）Bacillus velezensis NT35 with broad-spectrum antifungal activity had inhibitory effect on Ilyonectria.robusta CBLJ-3,and its EC₅₀ against I.robusta CBLJ-3was 0.93×10⁴ CFU·m L^-1.Different concentrations of NT35 fermentation broth had inhibitory effects on the mycelial growth of I.robusta CBLJ-3.When the concentration of NT35 fermentation broth was greater than or equal to 10⁷CFU·m L^-1,the mycelial growth of I.robusta CBLJ-3 was significantly inhibited,and the inhibition rate of mycelial growth was up to 99.51%.Similarly,different concentrations of fermentation broth significantly inhibited the spore production and germination of rust rot pathogens with normal morphology.When the concentration was greater than or equal to 10⁴CFU·m L^-1,I.robusta CBLJ-3 did not produce spores.When the concentration of fermentation broth was greater than or equal to 10⁸CFU·m L^-1,the inhibition rate of spore germination of I.robusta CBLJ-3 was significantly higher than that of other concentrations,up to 90.31%.Therefore,the optimal concentration of NT35 to inhibit the growth of rust rot pathogen was 10⁸ CFU·m L^-1.According to this concentration,the mycelial accumulation and biocontrol effect of biocontrol strain NT35 on I.robusta CBLJ-3 were verified.The results showed that NT35 significantly inhibited the mycelial accumulation of rust rot pathogen under liquid culture,and ginseng in vitro inoculation test proved that NT35 had both prevention and control effects on ginseng rust rot.（2）The application effect of NT35 strain was evaluated;the first is the effect of disease prevention.The application of NT35 can prevent and control the rust rot of ginseng seedlings,reduce the content of rust rot pathogens in seedlings,and reduce the colonization of pathogens in seedlings.After NT35 control,the content of pathogens in seedlings decreased by nearly 3 times,and the death rate of potted seedlings infected with rust rot pathogens decreased from 26.50%to 11.72%after NT35 WP control.The control effect on ginseng rust rot in field plots reached 51.99%.The second is the growth-promoting effect.NT35 has growth-promoting characteristics for ginseng seeds germinated under dark conditions.The yield increase rate of ginseng planted in field plots is as high as 26.7%.NT35 treatment significantly up-regulated the expression of squalene synthase gene（Pg SS）,squalene epoxidase gene（Pg SE）and dammarenediol synthase gene（Pg DDS）,which were related to the synthesis of ginsenosides in ginseng.（3）The biocontrol mechanism of NT35 against ginseng rust rot was studied.The double antibacterial strain NT35-Rif¹⁶⁰-Stre⁴⁰⁰ was screened,which could be colonized in the rhizosphere soil,root,stem and leaf of ginseng for 90 days.The determination of ginseng-related defense-related enzyme genes showed that NT35 induced ginseng resistance,and the expression levels of PAL,CHI,POD,β-1.3-GA,and SOD in ginseng roots were up-regulated within 11 days.NT35 could affect the changes of enzyme activities in ginseng rhizosphere soil.The changes of sucrase activity and urease activity increased first and then decreased at the overall level,reaching the maximum at the flowering stage,which were 148.58 mg·g^-1 and 572.26μg·g^-1,respectively.Phosphatase showed a rising trend,up to 1988.94μg·g^-1;catalase activity changes in the range of 0～2ml/g;during the four periods of ginseng growth and development,the soil enzyme activity after NT35 treatment was significantly higher than that of clear water control group and Yiwei control group.The determination of rhizosphere soil microecology showed that NT35 could increase the richness and diversity of soil bacteria and fungi,affect the proportion of microbial community at phylum level and the composition of genus level,reduce the relative abundance of harmful bacteria Fusarium,Neonectria,Ilyonectria and Dactylonectria,and recruit beneficial bacteria Luteimonas and Nocardioides.Through the study of biocontrol mechanism,it is speculated that NT35 prevents and controls ginseng rust rot through the following ways:inhibiting the growth of rust rot pathogen through competition and antagonism,exerting biocontrol effect by colonization into ginseng,improving soil enzyme activity,reducing the relative abundance of pathogenic bacteria in soil,and recruiting beneficial bacteria.