Studies On The Effect And Mechanism Of A Bacillus Siamensis LZ88 On Tobacco Brown Spot Disease

Tobacco brown spot disease is a harmful and serious leaf spot disease in tobacco production and which caused by A.alternata.Pathogens was spread by conidia,and large-scale outbreaks occur in a short period of time.The highly related to brown spot disease incidence of the degree of maturity and the aging of tobacco leaves.As the maturity of tobacco leaves increases which decreases of tobacco resistance and cause huge losses.Therefore,timely prevention is an effective method to control tobacco brown spot disease.At present,the prevention and control measures adopted in production are mainly chemical prevention and control.However,due to some disadvantages of chemical control,the use of biological agents to control tobacco brown spot disease has become an urgent need in production.So it’s more difficult to prevent and control diseases.In order to enrich the resources of tobacco antifungal strains and effectively use biological control methods to control tobacco brown spot disease.In this study,a total of 40 rhizosphere soil samples from healthy tobacco plants and screened a strain LZ88 which was identified as B.siamensis and that obvious inhibition A.alternata.The main results are as follows:1.224 strains of bacteria was isolated and purified from soil by plate dilution and plate scribing.A strain LZ88 was screened by the method of plate confrontation,which had obvious inhibition on A.alternata.It not only inhibited the growth of A.alternata,but also inhibit P.parasitica var.nicotianae、C.Güssow、C.gloeosporioides et.al;2.LZ88 was identified by colony form,physiological and biochemical characteristics and sequence analysis of 16 S r DNA and gyr B genes.By constructing a phylogenetic tree,the results showed that strain LZ88 and B.siamensis were clustered on the same branch,and the sequence similarity reached 99.72% and 99.91%,respectively.Finally,strain LZ88 was identified to be B.siamensis.3.The volatile substances produced by the strain LZ88 can effectively inhibit the mycelial growth and sporulation of A.alternata.The sterile fermentation filtrate of LZ88 can effectively inhibit the growth of A.alternata,at the same time destroy the structure of mycelia and affect the sporulation.The antifungal substance of the fermented crude extract of the strain LZ88 can inhibit A.alternata,and it is relatively resistant to high temperature and p H,and has good stability.4.Strain LZ88 can significantly improve the systemic resistance of tobacco plants,mainly by improving the activity of resistance related enzymes.5.LZ88 fermentation liquid can effectively control tobacco brown spot disease.Greenhouse experiments showed that the tobacco treated with fermentation broth had almost no disease,while the tobacco treated without any treatment had a serious disease.The potting experiment control effect reached 78.64% and 66.15% respectively,indicating that the strain has the potential to develop a biocontrol strain6.The fluorescence quantitative PCR detection system of A.alternata was established,so the content of A.alternata in tobacco leaves could be detected quantitatively,which could be used to guide the disease control period and actual production.