Isolation And Identification Of Bacillus Velezensis SDTB038 And Its Biocontrol Effect

Potato is one of the four major food crops in our country and it is widely grown in the world.Potato late blight caused by Phytophthora infestans is highly prevalent and harmful.It can infect all parts of potatoes,cause stems,leaves and rot,and cause significant economic losses.The use of chemical pesticides is still the main control measure for potato late blight in agriculture.However,the improper use of chemical pesticides can easily cause environment pollution and poses a threat to human health.Biological control has the characteristics of nontoxic,non-polluting,good control effect,can reduce the residual amount of fungicides,and protect the environment and human health compared with chemical pesticides.Bacillus velezensis is a gram-positive bacteria.It is widely distributed in nature,easy to separate and cultivate,non-toxic and harmless to humans and animals,and has good antibacterial activity.B.velezensis has broad application prospects in biological control,and has gradually become one of the important methods for plant disease control.The use of a combination of biological control and chemical control strategies can not only reduce the application of chemical agents,improve the stability of biological control,but also achieve the effect of effective disease control.Therefore,more and more attention has been paid in the field of plant disease control.However,there are few reports on the research on the use of biocontrol bacteria and chemical agents to prevent and control potato late blight.In this study,a biocontrol strain SDTB038 was isolated from the tomato rhizosphere soil,which has a good inhibitory effect on bacteria,fungi and oomycetes.The strain SDTB038 was identified as B.velezensis based on morphological characteristics,physiological and biochemical indicators,and phylogenetic tree analysis results.The strain can produce secondary metabolites with antagonistic effect on potato late blight,and can effectively inhibit the infection of potato leaves by P.infestans.Strain SDTB038 can be developed as a biological pesticide with inhibitory effect on the pathogen of potato late blight.This study explored the effects of chemical agents and B.velezensis in the prevention and control of potato late blight,providing a new idea for the development of agents for preventing and controlling potato late blight,laying a foundation for the future development and utilization of Bacillus spp.,and evaluating the effects of biological pesticides.The safe and reasonable use of pesticides provides a theoretical basis for the comprehensive prevention and control of biological and chemical pesticides in production.The main results are as follows:1.This study mainly screened the antagonistic strain SDTB038,which has a better inhibitory effect on potato late blight pathogens.The strain also had a good antibacterial effect on various pathogens such as the fungal pathogen Fusarium oxysporum f.sp.fragariae and Rhizoctonia solani,and the bacterial pathogen Ralstonia solanacearum.According to its morphological,physiological and biochemical characteristics,the results of phylogenetic trees constructed by 16 S r RNA genes,gyr A genes and gyr B genes,the strain SDTB038 was identified as B.velezensis through those analysis.2.B.velezensis SDTB038 had shown a good control effect on potato late blight in both the greenhouse test and the field test,and it had promoted the growth of potatoes.In the greenhouse experiment,B.velezensis SDTB038 promoted plant growth(plant height and stem thickness).Two-years of field trials(2018,2019)showed that B.velezensis SDTB038 could reduce the incidence of potato late blight by 40.79%(2018)and 37.67%(2019).The control effect of B.velezensis SDTB038 and the highest concentration(170 g/ha)of fluopimomide was better than other treatments,reached 81.75%(2018)and 79.45%(2019).There was no statistically significant difference(P <0.05)in the control effects of 85 g/ha fluopimomide and B.velezensis SDTB038 and 170 g/ha fluopimomide alone.These field results show that low-concentration fluopimomide and the strain SDTB038 can play an effect in field control.Meanwhile,fluopimomide and SDTB038 antibacterial substance showed synergistic effects.These results show that low-concentration fluopimomide and the strain SDTB038 could be effective in controlling potato late blight in field control.3.Foliar tests showed that the extracted lipopeptides(LP)have an inhibitory effect on P.infestans.The lipopeptide substance can affect the permeability of the cell membrane of P.infestans,and the oozing content substance increases the conductivity value.Analyze the production of B.velezensis SDTB038 by ultra-highperformance liquid chromatographyquadrupole-time-of-flight mass spectrometry(UPLC-Q-TOF-MS)to produce surfactant.Through the amplification of lipopeptide genes,B.velezensis SDTB038 contains surfactin genes(srf AB,srf AC)and fengycin genes(fen B).Therefore,the lipopeptide secreted by B.velezensis SDTB038 is one of the main biocontrol mechanisms that can prevent potato late blight.