Research On The Control Effect And Mechanism Of Bacillus Velezensis SDTB038 On Fusarium Crown And Root Rot Of Tomato

In recent years,with the rise of the facility tomato industry,diseases have been spread with the process of cultivation,especially the soil-borne diseases.Fusarium crown and root rot of tomato is one of the soil-borne diseases that cause serious damage to the facility tomato industry.Due to the late discovery of the disease in China,there was few report about the disease,especially the research on the biological control.A strain of Bacillus velezensis SDTB038 with biocontrol effect was isolated in the early stage.Based on previous studies,in this research the antibacterial activity of SDTB038 fermentation broth and crude lipopeptide extracts of different concentrations on Fusarium oxysporum f.sp.radicis-lycopersici（FORL）,the growth promotion effects of SDTB038 on tomato seed germination and plant growth,and the colonization dynamics of SDTB038 in soil and inside plants.Finally,it was verified that the control effect of SDTB038 fermentation broth on fusarium crown and root rot of tomato was 42.98%through field experiments.Through the sequencing analysis of the whole genome of SDTB038,its biosynthetic gene clusters were predicted,and the possibility of biocontrol were explained from the genome level.This study preliminarily explored the mechanism of its prevention and control of Fusarium crown and root rot of tomato,so as to provide a certain theoretical reference for the biological control of Fusarium crown and root rot of tomato.The main results of this study are as follows:1.The results of indoor antibacterial activity assay showed that different concentrations of SDTB038 fermentation broth had antibacterial activity on FORL,and the maximum antibacterial band width was 7.66 mm.The plate confrontation culture test showed that the crude lipopeptide extract could inhibit the growth of FORL mycelia,the EC₅₀value was 59.95mg/L,and the bacteriostatic rate was 97.42%at the concentration of 256 mg/L.2.The results of physiological and biochemical tests showed that SDTB038 could grow in the range of 5-50℃.SDTB038 produced metabolites such as protease,siderophore,and indole acetic acid,except chitin.It had the ability of biofilm formation and migration,but had no phosphorolysis activity.3.The results showed that the treatment of tomato seeds with SDTB038 fermentation broth could significantly promote seed germination on the 2^nd and 3^rd day,and the shoot length and root length of 10~7CFU/m L SDTB038 fermentation broth treatment was significantly higher than those of water and LB control treatments.In addition,the results of hydroponic experiments showed that SDTB038 fermentation broth had the most obvious effects on the plant height,fresh weight and dry weight.On the 40^th day after treatment,the fresh weight of plants treated with 10~8CFU/m L SDTB038 fermentation broth was not significantly different from that of trans-Abscisic Acid treatment,but was significantly higher than that of water and LB.The dry weight of plants treated with 10~8CFU/m L SDTB038 fermentation broth was significantly higher than that in water treatment,liquid LB treatment and trans-Abscisic Acid treatment.The above results indicated that SDTB038 could promote seed germination and plant growth.And since SDTB038 could produce indoleacetic acid,we speculated that indoleacetic acid may play a key role in promoting growth.4.The colonization dynamics of rifampicin-labeled strains in the rhizosphere soil and tomato roots,stems,and leaves were determined by the plate recovery detection method within60 days.In the rhizosphere soil,the amount of biocontrol bacteria recovered and detected was2.05×10~9CFU/g on the first day,6.39×10~7CFU/g on the 14th day,and stabilized between2.89×10~6and 5.91×10~6CFU/g in the later period.At 14 days after treatment,the colonization amount in roots,stems and leaves was the highest during the whole experiment period,which were 3.89×10~9,4.07×10~9,9.13×10~7（original leaves）,and 2.07×10~9（new leaves）,respectively.On the 60th day after treatment,the colonization amount of roots and stems exceeded 10~5CFU/g,and the colonization amount of leaves exceeded 10~4CFU/g.The results showed that the strain SDTB038 could colonize the soil and plants normally,and the colonization amount gradually decreased with the passage of time,and tended to be stable in the later period.5.The whole genome of SDTB038 was sequenced by combining the second and third generation sequencing technology.The genome size was 3929791 bp,and its GC content was47.26%.Through the comparison and analysis of functional databases with GO,COG and KEGG,it was found that SDTB038 had 303 genes involved in amino acid transport and metabolism,288 genes involved in transcription,266 genes involved in carbohydrate transport and metabolism,and 222 genes involved in translation,ribosome structure and biogenesis,127genes were involved in ABC transporters,and 114 genes were involved in two-component system.In addition,through software prediction,seven biosynthetic gene clusters of secondary metabolites were found,and the secondary metabolites were inseparable from the antibacterial activity,which explained the reasons for their biocontrol effects from the genome level.