Isolation And Characterization Of Rhizoshpere Bacteria JX-1 Against Tomato Bacterial Wilt

Tomato bacterial wilt,caused by Ralstonia solanacearum,is an important soil-borne disease,which seriously affects the yield and planting area of tomato.At present,there is no effective chemical pesticide to control tomato bacterial wilt in the market.And biological control has gradually become a research hotspot because of its advantages of less environmental impact and less resistance.In this study,a bacterial strain,which inhibited the growth of R.solanacearum was isolated from the rhizosphere soil collected from different areas of Guangxi,and the bacteriostatic effect of the strain against R.solanacearum was preliminarily analyzed.The main results are as follows:1.A total of 2929 strains were isolated from rhizosphere soil samples collected in different areas of Guangxi.There were 146 strains screened with antagonistic activity against R.solanacearum by plate resistance method,and 7 strains with strong antagonistic activity were obtained after re-screening.Of which,7 strains with strong antagonistic activity were selected to test their control efficiency against tomato bacterial wilt.The result shows that strain JX-1 at the concentration of 1×10~8cfu/m L could control tomato bacterial wilt effectively,with the control effect of80.89%in pot and 55.03%in the field.Strain JX-1 was identified as Burkholderia cepacia based on morphological,physio-biochemistry features,and sequence analysis of 16S r DNA and gyr B.Strain JX-1 presented highly inhibitory against Fusarium oxysporum,Deightoniella torulosa,Phoma sorghina,Phythium aphanidermatum,Rhizoctonia solani,Sclerotium rolfsii,Phomopsis citri,which inhibition diameter were 6.57 mm,9.67 mm,7.00 mm,6.50 mm,7.93 mm,5.50 mm and 11.50 mm,respectively.Andit has no antagonistic activity against Pseudomonas syringae pv.tomato and Pectobacterium carotovorum subsp.carotovorum.2.Strain JX-1 produces several antimicrobial compounds,such as siderophores and extracellular proteinase.PCR analysis demonstrated that the specific genes within the biosynthetic loci for pyrrolnitrin and pyoluterin are conserved in strain JX-1,but no 2,4-DAPG related genes.3.Random mutagenesis was performed to identify novel regulator of antimicrobial traits in strain JX-1,and the mutants with significantly increased or decreased the antimicrobial activity were identified.The results showed that the mutant M645 could increased the antimicrobial activity against R.solanacearum.The diameter of inhibition was 15.50 mm,which was larger than 13.17 mm of wild type JX-1.And the mutant M1710 completely lost its antimicrobial activity on R.solanacearum.Our data showed that the antagonistic ability was negatively regulated by gnt R gene,and positively influenced by the pks/nrps gene in strain JX-1.The control effect of mutant M645 was significantly higher than that of wild type JX-1,while the control effect of mutant M1710 was significantly lower than that of wild type JX-1.Genetics experiment further showed that the complementary gnt R gene restored the antimicrobial activity of the mutants to the wild-type level;However,overexpression of gnt R gene made strain JX-1 completely lose its antagonistic ability against R.solanacearum.In summary,strain JX-1 is a biocontrol strain with antagonistic ability against R.solanacearum and produces a variety of secondary metabolites,which is suitable for controlling tomato bacterial wilt.