Suppression Of Bacterial Wilt Of Tomato And Fusarium Wilt Of Banana With Bacillus Velezensis Y6 And F7

Intensive agriculture has led to a significant increase in agricultural productivity and crop yields.However,long time and over-use of chemical fertilizers and pesticides,or unreasonable planting methods have resulted in serious soil-borne disease in crops.Thus,it reduced the yields and quality of the crops.Plant growth promoting rhizobacteria(PGPR)provide an effective and environmentally sustainable method to protect crops against pathogens.The spore-forming Bacilli are attractive PGPR due to their ease of storage and application.Here we characterized two rhizosphere-associated B.velezensis strains(Y6 and F7)from a local farm in South China.These strains exhibit potent biocontrol activity against tomato bacterial wilt and banana Fusarium wilt under greenhouse conditions.We identified three lipopeptide(LP)compounds(surfactin,iturin and fengycin)as responsible for the antimicrobial activity of these two strains.The results as follows:We characterized two rhizosphere-associated Bacillus velezensis isolates(Y6 and F7)that possess strong antagonistic activity against Ralstonia solanacearum and Fusarium oxysporum under both laboratory and greenhouse conditions.We identified the LPs from the extracts using UPLC-MS.Three major LPs were detected: iturin,fengycin,and surfactin.Thus,we evaluated the influence of R.solanacearum on the production of LPs by Y6 and F7.The elevated LP production by F6 and Y7 in response to R.solanacearum might be due to an increase in expression of LP biosynthesis genes.The srfAA:mls,ituA:mls,and fenC:spc single mutants and the double mutants ituA:mls fenC:spc and ituA:mls fenB:spc were generated by replacing the coding region with a resistance cassette using long flanking homology PCR(LFH-PCR)followed by DNA transformation.We further dissected the contribution of LPs to various biological processes important for rhizosphere colonization.Although either iturin or fengycin is sufficient for antibacterial activity,cell motility and biofilm formation,only iturin plays a primary role in defense against the fungal pathogen F.oxysporum.Additionally,we found that LP production is significantly stimulated during interaction with R.solanacearum.In a word,these results demonstrate the different roles of LPs in the biology of B.velezensis and highlight the potential of these two isolates as biocontrol agents against phytopathogens.The lipopeptide compounds have different structures and antagonistic effects on bacterial wilt.In this study,Iturin A and fengycin play a redundant role in defense against R.solanacearum,and Iturin is the primary factor responsible for antifungal activity against Foc in vitro and in vivo.These results demonstrate the different roles of and highlight the potential of these two isolates as biocontrol agents against phytopathogens.