Screening endophytic bacteria from soybean root nodules to inhibit Fusarium oxysporum f. sp. Vasinfectum

Abstract:

[Objective] Using desirable strain resources to control Fusarium wilt of cotton is an effective way. This study aimed to acquire antagonistic endophytic bacteria from soybean nodules, explore their inhibition mechanism and strain characteristics. [Methods] Confrontation and metabolic liquid culture methods were adopted to screen endophytic bacteria from soybean nodules against Fusarium oxysporum f. sp. vasinfectum. The effect of screened strains on pathogen hyphae changes were analyzed with microscopic observation method. Combined with cultural, physical and chemical characteristics, 16S rDNA sequencing results and homology analysis of screened strains, phylogenetic status were determined. Disease-control effects were demonstrated by greenhouse inoculation test. [Results] Five strains of endophytes have inhibitory effect by the second screening and metabolic liquid test. Pathogen hyphae treated with endophytes became deformity, its cell wall disappeared, autolysis, bold at the base of the mycelium, branches increased and root shape appeared. Hyphae were embeded, dissolved and fractured by lawn formed by endophytic bacteria, and presented spherical expansion of its terminal. The inhibition of endophytic bacteria against Fusarium oxysporum f. sp. vasinfectum was mainly caused by extracellular metabolites. DD174, DD176 and DD179 were similar to Bacillus oceanisediminis H2^T(GQ292772) and B. thuringiensis ATCC 10792^T(AF290545), respectively. DD165 and DD166 were similar to Stenotrophomonas maltophilia LMG 958^T (X95923). DD174 tolerated 6% salt concentration and grew well at pH 10. Control effect of treatment group with DD174 was 76.32%, those of others were above 62%, so these strains can be used as biocontrol resources against Fusarium oxysporum f. sp. vasinfectum. [Conclusion] Endophytic antagonistic bacteria inhabited soybean root nodules against Fusarium oxysporum f. sp. vasinfectum.

Key words:Fusarium oxysporum f. sp. vasinfectum;soybean nodule endophytes;antagonistic effect;16S rDNA;phylogenetic analysis