Potential of a novel endophytic Bacillus velezensis in tomato growth promotion and protection against Verticillium wilt disease

Vascular wilts are one of the major threats to the growth and the productivity of crop plants. Repeated use of chemical fungicides to manage vascular wilt diseases are raising concerns. Other strategies including biocontrol using endophytic bacteria have been considered. To investigate the role of endophytic bacteria on Verticillium wilt, a novel bacterium C2, isolated from the crown tissue of tomato, was evaluated, in vitro and in vivo, against tomato wilt disease caused by Verticillium dahliae. C2 was identified by 16S rRNA gene sequencing as Bacillus velezensis. This strain exhibited, in vitro, significant antifungal activity against V. dahliae. This strain harbored genes involved in synthesis of lipopeptides (bacillomycin, fengycin and surfactin), polyketides (macrolactin, bacillaene and difficidin) and the dipeptide bacilysin. Moreover, GC-MS analysis of C2 showed the presence of volatile metabolites known by their antifungal activity, namely tetradecane, benzeneacetic acid, benzaldehyde, 1-decene and phenylethyl alcohol. Furthermore, the strain was able to produce lytic enzymes (protease, chitinase and beta-glucanase), siderophore and indole-3-acetic acid and to solubilize inorganic phosphate. Result of in vivo experiments indicated that the application of C2 at 10(7) CFU/mL, reduced significantly the Verticillium wilt incidence in tomato plant by 70.43 +/- 7.08%, compared to the untreated control. Besides protection, C2 improved markedly tomato plant growth which was evidenced by stem elongation and leaves number. The overall results of this study showed that B. velezensis C2 has a great potential to be commercialized as a biostimulant and biocontrol agent to manage effectively tomato Verticillium wilt disease.