Probiotic rhizospheric Bacillus sp. from Zingiber officinale Rosc. displays antifungal activity against soft rot pathogen Pythium sp.

Abstract

The bioactivity spectrum of antagonistic rhizobacteria isolated from Zingiber officinale was analyzed against the phytopathogen Pythium myriotylum, which causes Pythium rot in ginger. One of the isolates ZoRC2 showed broad bioactivity against P. myriotylum. By molecular identification, the rhizobacteria was identified as Bacillus vietnamensis. The distortions on phytopathogenic fungal structures by its purified fraction was studied by light microscopic and SEM analysis. The bioactive compounds produced by the isolate was separated by bioactivity-guided fractionation and was identified by GC–MS as 2,4-bis (1,1-dimethylethyl) phenol, a volatile phenolic compound with antifungal, anti inflammatory, anticancer and antibacterial activities. Here the presence of 2,4-bis (1,1-dimethylethyl) phenol produced by Bacillus strain was found to provide effective protection to ginger rhizome upon inoculation with Pythium myriotylum. This is the first report of 2,4-bis (1,1-dimethylethyl) phenol, being produced and act as the biologically active component by Bacillus vietnamensis. This compound was reported to have wide pharmaceutical and agronomic applications which include its use as a fungicide in agriculture. The in vivo antifungal activity of Bacillus strain was analysed by pre-inoculation of the purified antifungal compound to the ginger rhizome. Remarkably, during the rhizome protection studies, the purified compound was found to prevent P. myriotylum infection in ginger with associated enhancement in plant growth and bud development. The antifungal activity of the identified compound and the rhizospheric origin of Bacillus vietnamensis offers it as a biocontrol agent for Pythium rot in ginger as an alternative to fungicides.