In vitro study of plant growth promoting rhizobacteria (PGPR) and endophytic bacteria antagonistic to Ralstonia solanacearum formulated with graphite and silica nano particles as a biocontrol delivery system (BDS)

Antagonistic Lysinibacillus sp., Bacillus subtilis, and Pseudomonas fluorescens were proven to control Ralstonia solanacearum that causes bacterial wilt on potatoes. Present study reports in vitro evaluation of a formulation containing PGPR and endophytic bacteria with the novel biocontrol delivery system (BDS) consisted of graphite and silica NPs. Crystal structure, morphology, elemental analysis and size distribution of particles in the suspension were respectively observed by XRD, SEM, EDS, and PSA. While the morphology and bacterial existence were observed by SEM, UV–vis, and photoluminescence spectroscopy. The ability of above BDS to form synergistic effect and inducing antagonistic interactions against R. solanacearum was evaluated by measuring the diameter of inhibition zone (DIZ). It is highlighted that the widest inhibition zones were resulted from biocontrol with graphite + silica NPs, indicating that BDS significantly affects the biocontrol mechanism. Compared to control, the inhibition zones caused by Lysinibacillus sp. were widest in the formulation with 3% graphite +5% silica NPs; by B. subtilis were in the formulation with 5% graphite +5% silica NPs, and 5%; by P. fluorescens were in the formulation with 5% graphite +5% silica NPs. [Display omitted] •Isolates of endophytic Lysinibacillus and PGPR B. Subtilis, and P. fluorescens were viable in the biocontrol delivery system formulated with graphitic carbon and silica NPs.•Those bacterial isolates in the formulation were also able to inhibit the in vitro growth of R. solanacearum.•The widest inhibition zones were shown by the formulation with graphite and silica NPs, indicating that the delivery system significantly affects the mechanism of biocontrol.