Control of potato soft rot disease using silicon, silicon nanoparticles and antagonistic bacterium Bacillus methylotrophicus at glasshouse conditions

In this research, the effect of Bacillus methylotrophicus in biological control of Pectobacterium carotovorum subsp. carotovorum, the causal agent of potato soft rot disease, as well as the effects of silicon and silicon nanoparticles, the two systemic acquired resistance inducing compounds, against both pathogenic and antagonistic bacteria was evaluated in laboratory and glasshouse conditions. In the disc diffusion and well diffusion assays, silicon and silicon nanoparticles did not produce any inhibitory zone around the tested bacteria, but the antagonistic bacterium, B. methylotrophicus, produced an inhibitory zone of growth in the same and chloroform assays with a radius of 9, 8.5 and 15 millimeters, respectively. Although, silicon nanoparticles slightly reduced populations of both pathogenic and antagonistic bacteria after 6 and 10 hours post culturing in liquid medium, but after 24 hours, the differences between them and control treatment were not significant. Silicon did not inhibit the growth of the tested bacteria in liquid medium. At glasshouse conditions, all treatments of silicon and silicon nanoparticles as well as antagonistic bacterium were significantly increased the fresh and dry root and shoot weight in compare to positive control, but the best result was achieved by combined treatments of silicon or silicon nanoparticles with antagonistic bacterium. All the treatments completely inhibited disease development on potato plants in compare to positive control and no disease symptoms were observed whereas in control treatments all the tubers showed maceration and rotting symptoms and were destroyed.