Antibacterial effect of essential oils and monoterpene compounds against bacterial brown blotch disease of white button mushroom

Pseudomonas tolaasii is one of the most important pathogenic bacteria of the edible fungus (Agaricus bisporus) in Iran and the world. In this study, comparing the severity of pathogenicity of the isolates showed that the highest pathogenicity was related to isolate Pt 4. Antibacterial effect of 10 plant essential oils against isolate Pt 4 was measured by disk diffusion method and based on the diameter of the inhibitory halo, basil and thyme essential oils had the highest antibacterial effect, respectively. The results of chemical analysis of gas chromatography showed that methyl chavicol with 67.05% was the highest monoterpene compound of basil essential oil, which together with two well-known compounds of thyme including carvacrol and thymol showed a controlling effect against P. tolaasii. The results showed that the best effect in controlling the disease on the fungal cap at minimum inhibitory concentration (MIC) was for thymol, carvacrol and methyl chavicol, respectively, but at some concentrations higher than MIC, thymol and carvacrol caused symptoms of cap blackening. Methyl chavicol had no adverse effect against Agaricus bisporus in all concentrations used, despite having less effect on reducing pathogenicity. Therefore, the use of methyl chavicol combination can be a good option to prevent bacterial brown blotch disease in mushroom cultivation halls.