Antimicrobial activity of twenty-eight plant essential oils against pathogenic bacteria and fungi from different horticultural systems

Biopesticides based on plant oils have many ecological advantages in comparison with chemicals. Control of bacterial diseases is very difficult due to antibiotic resistance and ineffectiveness of chemical products, and essential oils offer a promising alternative. Six essential oils extracted from plants originated from Serbia and twenty-two commercial essential oils from Germany and Albania were assayed for inhibitory and lethal activity against bacterial and fungal pathogens in different horticultural systems. Bacteria tested were: Xanthomonas campestris pv. phaseoli (bean blight), Clavibacter michiganensis subsp. michiganensis (bacterial wilt and tomato canker), Pseudomonas tolaasii (mushroom bacterial brown blotch). Various fungal pathogens of cultivated mushroom were investigated: Lecanicillium fungicola var. fungicola (dry bubble), Mycogone perniciosa (wet bubble), Cladobotryum dendroides (cobweb disease), Trichoderma harzianum, Trichoderma atroviride, Trichoderma aggressivum f. europaeum (green mould) and phytopathogen Verticillium albo-atrum (verticillium wilt on pepper). Minimal inhibitory and lethal concentrations were determined by applying a single drop of oil onto the inner side of each plate cover using macrodilution fumigant method. Among all tested substances, the strongest and broadest activity was shown by the oils of oregano (Origanum vulgare) and wintergreen (Gaultheria procumbens) against bacteria. Mint oil (Mentha piperita L.) and cade (Juniperus oxycedrus L.) were the most toxic to pathogenic fungi. Carvacrol (64.0-75.8%) was the dominant component of oregano oils and menthone (37.2%) of mint oil. X. campestris pv. phaseoli, was the most sensitive bacteria to plant essential oils, and the least sensitive was P. tolaasii. The most susceptible fungus to plant essential oils was M. pernicosa, and the least V. albo-atrum. These results imply that oregano, wintergreen, mint and cade oils could contribute to disease control against different horticu