Thymus vulgaris essential oil and thymol against Alternaria alternata (Fr.) Keissler: effects on growth, viability, early infection and cellular mode of action

BACKGROUND In initial assays, Thymus vulgaris essential oil (TEO) has demonstrated activity against several plant‐pathogenic fungi and has reduced the fungal diseases to levels comparable with commercial fungicides. Thus, the goal of this work was to identify the mode of action in fungi of TEO and its major compound thymol (TOH) at the cellular level using an ultrastructure approach. RESULTS TEO from leaves and TOH had minimum inhibitory concentrations (MICs) of 500 and 250 µg mL−1 respectively against A. alternata; under the same conditions, MIC for a commercial fungicide was 1250 µg mL−1. Ultrastructure analysis showed that TOH phenolic substance prevented fungal growth, reduced fungal viability and prevented the penetration in fruits by a cell wall/plasma membrane interference mode of action with organelles targeted for destruction in the cytoplasm. Such mode of action differs from protective and preventive–curative commercial fungicides used as pattern control. CONCLUSION These findings suggest that TOH was responsible for the antifungal activity of TEO. Therefore, both the essential oil and its major substance have potential for use in the development of new phenolic structures and analogues to control Alternaria brown spot disease caused by Alternaria alternata. © 2014 Society of Chemical Industry