Natural Preservation of Horticultural Produce: Antimicrobial Efficacy of Thymus hiemalis Essential Oil in in Vitro and in Situ Models

The present study evaluated the antimicrobial activity of Thymus hiemalis essential oil (THEO) against selected phytopathogenic bacteria and fungi using both in vitro and in situ approaches. Seven plant pathogens were tested: Xanthomonas arboricola, Pectobacterium carotovorum, Pseudomonas syringae, Agrobacterium radiobacter, Fusarium solani, Monilia fructigena, and Botrytis cinerea. In vitro antimicrobial activity was assessed using the disk diffusion method and determination of minimum inhibitory concentrations (MICs). THEO exhibited broad-spectrum antimicrobial effects, with the strongest inhibition observed in fungal isolates, particularly B. cinerea and F. solani. In situ assays were conducted on fresh-cut horticultural produce models – strawberry, apple, carrot, and parsley – to simulate natural microbial contamination. The antimicrobial efficacy of THEO in the vapour phase was tested at concentrations of 500, 250, 125, and 62.5 µL.L⁻¹. Growth inhibition was quantified using stereological image analysis, and the percentage reduction in microbial volume density (Vv) was calculated. Statistically significant inhibitory effects were observed across all tested matrices, especially at higher concentrations. The highest biological growth inhibition (BGI) values were recorded for F. solani and M. fructigena, indicating strong fungistatic potential of THEO vapours in horticultural systems. These findings suggest that Thymus hiemalis essential oil possesses effective antimicrobial properties with practical relevance for horticultural applications, particularly in the control of postharvest spoilage and decay caused by phytopathogens.