Antifungal efficacy of plant essential oil nanoemulsions against cucumber powdery mildew

Abstract

Plant essential oil nanoemulsions (PEO-NEs) offer a sustainable alternative to synthetic fungicides for managing plant diseases. This study evaluated the antifungal efficacy of PEO-NEs derived from seven medicinal plants against cucumber powdery mildew. In vitro experiments revealed that PEO-NEs from Satureja khuzistanica (savory), Cymbopogon citratus (lemongrass), and Syzygium aromaticum (clove) at 1, 2, and 3 g/l significantly inhibited conidia germination by 83%, 74%, and 83%, respectively, while PEO-NEs from pine, thyme, eucalyptus, and peppermint were ineffective. Comparatively, synthetic fungicides Topas and Stroby showed lower inhibition rates of 75% and 65%. Greenhouse trials demonstrated that savory, lemongrass, and clove PEO-NEs at 3 g/l reduced disease severity by 54.05%, 40.54%, and 35.13%, outperforming synthetic fungicides Topas (24.32%) and Stroby (18.91%). Preventive application 48 h before pathogen inoculation further reduced severity by 72.41%, 55.17%, and 41.3% for savory, lemongrass, and clove, respectively. Phenolic compound analysis using HPLC-DAD revealed significant differences in 3,4-dihydroxybenzoic acid, Caffeic acid, Ferulic acid, Gallic acid, Rutin, and Rosmarinic acid levels in treated plants. GC-MS identified key compounds, including carvacrol (88.6%) in savory, eugenol (56.6%) and β-caryophyllene (29.93%) in clove, and citral (42.6%) in lemongrass. These findings highlight the potential of PEO-NEs as eco-friendly alternatives for managing cucumber powdery mildew.