Determination of chemical compositions of rosemary and sweet marjoram essential oils and their blends and their antifungal potential against potato rubbery rot disease agent Geotrichum candidum

In this study, the chemical compositions of rosemary (Rosmarinus officinalis Spenn.) and sweet marjoram (Origanum majorana L.) essential oils, both individually and in various blend ratios, were investigated by using Gas Chromatography-Mass Spectrometry. Their antifungal activities were also determined against the potato rubbery rot disease agent, Geotrichum candidum, under in vitro and in vivo conditions. Camphor (20.69%) and terpinen-4-ol (35.13%) were determined as primary constituents in rosemary and sweet marjoram essential oils, respectively. Sweet marjoram and rosemary essential oils completely inhibited mycelial growth of G. candidum at 55.0 and 65.0 µL/Petri concentrations, respectively. Essential oils at these concentrations were found as fungicidal. Notably, a synergistic fungicidal antifungal effects were also observed in essential oil blends. Blend of sweet marjoram and rosemary essential oil in a 3:1 ratio (O₇₅R₂₅) significantly enhanced antifungal activity at the relatively lower concentration (45.0 µL/Petri). Microscopic observations revealed structural deformations in exposed hyphae, including cytoplasmic coagulation and vacuolization. Essential oil blend (O₇₅R₂₅), sweet marjoram and rosemary essential oils completely inhibited the disease lesion caused by G. candidum on potato tubers at concentrations of 100.0, 125.0, and 150.0 µL/L air, respectively. These findings emphasized that essential oil blends of rosemary and sweet marjoram have synergistic antifungal potential and can be used as effective biofungicides against plant fungal diseases.