Antifungal Activity and Chemical Composition of Seven Essential Oils to Control the Main Seedborne Fungi of Cucurbits

Abstract

Essential oils represent novel alternatives to application of synthetic fungicides to control against seedborne pathogens. This study investigated seven essential oils for in vitro growth inhibition of the main seedborne pathogens of cucurbits. Cymbopogon citratus essential oil completely inhibited mycelial growth of Stagonosporopsis cucurbitacearum and Alternaria alternata at 0.6 and 0.9 mg/mL, respectively. At 1 mg/mL, Lavandula dentata, Lavandula hybrida, Melaleuca alternifolia, Laurus nobilis, and two Origanum majorana essential oils inhibited mycelia growth of A. alternata by 54%, 71%, 68%, 36%, 90%, and 74%, respectively. S. cucurbitacearum mycelia growth was more sensitive to Lavandula essential oils, with inhibition of ~74% at 1 mg/mL. To determine the main compounds in these essential oils that might be responsible for this antifungal activity, they were analyzed by gas chromatography-mass spectrometry (GC-MS). C. citratus essential oil showed cirtal as its main constituent, while L. dentata and L. nobilis essential oils showed eucalyptol. The M. alternifolia and two O. majorana essential oils had terpinen-4-ol as the major constituent, while for L. hybrida essential oil, this was linalool. Thus, in vitro, these essential oils can inhibit the main seedborne fungi of cucurbits, with future in vivo studies now needed to confirm these activities.

Keywords: Alternaria alternata; Cymbopogon citratus; GC-MS; Stagonosporopsis cucurbitacearum; cucurbits.

Figure 1

Representative experiment showing inhibition of Alternaria alternata mycelial growth by Cymbopogon citratus essential oil at 0.1 to 1 mg/mL and by the fungicide combination of 25 g/L difenoconazole plus 25 g/L fludioxonil at 0.1, 0.5 and 1 mg/mL, as seen after 8 days of incubation at 22 ± 2 °C.

Figure 2

Representative experiment showing inhibition of Stagonosporopsis cucurbitacearum mycelial growth by the seven essential oils: C.cit, Cymbopogon citratus; L.dent, Lavandula dentata; L.hyb, Lavandula hybrida; M.alt, Melaleuca alternifolia; L.nob, Laurus nobilis; O.maj1/2, Origanum majorana 1/2, at increasing concentrations (right to left; as indicated) from 0 mg/mL (control) to 1 mg /mL, and by the fungicide combination of 25 g/L difenoconazole plus 25 g/L fludioxonil (positive control) at 0.1, 0.5 and 1 mg/mL, after 7 days of incubation at 22 ± 2 °C.

Figure 3

Inhibitory concentration for 50% reduction (IC₅₀) of mycelial growth of Alternaria alternata (A) and Stagonosporopsis cucurbitacearum (B) by the seven essential oils: C.cit, Cymbopogon citratus; L.dent, Lavandula dentata; L.hyb, Lanvandula hybrida; M.alt, Melaleuca alternifolia; L.nob, Laurus nobilis; and O.maj1/2, Origanum majorana 1/2. Data with different letters (a–f) are significantly different between treatments (p ≤ 0.05; Fisher’s LSD).