Chemical characterization and antifungal activities of four Thymus species essential oils against postharvest fungal pathogens of citrus

The aim of this study was to find an alternative to synthetic fungicides currently used in the control of postharvest fungal diseases of citrus. Antifungal activities of essential oils from four Thymus species were investigated against Penicillium digitatum, Penicillium italicum and Geotrichum citri-aurantii. The essential oils, obtained by hydrodistillation from aerial parts of four Thymus species were submitted to gas chromatography hyphenated with mass spectrometry analysis. The main constituents were carvacrol (76.94%) for Thymus leptobotrys, borneol (27.71%) and thymol (18.47%) for Thymus satureioides subsp. pseudomastichina, camphor (46.17%) and α-terpineol (7.69%) for Thymus broussonnetii subsp. hannonis and carvacrol (32.24%), γ-terpinene (19.60%) and p-cymene (13.52%) for Thymus riatarum. In the in vitro mycelial growth assay, complete inhibition of the three pathogens was obtained by T. leptobotrys and T. riatarum essential oils, at 1000 μl L-1. The effect of essential oils on spore germination varied significantly between tested Thymus species. T. leptobotrys essential oil displayed the highest bioactivity, inhibiting completely the spore germination of G. citri-aurantii at 250 μl L-1 and of P. digitatum and P. italicum at 500 μl L-1. T. riatarum essential oil was able to inhibit completely the spore germination of G. citri-aurantii (2000 μl L-1) and both Penicillium species used as target organisms (1000 μl L-1). The essential oil of T. leptobotrys had the lowest minimum inhibitory concentration (MIC) for the three pathogens (MIC value < 500 μl L-1). These findings suggest that essential oils obtained from T. leptobotrys, T. riatarum and T. satureioides subsp. pseudomastichina may be useful and effective agents for control of citrus fungal pathogens.