Effect of seasonal variations on essential oil production and composition of Plectranthus amboinicus (Lour.) grow in Egypt

Essential oils extracted from aerial parts of Plectranthus amboinicus (Lour.) and its chemical constituents as affected by four seasonal, namely summer, winter, spring and autumn growing variation were investigated. The hydro - distilled essential oil content ranged from tr ( 0.1%) to 0.5%. The highest essential oil contents (0.2% or 0.5 ml plant-1) were recorded in summer. The lowest essential oil contents (tr % or 0.1 ml plant-1) were recorded in winter. The essential oils consists of carvacrol as the most abundant component, followed by thymol. The highest amount of carvacrol (15.9%) resulted from the essential oil extracted from herbs collected in autumn. On the other hand the highest amount of thymol (12.7%) produced from the essential oil extracted from herbs collected in spring. The chemical classes of essential oil such as oxygenated monoterpenes and oxygenated sesquiterpenes increased in summer and were recorded values of 62.3 and 11.5%, respectively compared with other seasons. On the other hand monoterpene hydrocarbons and sesquiterpene hydrocarbons were increased in winter and autumn seasons which recorded the values of 31.4 and 22%, respectively. Alcohols are the major constituents of the oxygenated monoterpenes of Plectranthus amboinicus (Lour.) essential oil. Carvacrol and thymol represented the highest concentrations among the alcohols. This indicates that Plectranthus amboinicus (Lour.) essential oil grown in Egypt belongs to the carvacrol and thymol chemo - type.