Impact of four hemp (Cannabis sativa L.) varieties and stage of plant growth on yield and composition of essential oils

Essential oil of Cannabis sativa L. is a valuable bio-product due to its versatility, particularly in terms of its commercial values and potential applications in medicine, cosmetics and bio-pesticide. In this study, the effect of different stages of plant growth on essential oil yield and composition of four hemp varieties, (two monoecious non-native (Fedora 17 and its progeny) and two dioecious native (Fars and Yazd) samples) were investigated. The plant materials, consist of foliage in vegetative stage, inflorescent of flower in flowering stage and inflorescent of seeds in seeding stage were subjected to hydro-distillation. The essential oils were analyzed by GC and GC/MS. The oil yields varied from 0.40 % (Fedora17) to 0.65 % (Yazd). Interaction of cultivar and growth stage showed Fed17-2 at vegetative (0.86 %) and Fed17 at flowering stage (0.20 %), had the most and least oil content, respectively. Twenty-nine compounds were identified representing 81.9%-99.5% of the essential oils. The most abundant sesquiterpenes in the oils were E-caryophyllene (16.40 %-44.70 %), alpha-humulene (4.1 %-15.1 %) and Z-caryophyllene (2.4 %-10.7 %), while the major monoterpenes were (0.4-24.9 %), beta-pinene (4.6-24.3 %) and 1,8-cineole (0.8 %-9.3 %) in all growth stages and cultivars. The ratio of sesquiterpenes to monoterpenes were found to decrease during the developing plants. In conclusion, there was no significant difference between mean oil yields of native and non-native samples, but non-native samples produced the highest oil yield in vegetative stage. E-caryophyllene was found at the highest percentage in the oils of non-native samples at vegetative stage. For all samples, the essential oils at vegetative stage contained much lower production of monoterpenes than flowering stage. In addition, to obtain the highest amount of beta-pinene and 1,8-cineole, the flowering and seeding stages of hemp are recommended.