Effect of foliar application of ordinary and nano-zinc fertilizers on growth and essential oil profile of dragonhead

In this work, the effects of foliar zinc sprayings on some growth parameters and essential oil composition of dragonhead ( Dracocephalum moldavica L.) were assessed. A greenhouse experiment was carried out with two sources of zinc including zinc oxide (ZnO, as ordinary fertilizer) and zinc oxide nanoparticles (ZnO-NP, as nano-fertilizer), each having four concentrations (0, 25, 50, and 100 mg/l). Results showed that sprayings with zinc had significant influence on the evaluated parameters. Treatments with ZnO and ZnO-NP significantly increased root length, shoot height, root and shoot dry weights, photosynthesis pigments contents, antioxidant enzymes activity, and essential oil percentage, and in the impact of ZnO-NP was more effective than ZnO. The highest growth parameters and pigment contents were observed at 100 mg/L ZnO-NP. Based on the results, 27 components were identified in the dragonhead essential oil in which the maximum values belonged to oxygenated monoterpenes with four main components as geranial (27.91-36.09%), geranyl acetate (18.36-25.48%), neral (19.18-21.7%), and geraniol (5.93-8.30%). The amounts of these monoterpenes under ZnO-NP (especially at 100 mg/L) were higher than ZnO treatment and control plants. The findings of this study showed that the effect of ZnO-NP in increasing the growth, the antioxidant enzymes, and bioactive ingredients of dragonhead was more than ZnO, and it may be possible to use ZnO-NP as a nano-fertilizer in the sustainable production of essential oil in medicinal plants.