Foliar application of salicylic acid and chitosan on the growth and quantity and quality of the essential oil from lemon balm (Melissa officinalis L.)

Lemon balm (Melissa Officinalis L.) is an aromatic and perennial bushy plant with interesting pharmacological and biological properties, which is extensively distributed in the Mediterranean region and Asia. This research was conducted to address the effects of salicylic acid and chitosan foliar application on plant parameters, essential oils and chemical compositions of lemon balm at two different harvest stages. The first experiment was employed based on a completely randomized design (CRD) with 9 foliar treatments (water, salicylic acid with concentrations of 50, 100, 150 and 200 mg/L and chitosan with concentrations of 50, 100, 150 and 200 mg/L) and three replicates. The second experiment was performed as a factorial experiment based on completely randomized design with mentioned foliar treatments and two different harvest stages (seedling and flowering) and three replicates. The essential oil content of the air-dried aerial parts was obtained by hydro-distillation using a Clevenger apparatus. The constituents of essential oil were detected using the chromatography apparatus connected to the mass spectrometry (GC/MS). The results showed that the highest values of chlorophyll index (34.39 and 34.03 Spad) obtained from foliar application of 150 and 200 mg/L chitosan. Application of chitosan (150 mg/L) significantly improved the plant height (27.3%) of lemon balm compared with the control. Leaf and total dry weight per plant increased with increasing in salicylic acid and chitosan concentrations. The essential oil compounds of lemon balm (except caryophyllene oxide, z-citral and e-citral) at flowering harvest stage were significantly higher than the seedling harvest stage. Foliar application of chitosan was more effective than salicylic acid in increasing essential oil compounds of lemon balm. The essential oil content ranged between 0.07% and 0.09% in the seedling harvest stage and between 0.30% and 0.52% in the flowering harvest stage. The highest value of essential oil (0.52%) was recorded from the flowering harvest stage with foliar application of 200 mg/L chitosan. The findings of the current study showed that both elicitors possess strong potential in biomass production and enhancement of essential oil compounds in lemon balm.