Effect of Foliar Application of Chitosan and Salicylic Acid on Morphological Traits and Essential Oil Quality of Lemon Balm (Melissa officinalis L.)

Lemon balm is an aromatic and perennial bushy plant with interesting pharmacological and biological properties, which extensively distributed in the Mediterranean region and Asia. The effects of salicylic acid (50, 100, 150 and 200 mg.L-1) and chitosan (50, 100, 150 and 200 mg.L-1) foliar application on plant parameters, essential oil and chemical compositions of lemon balm at two different harvest stages (seedling and flowering) were evaluated. The results showed that the highest values of chlorophyll index obtained from foliar application of 150 and 200 mg/L chitosan. Application of chitosan (all concentration levels except 50 mg.L-1) significantly improved the plant height of lemon balm compared with the control. Leaf and dry weight of aerial parts per plant increased with increasing in salicylic acid and chitosan concentrations. The essential oil compounds of lemon balm (citronellal, caryophyllene, linalool, carvacrol, α-pinene, geraniol) 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-1 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.