Application of natural elicitors to promote growth, photosynthetic pigments, and the content and composition of essential oil in Melissa officinalis L.

Elicitors play key roles in plant defense and development, inducing an increase in secondary metabolites in many species. The objective of this study was to determine the effect of foliar application of different types and concentrations of elicitors on the production of dry weight, photosynthetic pigments, total soluble proteins, and phenols, as well as the content, yield and chemical composition of the essential oil (EO) of Melissa officinalis. Three experiments were conducted in a protected environment for 90 days. The design was completely randomized with four replicates, and the treatments consisted of foliar application of methyl jasmonate (0, 0.5, 2 and 8 mM), salicylic acid (0, 0.25, 0.5 and 1.0 mM) and chitosan (0, 2, 4 and 6 g L-1). The results indicated that the concentrations used of MeJA and SA did not increase total dry weight accumulation, however, all concentrations of Ch inhibited the total dry weight per plant. The EO contents were favored with the elicitation. The elicitors MeJA (8 mM) and Ch (2 g L-1) resulted in a 1.83- and 1.61-fold increase in productivity of EO compared to the control. However, the highest content was obtained with the application of 1 mM SA (0.49%), which was three times more compared to the control (0.16%). Fifteen chemical constituents were identified, which represented more than 85% of the total chemical composition of the essential oil in the plant. The three major compounds neral, geranial, and citronellal, make up approximately 92% of the EO, on average. Therefore, the application of elicitors in M. officinalis plants, especially at concentrations of 8 mM of MeJA and 4 g L-1 of Ch, has the potential to stimulate citral. Furthermore, the highest concentration of salicylic acid (1 mM) favored citronellal content (1.92 mg mL-1) and 0.5 mM the concentrations of citral (neral + geranial) in the essential oil of the plant. It can be said that the exogenous application of elicitors in M. officinalis plants can stimulate the content and the major constituents of its essential oil.