Water stress is the most common abiotic environmental factor that influenced the morphological and physiological traits of the plants. Application of antitranspirants substances such as chitosan can reduce water loss. Summer savory (Satureja hortensis L.) is one of the important medicinal and aromatic plants which is used in food and pharmaceutical industries. In this investigation, the response of summer savory to foliar application chitosan (acetic acid, 0, 0.5, 1 and 2 g/L) under three irrigation regimes (30, 60, and 90% field capacity (FC), as a pot factorial experiment in randomized complete design with three replications, was evaluated. Chitosan and irrigation regimes treatments had significant effects on studied parameters, including biomass, dry matter, essential oil content, and composition as well as selected physiological characteristics comprising photosynthetic pigments, osmotic adjustment, total phenolic content, and antioxidant activities of the extract of summer savory. The results showed that chitosan application was useful under severe water stress (30% FC) and 2 g/L of chitosan improved total phenolic, total soluble sugar and proline contents, antioxidant activity, and essential oil content of the plant. Elicitation of summer savory with chitosan under water stress modified essential oil compositions such as carvacrol, γ-terpinene, and p-cymene. In conclusion, the findings of the present experiment indicated that chitosan could be a favorable material used to decrease the deleterious effect of water stress. Furthermore, the chitosan spraying can behave beneficial effects on the essential oil quality and quantity as well as osmotic adjustment, antioxidant activity, and growth of summer savory under water stress conditions.

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