Effects of Elicitors on Physiological and Phytochemical Characters of Hyssop (Hyssopus officinalis L. Subsp. angustifolius Bieb.) in Various Irrigation Conditions

Introduction Hyssopus officinalis L. belongs to the family Lamiaceae, and is one of the endangered endemic species in Iran. This plant is rich in essential oil, flavonoids, monoterpene glycosides, trypanocidal terpenoids, rosmarinic acid, and linolenic acid6. The main compounds of the essential oil from H. officinalis L. collected from natural habitats are α-pinene, Sabinene, 3-Carene, Beta-Pinene, Cis- Pinocamphone, Myrtenol, Pinocamphone and Camphor. The environmental factors cause changes in the growth, quantity, and quality of active substances (such as alkaloids, glycosides, steroids and volatile oils) in the medicinal and aromatic plants. Among environmental stresses, water deficit stress plays an important role in the biosynthesis of secondary metabolites in medicinal and aromatic plants in arid and semi-arid regions like Iran. Drought stress has detrimental effects on growth and yield and can upset the balance between the antioxidant defense system and free radicals by stimulating a series of biochemical reactions, where free radicals cause cell damage. In sustainable production systems of medicinal and aromatic plants, stable quantitative and qualitative functions can be achieved under conditions of environmental stress and it is possible to improve the production of secondary metabolites in these plants under adverse environmental conditions. Therefore, this study was done to evaluate the organic elicitors on the physiological and phytochemical properties of H.officinalis to determine and introduce the best elicitor under water stress.   Materials and Methods This investigation was done from spring (May) 2022 to fall (September) 2023 at the Research Farm (latitude. 32°20′ N, longitude. 50°51′ E, altitude. 2061 m). Based on the Köppen climate classification, the climate of the area of study is classified as cold and semiarid. The present study was conducted in a randomized complete block design (RCBD) with three replications to investigate the effect of foliar application of different organic elicitors (chitosan, salicylic acid and phenylalanine) with control level (without any spraying) on the physiological and phytochemical characters of H. officinalis L. In each year, treatments were performed in 3 stages (end of vegetative, beginning of flowering and 50% of flowering) and in full flowering, harvesting was done. 3 irrigation regimes (4, 6, 8 day interval) in main plots and foliar application of elicitors in sub plots were done. The essential oils were extracted by hydro-distillation and analyzed using GC/MS.     Results and Discussion According to obtained results, applied organic elicitors significantly influenced the physiological and phytochemical characters of H. officinalis L. However the assayed traits showed slightly variation during the studied years. In two years, the highest chlorophyll content (17.12-17.31 mg.Kg-1 FW) and total phenol content (1.77-1.81 mg.g-1 DW) were obtained in chitosan (0.5 mg.l-1) and phenyl alanine (1000 mg.l-1) treatments respectively. In most of measured characters, plants treated with chitosan (0.5 mg.l-1) and phenyl alanine (1000 mg.l-1) were in the same group. Amounts of some characters in plants treated with phenyl alanine (2000 mg.l-1) and salicylic acid (3 mM) lesser than control plants. The main constituents of essential oil were Sabinene, 3-Carene, Beta-Pinene, Cis- Pinocamphone, Myrtenol, Pinocamphone and Camphor (cyclic monoterpenes) that made the most components of essential oil plants. Among of elicitors, the chitosan effect on increasing of physiological and phytochemical characters such as the  chlorophyll content was higher than other elicitors. Applied elicitors showed significant effects on essential oil content and composition of H. officinalis L. The highest essential oil content (0.89-0.91 %) was obtained from the treated plants by chitosan (0.5 mg.l-1). According to the biennial results of the chemical analysis of the essential oils from plants treated with treatments by GC/MS, the most important chemical compounds that determine the quality of H. officinalis L. essential oil including Beta-Pinene (17.93-18.53 %), Pinocamphone (24.97-25.12 %) and Cis-Pinocamphone (42.87-45.12 %) were identified. Cis-Pinocamphone belonging to bicyclic monoterpene was the predominant constituent of essential oil of H. officinalis L.   Conclusion According to the results of this study, water deficit stress caused significant phytochemical changes in the H. officinalis L. essential oil. The main constituents of the volatile oils of H. officinalis L. were Sabinene, 3-Carene, Beta-Pinene, Cis- Pinocamphone, Myrtenol, Pinocamphone and Camphor were identified in the H. officinalis essential oil. Generally, Foliar application of chitosan and phenyl alanine significantly increased the monoterpenes compounds in essential oils of Hyssopus officinalis L., so that the content of these compounds and essential oil content in treated plants by organic elicitors 63% was more than the control plants. Finally, the application of chitosan at 0.5 mg.l-1 can be a good strategy to improve physiological and essential oil quantity and quality of H. officinalis L. in cold and semi-arid climates.