Physiological and phytochemical responses of the superior populations of Iranian myrtle (Myrtus communis L.) to water stress conditions

Water stress is a major environmental constraint on plant growth and development, making the identification of resistant populations with economic value essential. Myrtus communis, with its wide range of industrial applications, was studied in four superior populations: ‘Kavar,’ ‘Bagh Nari,’ ‘Khergheh,’ and ‘Atashkadeh,’ which were preselected for their essential oil yield and composition. Plants were grown under three irrigation regimes: regular watering, temporary wilting, and recovery after re-irrigation. Water stress reduced chlorophyll a by up to 32 %, chlorophyll b by 29 %, total chlorophyll by 31 %, carotenoids by 24 %, relative water content by 28 %, membrane stability index by 22 %, protein by 26 %, and starch by 35 %, along with several morphological traits. Conversely, essential oil content increased by 15–40 %, antioxidant enzyme activities rose by 20–37 %, soluble sugars by 18–34 %, proline by 30–45 %, and ion leakage by 25–39 %, with differences among populations. Essential oils were dominated by α-pinene (0.1–41 %), linalyl acetate (7.8–39.9 %), limonene (0.2–22.6 %), 1,8-cineole (0.1–14.0 %), and linalool (0.8–23.8 %), with their relative proportions shifting under stress and recovery. The populations ‘Khergheh’, ‘Kavar,’ and ‘Atashkadeh’ showed the most substantial increases in essential oil yield during stress and recovery, highlighting their suitability for cultivation in arid and semi-arid regions and their potential as valuable industrial crops.