Seeds of Iranian native savory were obtained from the seed bank of the Research Institute of Forests and Rangelands, Tehran, Iran, and were sown in the field on 30 March 2000. Plants were 0.2 m apart with 0.5 m between rows. For the water stress study, each plot, four rows wide and 10 m long, with four replications in a randomized complete block design, was irrigated regularly with furrow irrigation. The timing of irrigation (frequency and duration) was based on the soil water potential, according to treatment criteria. Soil water potential was monitored using sensors and leaf water potential was measured using a pressure chamber. Five irrigation treatments were determined, consisting of: (a) a control, which was irrigated to full field capacity (FC) during the growing season; (b) two moderate water stress treatments (66% of FC) during vegetative and flowering stages; and (c) two severe water stress treatments during the vegetative and flowering stages (33% of FC). Because the severe treatment during the vegetative stage resulted in stopping of plant growth and adaptation, this treatment was omitted from our studies. For each treatment, measurements of plant height and fresh and dry weight were monitored by destructive harvests of eight randomly selected plants from the centre rows of each plot during the full flowering period. Plants were harvested at the soil surface, immediately weighed (fresh weight) and then oven-dried at 75 ℃ for 48 h and reweighed (dry weight). Also, for essential oil contents, the aerial parts of eight selected plants were collected and air-dried in the shade for 24 h and then were evaluated. All essential oil concentrations reported are based on the harvest of all aerial parts from whole plants.

The accumulation of oil increased significantly under severe water stress at the flowering stage, when the mean leaf water potential decreased from -0.5 to -1.6 MPa. This treatment affected the quantity of the essential oils more than moderate water stress during the vegetative and flowering stages. The main oil constituents are carvacrol and gamma-terpinene. The amount of carvacrol increased under moderate stress, while gamma-terpinene content decreased under moderate and severe water stress treatments.