Effect of water deficit on growth and concentration of secondary metabolites of Thymus vulgaris

Abstract

The aim of the experiment was to investigate the effect of the level and timing of watering on the productivity and chemical constituents of garden thyme ( Thymus vulgaris L., cultivar ‘Varico 3’) at growth stage (GS) 202 based on the extended BBCH scale in growth chamber for 13 weeks. Different irrigation regimes have been applied based on the soil water content (SWC%) as follows: 1) control (C: 1–13th weeks – 70% SWC), 2) mild drought stress (S1: 1–4th weeks – 70% SWC, from the 6th week, continuously decreasing drought stress to 40% DVD for 10–13th weeks), 3) sudden drought stress (S2: 1–9th weeks – 70% SWC, 10–13th weeks – 40% DVD), and 4) constant drought stress (S3: 1–4th weeks – 70% DVK, 5–13th weeks – 40% SWC). At the end of the experiment, it was determined that water deficiency induced no direct impact on the width and height of garden thyme plants, while internode and shoot lengths were affected significantly. The plants grown under constant drought stress (S3) conditions showed the minimum values concerning lengths (internode 1.30 cm, shoot 7.12 cm), while the highest ones (internode 2.50 cm, shoot 22.08 cm) were found in the control treatment. However, water supply had no significant effect on the shoot number and chlorophyll content of the leaves. The impact of drought stress both on rosmarinic acid and total phenolic content (TPC) was significant and showed the highest values in the S2 and S3 treatments: S2 had the highest rosmarinic acid concentration of 4.61%, and S3 had the highest total phenolic concentration of 0.75 mg GAE ml -1 . A similar result was found for antioxidant capacity in the S3 treatment, where plants reached the highest values (275.44 mg AAE g -1 dry weight), while the total flavonoid content was not significantly affected by different water supply levels. The results show that not only the level of water deficiency but also the change in water supply and the timing of the drought may have a significant effect on the quantity and quality of garden thyme production. of different irrigation regimes on the antioxidant capacity of dried and powdered Thymus