نوع مقاله : علمی پژوهشی - تنش محیطی یا زیستی
عنوان مقاله English
نویسندگان English
Introduction
Thyme (Thymus kotschyanus Boiss. & Hohen.) is one of the most important medicinal plants in Iran. The oil from Thyme species is used in about 288 pharmaceutical products. Essential oils of Thyme species contain many compounds with antioxidant activity. Thyme is one of the most important medicinal and culinary herbs, whose cultivation has recently increased significantly. This is why the effect of environmental factors on the herb’s growth, production and biochemical composition is of special importance for the effective cultivation of this plant. Among the various environmental factors affecting crops, salinity of soil and water is a major factor reducing crop yield. Plant hormones, particularly salicylic acid, have been reported to alleviate stress effects on plants.
Materials and Methods
A two-factor factorial experiment was conducted in a greenhouse during the 2022–2023 growing season. The experiment consisted of a completely randomized design (CRD) with three replications. The first factor was NaCl concentration at four levels (0, 50, 100 and 150 mM) while the second factor was salicylic acid (SA) at two levels (0 and 2 mM). For each experimental unit five plants (five pots) were chosen to measure number of stems per plant, plant height, shoot fresh weight, root fresh weight, shoot dry weight, and leaf area. In addition, proline and total protein contents, as well as chlorophyll and carotenoid pigment concentrations, were determined for each experimental unit.
Results and Discussion
Analysis of variance revealed that salinity stress had a significant effect on all measured traits (p < 0.01). Salicylic acid significantly affected chlorophyll b and carotenoid contents (p < 0.05), while its effect on root fresh weight was not significant. All other traits were significantly affected by salicylic acid (p < 0.01). The interaction between salinity stress and salicylic acid was significant for all traits except root fresh weight (p < 0.01). Mean comparisons indicated that increasing salinity levels significantly reduced all agronomic traits and photosynthetic pigment contents. These reductions became significant at 50 mM NaCl, with each salinity level forming a distinct statistical group. In contrast, proline and total protein contents increased with increasing salinity up to 100 mM but declined significantly at 150 mM. Furthermore, salicylic acid application significantly increased all measured traits except root fresh weight and plant height.
Conclusion
Thyme showed moderate tolerance to salinity. Under mild salinity stress (50 mM NaCl, 6.5 dS m⁻¹), SA treatment increased agronomic and biochemical traits of thyme. In higher salinity (100 mM NaCl; approximately 9 dS m⁻¹) thyme plants salicylic acid (2 mM) was able to counteract negative effects caused by high salinity. However, under severe salinity stress (150 mM NaCl; 13 dS m⁻¹) negative effects for thyme plant’s agronomic and biochemical characteristics were observed even under application of salicylic acid. In general, salicylic acid at the concentration of 2 mM is recommended to be used in salinity stress up to 9 dS m⁻¹ and it moderates stress effects on thyme. The findings of this study suggest that the 2 mM salicylic acid could be used to alleviate salinity stress in thyme at salinity up to 9 dS m⁻¹.
کلیدواژهها English
