The effect of drought stress on morphophysiological characteristics of Verbascum thapsus during plant growth stages

Due to the lack of water in different regions of Iran, the introduction and use of indigenous species with valuable ornamental features such as mullein (Verbascum thapsus) is very important. V. thapsus is a perennial and evergreen herb belonging to the Scrophulariaceae family, which like other ornamental plants, can be affected by drought stress in the green space. Drought is an environmental stress that induces adverse effects on most stages of growth, structure and activities of plants. The response of plants to environmental stresses is different in morphological, cellular and molecular levels. Therefore, the present study was conducted to investigate the effect of drought stress on morphological, physiological and biochemical characteristics of V. thapsus during two stages of vegetative and reproductive growth.

In the present study, the reaction of V. thapsus to drought stress and its effect on vegetative and reproductive stages were investigated. The experiment was carried out as factorial in a completely randomized design with two factors as drought stress in 5 levels (control (0.3), 2, 5, 10 and 15 bar) and plant growth stages at two levels (vegetative and reproductive). For this purpose, shoot and root fresh weight, burn and wilt condition, leaf chlorophyll, activity of antioxidant enzymes and proline were measured.

The highest and lowest irrigation interval in both vegetative and reproductive stages was respectively found in 15 bar and control. The water volume used in vegetative stage was higher than reproductive stage. Shoot and root fresh weight in was reproductive stage was more than vegetative stage. The highest fresh weight of shoots was reported under drought stress in control and 2 bar and the lowest amount was observed in 15 bar, but the highest root fresh weight was observed in 5 bar. The highest percentage of leaf burns and wilt was observed in treatment of 15 bar × reproductive stage and its lowest in the treatments of control × vegetative stage and control × reproductive stage. Total chlorophyll in reproductive stage was more than vegetative stage. Also, the highest total chlorophyll was observed under drought stress in control and 2 bar and the lowest was found in 15 bar. The highest activity of superoxide dismutase and catalase was observed in 15 bar × reproductive stage and its lowest value was recorded in control × vegetative stage. Proline in reproductive stage was greater than the vegetative stage. The highest and lowest amount of peoline was observed in 15 bar and control, respectively.

The results of the research showed that the drought stress up to 5 bar did not cause significant changes in the plant, but increasing the intensity of drought stress from 5 bar to 10 bar induces the significant change of most traits in the plant. Therefore, with applying an appropriate plan, we can reduce the water use from 570 m3 (control) to 130 m3 (5 bar) during the vegetative stage and 500 m3 to 140 m3 for reproductive stage.