عنوان مقاله [English]
Medicinal plants are economical important plants that are used in traditional medicine and industry as raw or processed materials. Valerian (Valeriana officinalis L.) is one of the important medicinal plants which belong to Valerianaceae family. The valerian rhizome and roots have been considered as a valuable medicinal plant that essential oil content (between 0.1 to 2 percent) varied according to climatic conditions of production location. Valerian needs a lot of water during the growth period and enough moisture around the roots and rhizome increase root yield. Iran is located in arid and semi-arid region. If the least water requirement of plant does not provide, plant face to drought stress and irreparable damage is imported to the product. Nowadays, the use of superabsorbent polymers is one of the ways to increase irrigation efficiency. They are made of hydrocarbons, can store high water or aqueous solutions in root zone of plants and to reduce negative effects of drought stress. So, improvement of plant growth, increasing of irrigation intervals, reducing water loss and costs of irrigation are due to application of superabsorbent polymers. Generally, water efficiency, dry matter production and root development, are positive reactions to the use of superabsorbent. In this regard, Stockosorb® copolymer is potassium-based nutrients that have a high ability to absorb water and nutrients and high strength polymer maintained the water has been proven. The aims of this investigation were to study the effects of Stockosorb® hydrophilic polymers, on some morphological (root dry weight and yield, leaf area), biochemical (chlorophyll a, b), physiological (electrolyte leakage, leaf relative water content) characteristics and essential oil content and yield of valerian under drought stress.
Materials and Methods
This research was conducted in field (1×1 m2) at Department of Horticultural Science‚ College of Agriculture‚ Ferdowsi University of Mashhad. The research was set out in a factorial experiment on the basis of completely randomized block design. The Stockosorb® hydrophilic polymer at four concentrations (0, 100, 200, 300 gr/m2) and two irrigation period (6 and 10 day) with three replications were set as treatments and leaf area, root dry weight and yield, chlorophyll a, b, electrolyte leakage, leaf relative water content and essential oil content and yield were evaluated at the end of the growth period. The seeds of Valeriana officinalis were sown in protected open field for seedling production and the seedling were transplanted to the field at four-leaf stage (12 plant per plot). Stockosorb® mixed with soil, after weighing the polymers based on determined concentration. After seedling establishment, all plots were irrigated with a determined amount and equal of water.
Results and Discussion
The results showed, using Stockosorb® superabsorbent polymer be useful for water supply the plant in water stress condition. Application of this substance on some morphological, biochemical and physiological characteristics and valerian essential oil, was significant at 1% and superior to the control. According to the results obtained, Stockosorb® 300gr/m2 with irrigation period 6 day interval, increased leaf area, root dry yield, leaf relative water content, chlorophyll a and essential oil yield. While, the highest valerian root dry weight and essential oil content were obtained with application of Stockosorb® 200gr/m2 and irrigation period of 6 days interval. The highest electrolyte leakage was related to control and irrigation period 10 days interval and the maximum chlorophyll b was belonged to Stockosorb® 100 gr/m2 with irrigation period 10 days interval.
Since final goal in cultivation of valerian as other essential oil bearing plants is providing the best conditions for increasing the yield and quantity of essential oil at the same time, according to the results of this study superabsorbent polymer in higher concentrations and less irrigation period, controlled the drought stress and improved all measured characteristics. The highest root dry weight under drought stress was related to more accessible and preservatives water in the root zone and it found by using the middle concentrations (200 gr/m2) super absorbent polymer and irrigation period shorter (6 day). Using of mentioned treatments, according to the middle water stress, leads to increased valerian essential oil. The best root dry yield and essential oil yield, with sufficient amounts of water and better growth conditions were achieved by application of 300 gr/m2 Stockosorb® and irrigation period 6 days interval. In general, superabsorbent polymer was able to increase irrigation period and this was evident in qualitative and quantitative results related to the valerian in the treatment of 300 gr/m2 with irrigation period 10 day and 100 gr/m2 of polymer 6 day irrigation period.