Abstract
One of the major factors limiting the production of medicinal plants in arid and semi-arid areas is water deficit or drought stress. One-third of the land in the world is arid and semi-arid and is inhabited by nearly 4 × 108 people. Ocimum basilicum (sweet basil) is a valuable medicinal plant that is sensitive to water deficit, and water shortage negatively affects sweet basil yield and quality. Water availability in the root zone of basil could ameliorate the negative effects of water shortage. To the best of our knowledge, although the effects of hydrophilic polymers (HPs) have been studied in different agricultural crops, the effects of HP application in medicinal plants have not been previously investigated. This investigation was conducted to explore the effects on water use efficiency when using Stockosorb® (STS) and psyllium seed mucilage (PSM) as hydrophilic polymers (HPs) and the effects of these HPs on essential oil quality, quantity, and yield. The research was set up in a factorial experiment on the basis of completely randomized block design with three replications. We used two HPs, STS (industrial) and PSM (herbal), with two methods of application (mixed with soil, mixed with soil + root) at four concentrations (0%, 0.1%, 0.2%, and 0.3% (w/w)). Results showed that the STS and PSM significantly increased the dry herb yield (both shoot and root) in comparison to the control, and the improving effect was higher when these HPs were mixed with soil + root. The highest dry herb yield (6.74 and 3.68 g/plant for shoot and root, respectively) was detected in the PSM at 0.1% mixed with soil + root. There was not any significant difference in dry herb yield among PSM (0.1%), PSM (0.2%), and STS (0.2%) when mixed with soil + root. Soil application of PSM and soil + root application of STS at a concentration of 0.3% increased the Essential Oil (EO) content almost three-fold in comparison to the control (0.5% and 0.52% to 0.18% v/w, respectively). The maximum essential oil yield was recorded in plants treated with STS (0.2% in) or PSM (0.1%) by soil + root application (0.21 and 0.19 mL/plant, respectively). PSM at concentrations of 0.1% and 0.2% (mixed with soil + root) showed the highest water use efficiency (1.91 and 1.82 g dry weight (DW)/L H2O, respectively). STS mixed with soil also significantly improved water use efficiency (WUE) in comparison to the control. The application of these HPs improved the quality of sweet basil essential oil by increasing the linalool and decreasing the eugenol, epi-α-cadinol, and trans-α-bergamotene content.
Highlights
Medicinal and aromatic plants are of prime economic importance because of the continuous and increasing demand for their products by local and foreign markets [1]
The highest dry herb yield (6.74 and 3.68 g/plant for shoot and root, respectively) was detected in the psyllium seed mucilage (PSM) at 0.1% mixed with soil + root
Soil application of PSM and soil + root application of STS at a concentration of 0.3% increased the Essential Oil (EO) content almost three-fold in comparison to the control
Summary
Medicinal and aromatic plants are of prime economic importance because of the continuous and increasing demand for their products by local and foreign markets [1]. Basil (Ocimum basilicum L.), part of the Lamiaceae family, is one of the most important medicinal plants [2] that can be used for dry leaves and flowers, its essential oil, fresh vegetables, and as an ornamental plant [3]. The export of sweet basil dry leaves, essential oils, and chemical derivatives annually is worth 10,000 tons [7,8,9]. Basil is very sensitive to water stress [10] and displays wilt symptoms shortly after water deficiency because it has large leaves and a high water consumption that can be more than 800 mm [11]. The main constituents of basil essential oil are methyl chavicol, eugenol, and linalool [12,13]. The amount of each of these chemical constituents varies depending on the species, variety, and chemotype [7,8,9,14,15]
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