Significance of Arbuscular Mycorrhizal Fungi in Mitigating Abiotic Environmental Stress in Medicinal and Aromatic Plants: A Review

Medicinal and aromatic plants (MAPs) have been used worldwide for thousands of years and play a critical role in traditional medicines, cosmetics, and food industries. In recent years, the cultivation of MAPs has become of great interest worldwide due to the increased demand for natural products, in particular essential oils (EOs). Climate change has exacerbated the effects of abiotic stresses on the growth, productivity, and quality of MAPs. Hence, there is a need for eco-friendly agricultural strategies to enhance plant growth and productivity. Among the adaptive strategies used by MAPs to cope with the adverse effects of abiotic stresses including water stress, salinity, pollution, etc., their association with beneficial microorganisms such as arbuscular mycorrhizal fungi (AMF) can improve MAPs’ tolerance to these stresses. The current review (1) summarizes the effect of major abiotic stresses on MAPs’ growth and yield, and the composition of EOs distilled from MAP species; (2) reports the mechanisms through which AMF root colonization can trigger the response of MAPs to abiotic stresses at morphological, physiological, and molecular levels; (3) discusses the contribution and synergistic effects of AMF and other amendments (e.g., plant growth-promoting bacteria, organic or inorganic amendments) on MAPs’ growth and yield, and the composition of distilled EOs in stressed environments. In conclusion, several perspectives are suggested to promote future investigations.

Effects of Drought Stress on Biomass, Essential Oil Content, Nutritional Parameters, and Costs of Production in Six Lamiaceae Species

Lamiaceae is one of the largest families of aromatic plants and it is characterized by the presence of external glandular structures which produce essential oils highly valued in cosmetics and medicine. Plants of Lavandula latifolia, Mentha piperita, Salvia sclarea, Salvia lavandulifolia, Thymus capitatus, and Thymus mastichina were grown for one year. In order to evaluate the effects of drought stress, plants were subjected to two water treatments (100% ETo and 70% ETo, including the rainfall during the experimental period). At the end of the experiment, the biomass, the essential oil content, and leaf nutrients concentration were assessed for each water treatment and species studied. At the end of the experiment, L. latifolia, M. piperita and T. capitatus plants showed a significant fresh weight reduction under drought stress conditions whereas the other species studied remained unchanged. With respect to dry weight, only L. latifolia plants showed a reduction under water deficit conditions. As far as essential oil content was concerned, L. latifolia and S. sclarea plants had a reduction under water deficit conditions. Leaf nutrient concentration showed different trends between species considering the nutrient assessed. The economic viability of the growth of this species will be dependent on the benefits achieved which are related to yield production obtained and the price accorded for both raw material and the essential oil extracted.

Plant extracts with potential to control of two-spotted spider mite

ABSTRACT: Tetranychus urticae Koch (Acari: Tetranychidae) is a species of great economic importance to Brazil. In its control, the main option is the use of synthetic miticides, which, if used indiscriminately, can contaminate the environment, farmers and consumers. In the search for control alternatives, this study aimed to evaluate the effect of plant extracts and essential oils on females of this pest. For this, T. urticae females, reared in laboratory, were sprayed in Potter tower. Fourteen plants were tested in the form of aqueous extracts (AE), hydroethanolic extracts (HE) or essential oils (EO). The experimental plot consisted of a Petri dish with a Canavalia ensiformis L. leaf disk containing five T. urticae females, using ten plates per treatment. Mortality evaluations were performed 24, 48, 72, 96 and 120 hours after spraying, recording the number of dead females on the disc and the number of dead females on the moistened cotton. We considered that females found on cotton were repelled by treatments. Matricaria chamomilla L. HE and Pimpinella anisum L. AE have acaricidal effect for females, providing above 83% of mortality, after 120 hours. Origanum vulgare L. HE causes at least 75% mortality after 24 hours. Also 120 hours after spraying, P. anisum HE and O. vulgare AE cause repellency of females above 16%, and A. absinthium HE exceeds 22% for this parameter. The results stimulate further researches to determine the optimum dose and evaluation of additional effects on the fertility of surviving females.

Effects of irrigation intervals and organic manure on morphological traits, essential oil content and yield of oregano ( Origanum vulgare L.)

In order to evaluate the effect of irrigation intervals and cattle manure levels on morphological traits, essential oil content and yield of oregano, an experiment was conducted at the experimental Farm of the Faculty of Agriculture, Urmia University, Iran. The experimental design was split-plots, arranged in randomized complete blocks with three replications. Main plots including irrigation intervals (1, 2 and 3 weeks) and four levels of cattle manure at 0, 10, 20 and 30 t ha-1 were allocated to sub plots. Our results showed that increasing irrigation intervals reduced values of all morphological traits except for proportion of stems. Also, values for stems number, plant spread, stem diameter, leaf area, fresh and dry herb yield increased by increasing cattle manure levels. On the other hand, morphological traits not influenced by interaction of treatments except for plant spread and leaf area. The highest essential oil content (2.07%) and yield (66.62 kg ha-1) obtained in highest irrigation intervals and cattle manure levels. Whereas, 1 week irrigation interval without use of cattle manure produce lowest essential oil content (1.55%). For essential oil yield, the lowest value (46.37 kg ha-1) was found in 2 weeks irrigation interval with application of 20 t ha-1 cattle manure.

Effect of prolonged water stress on essential oil content, compositions and gene expression patterns of mono- and sesquiterpene synthesis in two oregano (Origanum vulgare L.) subspecies

Origanum vulgare L., recognized throughout the world as a popular medicinal and flavoring herb, contains a wide array of medicinally active components, including phenolic glucosides, flavonoids, tannins, sterols and high amounts of terpenoids. Especially the latter are often extracted by hydrodistillation resulting in the so-called essential oil that is rich in monoterpenes (e.g. carvacrol, thymol, linalyl acetate) and/or sesquiterpenes (e.g. (E)-β-caryophyllene, germacrene D, bicyclogermacrene, β-caryophyllene oxide). Water stresses in the arid and semiarid regions of the world severely affect growth and productivity of oregano. To determine the variation in essential oil and gene expression pathway of Iranian oregano under prolonged water stress, two native subspecies of O. vulgare (subsp. virens and subsp. gracile) were studied. The plants, grown in pots, were subjected to three water stress conditions, i.e. no stress, mild stress (60± 5% FMC) and moderate stress (40± 5% FMC). The studied subspecies exhibited significant differences in essential oil content, compositions, and patterns of gene expression under water stress conditions. The essential oil of O. vulgare subsp. gracile was rich in the phenolic monoterpene carvacrol (46.86-52.07%), whereas the sesquiterpene hydrocarbon (Z)-α-bisabolene (39.17-42.64%) was the major constituent in the oil of O. vulgare subsp. virens. Both the mild and moderate water stresses significantly increased the essential oil content of O. vulgare subsp. gracile, but did not significantly change the essential oil content of O. vulgare subsp. virens nor the level of carvacrol and (Z)-α-bisabolene in the investigated subspecies. Interestingly, the amount of (E)-β-caryophyllene in O. vulgare subsp. virens was significantly increased under water stress conditions. Gene expression studies supported the above findings and demonstrated that there are two different pathways affecting the biosynthesis of the terpenoid precursors geranyl pyrophosphate (GPP) and farnesyl pyrophosphate (FPP). In O. vulgare subsp. gracile, HMGR, Ovtps2 and CYP71D180 transcript were up-regulated under mild and moderate water stress conditions. Transcription of FPPS was apparently down-regulated in water-stressed O. vulgare subsp. gracile. Investigation of terpene synthases expression levels in oregano subspecies demonstrated that Ovtps2 and Ovtps6 controlled the concentration of carvacrol and (E)-β-caryophyllene in oregano essential oils, respectively.

Irrigation dose and plant density affect the volatile composition and sensory quality of dill (Anethum graveolens L.)

BACKGROUND

Two independent field experiments were carried out to investigate the influence of (i) three irrigation treatments (ID0 = 1585 m³ ha^-1 , considered as a control; ID1 = 1015 m³ ha^-1 ; and ID2 = 2180 m³ ha^-1 ) and (ii) three plant density treatments (PD0 = 5.56 plants m^-2 , considered as a control; PD1 = 4.44 plants m^-2 ; and PD2 = 7.41 plants m^-2 ) on the production, volatile composition of essential oil, and sensory quality of dill.

RESULTS

The highest plant yield was obtained with intermediate conditions of both irrigation dose (ID0) and plant density (PD0). The main compounds of the essential oil were α-phellandrene, dill ether and β-phellandrene. The highest irrigation dose (ID2) produced the highest concentrations of most of the main compounds: α-phellandrene (49.5 mg per 100 g), β-phellandrene (6.89 mg per 100 g) and limonene (2.49 mg per 100 g). A similar pattern was found for the highest plant density (PD2): α-phellandrene (71.0 mg per 100 g), dill ether (16.7 mg per 100 g) and β-phellandrene (9.70 mg per 100 g). The use of descriptive sensory analysis helped in reaching a final decision, and the dill plants with the highest sensory quality were those of the ID2 and PD0 treatments.

CONCLUSION

The final recommendation is to use the irrigation dose ID2 and the plant density PD2 if the objective is to produce dill samples with the highest aromatic and sensory quality; however, if the only objective is to produce high amounts of dill, the best options are ID0 and PD0. © 2016 Society of Chemical Industry.

Effect of Salt, Drought and Metal Stress on Essential Oil Yield and Quality in Plants

Essential oil extracted from plants is of high commercial value in medicine, cosmetics and perfumery. Enhancing yield and maintaining the quality of oil is of significant commercial importance. Production of oil in plants is dependent on various biotic and abiotic factors to which the plants are subjected during their growth. Plants are exposed to various degrees of stress on account of natural and human-induced factors. Salinization, drought and presence of heavy metals in the substratum cause substantial effect on the yield and quality of bioactive constituents in the oil. In many plants, the level and kind of stress have detrimental effects on the growth and development. This review provides an account of the studies on some common abiotic stresses to which essential oil plants are exposed during their growth period and their influence on quality and quantity of oil. The yield and quality vary in different plants and so is the response. Enhancing essential oil productivity is an important challenge, and understanding the role played by stress may offer significant advantages to the essential oil farmers and processing industry. Scientific evaluation of the data on many important but unexplored essential oil plants will also help in mitigating, ameliorating and minimizing the harmful effects caused by stress.

Water-deficit impact on fatty acid and essential oil composition and antioxidant activities of cumin (Cuminum cyminum L.) aerial parts

This study is designed to examine the effect of water deficit on growth, fatty acid and essential oil composition, and antioxidant activities of Cuminum cyminum aerial part extracts. Plants were treated with different levels of water deficit: control (C), moderate water deficit (MWD), and severe water deficit (SWD). Plant growth (height, fresh and dry matter weights) as well as yield components were significantly increased under moderate water deficit and conversely reduced at severe level. Total fatty acid content decreased significantly with severity of constraint. Drought reduced considerably the proportions of major fatty acids and the unsaturated to saturated fatty acid ratio. The essential oil yield was 0.14% (based on the dry weight); it increased by 2.21-fold at MWD but decreased by 42.8% under SWD in comparison to the control. Drought results in the modification of the essential oil chemotype from 1-phenyl-1-butanol to 1-phenyl-1,2-ethanediol. Antioxidant activities of the acetone extracts were determined by two complementary test systems, namely, DPPH and β-carotene/linoleic acid. The highest activity was exhibited by moderately stressed plants and was reduced significantly under SWD. In control plants, the total phenolic amount was 10.23 mg GAE/g DW, which increased by 1.5-fold under MWD and decreased by 42% under SWD.