Botanical Description, Cultivation Practices, Essential Oil Composition and Therapeutic Values of Origanum vulgare L. and its Future Prospective

Introduction

The Lamiaceae family is of great diversity and variety, with a cosmopolitan distribution. It is comprised of about 7200 species organized into 236 genera, which includes plants, herbs, shrubs and trees.^1,2 Plants in this family are characterized by verticillaster inflorescence, two-lipped open-mouthed tubular corolla, opposite decussate leaves, quadrangular stem, etc.^1,2 Most of the species are aromatic and possess essential oils. Many members of the Lamiaceae family are widely cultivated for their aromatic qualities and for medicinal properties. The plants of this family are easy to grow and can be easily propagated.  Species of this family are grown for their edible leaves, as decorative (e.g. Coleus), as edible seeds (e.g. Salvia hispanica: Chia seeds), apart from their culinary and medicinal applications (e.g. Ocimum spp.).

Oregano (Origanum vulgare L.), is one of the multipurpose aromatic perennial herb of the Lamiaceae family which is commonly known as Badri tulsi, Vantulsi, Sathra, Jakhambooti, Baslooghas, and Jonk-Jari in India. Centre for origin of Origanum is hills in Western Asia and the Mediterranean region, but it has now naturalised in some areas of Mexico and the United States.³ O. vulgare is cultivated in sub- and temperate regions of India, particularly in the Himalayan area.^4,5 It is one of the most traded culinary herbs in the world.^6,7

Plants are generally perennial herb and reach up to 80 cm height and have ovate leaves, white or purple flowers and terminal corymbose cyme. The plants are also characterized with gynodioecious and male sterility conditions. The essential oil of Oregano is composed of carvacrol and/or thymol as dominant components, followed by γ-terpenine, p-cymene, linalool, terpenine 4-ol, and sabinene hydrate. The oil is known to possess anti-bacterial, anti-viral, anti-septic, anti-microbial, anti-oxidant, anti-fungal, anti-coagulant and energetic action and flavouring properties.^5,9 Many studies have reported  intra-species variations in morphology, anatomy, volatile composition chemotypic, pharmacogonostical values and geographical variations in O. vulgare, O. vulgare ssp. vulgare and O. vulgare ssp. hirtum (Link).^4,7-23 In this review article, we shed light on the origin, distribution, botanical description, cytological and breeding studies, phytoconstituents and biological activities, cultivation practices and its therapeutic studies of  O. vulgare.

Classification

Kingdom: Plantae

Class: Magnoliopsida

Order: Lamiales

 Family: Lamiaceae

Genus: Origanum

Species: vulgare                    

Figure

Figure 1: A plant of Origanum vulgare L. Click here to view Figure

Origin and Geographical distribution

 Mediterranean, Euro-Siberian and Irano-Siberian regions are centre for diversity of the genus Origanum. About 75%  of the Origanum species are concentrated in the East Mediterranean sub region.²⁴ Presently, it’s found throughout Central Europe, North America and in some countries of Asia Minor. In India, the plant is generally found in the temperate Himalaya between 1,500 and 3,600 m high from Kashmir to Sikkim. O. vulgare was discovered in seven districts of Uttarakhand including Nainital (1480-2240 m), Uttarkashi (2500-2800 m), Rudraprayag (3555 m), Chamoli (3260 m), Bageshwar (2260 m), Champawat (1840 m) and Almora (2220 m), all of which are located at various altitudes.

Botanical discription

Origanum is one of the genera represented by 10 sections with 43 species, 6 subspecies, 3 botanical varieties and 18 naturally occurring hybrids.²⁴ It is an aromatic, branched, perennial herb and average plant height of 30-80cm has been reported by many researchers.^25,26 Weglarz et al. (2020) studied the differences between Greek oregano, O. vulgare L. subsp. hirtum (Link) Letswaart, and common Oregano, O. vulgare L. subsp. vulgare, in central Europe, and reported that the plant height in common Oregano was 36.11 ± 1.93 cm while in Greek Oregano, it was 26.15 ± 1.86 cm. Greek Oregano plants grown in Poland were about 10 cm lower than common Oregano plants.²⁷ For instance, common Oregano plant’s height ranged from 18 to 59 cm while in Greek Oregano, it vared from 67.8 to 79.9 cm. Leaves are  broadly ovate, 10-44 mm long and 5-25 mm wide with opposite  phyllotaxy and the number of primary branches ranged from 5 to 55.²²

The flowers grow in terminal corymbose cyme. Flowers are pale, white or pink in colour and 5-8 mm long. The calyx has five sepals and four stamens. The nutlets are brown in colour.^4,28-32 Dorsiventral leaves have diacytic type of stomata. Trichomes are simple or covering type and glandular type. The peltate trichomes consists of enlarged secretory head, made up of 12–16 glandulous cells covered by a common cuticle. Volatile oils are released upon rupture of the cuticle, which are responsible for synthesis of other more hydrophilic metabolites like phenolic compounds and polysaccharides.^27,33,34 The upper and lower epidermal cells were found to be wavy with thin cell wall. Vascular bundle is restricted to the midrib region and comprises of collateral arrangement of xylem and phloem in stem.²²

The variation in O. vulgare L. populations in terms of morphological,  anatomical, histo-chemical, germination and essential oil composition was primarily restricted to European nations, whereas such studies from India are limited.^{22,23,24,35-38}

Cytological and Breeding Studies

Most of the Oregano spp. consists of 2n=30 chromosome number and the basic number of chromosome are x = 15.^23,39 In Origanum species, controlled hybridization using the flower emasculation technique is very expensive due to small size of the flowers and the type of inflorescence.⁴⁰ The well-known dioeciousness in Origanum genus can provide us with tools to control crossing.⁴¹ Male sterility is well-studied in O. vulgare subsp. vulgare and it has a complex genetic background.^42,43 This male sterility can be used in heterozygous breeding for higher dry matter production and improved homoplasmy dominance, or in interspecific crosses to combine desirable traits from different species. For genetic improvement, high variability is found in Origanum population which can be good source for selection work.^44-47 Conventional and molecular breeding can be used for enhancing essential oil content and its most distinctive chemical compounds.^48-50 Recent findings revealed that Random Amplified Polymorphic DNA (RAPD), Amplified Fragment Length Polymorphism (AFLP) and Selectively Amplified Microsatellite Polymorphic Loci (SAMPL) markers were effective instruments for identifying the genetic makeup of  O. vulgare taxa.^{51, 52-63}

Essential oil and its chemical composition

Plants of the family Lamiaceae comprise a rich storehouse of phytochemical and biochemical such as flavonoids, phenolic compounds, and terpenoids etc. which can be oppressed for its antimicrobial activities, antioxidant activities, food preservatives, insect repellants and other therapeutic properties.²²

The essential oil of Oregano contains carvacrol and/or thymol as the main component(s) and other minor constituents such as c-terpinene, p-cymene, linalool, terpinen-4-ol, and sabinene hydrate. Carvacrol is an important impact compound of Oregano aroma and the largest component of the active extract of the aroma.^64,65 Thymol and carvacrol are biosynthesized by aromatization of c-terpenine to p-cymene followed by hydroxylation of p-cymene.⁶⁶

The yield of essential oil was affected by various factors which include geographical variation, genetic variation, seasonal and maturity variation, growth stages, part of plant utilized and postharvest drying and storage.^67-74 During the flowering period, the essential oil content is at its highest level.⁷⁵

Different studies reported different percentages of the compounds of the essential oil. Kokkini et al.( 2004) analyzed samples from six different locations in Greece and found that carvacrol amounts ranged from 1.7 to 69.6% and thymol ranged from 0.2 to 42.8%.⁷⁶ The phytochemical screening by Prieto et al. (2007) disclosed 41 compounds in the essential oil contributing to about 99.6% to the total oil and the percentage of the dominant compounds viz. carvacrol and thymol was 54.7% and 22.1%, respectively.⁷⁷ Studies conducted by Dimitrijevic et al. (2007) revealed that the amount of carvacrol was 33.51% and thymol to be 5.67% in the O. vulgare essential oil.⁷⁸ Pande et al. (2012) collected different samples of O. vulgare from Kumauon region of Uttarakhand and their study revealed that the percentage of main compounds as Thymol (29.70 to 35.10%), Carvacrol (12.40 to 20.00%), y-terpinine (12.37 to 14.00% and p-cymene (6.69% to 9.80%).¹⁹ Similarly, Verma et al.  (2012) studied the essential oil composition of O. vulgare and they reported that major components of oils were thymol (40.9-63.4%), p-cymene, (5.1-25.9%), γ– terpinene (1.4-20.1%), bicyclogermacrene (0.2-6.1%), terpinen4-ol (3.5-5.9%), α-pinene (1.6-3.1%), 1-octen-3-ol (1.4-2.7%), α-terpinene (1.0-2.2%), carvacrol (<0.1-2.1%). β-caryophyllene (0.5-2.0%) and β-myrcene (1.2-1.9%). Thymol, terpinen-4-ol, 3- octanol, α-pinene, β-pinene, 1,8-cineole, α-cubebene and (E)-β ocimene were observed to be higher during full flowering season.¹⁶

Table 1: Structure of chemical constituents found in O. vulgare and its biological activities. Click here to view Table

Biological activities

The fresh leaves and dried herb of oregano contains many biological activities which are as follows:

Antioxidant activity

O. vulgare‘s essential oil and plant product both have antioxidant properties. Several scientist demonstrated potent DPPH scavenging, protective actions against lipid peroxidation in liposomes, and activities to neutralise NO and H₂O_2.^89-92

Anti-Inflammatory Activity

Due to the presence of carvacrol, Origanum essential oil has anti-inflammatory effects by preventing the release of pro-inflammatory cytokines and repressing the expression of inflammatory genes.⁹³

Antimicrobial activity

O. vulgare extracts with phenolcarboxylic acids (cinnamic, caffeic, p-hydroxybenzoic, syringic, protocatechuic, and vanillic acid) as presumably active ingredients were found to have antimicrobial activity. Additionally, oregano essential oils’ fumigant toxicity for storage insects has been proven.⁹⁴ The essential oil of Origanum have high biological and antimicrobial activity against Pseudomonas aeruginosa, Escherichia coli, Aeromonas hydrophila, Klebsiella pneumonia, Bacillus subtilis, Streptomyces candidus and Candida albican.²² O. vulgare essential oil demonstrated antibacterial effects against Helicobacter pylori, which is associated with ulcers, Enterobacter cloacae, Micrococcus flavus, Proteus mirabilis, Salmonella enteritidis, S.epidermidis, and S. typhimurium.¹⁰ The essential oil of O. vulgare showed antifungal effects against Aspergillus flavus, A. parasiticus, A. fumigatus, A. terreus and A. Ochraceus.^101-103

Antitumoral Activity

Tuncer et al. (2013) showed that O. vulgare L. has antitumor activity against breast cancer cell lines in vitro and in vivo.⁹⁵

Antihyperlipidemic activity

O. morjorana and O. vulgare leaf preparations in volatile oil, methanol, and water reduced elevated triglyceride and cholesterol levels in streptozotocin containing diabetic rabbits.⁵² O. vulgare aqueous extracts also demonstrated analgesic action.⁹⁶

Anti-obesity Activity

Methanol extract of O. vulgare inhibits pancreas lipase.⁹⁷ Pancrelipase is an important enzyme in the breakdown of triglycerides. Modifying lipid metabolism by preventing dietary fat uptake is one method for preventing or treating obesity.

Anti-hyperglycaemic Potentials

Essential oil, methanol, and water extracts of O. vulgare leaves substantially lowered blood glucose levels indicating that these extract are effective without affecting insulin secretion in diabetic rats.⁹⁸

Hepatoprotective Activity

Aqueous extract of O. vulgare leaves has  been shown to have hepatoprotective activity on CCl4-induced liver damage.^99-100

Antiurolithic Activity

A crude aqueous methanolic extract of O. vulgare was reported to have anti-urolithic activity in addition to reducing the amount of calcium oxalate monohydrate crystals produced in metastable calcium oxalate solutions. It also prevented and reversed toxic changes like weight loss, polyuria, crystal Luria, oxaluria, elevated serum urea and creatinine levels, and crystal deposition in the kidney compared to their respective controls.¹⁰⁵

Antimelanogenic Properties

Rosmarinic acid methyl ester, which was isolated from O. vulgare  had the capacity to lower the levels of melanin, tyrosinase, and DOPA oxidase in B16 cells. This research found that the isolated compound has anti-inflammatory and depigmenting properties that may be helpful as food additives and for the regulation of skin pigmentation.¹⁰⁶

Effects on Human Sperm Mobility

Mbaye et al. (2019) examined the effects of Oregano essential oil (obtained from Fes, Morocco) on the viability and motility of sperm. Sperm vitality was determined by eosin 2% staining and examined under an optical microscope. Sperm movement was determined using a computer-assisted sperm analysis.¹⁰⁷ This study emphasied that application of oregano oil has shown increased biological potential  with best progressive sperm mobility and vitality.

Antiplatelet Activity

O. vulgare essential oil exhibited antiplatelet activity by preventing clot regression in plasma from Guinea pig and rat models. Phenylpropanoids were found to have a substantial correlation with antiplatelet potency, indicating a crucial function for this moiety in the suppression of clot formation.¹⁰⁸

Other activities

Chopped oregano leaves and stalks could be used to control weeds in fields and pots due to presence of aroma-impact compounds like eucalyptol, borneol, b-bisabolene, and other  minor constituents.^109,110 Oregano essential oil had an anticoccidial influence on broiler chickens, while oregano herbal extract had a positive impact on rabbits’ resistance and production.¹¹¹ According to studies conducted by Hussain et al. (2011),  oregano essential oil has antimalarial properties and was efficacious against Trypanosoma cruzi.^112-115

Therapeutic uses

Origanum vulgare L. has traditionally been used to treat gastrointestinal disorders, urinary tract disorders, dermatological affections, and disorders of the respiratory tract, including cough and bronchial catarrh (as expectorants and spasmolytic agents), as well as disorders of the urinary tract (as a diuretic and antiseptic).¹¹⁶ According to the National Library of Medicine, oregano products are taken orally for conditions such as allergies, headaches, painful menstrual cramps, urinary tract infections, and psoriasis. Oregano oil is also applied topically for conditions such as acne, dandruff, warts, wounds, muscle and joint pain, varicose veins and psoriasis.

Cultivation of Origanum vulgare

Oregano grows in regions with medium fertile soils, high elevations, and cool summers and is tolerant of cold and dryness. For oregano cultivation, light, well-drained loam is best. Compost is not required for growth because it thrives in soil that is only relatively fertile. The optimum oil pH for its growth ranges from 6.5 to 7.0. Suitable growing region with 5-28 °C, with 0.4-2.7 m of water per year.²² There is an effect of temperature on the qualitative and quantitative parameters of essential oil. According to Karamanos et al. (2013), levels of other compounds in essential oil are higher in cooler seasons, while carvacrol concentration is higher in warmer seasons (70.75-84.88%) in both leaves and inflorescences.¹¹⁷

Sowing time and methods of sowing

The Oregano germplasm (seeds) are planted in poly houses or green houses in the months of October and November in low altitude regions and in March and April in high altitude regions. In poly bags (12 × 9 inch and 150 gauge), 50 to 100 seeds, 20 to 30 recently sprouted soft or semi-wood cuttings (5-8 cm long aerial parts), or 5 to 10 perennial sprouted roots pieces (3 to 5 cm) could be directly sown. In the months of March and April, nursery growth is accomplished through stem cutting and sprouted root divisions²². After the development of nursery in poly house or greenhouse, the seedlings/ saplings of Oregano are transplanted on raised beds of nursery in the month of March and April.

Optimum spacing for plantation

Spacing of seedlings vary from 40, 50 and 60 cm in row to row and plant to plant spacing vary from 20, 30 and  40 cm . It has been reported by Ojha   et al. in 2014 that plant biomass and plant weight has been increased by using 50 to 60 cm distance between rows and 25-30 cm within row respectively.²²

Manure and fertilizers

Generally Origano plants do not require application of fertilizers for growth and development. Whereas studies conducted by Dordas et al. (2009) revealed that nitrogen is crucial for improving dry matter yields without significantly changing the essential oil content.¹¹⁸ Ojha et al. (2014) reported that application of farmyard manure at the rate of 20 t/ha was sufficient for proper growth of plant while treatment with 20:40:40: Kg N:P:K per hectare was correlated with high yield.²²

Water and Weed management

For the proper growth of crop, the area should be effectively irrigated at the time of nursery establishment to maintain moisture.²² Watering should be done every 24 to 48 h when propagating through stem or root cuttings. A week’s worth of watering was needed during the field transplanting process. 3–4 times per month in the summer and 2–3 times per month in the cold. Weeds should be carefully removed from the beds.²²

Harvesting and Post harvest management

To ascertain the economic yield of the plants, aerial parts are manually harvested two to three times. Aerial parts are harvested at various times and dried in shade and moderate heat to preserve their original colour and fragrance. Fully dried leaves and flowering spikes are stored and maintained in gunny bags and airtight bags. According to Chauhan et al. (2013), harvesting herbage at the full bloom stage had marginally better parameters than harvesting it at the early and late vegetative, flower initiation, and fruit set phases.¹¹⁹

Conclusion and Future prospective

The present review highlighted the classification, geographical distribution, botanical description, cytological and breeding aspects, chemical constituents, cultivation practices and various biological potential of Origanum vulgare.

Acknowledgment

Authors are grateful to  Prof. (Dr.) Arun Kumar Dean, School of Basic and Applied Sciences, Shri Guru Ram Rai University, Patel Nagar, Dehradun for his kind support and suggestions.

Conflict of Interest

Authors have declared that no competing interests exist.

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