Keywords

11.1 Introduction

Ocimum L., a versatile aromatic genus of the family Lamiaceae, is represented by 66 species across the World (TPL 2013), and is well known for its medicinal properties and economically important essential oils (Kalita and Khan 2013; Singh 2019a). The genus is very variable and possesses wide range of intra- and inter-specific genetic diversity (Singh et al. 2019). The nomenclature of Ocimum species and its varieties is complicated and confusing, and in several instances the oil extracted from morphologically identical plants show different physico-chemical properties. Species like Ocimum gratissimum L., Ocimum africanum Lour., Ocimum basilicum L., Ocimum kilimandscharicum Baker ex Gurke L. and Ocimum tenuiflorum L. are examples of well-known important species of the genus that grow in different parts of the World and are known to have curative biological functions (Lal et al. 2004; Barik et al. 2006; Singh 2019b). The plants flourish predominantly as herbs and shrubs and usually survive as annuals or perennial plants in habit. They possess glandular hairs or sessile glands secreting strongly scented volatile secondary metabolites in the form of oils. The dry leaves of Ocimum used as leaf herbal tea, essential oils and its chemical derivatives (eugenol, methyl eugenol, linalool, methyl chavicol, germacrene A and D, elemicin, ß-elmene, (Z)-ocimine) are exported to European and Arab countries in sizable quantity every year. The annual export of dry leaves herb, its products, essential oils and derivatives of chemical constituents of Ocimum is worth 5000 tons (Bhasin 2012). People know the plant as surasah in sanskrit and tulsi in hindi. Due to antioxidant and anti-ageing effects of tulsi, people use fresh leaves in panchamrut/charanamrut drink after Holi puja (Kumar et al. 2013). In India, tulsi is considered divine and is regarded not merely as a Godsent utility, as most sacred plants are viewed to be, but as an incarnation of the Goddess Herself. The classic Hindu myth, Samudramanthana, or the ‘Churning of the Cosmic Ocean’, explains that Vishnu spawned tulsi from the turbulent sea as a vital aid for all mankind (Anonymous 1973, Singh 2020). The tulsi leaves, when consumed, can control thirst and so is invaluable to weary travellers.

Apart from religious importance, Ocimum has several medicinal properties. Phytochemical investigation reveals that they are rich in carbohydrate, fibre, phosphorous, calcium, protein, iron, beta-carotene, vitamins B1 and B2 and in aromatic oils (Lal et al. 2004). It is effective against cold and cough, indigestion, stomach pain and diarrhoea. Nausea, ulcers, ringworm and asthma can also be effectively treated by using tulsi ingredients or extract. It is also helpful in lowering blood sugar and increasing lactation (Lal et al. 2003; Singh and Bedi 2017). The oil is used as antiperspirant as well as fly and mosquito repellent (Table 11.1). Available genetic stocks at the CSIR-Central Institute of Medicinal and Aromatic Plants (CIMAP, Lucknow) include 105 genetic stocks (or accessions) belonging to five Ocimum species – Ocimum kilimandscharicum, Ocimum africanum, Ocimum gratissimum, Ocimum tenuiflorum and Ocimum basilicum – and 7 varieties, which include CIM-Ayu, CIM-Angana, CIM-Kanchan, CIM-Saumya, CIM-Surabhi, Kushmohak and Vikarsudha (Figs. 11.1 and 11.2). In future, there will be possibility to develop more varieties of herbs, increase oil yield containing specific chemicals like eugenol, methyl eugenol, germacrene A and D, linalool, elemicin, ß-elmene and (Z)-ocimine, and produce other chemical contents from other herbal products (Ismaile 2006).

Table 11.1 Medicinal uses of different Ocimum species
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Fig. 11.1
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Ocimum germplasm for genetic improvement and development of value-added products: (a) O. tenuiflorum (synonym: O. sanctum, CIM-Ayu), (b) O. tenuiflorum (CIM-Kanchan), (c) O. tenuiflorum (synonym: O. sanctum, CIM-Angana), (d) O. kilimandscharicum, (e) O. basilicum (French basil), (f) O. basilicum (Indian basil)

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Fig. 11.2
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Ocimum germplasm for genetic improvement and development of value-added products: (a) O. basilicum (Sweet basil), (b) O. gratissimum, (c) O. africanum (d) African basil

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11.2 Methodology

In total, 180 collections were assembled from different States of India including few exotic ones from 6 countries (Tanzania, Thailand, Singapore, Slovak Republic, the USA and South Africa). After removing of duplicates, 40 genetic stocks were examined (Table 11.2) for high herbage content and essential oil yield with type of quality during an initial evaluation trial in field (design RBD, rep-2) (Lal 2012). The fresh 100 gm aerial parts of Ocimum spices were collected from plants from the field of CSIR-Central Institute of Medicinal and Aromatic Plants and processed by hydro-distillation for 3–4 h in a clevenger apparatus to obtain the crude essential oils. Identification of the essential oil composition was done by gas chromatography (GC; Clevenger 1928).

Table 11.2 Total representation of Ocimum accessions used in the study
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Table 11.3 BST trial of methyl chavicol type Ocimum (entries 13, design RBD, replications 3, plot size: 12.25 m2)
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11.3 Results and Discussion

The morphological and essential oil yields were observed in 40 accessions (or lines of five Ocimum species: Ocimum tenuiflorum, O. kilimandscharicum, O. africanum, O. gratissimum and O. basilicum) and 7 varieties, viz. CIM-Ayu, CIM-Angana, CIM-Kanchan, CIM-Saumya, CIM-Surabhi, Kushmohak and Vikarsudha. Essential oil yield, oil content and herb yield were found to vary from 98.98 to 465.00, 0.30 to 1.20 and 28.18 to 53.08, respectively, in different populations of O. basilicum (Lal et al. 2008; Verma et al. 2011).

The percentage of methyl chavicol is 89% and linalool is 1.01% in population 1 (EOH-1) chemotype (Table 11.4). Essential oil yield, oil content and herb yield were found to vary from 48.0 to 183.67, 0.29 to 0.54, and 15.83 to 36.17, respectively, in O. africanum. The maximum oil yield found in population 1 had high oil content (0.54%), with high citral 76.62% (geranial 46.59% + neral 30.03%) genotype (OC-1) identified (Table 11.4). Literature surveys revealed that the essential oil of Ocimum basilicum has been investigated in detail. Chemotypes described so far for this species are methyl chavicol, linalool and β-ocimene (Ozcan and Chalchat 2002). Essential oil compositions of Ocimum africanum are citral (geranial + neral) and β-ocimene. The occurrence of huge chemical variations among Ocimum populations collected from diverse localities seems to be due to the divergent climatological and geographical conditions as well as different genetic factors (Ojo et al. 2012). The major chemical constituents found in Ocimum having industrial importance are given in Fig. 11.3.

Table 11.4 BST trial of citral type Ocimum (entries 12, design RBD, replications 3, plot size: 12.50 m2)
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Fig. 11.3
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The major chemical constituents in the genus Ocimum: (a) Eugenol, (b) Citral, (c) Methyl chavicol, (d) β-Ocimene, (e) Linalool, (f) Elemicin

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11.4 Conclusion

In recent few decades, there has been a resurgence of interest in investigating the health-promoting uses of Ocimum species across the globe. The nutritional and pharmacological properties of O. tenuiflorum, O. kilimandscharicum, O. africanum, O. gratissimum and O. basilicum, including several varieties, viz. CIM-Ayu, CIM-Angana, CIM-Kanchan, CIM-Saumya, CIM-Surabhi, Kushmohak and Vikarsudha in its natural form, have been traditionally used since ancient times, and have provided a new platform for researchers for synergistic interactions of several different active phytochemicals. However, because of its inherent genotypic variations and biochemical complexity, Ocimum standardization has eluded modern science. Ocimum ingredients are general vitalizers that increase physical endurance in humans, the reason being it contains no caffeine or other stimulant. Chemical characterization of two new species of Ocimum was observed in this study. In O. basilicum and O. africanum population, EOH-1 and OC-1, respectively, obtained maximum essential oil yield. Ocimum is traditionally used as a cure-all in many parts of the world, including India. The essential oil compositions of available species of the genus is very much helpful in the pharmaceutical industry and in formulation of drug principles. Preclinical studies in animal models have demonstrated several therapeutic applications of Ocimum and recognized them as useful active constituents having anti-diabetic, wound healing, anti-oxidant, anti-microbial, gastroprotective, immunomodulatory, anti-inflammatory, anti-cancerous and several other biological properties, which provide leads for industries in the development of new medicines and drug formulations.