Ocimum basilicum (PROSEA)

Plant Resources of South-East Asia
Introduction

List of species

1, flowering shoot; 2, shoot in full bloom; 3, section of the inflorescence; 4, flower

Ocimum basilicum L.

Protologue: Sp. pl.: 597 (1753).

Family: Labiatae

Chromosome number: 2n = 48, 50-74

Vernacular names

Sweet basil, French basil, Réunion basil (En)

Basilic commun (Fr)

Indonesia: selasih, kemangi (general), surawung (Sundanese)

Malaysia: kemangi, selasi jantan, selasi hitam

Philippines: balanoy, solasi (Tagalog), kamangi (Culion)

Cambodia: chi neang vong

Laos: phak 'i:x tu:x

Thailand: horapha

Vietnam: húng giỏi, é trắng, é tía.

Origin and geographic distribution

Sweet basil probably originated in western Asia and occurs naturally or naturalized throughout the tropics (including South-East Asia), subtropics and warm temperate areas. It was already being cultivated in Egypt 3000 years ago and made its way from the Middle East to Greece, Italy, and the rest of Europe. It reached England in the 16th Century and North America in the early 17th Century. Sweet basil is now cultivated throughout the world.

Uses

Sweet basil is a popular savoury herb. Both fresh and dried leaves are used to impart a fragrant, warm and sweet flavour with pungent and clove-like notes to dishes and drinks. The leaves complement many soups and salads and vegetable dishes and have a special affinity with tomatoes, e.g. in tomato paste, pasta sauces and even in a bloody Mary. Lamb is also often flavoured with basil leaves. In Italian cooking the leaves are used in pizzas, pasta, chicken and cheese dishes and in the famous pesto. In France the leaves are particularly popular in omelettes and soups. Sweet basil leaves should be added towards the end of cooking to best retain their flavour. The leaves are a source of essential oil and oleoresin mainly applied in industry to flavour baked goods, sauces, pickles, vinegar and meat products and to modify the flavour of chartreuse liqueurs. The oil is also used in cosmetics, dental and oral products and occasionally in perfumes. In the United States the regulatory status "generally recognized as safe” has been accorded to sweet basil (GRAS 2118), sweet basil oil (GRAS 2119) and sweet basil oleoresin (GRAS 2120).

In medicine a decoction of the leaves is applied as stimulant and carminative and to treat vomiting, cough, chronic dysentery and diarrhoea. In Vietnam sweet basil is used to treat fever and malaria. The mucilaginous seed enters into the preparation of non-alcoholic drinks and in medicine. The essential oil is used to repel bugs and flies. Purple-leaved selections are popular ornamentals, but many are as aromatic as green-leaved ones and may be used similarly.

Production and international trade

Sweet basil is grown commercially mainly in the Mediterranean, the United States, Madagascar and neighbouring islands, India and Thailand. Reliable data on production are hardly available. World production of sweet-basil essential oil was estimated in 1992 at 42.5 t, valued at US$ 2.8 million.

Properties

Commercial sweet basil leaves contain per 100 g fresh material approximately: water 87 g, protein 3 g, fat 1 g, carbohydrates 5 g, fibre 2 g and ash 2 g. The seed is rich in protein and fat, but contains little carbohydrates. The major types of sweet basil in trade are "French basil” (also called "sweet basil”) and "Réunion basil” (also called "Egyptian basil”), and "Bulgarian basil”. Sweet basil leaves owe their flavour and fragrance to their volatile oil content (about 1.5 per cent). The volatile oil of French basil oil has a soothing, sweet-spicy, slightly green and fresh aroma with a faint balsamic undertone and a lasting sweetness. Only minute amounts of the oil are needed in foods and perfumes; its minimum perceptible concentration is 0.4-1.0 ppm. Réunion basil is more coarse-herbaceous with a slightly camphoraceous top note. The major components of French basil oil are methyl chavicol and linalool, Réunion basil oil contains mainly methyl chavicol with little linalool. The essential oil of plants of other provenances may have different characteristics.

The oil possesses antiseptic properties against a number of Gram-positive and Gram-negative bacteria and inhibits the activity of several fungi. An alcoholic extract of O. basilicum has some anti-HIV-1 activity in vitro.

A monograph on the physiological properties of sweet basil oil has been published by the Research Institute for Fragrance Materials (RIFM).

The 1000-seed weight is 0.8-1.3 g.

Composition

French basil oil (from Philippines) (Source: Hasegawa et al., 1997.)

53.3% methyl chavicol
22.0% linalool
4.5% β-caryophyllene
3.7% 1,8-cineole
1.4% eugenol
1.4% α-cubebene
0.8% geranyl acetate
0.7% (E)-β-ocimene
0.7% geraniol
0.5% δ-guaiene
0.5% α-terpineol
0.5% myrcene
0.4% neral
0.3% camphor
0.3% β-pinene
0.3% δ-3-carene
0.3% limonene
0.3% α-pinene
0.1% terpinolene
0.1% chavicol
0.1% para-cymene
0.1% methyl eugenol
0.1% γ-terpinene
0.1% copaene (unknown isomer)
0.1% 3-octanol
0.1% camphene
trace (Z)-β-ocimene
trace (Z)-3-hexenol
trace octyl acetate
trace α-phellandrene
trace α-terpinene
trace α-thujene
trace benzaldehyde
trace borneol
trace (Z)-3-hexenyl acetate
92.6% total

Réunion basil oil (from Taiwan) (Source: Sheen et al., 1991.)

84.7% methyl chavicol
5.5% 1,8-cineole
2.4% methyl eugenol
1.3% (Z)-β-ocimene
0.9% β-elemene
0.9% T-cadinol
0.9% α-terpineol
0.7% α-muurolene
0.5% (E)-β-farnesene
0.4% linalool
0.4% β-pinene
0.2% sabinene
0.2% 1-octenol-3
0.1% myrcene
0.1% α-pinene
0.1% cadina-1,4-diene
0.1% β-eudesmol
0.1% β-phellandrene
0.1% (E)-anethole
trace (Z)-3-hexenol
trace α-cadinol
trace chavicol
trace α-copaene
trace eugenol
trace limonene
trace 3-octanol
trace trans-α-bergamotene
trace γ-elemene
trace ethyl linolenate
trace germacrene B
trace 1-hexanol
trace sabinene hydrate
trace viridiflorol
99.7% total

Adulterations and substitutes

Linalool is sometimes added to Réunion basil oil to mimic French basil oil. It is, however, a poor, easily recognized substitute for the much richer true product.

Description

Aromatic, erect or ascending, annual or short-lived perennial herb, up to 1 m tall, with a brown, thick taproot up to 6 mm and many secondary roots.
Stem quadrangular, up to about 6 mm thick, much branched, glabrous or pilose when young, light green to dark purple, base sometimes somewhat woody.
Leaves simple, decussately opposite; petiole 1-2(-4.5) cm long; blade ovate to elliptical, 1-5(-8) cm × 0.5-2(-4) cm, base attenuate, margin entire to crenate-serrate, apex acuminate, densely glandular punctate, light green to purplish-green, glabrous to slightly pilose.
Inflorescence terminal, lax, up to 30 cm long, composed of decussate, 3-flowered cymes, appearing as verticils 1-3 cm apart; bracts oblanceolate to rhombic, 3-11 mm × 1-3 mm, pilose.
Pedicel 3-4 mm long, strongly recurved at top, densely white-pilose; calyx bilobed, tubular, with a flat suborbicular upper lobe 3.5 mm in diameter (in fruit 4.5 mm) and a canaliculate lower lobe 3.5 mm long (in fruit 4.5 mm) which is sharply 4-toothed at top with the 2 central teeth longest, densely glandular punctate, tube densely long-haired inside above the ovary; corolla tubular, two-lipped, 5-8 mm long, pilose outside, whitish-purplish, white or creamy yellow, upper lip 4-lobed and strongly recurved at top, lower lip entire, ovate; stamens 4, didynamous, exceeding corolla by 2-4 mm, 2 outer ones longest and near their base with a fleshy, downward directed, glabrous to pilose outgrowth up to 1 mm long; pistil with a 4-lobed ovary, a gynobasic style up to 9 mm long at top splitting into 2 stigmatic lobes up to 1 mm long.
Fruit composed of 4 distinct nutlets enclosed within the tube of the persistent calyx; nutlet ovoid, 1-2 mm × 1 mm, black to dark brown; in water the nutlet-wall produces a thick white slimy coating within some minutes.

Growth and development

Once established, seedlings grow rapidly. When plants have reached a height of 50-70 cm, branching starts. Pinching out the tip during active vegetative growth encourages further vegetative growth. Flowering starts 3-4 months after planting and occurs year-round in the tropics and in summer in temperate areas. Sweet basil is mainly autogamous, but 5-10% outcrossing occurs.

The volatile oil is contained in glandular hairs on the leaves. The hairs are formed in young meristematic leaves and their number does not increase during expansion of the leaves.

Other botanical information

Although one of the oldest herbs known, sweet basil is not well understood taxonomically and is in need of a thorough worldwide revision to clarify its real identity. Opinions differ concerning its delimitation from other Ocimum species and still more about its classification below species level.

For South-East Asia, Flora Malesiana distinguished 3 other Ocimum species:

O. americanum L. (syn. O. africanum Lour., O. canum Sims, O. brachiatum Blume); hoary basil, occurring wild and cultivated; by some considered as identical to O. basilicum, being a slightly smaller-flowered wild form of it; primarily used as a vegetable.

O. gratissimum L. (syn. O. suave Willd., O. viride Willd., O. viridiflorum Roth); shrubby basil, occurring wild and cultivated, best known from Africa; relatively easily distinguishable from the other species because here the lower lobe of the calyx closes the mouth of the fruiting calyx; primarily used as an essential-oil plant.

O. tenuiflorum L. (syn. O. sanctum L.); holy basil, only known from cultivation; distinguishable from other species because the pedicel is situated transverse to the rachis of the inflorescence); primarily used as a minor spice herb.

O. basilicum is very variable and comprises taxa differing in morphology, chromosome number and chemical content. Many subclassifications have been made, with subspecies, varieties and forms. A classification into cultivar groups and cultivars would be preferable for cultivated plants, but remains to be made.

In the literature the most commonly encountered variety names and their actual taxonomic positions are:

var. anisatum Benth.: now considered to be the hybrid O. ×citriodorum Vis., which originates from a cross between certain chemotypes of O. basilicum and O. americanum, producing plants that smell of anise;

var. basilicum (including var. album Benth., var. densiflorum Benth., var. glabratum Benth., var. majus Benth.): two forms occur - one with thin flat leaves and one with thicker convex leaves (synonym var. lactucaefolium sensu Darrah);

var. difforme Benth. (syn. var. crispum (Thunb.) E.A. Camus): leaves laciniate, bullate, thick or crisped;

var. minimum sensu auct.: considered a separate species O. minimum L. with all parts smaller and woody stem (perennial plant);

var. pilosum Benth.: has been transferred to O. americanum L. var. pilosum (Willd.) A.J. Paton;

var. purpurascens Benth.: upper part of plant purple;

var. thyrsiflorum (L.) Benth. (syn. O. thyrsiflorum L.): inflorescence densely branched and with lax verticils.

Several chromosome counts indicate a diploid chromosome number of 48 for O. basilicum. However, a number of studies of Ocimum germplasm found a complex polyploid series with chromosome numbers for O. basilicum ranging from 50-74. The chromosome counts do not directly match the morphological or chemotaxonomical classification.

At least 6 chemotypes are recognized in O. basilicum. An important source of variation is the presence or absence of a single gene that controls the formation of phenolic aroma products, e.g. methyl chavicol (estragole). In 1996, a study based on 16 selections recognized 5 chemotypes with as major essential-oil components: (1) methyl chavicol; (2) linalool; (3) a mixture of methyl chavicol and linalool; (4) linalool and eugenol; and (5) a mixture of methyl eugenol and methyl chavicol. Type 3 may or may not contain considerable amounts of geraniol. Other studies have found selections rich in methyl cinnamate and camphor. In trade a few selections are recognized based on their fragrance and chemical composition: French basil, a sweet and flavourful strain rich in linalool and methyl chavicol and free of camphor notes; Réunion basil, richer in methyl chavicol but with less linalool; and Bulgarian basil characterized by methyl cinnamate.

Widely grown cultivars and cultivar groups of sweet basil are: "Sweet”, "Genovese”, "Large-leaf” and "Mammoth”; examples of purple-leaved cultivars are: "Dark Opal” and "Purple Ruffles”. O. basilicum cultivars with a different aroma and taste are: "Lemon-scented”, "Sweet Dani”, "Cinnamon Basil”, "Spicy Bush”, "Camphor”, "Anise” and "Licorice”.

Ecology

Sweet basil can adapt to a wide range of conditions favourable for vegetable production. In the Philippines, sweet basil is widely distributed in settled areas from Batanes to Mindanao at low and medium altitudes up to 1000 m and often grows spontaneously in open wastelands. In Java it occurs naturalized up to 450 m altitude and is cultivated up to 1100 m. It thrives in the field as well as indoors or as a pot plant. Sweet basil is susceptible to frost and is grown as a tender annual in temperate areas. In the tropics and subtropics it can be grown as a short-lived perennial. Seed germinates well between 13-25°C. Growth occurs between 5-30°C and is optimal at about 20°C. It needs at least 5 hours of daily direct sunlight, whereas indoors it needs 12 hours of artificial light. It is a particularly robust plant in areas of high light intensity. Plants grown under direct sunlight exhibit more vigorous leaf production, formation of more numerous branches and inflorescences and more extensive root proliferation than those grown under partial shade. Flowering is little affected by photoperiod, but long days appear to favour floral initiation. Sweet basil is susceptible to both water stress and waterlogging at any stage of development.

Sweet basil grows best on fertile, light, well-drained soils and has relatively high nitrogen and water requirements. A pH tolerance of 4.3-8.4 has been reported, but 5.5-6.5 is optimal. The crop benefits from applications of manure or compost.

Propagation and planting

Sweet basil is propagated by seed or cuttings. Seeds remain viable for over 10 years if refrigerated. The tiny seed is sown evenly at a depth of 2-10 mm in germination boxes on a previously moistened medium consisting of equal parts of compost or farm manure, garden soil and river sand. Watering should be done gently using a hand sprayer. In the tropics seeds take 4-6 days to germinate, at lower temperatures 8-14 days. Seedlings are sometimes transplanted into polythene bags or cups upon emergence of the first pair of true leaves. When seedlings are 5-8 cm tall, they are transplanted into the field, planted in rows 30-45 cm apart and 20 cm between plants. Transplanting is sometimes postponed until seedlings are 15 cm tall. In mechanized cultivation rows may be spaced at 60-90 cm with 15 cm between plants. Seedlings are then trimmed to encourage branching and growth. In Italy sweet basil is often direct-seeded in greenhouse beds. Sweet basil can also be propagated using stem cuttings. Stem sections with 4-5 leaf pairs cut right below the fifth node from the shoot apex are suitable. Roots develop within 3-4 weeks.

Husbandry

Weed control in sweet basil is important for good growth. In the United States no herbicides are registered for use in sweet basil and weeding is mechanical or manual. Mulching with straw or black polythene sheeting also gives effective weed control. When grown for the leaves, flowering branches should be removed regularly to promote branching and continued growth. Plantings for essential-oil production are often staggered, to ensure a prolonged harvesting period.

Diseases and pests

Until recently few diseases and pests were reported to seriously affect sweet basil. However, intensified cultivation and increasing restrictions on the use of fungicides have led to severe outbreaks of diseases. In countries where no fungicides are registered for use in sweet basil, e.g. the United Sates, prevention through cultural measures is the only means of controlling diseases. Basil wilt caused by Fusarium oxysporum f. sp. basilici can devastate a crop. Initial symptoms are brown streaks on the stems, but plants grow normally until 15-30 cm tall, then become stunted and suddenly wilt from the apex downwards. Only French basil is seriously affected, other types show some resistance. The disease is spread through macroconidia dispersed by soil particles and during harvest; seed-borne inoculum is held responsible for long distance transmission. Disinfection of seed with benzimidazoles effectively controls seed-borne infection. The Fusarium strain may survive in the soil for 8-12 years. Biological control through antagonistic fungi, including antagonistic strains of F. oxysporum, is being developed. Basal rot is caused by Rhizoctonia solani, to a lesser extent by Microdochium tabacinum and below 20°C also by Sclerotinia spp. Rhizoctonia causes damping-off in rapidly expanding circular patches. It spreads rapidly through the soil. Grey mould caused by Botrytis cinerea is very common in sweet basil. Young plants grown from stem cuttings are particularly susceptible and the disease may kill all the leaves and buds of affected plants. Susceptibility diminishes gradually with time. Black spot (Colletotrichum spp.) causes dry necrotic spots to develop on the leaves. An increase in outbreaks of black spot in Italy has been associated with reduced use of fungicides against grey mould.

Few pests are recorded in sweet basil. In Thailand the larvae of the Ocimum leaf folder (the Lepidoptera Syngamia abruptalis) cause some damage by feeding inside folded leaves. The generation time of this insect can be as short as 1 month. In the United Kingdom, birds are reported to cause extensive damage to seedlings after transplanting.

Harvesting

When grown for fresh or dried leaves, sweet basil is best harvested just prior to the start of flowering. Leaves and shoots may be harvested when 15-20 cm long, 80-110 days after transplanting. In temperate areas 1-2 cuts may be taken, in warmer areas 3-5 cuts per year are possible. Plants should be cut 10-15 cm above the ground, leaving 2-4 pairs of leaves to ensure good regrowth and allow subsequent harvests to be taken at 15-20 days. For essential oil production, sweet basil is harvested in full bloom.

Yield

Reported yields of fresh sweet basil leaves range from 5-20 t/ha. The yield of essential oil is about 40 kg/ha. Very productive beds were observed in the Philippines, where inflorescences were continuously removed, the first harvest took place about 50 days after sowing, and harvesting continued for 18 months at intervals of 3-4 weeks, yielding an estimated 7 t/ha of fresh leaves per harvest (85-140 t/ha in 18 months). In India where flowers and leaves are sometimes distilled separately, a good crop yields about 13 kg of flower oil and 27 kg of leaf oil.

Handling after harvest

Before processing, leaves and branches of sweet basil are washed, and cleaned by removing all weeds and extraneous material. To maintain their aroma and colour, leaves should be dried at temperatures not exceeding 35°C. Dried leaves are chopped to specific sizes and graded. For essential oil, sweet basil is usually dried for 1-3 days in the field. In Italy, dried leaves are preserved in olive oil. They turn black, but keep their flavour for several months. Most essential oil is obtained by steam distillation.

Genetic resources

Many germplasm collections of Ocimum spp. including O. basilicum are maintained, in the United States e.g. at the United States Department of Agriculture (USDA) North Central Regional Plant Introduction Station, Ames, Iowa, United States. In Europe there are large germplasm collections at the Vavilov Research Institute of Plant Industry, St. Petersburg, Russia (169 accessions), the Gene Bank of the Institute for Plant Genetics and Crop Plant Research, Gatersleben, Germany (95 accessions) and at the Gene Bank Department of the Research Institute of Crop Production, Olomouc-Holice, Czech Republic (56 accessions).

Breeding

Most breeding work in sweet basil aims at developing resistance against Fusarium oxysporum and to a lesser extent at developing cultivars with a desirable flavour.

Prospects

Although sweet basil is only a minor crop in terms of area, it is an important spice and its popularity is still growing. Sweet basil is an important ingredient of the popular Thai cuisine. Its importance in various prepared foods and the increasing popularity of health foods, including pastas and other Italian foods, also contributes to the steadily growing popularity and increasing demand for this herb.

Literature

Darrah, H.H., 1974. Investigation of the cultivars of the basils (Ocimum). Economic Botany 28: 63-67.
Garibaldi, A., Gullino, M.L. & Minuto, G., 1997. Diseases of basil and their management. Plant Disease 81: 124-132.
Grayer, R.J., Kite, G.C., Goldstone, F.J., Bryan, S.E., Paton, A. & Putievski, E., 1996. Infraspecific taxonomy and essential oil chemotypes in sweet basil, Ocimum basilicum. Phytochemistry 43: 1033-1039.

Lachowicz, K.J., Jones, G.P., Briggs, D.R., Bienvenu, F.E., Wan, J., Wilcock, A. & Coventry, M.J., 1998. The synergistic preservative effects of the essential oils of sweet basil (Ocimum basilicum L.) against acid-tolerant food microflora. Letters in Applied Microbiology 26: 209-214.

Lawrence, B.M., 1998. Progress in essential oils. Perfumer & Flavorist 23(6): 35-48.

Paton, A. & Putievsky, E., 1996. Taxonomic problems and cytotaxonomic relationships between and within varieties of Ocimum basilicum and related species (Labiatae). Kew Bulletin 51: 509-524.

Pushpangadan, P. & Bradu, B.L., 1995. Basil. In: Chadha, K.L. & Rajandra Gupta (Editors): Advances in horticulture. Vol. 11. Medicinal and aromatic plants. Malhotra Publishing House, New Delhi, India. pp. 627-657.

Small, E., 1997. Culinary herbs. National Research Council of Canada. NRC Research Press, Ottawa, Canada. pp. 411-424.

Wan, J., Wilcock, A. & Coventry, M.J., 1998. The effect of essential oils of basil on the growth of Aeromonas hydrophila and Pseudomonas fluorescens. Journal of Applied Microbiology 84: 152-158.

Sources of illustrations

Mansfeld, R., 1986. Verzeichnis landwirtschaftlicher und gärtnerischer Kulturpflanzen (ohne Zierpflanzen) [Register of agricultural and horticultural plants in cultivation (without ornamentals)]. Schultze-Motel, J. et al., editors 2nd edition. Vol. 3. Springer Verlag, Berlin, Germany. Figs 154A & B, pp. 1130 & 1131 (flowering shoot, section of inflorescence, flower); Li, Hui-Lin et al. (Editors), 1975--1978. Flora of Taiwan. Epoch Publishing Company, Taipei, Taiwan. Vol 2. Fig. 1080, p. 492 (shoot in full bloom). Redrawn and adapted by P. Verheij-Hayes.

Authors

N.0. Aguilar, Pham Truong Thi Tho & L.P.A. Oyen