Allium sativum (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

1, plant habit; 2, bulb; 3, plantlets; 4, inflorescence (Iskak Syamsudin)

Allium sativum L.

Protologue: Sp. pl.: 297 (1753).

Family: Liliaceae

Chromosome number: 2n= 16

Vernacular names

• Garlic (En)
• Ail (Fr)
• Indonesia: bawang putih, bawang bodas (Sundanese)
• Malaysia: bawang putih
• Papua New Guinea: galik (Pidgin)
• Philippines: bawang (Tagalog, Ilocano), ahos, ajos (Bisaya), ahus (Ibanag)
• Cambodia: khtüm sââ
• Laos: kath'ièm
• Thailand: krathiam (general), hom-tiam (northern)
• Vietnam: tỏi.

Origin and geographic distribution

Garlic is only known from cultivation but is believed to originate from central Asia (Tien Shan), where its wild ancestor A. longicuspis Regel is endemic. Garlic spread to the Mediterranean region in ancient times, and was already known in Egypt in 3000 BC. It is an ancient crop in India and China as well. The Spanish, Portuguese and French introduced it to the New World. At present garlic is grown all over the world at latitudes between 5-50 ° in both hemispheres, but is most popular in the Mediterranean and in China.

Uses

After onions, garlic is the second most widely used of the cultivated Alliums. It is mainly used as a condiment for flavouring meat, fish and salads, in fresh or dehydrated form. Apart from the mature bulbs, the green tops and immature bulbs are also widely used in Asia.

Garlic is much valued as a medicinal crop. It has a strong reputation for lowering the blood sugar and cholesterol levels and inhibiting thrombus formation. It is used externally to cure headache, insect bites, rheumatism and toothache, and a decoction internally as febrifuge. Leaves and bulbs are considered to have hypotensive, carminative, antiseptic, anthelmintic, diaphoretic and expectorant properties. Many attributed prophylactic activities are questionable, but have resulted in a rich supply of and demand for medicinal pills, drinks and powders based on garlic extracts. Garlic users extol its tasty and healthy qualities. Non-users abhor the offensive odour exhaled by users.

Production and international trade

FAO estimates the 1990 world acreage at 469 000 ha with a production of 2 932 000 t. The leading producers are China (658 000 t), South Korea (417 000 t), India (280 000 t), Spain (202 000 t) and the United States (150 000 t). Thailand is listed by FAO with a production of 120 000 t, but Thai statistics report a production of 330 000 t from 31 000 ha in 1988. In that same year Indonesia produced 90 000 t from 16 000 ha, and imported considerable amounts from abroad. The Philippines produced 18 000 t from 6400 ha, and imported large amounts of dehydrated, powdered garlic from the United States, United Kingdom and Germany.

Properties

The edible portion amounts to 50-70% of the total plant if used immature (pseudostem and immature bulb) or 20-30% if used mature (dry bulbs). The nutrient composition of dry bulbs per 100 g edible portion is: water 68 g, protein 3.5 g, fat 0.3 g, carbohydrates 27 g, ash 1 g, Ca 29 mg, P 202 mg, K 529 mg. The vitamin content is rather low. The energy content is 490 kJ/100 g.

The flavour is based on sulphur compounds, collectively referred to as S-alk(en)yl cysteine sulphoxides. Garlic is characterized by a dominance of S-allylcysteine sulphoxide (alliin) which is odourless but on crushing breaks down to allicin, the principal ingredient of which is the odoriferous diallyl disulphide.

Description

• Erect herb, up to 60 cm tall, grown as an annual from small bulbs called cloves.
• Roots adventitious, superficial.
• Bulb depressed globular to ovoid, up to 7 cm in diameter, mainly composed of 1-15 sessile lateral bulbs (cloves) which have developed from axillary buds of the younger foliage leaves; protective bulb-coat leaves papery or chartaceous, smooth, whitish or purplish; cloves ovoid to ellipsoid-oblong, each consisting of a protective cylindrical sheath, a single thickened storage leaf-sheath and a small central bud.
• Real stem very short, flattened, forming a disk at the base of the bulb; pseudostem formed by the sheathing bases of successive leaves.
• Leaves 4-10, distichous, glabrous, scattered along the pseudostem; leaf-blade linear-oblong, up to 50 cm × 2.5 cm, flat or often V-shaped in section, margin smooth or crenulate, top acute.
• Scape 1, up to 1.5 m long, erect, straight, solid.
• Inflorescence a subspherical umbel, 2-5 cm in diameter, composed of only bulbils or of bulbils and flowers, protected by a membranous spathe that splits on one side when it opens; pedicels slender, up to 4 cm long; flowers subcampanulate, usually ill-developed, rudimentary or absent; tepals 6 in 2 whorls, lanceolate, acuminate, up to 3 mm long, greenish-pink to purple; stamens shorter than the tepals, arranged in 2 whorls; pistil more or less rudimentary, tricarpellate.
• Fruit abortive, without seeds.

Growth and development

The propagule (clove) forms dorsi-ventral flat leaves from a central meristem situated on top of the clove disk (= true stem). Younger leaves emerge inside older ones, the leaf-sheaths forming a pseudostem. The top meristem ends its activity by forming a flower stalk or a last leaf.

A new clove develops from a lateral bud in the axil of the first or second foliage leaf of the mother clove. The bud (rudimentary side-shoot) consists of a rudimentary stem and leaf initials. The rudimentary stem develops into a new clove disk and the first two successive leaf initials into a swollen storage leaf and a protective skin. The following 5-6 leaf initials remain dormant until the next planting.

The garlic bulb normally consists of a number of cloves generated from as many lateral buds which are enveloped by the sheaths of the third and subsequent foliage leaves of the mother clove.

The duration of the subsequent growth and development phases strongly depends on the prevailing conditions. The total growing period varies from 3-4 months (in the tropics) to about 9 months (for winter garlic in temperate regions).

Other botanical information

Garlic is an extremely variable species with many strikingly distinct cultivars (clones) known in cultivation. No satisfactory classification of the cultivars into groups exists, as too many intermediate cultivars remain unclassifiable. Nevertheless, two groups are often distinguished: cv. group Common Garlic (synonyms: A. sativum L. var. sativum and var. typicum Regel, A. pekinense Prokhanov) and cv. group Ophioscorodon (synonyms: A. sativum L. var. ophioscorodon (Link) Döll and var. controversum (Schrader) Moore, A. ophioscorodon Link). Cv. group Common Garlic has a straight scape and cv. group Ophioscorodon has a scape with a distinct curve or coil towards the top (the latter group is also known by the common names rocambole or serpent garlic).

Great-headed Garlic is a cv. group of A. ampeloprasum. It has the appearance of extremely robust garlic and is frequently confused with garlic. It may be readily distinguished by its large umbel without bulblets and the presence of small bulblets around the main bulb.

A. longicuspis, the presumed wild ancestor of garlic, is only collected from the wild and not cultivated. For garlic breeding, this species is promising because it can produce perfect flowers and good seed.

Because of a lack of breeding activities in the tropics, only local garlic strains are usually grown. Each region has its own cultivars. Indonesian strains are "Lumbu Hijau", "Lumbu Putih", "Sanur" and "Layur". Philippine strains include "Ilocos White", "Ilocos Pink", "Cabuyao" and "Mindoro 1".

Ecology

Garlic growth is restricted to the temperature traject 9-28 °C. Temperature and daylength are decisive factors for bulbing and bolting. For normal bulbing, exposure of propagules to 10-15 °C for 2 months is required. Long days (> 12 hours) stimulate the formation of cloves. Lower temperatures (-2 °C to 6 °C) are needed for vernalization. Long days, low light intensity, drought and N deficiency hamper flower stalk development.

Garlic shows wide genetic variation in its response to temperature and daylength. This variation has been exploited for adapting the crop to all latitudes from the equator to 50 °. Near the equator, garlic is grown in the highlands, since in the lowlands high day temperatures severely limit growth. On Java, garlic is grown from May until October, which corresponds with the dry season and conditions of relatively short days. As a rule of thumb, garlic should be grown at high altitudes in the tropics and during the prevailing long-day season, if possible.

Propagation and planting

Garlic is normally propagated by cloves and seldom by big topsets (bulbils in the inflorescence). Dormancy lasts only 1-2 months, so dormancy-breaking is not normally necessary. In most areas in the tropics, e.g. Indonesia, garlic is planted once a year, and consequently the planting material has to be stored for 7-8 months. Optimum clove weight for planting depends on the cultivar. Planting cloves of about equal weight results in greater uniformity of maturity and size. Depending on the size (1.5-4 g per clove) and the plant density (50-70 plants per m²), the quantity of planting material may vary from 750-2800 kg/ha. Planting distances are 15-20 cm between rows and 8-10 cm in the rows.

Husbandry

The best field conditions are sole cropping on raised beds alternated with furrows. During the dry season, the crop has to be irrigated regularly. Planting, watering, weeding, harvesting are all done by hand.

The recommendations for fertilizer rates in Indonesia mention a basal dressing of 200 kg/ha of triple superphosphate during soil tillage. No organic manure is applied. A mixture of 80 kg/ha of urea, 80 kg/ha of ammonium sulphate and 50 kg/ha of potassium chloride is applied as side dressings at 15, 30 and 45 days after planting.

Diseases and pests

The main problem for garlic growers is the control of purple blotch (Alternaria porri), especially during the rainy season. This disease is less of a problem at lower elevations. Growers spray regularly and intensively with fungicides. Healthy planting material, a modest N gift, and a lower planting density can reduce the disease. Other diseases often mentioned for garlic, but less troublesome in tropical areas, are basal rot (Fusarium oxysporum) and bacterial rot. Rust (Puccinia porri) and white rot (Sclerotium cepivorum) are less serious in the tropics than in temperate areas.

The main pest problems in Indonesia are army worm (Spodoptera exigua) and thrips (Thrips tabaci). Virus diseases probably severely depress yields. Onion yellow dwarf virus (OYDV) has infested the garlic crop almost everywhere (in Java for 87%). Leek yellow stripe virus (LYSV-G) is also very common in Java (ca. 19%). It is possible to produce virus-free plants by meristem culture, but for tropical conditions it seems more practical to visually select all planting material and rogue infected plants. This is common practice in several western countries.

Harvesting

Harvesting takes place 3-4 months after planting, when the leaves start turning yellow and begin to dry up. Bulbs are pulled up and tied in bunches of several kg for drying and storage in sheds or kitchens.

Yield

FAO figures (1988-1990) on yields per ha are 4-4.5 t for Indonesia, 3.5-4 t for Thailand and 2.5-3 t for the Philippines. These yields are low compared to the world average of 6 t/ha, and very low compared to data from certain subtropical countries such as Israel (10-12 t), Yemen (16 t), India (10 t) and Sudan (15-20 t). However, statistics from the Thailand Department of Agricultural Extension mention an average yield in Thailand of 10.6 t/ha in 1988. The Lembang Horticultural Research Institute (LEHRI) reported an average yield in Indonesia of 5.6 t/ha, with a potential yield of 12 t/ha.

Handling after harvest

Garlic is transported in bunches, on strings, or in crates. It has a good keeping quality at a range of temperatures, -2 °C being the optimum. Good ventilation during storage is essential.

Genetic resources

Substantial germplasm collections of A. sativum are available in the Czech Republic, Israel and Spain. In Asia, important collections are held in Taiwan (Taiwan Agricultural Research Institute, Wufeng), India (National Bureau of Plant Genetic Resources, New Delhi) and Japan (Vegetable and Ornamental Crops Research Station, Ano). Smaller collections are available at research institutes in South-East Asia, e.g. LEHRI, Lembang, Indonesia.

Breeding

Major breeding objectives are improved yields and better keepability, especially in tropical lowlands. When selecting for growing in the lowlands, the planting material should be stored at high altitude; if stored in the lowlands as well as grown there, the material is subjected to an unnecessary excessive high temperature stress, and the gap between genetic variation and adaption requirements seems to be unbridgeable.

Prospects

For South-East Asia, several improvements seem very promising, i.e. better storage facilities (lower temperatures), and virus eradication by meristem culture and visual selection in the field. Screening of international germplasm collections, and possibly selection after generative multiplication, will yield improved planting materials.

Literature

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• Augusti, K.T. & Sheela, C.G., 1996. Antiperoxide effect of S allyl cysteine sulfoxide, an insulin secretagogue, in diabetic rats. Experientia 52(2): 115-120.
• Bruneton, J., 1995. Pharmacognosy, phytochemistry, medicinal plants. Technique & Documentation Lavoisier, Paris, France. 915 pp.
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Main genus page

• Allium (Medicinal plants)

Authors

• Q.P. van der Meer & Anggoro H. Permadi
• Diah Sulistiarini, Juliasri Djamal & Iman Raharjo