Allium fistulosum (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Allium fistulosum L.

Protologue: Sp. pl.: 301 (1753).

Family: Liliaceae

Chromosome number: 2n= 16

• Allium bouddhae O. Debeaux (1877),
• A. bakeri Hoop. (1929), non Regel (1875).

• Welsh onion ("welsh" probably derived from the German "welsche" meaning foreign), (Japanese) bunching onion, spring onion (En)
• Ciboule (Fr)
• Indonesia: bawang daun, bawang bakung (Sundanese), bawang oncang (Javanese)
• Malaysia: daun bawang
• Philippines: buyah (Ifugao)
• Cambodia: khtüm sânlök
• Thailand: hom-ton (central), hom-chin (peninsular)
• Vietnam: hành hoa, hành hương.

Welsh onion is only known in cultivation and probably originated in north-western China, although its ancestry remains unknown. The closely related wild species A. altaicum Pallas is still common in Siberia and Mongolia, where it is occasionally collected as a vegetable for local use or for export to China. Cultivation of the welsh onion dates back to at least 200 BC in China. It reached Japan before 500 AD and spread further to South-East Asia. The earliest description of the crop and its cultivation is found in a Chinese book of 100 BC. It is first mentioned in Japanese literature in 720 AD. Until the early 20th Century, the welsh onion was the most important Allium species in these countries, fulfilling the culinary role of both the common onion and leek in Europe. In Japan the welsh onion is now second in importance to A. cepa L., but in China, where welsh onion and common onion are used in different dishes, the welsh onion has retained its first place. The crop is grown throughout the world, but the main area of cultivation remains East Asia from Siberia to Indonesia. In other parts of the world it is mainly a crop of home gardens.

The forms grown in East Asia for their thick, blanched pseudostems are eaten as a pot herb, e.g. in sukiyaki and chicken dishes. In South-East Asia the welsh onion is mainly grown for its green leaves, which are used in salads, or as a herb to flavour soups and other dishes. In Java the plants are also eaten whole, either steamed or after heating over a fire for a short time. In Japan seedlings of 7-10 cm are used in special dishes. Welsh onion has not been used in a processed form until recently, when a dehydration industry started. The product is mainly used as an additive to preprocessed food such as instant noodles. The young inflorescence is sometimes deep-fried and eaten as a snack.

The plants are said to reduce or prevent white ant infestation in gardens. Diluted pressed juice is used against aphids in China.

The therapeutic qualities attributed to the welsh onion are many, especially in Chinese medicine. It is used to improve the functioning of internal organs and the metabolism, and to prolong life. It is further reported to improve eyesight, to aid digestion and perspiration, and to enhance recovery from common colds, headaches, wounds and festering sores.

No worldwide statistics for the welsh onion are available, as information on its production is often combined with that of other Allium spp. Japan, Korea, China and Taiwan are the main producers. Production in Japan reached 563 000 t from 24 100 ha, in Korea 432 000 t from 18 900 ha (1984). Production in Indonesia in 1988 amounted to 163 000 t from 24 500 ha. International trade in welsh onion is very limited.

The odour of the welsh onion is not very strong. It is chemically related to the odour of A. cepa and derives from volatile allyl-sulphides. The composition of green tops and blanched pseudostems differs, green tops being more nutritious. Green tops contain per 100 g edible portion: water 92 g, protein 1.7 g, fat 0.2 g, digestible carbohydrates 5.4 g, vitamin A 480 IU, vitamin B₁ 60μg, vitamin B₂ 100μg, niacin 400μg, vitamin C 33 mg, Ca 80 mg, Fe 1.0 mg, K 200 mg, P 38 mg. The energy value is 105 kJ/100 g. A large proportion of the storage carbohydrates are sugars and oligosaccharides. Besides glucose, fructose and sucrose, they consist of maltose, rhamnose, galactose, arabinose, mannose and xylose. Sugar and protein contents increase in plants grown under low temperatures, and this improves eating quality.

The weight of 1000 seeds is 2.2-2.5 g.

• Gregarious, perennial herb, often growing in large tufts, usually cultivated as an annual or biennial plant.
• Bulb indistinct, ovoid to oblongoid, up to 10 cm long, gradually passing into a more or less thick scape; lateral bulbs few to several, virtually absent in some cultivars, narrow and inconspicuous; protective bulb-coat leaves several, papery or chartaceous, smooth, reddish, purplish or brownish.
• Sproutleaf 1, of variable length, apex oblique; foliage leaves bluish-green with light bloom, distichous, glabrous, 4-6 in bunching types, 10-12 in single stem types, actively growing green leaves usually 3 and 5-6 respectively; blades tapering cylindrical, scattered in the lower part of the scape, (10-)30-150 cm × 1.0-2.5 cm, hollow, top acute, circular in cross-section.
• Scape 1, exceeding the leaves, erect, straight without localized swelling, hollow, 8-25 mm broad.
• Inflorescence umbellate, hemispherical to spherical, 3-7 cm across, composed either of flowers only or of bulbils only, flowering centrifugal; spathe 1, hyaline, persistent, up to 10 mm long, acuminate, opening with (1-)2-3 slits into spathe valves; bracteoles absent; pedicels subequal to unequal, the lower ones shortest, 10-30 mm long; flowers narrowly campanulate to urceolate; tepals 6, ovate-oblong to oblong-lanceolate, 6-10 mm long, smooth, (greenish-)white, with greenish midvein, top acuminate; stamens 6, exceeding perianth; inner and outer filaments similar, 8-15 mm long, simple, narrow, also at base; anthers 1.5 mm long, yellow; pistil rather long, exceeding perianth; ovary globose to broadly obovate; style slender, 10-15 mm long.
• Fruit globose, about 5 mm across.
• Seed 3-4 mm × 2-2.5 mm, black.

Welsh onion is a perennial plant, grown commercially mostly as an annual, in home gardens often as a perennial. It does not have a long-day dormant stage like A. cepa, so it continues its vegetative growth and does not develop a real bulb. However, some cultivars which originated from cold temperate areas show short-day dormancy, even when grown in warmer areas. They stop growing and their leaves dry out and die off under short days, even when the temperature would permit normal growth.

The lateral buds in the leaf axils elongate and develop as tillers to form a vigorous clump. This tillering characteristic is more pronounced in cultivars grown for the green leaves than in those grown for the long blanched pseudostems.

Flower induction is controlled by temperature and daylength. Low temperatures and short days induce flowering, but requirements vary strongly with the origin of cultivars. Flowering is generally induced by temperatures below 13 °C, when seedlings have formed a certain number of leaves or a pseudostem of a certain thickness. Plants grown at 13-18 °C bolt only under short days. When grown at 20 °C and under a photoperiod of 16 hours, they are not vernalized. For certain Taiwanese cultivars like "Pei Chung", 5 days at 5 °C or 20 days at 10 °C are sufficient for vernalization. In the tropics, where conditions favour vegetative rather than generative growth, only some well-adapted cultivars will flower.

Superficially there is a strong resemblance to A. cepa. Foliage leaves of A. fistulosum are somewhat rounder in cross-section, not flattened adaxially. Differences are more prominent in the inflorescence: A. fistulosum lacks bracteoles, has flowers about twice the size of A. cepa, the filaments of the stamens are more protruded, they lack basal teeth and are not broadened at the base. Moreover, A. cepa has a much better developed bulb.

A. fistulosum hybridizes readily with the related wild species A. altaicum. These hybrids have high pollen and seed fertility.

A. × wakegi Araki (synonym: A. fistulosum var. caespitosum Makino) is a hybrid between A. fistulosum and A. 'cepa cv. group Aggregatum (shallot), with A. fistulosum as the female parent. It is a perennial plant forming small bulbs. Its inflorescence forms only bulbils, no fertile seeds. In the vegetative stage it is morphologically similar to A. fistulosum. Its leaves are slender, 60-70 cm long. One bulb may produce 20-30 tillers.

Other commercial hybrids between A. fistulosum and A. cepa, grown for their green tops, include "Beltsville Bunching", "Louisiana Evergreen", and "Delta Giant". These hybrids are fertile and normally propagated by seed.

The very large area of cultivation, the great adaptability to temperature and the varied uses of the crop have resulted in a very large number of cultivars. In Java three types of plants are identified:

• bawang bakung: robust plants grown for their pseudostem.
• bawang cina: meagre, strongly tillering plants, grown for their leaves.
• bawang daun: intermediate between the two and the most common type.

Popular Indonesian cultivars are "Plumpung", "Mambo", "Nyonya", "Siih Kecil" and "Tosari".

In Japan, four cultivar groups are generally discerned (system of Kumazawa):

• Kaga: this group has dark green thick leaves and pseudostems; they show little tillering and are grown for their pseudostems; the plants become dormant in winter.
• Kujyo: this group has tender, green leaves of excellent eating quality; they tiller profusely and are mostly grown for their green tops; they remain green during winter and their cold tolerance is generally low.
• Senju: this group is intermediate between the former two; they are mainly grown for their pseudostems, but growth continues during winter, although at a reduced rate.
• Yagura negi (A. fistulosum var. viviparum Makino): this group produces numerous tillers in spring and summer; its growth stops in winter, and it produces no flowers but only bulbils; it is propagated by division of the basal cluster or by bulbils.

Welsh onion is adapted to a remarkably wide range of climates. It is very tolerant of cold weather and can overwinter even in Siberia. It is also tolerant of hot humid conditions as occur e.g. in Bangladesh. In Java it grows well above an altitude of 200 m, but it is more common above 500 m. There are many local selections and commercial cultivars, reflecting the adaptation to this wide range of climatic conditions. Most cultivars are well adapted to variations in rainfall and more tolerant of heavy rainfall than other Allium spp. A well-drained loamy soil, rich in organic matter is preferred. Welsh onion is very susceptible to waterlogging, which quickly kills the active roots. Established plants are very tolerant of moisture stress and drought will rarely kill them.

For optimal growth a neutral soil pH is required, but even at a pH of 8-10 good growth is possible. In acidic soils growth is generally poor.

In South-East Asia the crop is propagated mainly using basal tillers and can be planted the whole year round. Although seed production is possible at elevations above 1000 m, and imported seed of Taiwanese and Japanese cultivars is also available, plants are rarely raised from seed because this is more difficult under tropical conditions and is more time-consuming.

In temperate areas where seed production is more successful, propagation is mainly by seed, which is either sown directly into the field or first in nurseries. Seed requirements are 8-16 kg/ha for direct seeding and 2-4 kg/ha in the case of transplanting. In nursery beds, seeds are either broadcast or sown in rows or in 5-6 cm wide bands. The area of nursery required is 10-12% of the field area. Seedlings are ready for transplanting when 25-30 cm tall and thick as a pencil.

In Indonesia welsh onion is planted on uplands as well as on dry paddy fields. For green leaf production, land preparation is light. Tillers are transplanted into raised beds or ridges, which are alternated with furrows for irrigation and drainage. Planting distances are about 20 cm × 25 cm (200 000 plants per ha). About one-third of the top part of the tiller is usually trimmed to reduce transpiration. Planting holes are filled with 50-100 g of manure (10-20 t/ha) and the shoots inserted slanting to stimulate tillering. Urea or ammonium sulphate at a rate of 3 g per plant (500-600 kg/ha) is applied 3 weeks after planting, and again at 6 weeks after planting if soil fertility is low. Weeding and earthing up are usually practised 6-7 weeks after planting. Welsh onion needs plenty of water. At lower elevations, it is usually grown during the rainy season. Daily irrigation is necessary during the dry season. Mixed cropping with white cabbage, carrot and potato is very common in the highlands.

For blanched pseudostem production, fields are deeply cultivated. Furrows of 10-20 cm deep are made, the soil being thrown to one side forming a ridge which will support the young plant and facilitate earthing up later. Earthing up is essential to blanch and soften the leaf-sheath cylinder. As earthing up also affects aeration and thus checks growth, it should be done gradually and not started too early.

Although welsh onion is generally a healthy crop, it may be affected by a number of diseases, many of them common to most Allium crops. Purple blotch (Alternaria porri), which causes characteristic concentric spots on the leaves, and downy mildew (Peronospora destructor) may cause severe problems. White rot (Sclerotium cepivorum) may cause serious losses under successive or repeated cropping, as the pathogen is very persistent in the soil. Poor nutrition and heavy rains stimulate the development of the diseases. The practice of vegetative propagation in South-East Asia is conducive to virus infestation, but many of the landraces seem to be relatively tolerant. In addition, many diseased plants are removed by rigorous visual inspection of the planting material. The most important virus disease is caused by the onion yellow dwarf virus, which is transmitted by over 50 aphid species. It causes mosaic-type symptoms, including chlorotic mottling, streaking and stunting, and distorted flattening of the leaves. Relative tolerance is found in the Kujyo group of cultivars.

The beet army worm (Spodoptera exigua) and the American bollworm (Heliothis armigera) are the most serious pests. They are difficult to control due to the waxy layer on the leaves, and the fact that the larvae hide inside the hollow leaves. Onion thrips (Thrips tabaci) may cause considerable damage.

In the tropics welsh onion can be harvested year-round. Plants are pulled out about 2½ months after planting the tillers. The part used as planting material for the next crop is left in the field until it is needed. Harvesting is a labour-intensive operation, especially for pseudostems, which have to be dug up, cleaned and bundled. Mechanized harvesting equipment has been developed in Japan, which has reduced the labour requirements considerably.

Average yields in Japan and Korea are about 25 t/ha, in Taiwan 10-15 t/ha. In Indonesia, they are considerably lower, averaging 7 t/ha, but also reaching levels of 15 t/ha; however, the growing period is only 2.5-3 months compared to 9 months in East Asian countries. Data for other countries are not available.

After harvesting, leaves and pseudostems are cleaned, dried or damaged leaves are removed, and the plants are bunched and packed in boxes or baskets for transport to the market.

Collections of germplasm exist in Japan, the United States, the United Kingdom, Germany and the former Soviet Union. IBPGR ranked the welsh onion second in importance in the genus Allium because of its disease resistance, ecological adaptability and close relationship to A. cepa. Breeders often maintain their own collections and commonly exchange materials, thus maintaining an adequate level of variability.

In most countries farmers produce their own seed or planting material. In Japan a seed industry has developed, and some ten new cultivars are released per year. Breeders aim at improved cultivar homogeneity and adaptation to specific ecological conditions. For pseudostem cultivars, breeding work aims at obtaining lines with minimal tillering. Male sterile lines exist and F₁hybrids have been developed.

The great adaptability of the crop and the example of Japan and Taiwan, where intensification of cultivation combined with selection, breeding and the development of a good marketing network has led to a greatly increased production, indicate that there is great scope for the development of better cultivars and for increased commercialization and intensification of production in South-East Asia too.

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• Allium (Medicinal plants)

• L.P.A. Oyen & Soenoeadji
• Diah Sulistiarini, Juliasri Djamal & Iman Raharjo