Allium fistulosum (PROTA)
|Geographic coverage Africa|
|Geographic coverage World|
|Carbohydrate / starch|
|Forage / feed|
- Protologue: Sp. pl. 1: 301 (1753).
- Family: Alliaceae
- Chromosome number: 2n = 16
- Welsh onion, Japanese bunching onion (En).
- Ciboule (Fr).
- Cebolinha, cozida (Po).
Origin and geographic distribution
Allium fistulosum is only known in cultivation and probably originated in north-western China. DNA studies indicate that it was derived from the wild Allium altaicum Pall., which occurs in Siberia and Mongolia, where it is occasionally collected as a vegetable for local use or for export to China. Cultivation of Allium fistulosum dates back to at least 200 BC in China. It reached Japan before 500 AD and spread further to South-East Asia and Europe. ‘Welsh’ in the name welsh onion is probably related to the old German ‘welsche’ meaning foreign, and has no connection with Wales in the United Kingdom. In China Allium fistulosum is the most important Allium species fulfilling the culinary role of both the common onion and leek in Europe; in Japan it is now second in importance to the bulb onion (Allium cepa L.). The crop is grown throughout the world, but the main area of cultivation remains eastern Asia from Siberia to Indonesia; elsewhere it is mainly a crop of home gardens. In Africa it is locally important only and is reported from Sierra Leone, Ghana, Cameroon, Congo, DR Congo, Sudan, Kenya, Zambia and Zimbabwe. A leaf onion reported from Nigeria probably also belongs to Allium fistulosum.
Two types of Allium fistulosum are grown and sometimes distinguished as cultivar-groups: Japanese Bunching Group and Welsh Onion Group. Japanese bunching onion is grown mainly in eastern Asia for its thick, blanched pseudostems and is eaten as a potherb, e.g. in sukiyaki and chicken dishes; welsh onion is grown for its green leaves, which are used in salads, or as a herb to flavour soups and other dishes. The latter is most common in Africa. In the Brazzaville-Kinshasa area (Congo and DR Congo), whole plants are harvested and eaten as a boiled vegetable. In South-East Asia (Java) the plants are also eaten whole, either steamed or after heating over a fire for a short time, and in Japan seedlings of 7–10 cm tall are used in special dishes. Allium fistulosum 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 termite infestation in gardens. Diluted pressed juice is used against aphids in China. The therapeutic qualities attributed to Allium fistulosum are many, especially in Chinese medicine. It is used to improve the functioning of internal organs and the metabolism, for the prevention of cardiovascular disorders, and to prolong life. It is further reported to improve eyesight, and to enhance recovery from common colds, headaches, wounds and festering sores.
Production and international trade
No worldwide statistics for Allium fistulosum are available, as information on its production is often combined with that of other Allium spp. China, Japan, Korea, Taiwan and Indonesia are the main producers. In 1984 production in Japan reached 563,000 t from 24,000 ha, in Korea 432,000 t from 19,000 ha.
The nutritional composition of raw green tops per 100 g edible portion is: water 90.5 g, energy 142 kJ (34 kcal), protein 1.9 g, fat 0.4 g, carbohydrate 6.5 g, Ca 18 mg, Mg 23 mg, P 49 mg, Fe 1.2 mg, Zn 0.52 mg, vitamin A 1160 IU, thiamin 0.05 mg, riboflavin 0.09 mg, niacin 0.40 mg, folate 16 μg, ascorbic acid 27 mg (USDA, 2002). The nutritional value of green tops and blanched pseudostems differs, green tops being more nutritious.
The odour of Allium fistulosum is not very strong. It is chemically intermediate between the odours of onion and leek. It derives from volatile propyl cysteine sulphoxide (characteristic of leek) and propenyl cysteine sulphoxide (characteristic of onion). These alkyl-sulphoxides are degradation products of non-protein amino acids of the S-alk(en)yl-cysteine group. When cells are damaged the amino acids break down under the influence of the enzyme aliinase into highly reactive sulphenic acids, ammonia and pyruvate. The sulphenic acids then react with other compounds to form a range of disulphides.
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.
Tests showed that welsh onion extracts can modulate vascular tone in vitro in the thoracic aortae of rats. This supports the use in traditional medicine to prevent cardiovascular disorders. Antifungal constituents have been isolated from the seeds.
- Perennial glabrous herb, growing in tufts, usually grown as an annual or biennial plant, up to 50(–100) cm tall, with indistinct, ovoid to oblongoid bulb up to 10 cm long, lateral bulbs few to several or virtually absent; tunic white to pale reddish brown.
- Leaves 4–12, distichously alternate, glaucous, with tubular sheath; blade cylindrical, hollow, 10–50(–100) cm × 0.5–2.5 cm, acute at apex.
- Inflorescence a spherical umbel 3–7 cm in diameter, on a long, erect, terete, hollow scape up to 50(–100) cm long and up to 2.5 cm in diameter; umbel composed either of flowers or of bulbils only; spathe 1, hyaline, persistent, up to 1 cm long, splitting into (1–)2–3 parts.
- Flowers bisexual, narrowly campanulate to urceolate; pedicel slender, up to 3 cm long; tepals 6, in 2 whorls, free, ovate-oblong to oblong-lanceolate, 6–10 mm long, white with greenish midvein; stamens 6, exceeding tepals, connate at base and adnate to tepals; ovary superior, 3-celled, style slender, exceeding tepals.
- Fruit a globular capsule c. 5 mm in diameter, splitting loculicidally, few-seeded.
- Seeds 3–4 mm × 2–2.5 mm, black.
Other botanical information
In Europe a classification into 2 cultivar-groups has been proposed: Japanese Bunching Group, single-stemmed cultivars grown for their thickened pseudostem, and Welsh Onion Group, multi-stemmed cultivars grown for their leaves. A classification into 3 groups is common in Japan: Kaga Group grown in the coolest parts of Japan for its pseudostems; Kujyo Group mainly grown in the warmest parts of Japan and mainly for its leaves; and Senju Group, intermediate in use and ecological requirements.
Superficially there is a strong resemblance to Allium cepa, but Allium fistulosum does not develop a bulb, although some slight thickening of the base of the pseudostem may occur. Its foliage leaves are somewhat rounder in cross-section, not flattened adaxially. Differences are more prominent in the flowers. In Allium fistulosum flowering progresses from the top of the umbel downwards. The flowers lack bracteoles, are larger and campanulate to urceolate, while those of Allium cepa have bracteoles, are smaller and stellate.
Allium fistulosum hybridizes easily with Allium altaicum; the hybrids have high pollen fertility and form ample seed. Hybridization is also possible with Allium cepa. The hybrids are perennial plants forming small bulbs. Several old hybrids between Allium fistulosum as female parent and tropical shallots (Allium cepa Aggregatum Group) exist. These are known as Allium ×proliferum, Allium ×wakegi or Allium fistulosum var. caespitosum. Examples are the Indonesian shallot ‘Sumenep’, which is well adapted to tropical conditions and never flowers, and the top onion in which the inflorescence is composed of bulbils. In the vegetative stage these plants resemble Allium fistulosum. Recent commercial hybrids between Allium fistulosum as female parent and Allium cepa, grown mainly in the United States and Europe for their green tops, include ‘Beltsville Bunching’ (a seed-producing tetraploid), ‘Louisiana Evergreen’ (a sterile diploid) and ‘Delta Giant’ (a sterile triploid originating from a backcross of the hybrid with Allium cepa). Another group of hybrids grown in Japan is Yakura Negi Group. Plants of this group tiller abundantly in spring and summer and are dormant in winter. Their inflorescence produces no flowers but only bulbils; they are propagated by division or by bulbils.
Growth and development
Allium fistulosum is a perennial plant, grown commercially mostly as an annual, but in home gardens also as a perennial. It does not have a long-day dormant stage like Allium 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. 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 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. In the tropics, where conditions favour vegetative rather than generative growth, only some well-adapted cultivars will flower.
Roots are readily colonized by arbuscular mycorrhizal fungi, which enhances P uptake and stimulates growth.
Allium fistulosum 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 such as those occurring near Brazzaville and Kinshasa in Central Africa. In Java (Indonesia) it grows well above an altitude of 200 m, but it is more common above 500 m. Most local cultivars are well adapted to variations in rainfall and they are more tolerant of heavy rainfall than other Allium spp. Established plants are tolerant of moisture stress and drought will rarely kill them.
A well-drained loamy soil, rich in organic matter is preferred. Allium fistulosum is very susceptible to waterlogging, which quickly kills the active roots. For optimal growth a neutral soil pH is required, but even at a pH of 8–10 good growth is possible. In acid soils growth is generally poor.
Propagation and planting
In the tropics Allium fistulosum is propagated mainly by 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. However, in the Brazzaville-Kinshasa area, both tillers and seed of local cultivars are used. 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. The weight of 1000 seeds is 2.2–2.5 g. 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.
For green leaf production, land preparation is light. Tillers or seedlings 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 (about 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. Allium fistulosum 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 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 of the roots and thus checks growth, it should be done gradually and not be started too early.
Diseases and pests
Although Allium fistulosum 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, unbalanced nutrition and heavy rains stimulate the development of the diseases. The practice of vegetative propagation is conducive to virus infestation, but many landraces seem to be relatively tolerant. Diseased plants should be removed by rigorous visual inspection of the planting material. Allium fistulosum is resistant to the onion yellow dwarf virus (OYDV), but susceptible to the welsh onion yellow stripe virus (WoYSV), occurring e.g. in Japan and Indonesia. It causes similar mosaic-type symptoms, including chlorotic mottling, streaking and stunting, and distorted flattening of the leaves. Relative tolerance is found in cultivars of Kujyo Group.
Allium fistulosum is resistant to several diseases affecting other Allium spp. including pink root caused by Pyrenochaeta terrestris, neck rot caused by Botrytis spp. and leaf rot caused by Botrytis squamosa. Partial resistance has been found to anthracnose (Colletotrichum gloeosporioides).
The beet army worm (Spodoptera exigua) and the American bollworm (Heliothis armigera) are the most serious pests. They are difficult to control because the larvae hide inside the hollow leaves and the waxy layer on the leaves hinders wetting. Onion thrips (Thrips tabaci) may cause considerable damage. Thrips damage is stimulated by pesticide sprayings against Spodoptera, which kill the natural enemies of the thrips. Overhead sprinkling reduces thrips damage.
In the tropics Allium fistulosum can be harvested year-round; in the Brazzaville-Kinshasa area it is mainly harvested during the rainy season. Plants are pulled out about 2.5 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.
Yield data for countries in Africa are not available. 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 they may reach 15 t/ha; however, the growing period is only 2.5–3 months compared to 9 months in East Asian countries.
Handling after harvest
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 are maintained in Japan, the United States, the United Kingdom, Germany and the former Soviet Union. IPGRI ranked Allium fistulosum second in importance in the genus Allium because of its disease resistance, ecological adaptability and close relationship to Allium 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 several new cultivars are released per year. Large breeding programmes also exist in China and Taiwan. 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 F1 hybrids 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 the tropics, including Africa.
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Sources of illustration
- Oyen, L.P.A. & Soenoeadji, 1993. Allium fistulosum L. In: Siemonsma, J.S. & Kasem Piluek (Editors). Plant Resources of South-East Asia No 8. Vegetables. Pudoc Scientific Publishers, Wageningen, Netherlands. pp. 73–77.
- L.P.A. Oyen, PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
- C.-M. Messiaen, Bat. B 3, Résidence La Guirlande, 75, rue de Fontcarrade, 34070 Montpellier, France
Correct citation of this article
Oyen, L.P.A. & Messiaen, C.-M., 2004. Allium fistulosum L. [Internet] Record from PROTA4U. Grubben, G.J.H. & Denton, O.A. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, Netherlands. <http://www.prota4u.org/search.asp>.
Accessed 12 November 2020.