Allium ampeloprasum (PROSEA)
Allium ampeloprasum L. cv. group Leek
- Protologue: Sp. pl.: 294 (1753). Cv. group name proposed here.
- Family: Liliaceae
- Chromosome number: 2n= 32 (tetraploid)
- Allium porrum L. (1753),
- A. ampeloprasum L. var. porrum (L.) J. Gay (1847).
- Leek (En)
- Poireau (Fr)
- Indonesia: bawang prei, bawang sayuran
- Philippines: leek (Tagalog, Ilocano), sibuyas-bisaya (Bisaya), kuse (Pampangga)
- Cambodia: khtüm khchâl
- Laos: pèènz fàlangx
- Thailand: krathiam-ton (central), krathiam-bai
- Vietnam: tỏi tây.
Origin and geographic distribution
Leek is a cultigen derived from the wild A. ampeloprasum L. It is an ancient crop already mentioned in the Bible. Most probably it was domesticated in the eastern Mediterranean area where many of the related types (Turkish leek, kurrat, tareé irani) and related Allium species occur. Some other domesticated types are found far away from the centre of diversity: "pearl onion" in Germany, "poireau perpétuel" in France, "prei anak" in Indonesia. Leek is a predominantly European crop, but has been widely distributed and is grown at higher elevations in the tropics. In Indonesia, it is particularly popular in East Java.
The edible part is a pseudostem consisting of the elongated bases and lower blade parts of the foliage leaves, which is grown partly below ground to promote blanching. Leek is eaten as a cooked vegetable and as an ingredient of soups in the same way as welsh onion (A. fistulosum L.), e.g. as a component of bakmi (noodle dish).
Production and international trade
Considerable acreages of leek are grown in France, Germany, Belgium, the Netherlands, the United Kingdom and Denmark, totalling about 25 000 ha. The small highland production in South-East Asian countries is not accounted for in official statistics. In Indonesia, leek is registered in the statistics as "bawang daun" together with welsh onion. In the highlands of northern Sumatra (Berastagi), "prei anak" is cultivated for export to Malaysia.
The edible portion (etiolated pseudostem) is about 65% of the whole plant. Per 100 g it contains: water 90 g, protein 2 g, fat 0.3 g, carbohydrates 5 g, ash 1.5 g, Ca 60 mg, Fe 1 mg, P 30 mg, ß-carotene 0.6 mg, vitamin B10.12 mg, vitamin C 0.03 mg. The corresponding energy value is 128 kJ/100 g. The 1000-seed weight averages 3 g.
- Robust, biennial erect herb, 40-60 cm tall in the vegetative state, with little or no bulb formation, and a suppressed stem consisting only of a basal plate or disk.
- Adventitious roots appear at the base of the stem after the early loss of the primary root.
- Leaves 3-10, alternate in 2 opposite rows; blades linear, suberect or curved, 10-50 cm × 0.2-7 cm, flat or more or less V-shaped in cross-section; sheaths tubular, 5-50 cm long, longest in upper leaves; a young leaf emerges inside an older leaf forming a pseudostem consisting of old leaf-sheaths on the outside and young leaves inside.
- Scape 1, solid, terete, 40-150 cm long, exceeding the leaves.
- Inflorescence a subglobose umbel bearing several hundreds of flowers, 4-12 cm in diameter, normally without bulbils, subtended by a single long-pointed spathe, which is shed at maturity; bracts absent, bracteoles numerous, membranous, 2-4 mm long, each subtending 1 flower; pedicel 1-5 cm long; flowers usually campanulate, purple or white; tepals 6, ovate-oblong, obtuse or acute, 4-6 mm long; stamens 6, exceeding the perianth; ovary with 3 locules, containing 2 ovules each.
- Fruit depressed globose to ovoid, 2-4 mm in diameter, containing up to 6 seeds.
- Seed 2-3 mm × 2 mm, black.
Growth and development
Leek seed does not show rest or dormancy and germinates epigeally. Germination is rather slow; for 50% germination, a heat sum of 222 degree-days is required. Lateral bulbs are sometimes produced in the axils of the leaves, especially under long-day conditions after flowering. Flowering occurs only in plants larger than a certain minimum size, usually at the age of about 6 months. In the tropics flowers are seldom produced. Pollination is effected by insects and both self- and cross-pollination occurs. Bulbils ("topsets") are easily formed in the umbel, especially if flower buds are removed at an early stage of development. Seeds require high temperatures and long time to develop. Leek grows continuously, thus it can be harvested over a long period of time, starting about 4 months after transplanting of seedlings until flowering.
Other botanical information
The taxonomy of A. ampeloprasum is rather confused. In the literature, the cultivated leek is most often named A. porrum. In A. ampeloprasum several cultivar groups can be distinguished, but their relations are not yet well known:
- Pearl Onion (sometimes classified as var. sectivum Lued.). Grown for the lateral bulbs, especially in western Europe. Plants lack pseudostems. Flowers white, but flower scapes are not regularly developed. They are very hardy.
- Great-headed Garlic (sometimes classified as var. ampeloprasum). Grown for the lateral bulbs, especially in western Asia and the eastern Mediterranean. Seed is not formed.
- Tarée Irani. Grown for its green leaves in Iran. The umbels form seeds and sometimes bulbils as well.
- Poireau Perpétuel. Occasionally grown for its leaves in France, Algeria and Greece.
- Prei Anak. Grown for its leaves in Indonesia, and possibly identical to Poireau Perpétuel. It is strongly tillering, producing up to 10 side-shoots. It has a firmer texture than the common European leek, and is propagated vegetatively.
- Kurrat (sometimes classified as var. kurrat Schweinf. ex Krause. Grown for its edible green leaves, especially in the Near East. The plant resembles a small leek, and is propagated by seed.
- Leek (as described here). Cultivars recommended for the tropics are "American Flag", "Broad Flat", "Carentan", "Early Market Colonna", "Elephant", "Italian Giant", "Improved Musselburg", "Prizetaker", "Swiss Giant" and "Goliath".
The best temperature for growing leek is 20-25 °C. In the tropics it is usually cultivated in the highlands at about 1000 m altitude. It is hardly affected by differences in daylength, except that long-day conditions are needed for the formation of lateral bulbs at the base of the flower stalk after flowering. Leek has greater cold tolerance than common onion. Does not require special soil types, except for a well-prepared loose top layer.
Propagation and planting
Leek can be propagated vegetatively by means of topsets (bulbils formed in the umbel), by plantlets formed in the basal plate (from lateral buds or bulbs in the axils of the leaves) or most easily by means of the lateral bulbs formed at the base of the flower stalk after flowering. However, it is usually grown from seed, in South-East Asia necessarily from imported seed.
In Indonesia a special type of leek occurs, called "prei anak" (leek with children). It grows normally, but readily forms sprouts in the leaf axils, resulting in a moderate-sized leek-like plant with up to 10 smaller side-shoots. At harvest, the small side-shoots can only be used for planting, so many of them are discarded.
In the tropics, seed is usually sown in a shaded nursery. When 15-20 cm tall, the 2-3-month-old seedlings are transplanted to deep planting holes spaced 15-25 cm × 15-25 cm. Maturity is reached 120-150 days after transplanting. The longer the etiolated part of the pseudostem the better, and this is promoted by deep planting or earthing-up.
Diseases and pests
In the tropics, leek suffers mainly from purple blotch (Alternaria porri), Fusarium and thrips (Thrips tabaci). They are usually controlled by spraying pesticides and by stringent crop rotation.
Year-round cropping is possible. Harvesting is by uprooting.
Yields are much lower in the tropics (5-15 t/ha of cleaned product) than in Europe (45 t/ha).
Handling after harvest
After uprooting, roots are cut, outer damaged leaves are removed, and the remaining leaves shortened. For transport, the pseudostems are best put upright in baskets, leaves upwards. Leek has a limited storage period of 1-2 months at 0° C with a relative humidity of 90%, but storage and processing are still not common practices in the area.
Germplasm of leek and related types is available at the Institute of Horticultural Research, Wellesbourne (United Kingdom), the Centre for Genetic Resources, Wageningen (the Netherlands), and the Western Regional Plant Introduction Station, Pullman, Washington (United States). Nevertheless, severe genetic erosion of landraces has taken place in several European countries.
The major breeding objectives in Europe are productivity, uniformity and resistance to diseases, i.e. virus, rust (Puccinia porri) and white tip (Phytophthora porri). Resistance to white tip is rare or absent in leek, and this character is sought in wild relatives. Resistance to purple blotch would be very welcome in leek cultivars for the tropics. Most probably all commercial leek types are tetraploids with tetrasomic inheritance for most genes. The high rate of self-pollination results in a high percentage of inbreds, a considerable plant-to-plant variability within cultivars, and a considerable inbreeding depression.
Leek is not expected to become more important in the near future in the South-East Asian region since the use is the same as the more popular welsh onion (A. fistulosum). Studying the optimization of the production of vegetatively propagated leek ("prei anak") might be worthwhile.
- Atanasov, N. & Carrazana, R., 1975. Formation of reproductive organs in leek in Cuban conditions. Revista de Agricultura Cuba 3: 94-102.
- Rismunandar, 1986. Membudidayakan 5 jenis bawang [The cultivation of 5 Allium species]. Sinar Baru, Bandung, Indonesia. 116 pp.
- Tindall, H.D., 1983. Vegetables in the tropics. MacMillan, London, United Kingdom. pp. 14-16.
- van der Meer, Q.P. & Hanelt, P., 1990. Leek (Allium ampeloprasum). In: Brewster, J.L. & Rabinowitch, H.D. (Editors): Onions and allied crops. Vol. 3. CRC Press, Boca Raton, Florida, United States. pp. 179-196.
- D. Sulistiorini & Q.P. van der Meer