Allium chinense (PROSEA)

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Plant Resources of South-East Asia
Introduction
List of species


Allium chinense G. Don

Protologue: Mem. Wernerian Nat. Hist. Soc. Edinb. 6: 83 (1827).
Family: Liliaceae
Chromosome number: 2n= 32 (tetraploid), seldom 16 (?)

Synonyms

  • Allium bakeri Regel (1875),
  • Allium schoenoprasum auct. non L.

Vernacular names

  • Rakkyo (En)
  • Indonesia: bawang ganda
  • Malaysia: lokyo
  • Thailand: krathiam-chin (Bangkok), hom-prang (central), hom-paenyuak (northern)
  • Vietnam: kiệu.

Origin and geographic distribution

Rakkyo is native to central and eastern China. It is widely grown in China and Japan, to a limited extent in South-East Asian countries, and probably in private gardens of Japanese and Chinese people in many other parts of the world.

Uses

The bulbs of rakkyo are mainly prepared as sweet or sour pickles after being steeped in brine for several days. In West Java they are also used raw and fried, often mixed with other vegetables.

Medicinally, the bulbs are of interest in the prevention of thrombosis. They are used for the treatment of heart failures in Chinese medicine. Rakkyo is also used against fever, stomach-ache and eye infections.

Production and international trade

Considerable production is restricted to China and Japan, which also export some of the crop. South-East Asia mainly imports rakkyo from Japan. Locally grown bulbs can be found in many markets in Indonesia (Java, Sumatra, Sulawesi) however.

Properties

The edible portion, i.e. the swollen leaf-sheaths (bulb), constitutes approximately 30-40% of the full-grown plant before the leaves wither. It has the following constituents per 100 g: water 86 g, protein 0.6 g, carbohydrates 12.6 g, fibre 0.3 g and ash 0.2 g. The energy value is 215 kJ/100 g. Recently phenolic compounds were extracted from A. chinense in Japan. They inhibit blood platelet aggregation and thromboxane synthesis, which are two important components of the thrombosis process.

Description

  • A. chinense is an unusual Allium species in that the leaves are hollow and the scape is solid (usually both the leaves and the scape are alike).
  • A biennial herb, up to 60 cm tall. Bulb ellipsoidal, 2-4 cm × 7-15 mm, at top gradually tapering into the leaf-blades; protective bulb-coat leaves several, membranous, white to purplish; after planting, the bulb divides rapidly and forms a cluster of sprouting shoots which can divide again and finally produce new bulbs.
  • Foliage leaves 3(-5), distichous, conical-cylindrical, 20-40(-60) cm × 1-5 mm, hollow, 3-5-ridged, D-shaped or nearly triangular in transverse section.
  • Scape terete, solid, up to as long as the leaves and ca. 2 mm wide.
  • Inflorescence umbellate, 6-30-flowered, without bulbils; spathe 2-lobed, persistent, hyaline; pedicel 1-3 cm long; flowers campanulate, purplish, tinged with red; tepals 6 in 2 whorls, 4-5 mm long; stamens 6, much longer than the tepals; inner 3 filaments with broadened bases and each with 2 short teeth; pistil much longer than the tepals; ovules 2 per locule.

Growth and development

After planting, the growing point of a bulb divides to form a cluster of sprouting shoots and the number and weight of roots and leaves increase rapidly. After the shoots have reached a certain size, bulbs are formed, and the leaves wither and die. At intermediate latitudes (30-40 °N and S), the flower stalk develops inside the bulb during the summer period, and in late summer the scape grows out of the old bulb whose leaves, by then, have already withered. The scape appears to stand outside the leaves as those are formed on new lateral bulbs. Since the flowers are female sterile, no seeds are produced. In the tropics, the full-grown crop remains small and development phases are much less pronounced than at intermediate latitudes; flowering is very rare in the tropics.

The rakkyo bulb resembles a small onion, but the bulb is formed by the thickened leaf-sheaths only and no bladeless scales are formed like those in the onion; consequently, no thin neck occurs.

Other botanical information

Many cultivars of rakkyo exist in China and Japan. They can be broadly divided into small- and large-bulbed cultivars. Small-bulbed ones (e.g. "Tama Rakkyo") produce 10-25 small bulbs (1.5-2.9 g) and large-bulbed ones (e.g. "Rakuda") 6-9 bulbs (4-10 g). In Indonesia, several types occur differing in bulb size (from very small to small) and transverse leaf section ("D"-shaped and nearly triangular).

In older literature, in particular in Indonesia, the scientific name Allium schoenoprasum L. (chives) has been often misapplied to A. chinense.

Ecology

The climatic requirements of rakkyo are not well known. Rakkyo is best adapted to intermediate latitudes (30-40 °N and S). Long days (16 hours) promote bulb and flower formation. The optimal temperature range for bulb formation is 15-25 °C. Photosynthesis decreases when the temperature increases from 15 °C to 35 °C, whereas transpiration increases. Rakkyo requires a well-drained soil, preferably not fertile (e.g. sand dunes). In fertile soils such as clay loam or volcanic ash, growth is too vigourous, resulting in too large and soft bulbs.

Agronomy

Rakkyo is always propagated vegetatively by bulbs which are planted after a storage period of 1-2 months to overcome dormancy. Plants are usually spaced 10-15 cm × 10-15 cm. It is resistant to drought and can be grown without irrigation, but watering in dry months considerably increases yield.

Chlorosis is one of the major physiological diseases of rakkyo. It is caused by zinc deficiency; the symptoms are yellowish stunted plants with thickened leaves and distorted new leaves. Foliar applications of zinc sulphate can reduce the damage. The only pest reported is the Rhizoglyphus mite.

Rakkyo can be harvested from 45-60 days after planting. Harvesting is by hand, and bulbs are sold fresh in small bundles. Yields of 15-20 t/ha have been reported in Japan, but are much lower in the tropics. After harvest, the bulk of the crop is steeped in brine and subsequently processed into sweet or sour pickles. A fraction is kept as planting material for the next growing season.

Genetic resources and breeding

Farmers' selections seem to be the only genetic resources available for further improvement. Collection of wild types has not yet been done. Breeding does not seem to be very urgent. An array of cultivars is available in China and Japan, but they do not set seed, since most cultivars are sterile tetraploids. Finding seed-producing selections could signal a breakthrough, as in garlic.

Prospects

The ability to inhibit thrombosis seems to be of remarkable medicinal value. This, together with the medicinal reputation of the genus Allium in general, might further stimulate the interest in rakkyo as a vegetable as well.

Literature

  • Goda, Y. et al., 1987. Inhibitors of the arachidonate cascade from Allium chinense and their effect on in-vitro platelet aggregation. Chemical and Pharmaceutical Bulletin 35: 2668-2674.
  • Jones, H.A. & Mann, L.K., 1963. Onions and their allies. Botany, cultivation and utilization. Leonard Hill, London, United Kingdom. pp. 44-45, 60, 241-244.
  • Kunitomo, S. & Kosuga, M., 1960. Cultivation of rakkyo in Fukui District. Agriculture and Horticulture 35: 523.
  • Toyama, M. & Wakamiya, I., 1990. Rakkyo, Allium chinense G. Don. In: Brewster, J.L. & Rabinowitch, H.D. (Editors): Onions and allied crops. Vol. 3. CRC Press, Boca Raton, Florida, United States. pp. 197-218.
  • van der Meer, Q.P., 1990. The tropics as a natural entourage for cheap daylength research. Bulletin Penelitian Hortikultura [Horticultural Research Bulletin] 18 (special edition No 1): 81-89.

76, 205, 490, 549, 799, 1081, 1082, 1123, 1356. medicinals

Authors

  • Q.P. van der Meer & L. Agustina
  • Diah Sulistiarini, Juliasri Djamal & Iman Raharjo