Spinacia oleracea (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Spinacia oleracea L.

Protologue: Sp. pl.: 1027 (1753).

Family: Chenopodiaceae

Chromosome number: 2n= 12

Vernacular names

• Spinach (En)
• Epinard (Fr)
• Indonesia: peleng, puileng, horenso (from Japanese)
• Philippines: sosolon a gadong a kamo (Marinduque)
• Thailand: puaileng (central)
• Vietnam: rau nhà chùa, bó xôi.

Origin and geographic distribution

Spinach is not known in a wild state. Probably it originated in North Iran, Afghanistan, and Turkmenistan where related wild species such as Spinacia tetrandra Steven and S. turkestanica Iljin still exist. It spread to China around 600 AD and from there to Korea and Japan in the 14th to 17th Centuries. In Europe it became a popular vegetable after 1200 AD. Now spinach is cultivated worldwide in temperate areas and in the cooler parts of the tropics.

Uses

Spinach is an important green leafy vegetable in temperate climates. In Asia it is almost entirely a fresh market product consumed after light cooking, while in western Europe and North America more than half is processed into a deep-freeze product.

Production and international trade

The area annually cultivated to spinach is as follows: western Europe 25 000 ha, North America 20 000 ha, Japan 26 000 ha, Korea 70 000 ha. The area in China is large but no precise data are available. In South-East Asia it is gaining in importance with the availability of well-adapted cultivars of Japanese origin. In Indonesia spinach is grown to a limited extent in the highlands of Java (above 1200 m) and sold to an expatriate clientele (Japanese, Taiwanese, Korean). Spinach from the Cameron Highlands (Malaysia) is exported to Singapore.

Properties

Spinach has a high nutritional value and is a good source of minerals and vitamins. Per 100 g fresh leaves it contains: water 91.6 g, protein 2.5 g, carbohydrates 3.4 g, Ca 125 mg, Fe 4.1 mg, β-carotene 4.1 mg, vitamin B complex 0.9 mg, vitamin C 52 mg. The energy value is 100 kJ/100 g. It also contains oxalic acid and free nitrates, but these are not considered harmful when average consumption is less than 100 g spinach per day.

The 1000-seed weight is 9-13 g.

Description

• Annual, glabrous, dioecious herb, 20-150 cm tall with a long taproot.
• Leaves form a rosette (25-50 cm in diameter and 10-20 cm high) of 12-20 leaves clustered at ground level.
• Leaves spirally arranged, simple, no stipules; leaf-blade angular-ovate or arrow-head shaped with round to sharply pointed basal lobes, 9-30 cm × 7-20 cm, smooth or savoyed (crumpled) surface, light to dark green in colour; petiole 6-12 cm long, at base green, pink or purple-red.
• Inflorescence 80-150 cm high, branching, angular-ribbed, bearing small oblong leaves; female flowers in numerous axillary clusters of 7-20 sessile flowers; male flowers arranged in 1-10 cm long spikes, often combined into a leafy panicle; sometimes both sexes occur on the same plant; flowers small with a green, 4-lobed perianth; stamens 3-5 in male flowers, 4-6 filamentous stigmas on a superior ovary with one ovule in female flowers; hermaphrodite flowers have a pistil and 1-2 anthers; the green anthers swell and turn yellow a day before anthesis; the perianth of female flowers grows out to a hard shell tightly enveloping the fruit.
• Fruit an utricle, indehiscent, teeth of perianth sometimes developing into prickles.
• Seed dull, obtusely margined.

Growth and development

Spinach is normally dioecious with almost equal proportions of male and female plants, but many gradations of monoecism and hermaphroditism are known. In horticulture, the fruit of spinach (utricle) is usually called the seed. Dry spinach seed will remain viable for 2-3 years at ambient temperatures and 5-6 years when stored at 5°C and 30% relative humidity. Germination is epigeal. Depending on season and genotype, seedlings emerge 6-20 days after sowing and 35-100 days later the rosette is fully grown with the first signs of the flower stalk. Spinach is wind-pollinated. Seeds are mature about 60-70 days after flowering when plants quickly senesce and die off.

Other botanical information

Asian-type spinach cultivars are fast-growing and quick-bolting, have arrow-head shaped, thin and smooth leaves, long petioles which are purple-red at the base, and often prickly seeds. Leaves should be dark green according to Japanese and light green to Chinese preferences. European cultivars vary from quick-growing light green winter to slow-bolting dark green summer types with thick, ovate, shortly petioled leaves, green or pink at the basal end.

Many cultivar classifications exist, based on leaf and seed (fruit) characteristics. A major division is into cultivars with prickly seed (2-4 spines), also classified as var. oleracea, and cultivars with non-prickly, globose or round seed, also classified as var. glabra (Miller) Moench.

Ecology

Asian spinach cultivars, being adapted to short-day autumn or winter seasons, bolt readily in response to photoperiods of 12-14 hours. In Europe spinach is grown mostly in early spring and summer (north-western Europe) and requires a daylength of at least 14 hours for stem and flower formation. Optimum growing temperatures are 15-20 °C, but spinach is tolerant of low temperatures (3 °C) and even of light frost in some winter types. Vegetative growth is retarded by temperatures in excess of 27 °C. Soils should be light in texture, fertile, well-drained, rich in organic matter and with a pH 6-7.5.

Agronomy

Spinach needs high doses of N and K fertilizers as well as a regular water supply throughout the season for optimum yield and quality. Seed rates in Asia are 15-25 kg/ha.

The most important disease is downy mildew (Peronospora farinosa f.sp. spinaciae). Control by fungicides is difficult. Host resistance to all 4 physiological races will soon be available in modern F₁ hybrids. Cucumber mosaic virus (CMV) is especially important in warm and humid conditions; chemical control of the vector aphids (Aphis fabae and Myzus persicae) reduces incidence. Fusarium decline (F. oxysporum f.sp. spinaciae) and white rust (Albugo occidentalis) are particularly important in the United States. Seedling damping-off caused by Pythium spp. and Rhizoctonia spp. can be prevented by seed-dressing with fungicides. Pests include aphids and nematodes (Ditylenchus dipsaci).

Whole plants with 8-10 leaves are harvested, the roots are cut one cm below the plant base and the product is sold in bundles of 10-15 plants. In Europe and North America spinach for the fresh market is harvested by mowing the crop just above ground level at a young stage (seed rates 100-200 kg/ha) and spinach for the processing (deep-freezing) industry just at the first sign of flower stalk formation (seed rates 40-50 kg/ha). Yields vary from 10 t/ha in Asia to 35 t/ha for summer crops in Europe and the United States.

Genetic resources and breeding

Working collections and germplasm of Spinacia spp. are present in some research centres in Europe (Wageningen, the Netherlands), the United States and Japan.

Present breeding programmes aim at F₁ hybrid cultivars between highly female monoecious and highly male monoecious lines. Sex expression is controlled by an X/Y heterosomal system and two strongly linked autosomal genes. The main breeding objectives depend on type and season: fast growth and slow bolting, high yields, round seed, resistance to downy mildew, cucumber mosaic virus and other diseases, dark green leaf colour, erect leaves (especially for Asian types), better heat tolerance.

Prospects

Spinach will continue to be a very important leafy vegetable, and improved heat tolerance promotes its distribution to the warmer climates of Asia.

Literature

• Bose, T.K. & Som, M.G. (Editors), 1986. Vegetable crops in India. Naya Prokash Press, Calcutta, India. pp. 655-669.
• Parlevliet, J.E., 1968. Breeding for earliness in spinach (Spinacia oleracea L.) as based on environmental and genetic factors. Euphytica 17: 21-27.
• Shinohara, S., 1984. Vegetable seed production technology of Japan. Vol. 1. Shinohara's Authorized Agricultural Consulting Engineer Office, Tokyo, Japan. 432 pp.
• Sneep, J., 1982. The domestication of spinach and the breeding history of its varieties. Euphytica 1982, Supplement 2. 27 pp.

Authors

• H.A.M. van der Vossen