Cucumis sativus (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Cucumis sativus L.

Protologue: Sp. pl.: 1012 (1753).

Family: Cucurbitaceae

Chromosome number: 2n= 14

Vernacular names

• Cucumber, gherkin (En)
• Concombre, cornichon (Fr)
• Indonesia: ketimun, mentimun (Javanese), bonteng (Sundanese)
• Malaysia: timun, mentimun
• Papua New Guinea: kukamba, kuikamba
• Philippines: pipino (Tagalog), kalabaga (Bisaya), kasimum (Bontoc)
• Burma: thakhwa
• Cambodia: trâsâk
• Laos: tèèng
• Thailand: taeng-kwa (general), taeng-ran, taeng-om (northern)
• Vietnam: dưa chuột, dưa leo.

Origin and geographic distribution

C. sativus is not known from the wild. Although most Cucumis species have an African origin, C. sativus is believed to originate from the foothills of the Himalayas, where the closely related wild species C. hardwickii Royle still occurs. In India the cucumber was already being cultivated 3000 years ago, and it was known in ancient Egypt, Greece and the Roman Empire. In the 6th Century it was cultivated in China and was probably the first cultivated cucurbit to reach Malesia. Now it is cultivated worldwide.

Uses

C. sativus is grown for the immature fruits which are used as a salad vegetable (slicing cucumber) and for pickles (gherkin). The slicing cucumbers are peeled, sliced and served with vinegar or dressing or as an ingredient of salads. The large, yellow types are boiled and eaten as an ingredient of stews. The young shoots are eaten raw or steamed, particularly in South-East Asia. In some areas ripe fruits are used for the preparation of jellies. In Irian Jaya (Indonesia), ripe cucumbers are often taken along by travellers on long foot trips to alleviate thirst. Seed kernels are sometimes consumed as a snack food and they also yield an edible oil.

Ripe raw cucumbers are said to be good for sprue, and in Indo-China cooked immature fruits are given to children to cure dysentery. The seed has some anthelmintic property.

Production and international trade

Compared with other vegetables, cucumber occupies fourth place in importance in the world, following tomato, cole crops and onion. In 1987 world acreage of C. sativus was estimated at about 850 000 ha with a total production of 12.5 million t; about half can be attributed to Asia, with China leading with 240 000 ha and 3.7 million t. In South-East Asia the totals are: Indonesia (1988) 40 000 ha, 291 000 t; the Philippines (1987) 1000 ha, 6000 t; Thailand (1988) 16 000 ha, 143 000 t. Pickling cucumbers (gherkins) are not popular in South-East Asia. Small-size gherkins are produced in Indonesia for export because of the high labour costs for harvesting in western countries.

Properties

Immature cucumber fruits have an edible portion of about 85%. Per 100 g edible portion they contain: water 96 g, protein 0.6 g, fat 0.1 g, carbohydrates 2.2 g, Ca 12 mg, Fe 0.3 mg, Mg 15 mg, P 24 mg, vitamin A 45 IU, vitamin B₁ 0.03 mg, vitamin B₂ 0.02 mg, niacin 0.3 mg, vitamin C 12 mg. The energy value is 63 kJ/100 g.

Seed kernels contain approximately 42% oil and 42% protein. The weight of 1000 seeds is 20-35 g.

Cucurbitacins are terpene components in cucumber which cause a bitter flavour in foliage and fruits. As a result of breeding, modern cultivars are not bitter. The presence of a saponin and the slightly poisonous alkaloid hypoxanthine might explain the anthelmintic property of the seed.

Description

• A monoecious, annual, creeping or climbing herb, up to 5 m long, with stiff bristly hairs.
• Root system extensive and largely superficial.
• Stem 4-5-angled, sparingly branched, robust, with simple tendrils up to 30 cm long inserted opposite the leaves.
• Leaves alternate, simple, in outline triangular-ovate, 7-20 cm × 7-15 cm; petiole 5-20 cm long; leaf-blade 3-7-lobed, deeply cordate at base, acute at apex, lobes triangular, acute at apex, dentate.
• Flowers axillary, unisexual, occasionally hermaphrodite, 2.5-4 cm in diameter, yellow; male flowers predominating, borne in clusters of 3-7 on pedicels 0.5-2 cm long, stamens 3, free; female flowers solitary, on short thick pedicels 3-5 mm long, lengthening in fruit to 2-5 cm, style simple, stigmas 3, ovary 2-5 cm long; calyx campanulate, 5-lobed, 5-10 mm long, densely pubescent; corolla widely campanulate, deeply 5-lobed, up to 2 cm long, hairy, wrinkled.
• Fruit a pepo, pendulous, very variable in shape, size and colour, from nearly globular to cylindrical, often slightly curved, with scattered spinous tubercles and warts when young; spines black or white; flesh pale green, many-seeded (seedless in parthenocarpic cultivars).
• Seed flat, ovate-oblong in outline, 8-10 mm × 3-5 mm, white, smooth.

Growth and development

Germination is epigeal and takes about 3 days at 25 °C and 6-7 days at 20 °C. The plants need a warm, frost-free period of 100-140 days from sowing to harvest. Flowering normally starts 40-45 days after sowing. Bees are the main pollinating agents. The female flowers develop later than the more numerous male flowers. The ratio of male to female flowers largely depends on daylength, temperature and cultivar. Generally, long days, high temperatures and other stress conditions tend to keep the plants in the staminate phase. Pruning, fertilizer application and hormone spraying are possible measures which can influence the sex ratio. Hand pollination assists fruit setting. However, the European forcing cucumber sets fruit parthenocarpically and pollination should be avoided, as seed set will cause ballooning at the fruit base.

Other botanical information

C. sativus and C. hardwickii, each with 2n = 14, are clearly distinct from all other Cucumis species, which have 2n = 24. C. hardwickii hybridizes readily with C. sativus, producing a fertile F₁ and F₂, which suggests that it might be a progenitor of the cultivated cucumber. C. hardwickii is considered by some as a weedy form of C. sativus which has escaped from cultivation (C. sativus L. var. hardwickii (Royle) Alef.).

Numerous cultivars have been developed all over the world, differing in size and shape of the fruits, in characteristics of the rind (thickness, spininess, colour), and in daylength sensitivity. These can be classified into two main groups:

• cv. group Slicing Cucumber: fruits of most current (hybrid) cultivars have white spines and uniform green exterior colour, are 15-25 cm long with a length/diameter ratio of more than 4 at time of harvest, e.g. "Poinsett". Older cultivars and landraces in Asia may have white, yellow or red-brown (e.g. Sikkim cucumber) skins, often with black spines. The gynoecious and parthenocarpic cucumber for greenhouse cultivation (fruits more than 30 cm long) is not popular outside Europe and Canada.

• cv. group Pickling Cucumber: fruit less than 12 cm long with a length/diameter ratio of 2.8-3.2, usually with white spines, older cultivars with black spines, on pronounced warts, green outer skin often slightly striped. It is used for processing into gherkins, mainly in the United States and Europe.

In Indonesia the most popular type of local cultivars is called "ketimun biasa", "ketimun wuku" (Javanese) or "bonteng turus" (Sundanese). The fruits are small to medium sized, with a soft rind, not very elongated, white to green with scattered warts when young, brownish when mature. Very young fruits used for pickles. Other cultivars have big, smooth fruits, with a thick rind, warty and white to green when young, dark yellow when ripe.

The Oriental Pickling Melon (Cucumis melo L. var. conomon Makino) is often erroneously considered as a type of ordinary cucumber. In Indonesia, the young green fruits are called "ketimun krai" and the mature fruits "ketimun poan".

Ecology

Cucumber requires a warm climate. In cool temperate countries it is grown year-round in greenhouses or during the hottest summer months in the open. The optimum temperature for growth is about 30 °C and the optimum night temperature 18-21 °C. In the tropics, elevations up to 1000 m appear to be suitable for cucumber cultivation. An abundance of light tends to increase the number of staminate flowers. Sensitivity to daylenth differs per cultivar; short daylength usually promotes leaf and fruit production. Cucumbers need a fair amount of water but they cannot stand waterlogging. High relative humidity encourages downy mildew. The soil should preferably be fertile, well-drained, with a pH of 6.5-7.5.

Propagation and planting

Cucumber is propagated by seed. Soil preparation requires generous incorporation of manure, about 30 t/ha. Sowing is done directly in the field with several seeds per hill, 90-120 cm apart, then thinned to 2-3 plants per hill, or seeds are sown in nursery beds and seedlings transplanted to the field at the 2-true-leaf stage at 30-40 cm within and 1-2 m between the rows. Sowing rates per ha are about 2.5-3 kg for direct seeding and 1 kg when transplanted. Cucumber cultivated for pickles is planted closer, up to 250 000 plants/ha.

Husbandry

The crop responds well to fertilizers. In addition to the initial manure, about 700 kg/ha of an NPK mixture can be applied, followed by nitrogen fertilizer every 2-3 weeks until the fruits form. Excessive use of N promotes excessive vine growth and maleness. A good practice for the application of mineral fertilizer is: 6 g triple superphosphate (in addition to 1 kg farmyard manure) in each planting hole, 6 g per plant of a mixture of urea and KCl (1 : 1) two weeks after emergence, 6 g per plant of urea or 12 g of ammonium sulphate two weeks later and again when needed.

Weed control is necessary until the plants cover the soil entirely. Support (stakes) should be provided for some cultivars, and the tip of the main stem may be nipped off to encourage branching. Irrigation is required at frequent intervals, and a high level of soil moisture should be maintained throughout the growing period. Lateral shoots may be pruned after the first fruits have formed to limit leaf and flower production.

Diseases and pests

A very devastating disease of cucumber in South-East Asia is angular leaf-spot caused by the bacteria Pseudomonas lacrymans. It occurs under wet and humid conditions. Control with bactericides is too expensive and not really effective. The most important fungal diseases are downy mildew (Pseudoperonospora cubensis' ), powdery mildew (Erysiphe cichoracearum) and damping-off (Pythium, Rhizoctonia). Chemical sprayings, e.g. with carbamates, are used to control the mildews. Desinfection of seed with thiram, treatment of the planting holes and spraying of seedlings on emergence with a suitable fungicide (e.g. metalaxyl) control damping-off. Cucumber mosaic virus (CMV), papaya ring spot virus (PRSV-W) and zucchini yellow mosaic virus (ZYMV) cause much trouble. The use of disease-free seed and sprayings against aphids may keep virus diseases under control. Other pathogens reported to cause damage are anthracnose Colletotrichum), fruit wet-rot (Choanephora cucurbitarum), Fusarium wilt, Cladosporium scab, bacterial soft rot (Erwinia), curly top virus and root-knot nematodes (Meloidogyne incognita, M. javanica).

The most noxious insects are Epilachna beetles, greasy worm (Agrotis ipsilon), the melon fruit fly (Dacus spp.) and aphids. They are controlled with insecticides. The combat of pests with natural ennemies is highly developed in greenhouses, but still has no practical application in open cultivation.

Harvesting

Cucumbers for fresh consumption are harvested before they are fully mature, usually starting about 60 days after planting, and thereafter every few days. For pickling, immature fruits of several stages are harvested. Only for seed production are cucumbers allowed to mature on the plant.

Yield

In 1987 average world yield for cucumbers reached 15 t/ha, but the range is wide and yields of 5-7.5 t/ha are considered reasonable. Yield figures for some South-East Asian countries are as follows: Indonesia (1988) 7.2 t/ha, Malaysia (1987) 2.1 t/ha, the Philippines (1987) 5.1 t/ha, Thailand (1988) 8.9 t/ha. In greenhouses in Europe yields of 350 t/ha are obtained.

Handling after harvest

Cucumbers should be handled with care as they damage easily during transport. The maximum storage period is approximately 14 days at 13 °C with a relative humidity of 95%. Below 10 °C, chilling injury may occur and above 16 °C fruits rapidly become yellow. Waxing or packaging in plastic film retards moisture loss. Pickling cucumbers are usually fresh-processed (quick pasteurization), or first brined and then processed.

Genetic resources

Old cucumber cultivars of South-East Asia should be collected for conservation since they are gradually replaced by improved cultivars, mostly hybrid cultivars from seed companies. Important germplasm collections are available in the Czech Republic (Breeding Station, Kvetoslavov), Germany (Institute for Plant Cultivation and Plant Breeding, Braunschweig), India (Kerala Agricultural University, Trichur), the Netherlands (Centre for Genetic Resources, Wageningen), the Philippines (Institute for Plant Breeding, Los Baños), Turkey (AARIR, Menemen, Izmir), Russia (Vavilov Institute of Plant Industry, Petersburg), United States (NCRPIS, Iowa State University, Ames; NSSL, USDA-ARS Colorado State University, Colorado).

Breeding

Slicing and pickling cucumber have been subject of intensive breeding work and genetic studies, particularly in the United States and in Europe. Much progress has been made with dramatically increasing yields and fruit quality, as well as with resistance to many important diseases and even some pests. The development of parthenocarpic, female and hybrid cultivars has led to very high yields, especially in greenhouse-grown cucumbers for fresh consumption. Most present day cultivars are F₁ hybrids based on at least one fully gynoecious line and on chemically regulated sex expression. Worldwide, cucumber research is mainly concentrated on issues like producing inexpensive hybrid seed through genetic manipulation of sex expression, disease and pest resistance, and the breeding of plant types with short internodes and large numbers of fruits that can be harvested mechanically. Hybridization with related wild species (e.g. Cucumis hardwickii) is a promising method to obtain new desirable characteristics.

Prospects

Cucumber is very important in South-East Asia as it is in temperate regions. Breeding work should aim at producing improved cultivars with resistances to diseases and pests for tropical lowland conditions.

Literature

• Bates, D.M., Robinson, R.W. & Jeffrey, C. (Editors), 1990. Biology and utilization of the Cucurbitaceae. Comstock, Cornell University Press, Syracuse, New York, United States. 485 pp.
• Dixon, G.R., 1981. Vegetable crop diseases. MacMillan, London, United Kingdom. pp. 307-336.
• Lower, R.L. & Edwards, M.D., 1986. Cucumber breeding. In: Bassett, M.J. (Editor): Breeding vegetable crops. Avi Publishing Company, Westport, Connecticut, United States. pp. 173-207.
• Ochse, J.J. & Bakhuizen van den Brink, R.C., 1980. Vegetables of the Dutch East Indies. 3rd English edition (translation of "Indische groenten", 1931). Asher & Co., Amsterdam, the Netherlands. pp. 191-194.
• Purseglove, J.W., 1968. Tropical crops. Dicotyledons 1. Longman, London, United Kingdom. pp. 114-116.
• Tindall, H.D., 1983. Vegetables in the tropics. MacMillan, London, United Kingdom. pp. 159-161.
• Seshadri, V.S., 1986. Cucurbits. In: Bose, T.K. & Som, M.G. (Editors): Vegetable crops in India. Naya Prokash Press, Calcutta, India. pp. 91-164.

Authors

• B.H. Gildemacher & G.J. Jansen