Prota 2: Vegetables/Légumes
2n = 14
Cucumber, gherkin (En). Concombre, cornichon (Fr). Pepino (Po). Tango (Sw).
Origin and geographic distribution
Cucumis sativus is believed to have originated in the southern Himalayan foothills region of Asia. The wild Cucumis sativus var. hardwickii (Royle) Gabaev (synonym: Cucumis hardwickii Royle), which is seen as the possible progenitor, can still be found there. It has small, very bitter, spiny fruits, and is fully compatible with Cucumis sativus. An alternative view, however, suggests that var. hardwickii is a derivative that escaped from cultivation.
Cucumber is said to have been cultivated in India for at least 3000 years and in eastern Iran and China probably for 2000 years. China is considered a secondary centre of genetic diversification. Cucumber was carried to Europe before our era and was introduced into the New World by early travellers and explorers. In tropical Africa it probably arrived first in the west with the Portuguese. Cucumber is now cultivated worldwide. In tropical Africa it can be found on all city markets and is common in most supermarkets.
The main use of cucumber is for the immature fruit in salads, either with the skin or peeled. Fruits are sliced or cut into pieces and served with vinegar or a dressing, on their own or mixed with other vegetables. Young fruits of special small-fruited cultivars called ‘gherkin’ are pickled in vinegar. Young or ripe cucumber fruits are occasionally used as cooked vegetables or made into chutney. Locally in Asia types with large, white or yellow fruits are boiled and eaten as an ingredient of stews, young shoots are consumed as a leafy vegetable, and seeds are consumed or used to extract an edible oil, but these uses have not been recorded for Africa. In tropical Africa cucumber is considered an exotic or Western vegetable of relatively recent introduction, mostly used by city consumers. However, it is rapidly gaining popularity in the African kitchen; in East Africa it is regularly used in ‘kachumbari’, a kind of African coleslaw.
Ripe raw cucumber fruits are said to cure sprue, and in Indo-China cooked immature fruits are given to children to treat dysentery. The seed has some anthelmintic property. Cucumber extract is known to have cleansing, soothing, and softening properties; it is used as an ingredient in a variety of health and beauty products for the skin. Cucumber peel when eaten by cockroaches is reported to kill them after several nights. Non-food uses of cucumber are not common in Africa.
Production and international trade
In 2002 the world area under Cucumis sativus was estimated at about 2 million ha, with a total production of 36 million t. Asia is the world leader, with China alone accounting for over 60%. Cucumber is grown in all countries of tropical Africa, but nowhere on a large scale. In 2002 Africa produced 507,000 t on 25,000 ha, accounting for just under 1.5% of production. Egypt is the largest African producer with 360,000 t. Detailed data on countries of tropical Africa are lacking. International trade in 2002 amounted to 1.5 million t, with Mexico, the Netherlands and Spain as the main exporters; international trade from African countries is modest and unrecorded.
The nutritional composition of cucumber per 100 g edible portion (ends trimmed, not peeled, edible part 97%) is: water 96.4 g, energy 42 kJ (10 kcal), protein 0.7 g, fat 0.1 g, carbohydrate 1.5 g, dietary fibre 0.6 g, Ca 18 mg, Mg 8 mg, P 49 mg, Fe 0.3 mg, Zn 0.1 mg, carotene 60 μg, thiamin 0.03 mg, riboflavin 0.01 mg, niacin 0.2 mg, folate 9 μg, ascorbic acid 2 mg (Holland, B., Unwin, I.D. & Buss, D.H., 1991). The edible portion is about 85% when peeled. Seed kernels contain approximately 42% oil and 42% protein.
The bitter principle cucurbitacin C occurs in Cucumis sativus. Cucurbitacins are terpene components in the foliage and fruits, the evolutionary role being to protect the plant against herbivore attack. 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.
Adulterations and substitutes
The fruits of Cucumis anguria L., the West Indian gherkin, may replace those of Cucumis sativus for pickling, and the fruits of snake melon (Cucumis melo L.) for pickling and fresh use.
Annual monoecious herb with trailing or scandent stems up to 5 m long, having simple tendrils up to 30 cm long; stem 4–5-angled, sparingly branched, with bristle-like hairs; root system extensive and largely superficial. Leaves alternate, simple; stipules absent; petiole 5–20 cm long; blade triangular-ovate in outline, 7–20 cm × 7–15 cm, palmately 3–7-lobed, deeply cordate at base, acute at apex, toothed, bristly hairy. Flowers unisexual, regular, 5-merous; sepals narrowly triangular, 0.5–1 cm long; corolla widely campanulate, lobes up to 2 cm long, yellow; male flowers in 3–7-flowered fascicles, with pedicel 0.5–2 cm long, stamens 3; female flowers solitary, with pedicel short and thick up to 0.5 cm long, lengthening in fruit up to 5 cm, ovary inferior, ellipsoid, 2–5 cm long, prickly hairy or warty, stigma 3-lobed. Fruit a pendulous, globose to cylindrical berry up to over 30 cm long, often slightly curved, beset with spinous tubercles and warts when young, skin usually green, but in some cultivars white, yellow or brown, flesh pale green, many-seeded. Seeds ovate-oblong in outline, 8–10 mm × 3–5 mm, compressed, white, smooth. Seedling with epigeal germination.
Other botanical information
With their chromosome number of 2n = 14, cucumber and its wild relative are different from all other members of the genus, which have 2n = 24. It is also the only Cucumis species thought to have originated in Asia; the other species are indigenous to Africa. Cucumis anguria is often confused with the small cucumber types that are used for pickles, since both are commonly called ‘gherkin’.
A satisfactory classification of the cultivated cucumber does not exist. A large variation of fruit shapes, sizes, colours and rind characteristics can be found in different combinations, and numerous cultivars have been developed all over the world. Commonly cultivated types include:
– American slicer: fruits dark green, smooth-skinned but quite spiny, medium-sized; popular open-pollinated cultivars grown worldwide are ‘Marketmore 76’, ‘Poinsett 76’, ‘Ashley’, and the hybrids ‘Cyclone’ and the gynoecious ‘Dasher II’; the hybrid ‘Kande’ was specifically developed for tropical climates by East-West Seed Company; popular open-pollinated cultivars, as well as hybrids such as ‘Tokyo’ and ‘Olympic’ are distributed in Africa by Technisem.
– European greenhouse cucumber: fruits very long, slim, nearly spineless but with a rough skin, grown in greenhouses; cultivars are all hybrids, gynoecious and with parthenocarpic fruit, e.g. ‘Mystica’ and ‘Sabrina’.
– Beit Alpha: mainly grown in and around the Middle East; fruits medium-sized, with a somewhat ribbed though spineless skin; often gynoecious and/or parthenocarpic, e.g. the hybrids ‘Basma’ and ‘Excel’, distributed in Africa by Technisem.
– Pickling cucumber: usually a bit smaller than slicers, around 15 cm or less, often with prominent warts, used for production of pickled fruits (gherkins); common and popular cultivars are ‘Calypso’ and ‘Eureka’, bush types such as ‘Little Leaf’ require less space and set fruits simultaneously.
– White cucumber: grown in India, Sri Lanka, and other Asian countries; fruits with white smooth skin, medium- to large-sized; a popular cultivar is ‘Long White’, hybrids are also available, e.g. ‘Keisha’ from East-West Seed Company and ‘Shivneri’ from Seminis.
– Asian or mottled cucumber: popular in many southern and eastern Asian countries; many hybrids are available in fruit sizes ranging from mini (around 7 cm), e.g. ‘Kiros’ (East-West Seed Company), to medium -sized, e.g. ‘Ninja’ (Chia Tai) and ‘Kasinda’ (East-West Seed Company).
– Chinese and Japanese (oriental) cucumber: fruits relatively long, slim, rather spiny; in southern China sometimes with black spines, in Japan perfect size 22 cm × 2–3 cm, white-spined; Chinese cultivars include ‘Beijing Dachi’ and ‘Ganfeng 3’ from GAAS, popular Japanese hybrid cultivars are ‘Sharp 1’ and ‘Nao-Yoshi’ from Saitama Gensyu Ikuseikai.
In tropical Africa mainly slicing cucumber is grown, for which mostly the open-pollinated cultivars ‘Ashley’ and ‘Poinsett’ are used. Beit Alpha types are also grown, especially in northern Africa. Pickling cucumber is planted as well, but this may often be Cucumis anguria instead of Cucumis sativus.
Growth and development
Germination takes 3 days at optimum temperatures. Flowering normally starts 40–45 days after sowing, but early cultivars such as ‘Kiros’ can start flowering within 30 days. The female flowers develop later than the more numerous male flowers. The ratio male/female flowers largely depends on daylength, temperature and cultivar. Long days and high temperatures tend to keep the plants in the male phase or change the ratio to a higher male proportion.
Several growth regulators can be used to influence sex expression; spraying of ethephon induces female flowering. Many modern cucumber cultivars are gynoecious (having only female flowers). To increase seed of a gynoecious line, or to use it as a male parent, spraying with silver nitrate, silver thiosulfate or gibberallic acid will induce male flowering. Concentration and duration of spraying depend on the genotype and the intended result; usually spraying can start at the 2–3 true leaf stage, and can be repeated every 2 days for up to 5 times.
For gynoecious or highly female cultivars that are not parthenocarpic, commercial seed is usually mixed with 10–15% of a highly male line. Bees are the main pollinating agents and should be sufficiently available for good fruit development. Poor pollination results in deformed or curved fruits. However, the European parthenocarpic greenhouse cucumber should not be pollinated, since this will result in unwanted seeded fruits and fruit deformation. Greenhouses are therefore kept insect free to prevent pollination.
Fruits are harvested 1–2 weeks after flowering, depending on the genotype, usually before they are physiologically mature. Frequent harvesting of immature, marketable fruits will result in a continuation of new fruitset and a longer life cycle of the crop. Large, maturing fruits that are left on the plant inhibit the development of additional fruits. Very early, field-grown cultivars can senesce quickly and may die after only 2–3 months, especially when diseases start to affect the plants during fruit setting stage. The crop cycle of cucumber grown in glasshouses in Europe can be extended to around 6 months under specific conditions.
Cucumber requires a warm climate. In cool, temperate countries it is grown in greenhouses; only during hot summers can it be grown in the open. The optimum temperature for growth is about 30°C and the optimum night temperature 18–21°C; the minimum temperature for good development is 15°C. Pickling cultivars are usually more adapted to low temperatures. Sensitivity to daylength differs per cultivar; short daylengths usually promote vegetative growth and female flower production. High light intensity is needed for optimum yields. Cucumber needs a fair amount of water but it cannot stand waterlogging. Low relative humidity results in high plant evaporation due to the large leaf area, and sufficient irrigation is then very important. High relative humidity facilitates the occurrence of downy mildew. The soil should be fertile, well-drained, with a pH of 6.0–7.0. In tropical Africa elevations up to 2000 m appear to be suitable for cucumber cultivation.
Planting on raised beds will improve drainage, which is especially important during the rainy season, and can support good root development. The use of plastic mulch makes weed control and water management easier, and can help in reducing insect populations at an early stage. Weed control is necessary until the plants cover the soil entirely. Support (stakes) can be provided, which will generally improve fruit quality, reduce disease incidence through better air circulation in the crop, and make it easier to pick the fruits. Irrigation is required at short intervals; a high level of soil moisture should be maintained throughout the growing period. The use of drip irrigation is highly recommended for an optimum and uniform use of available water.
Fertilizers can be included in the drip system. Cucumber responds well to fertilizers. In addition to the initial organic manure, a general recommendation is 700 kg/ha of an NPK mixture, followed by N fertilizer every 2–3 weeks until the fruits form. However it is always best to base fertilizer gifts on a soil analysis before planting. Micronutrients are also essential for a good development; shortages can result in strong deficiency symptoms in both plants and fruits, leading to lower and low quality yields.
The tip of the main stem may be nipped off to encourage branching; in plants with very strong vegetative growth lateral shoots may be pruned after the first fruits have formed to limit leaf and flower production. Excessive use of N promotes stem growth and the production of male flowers.
Propagation and planting
Cucumber is propagated by seed. The 1000-seed weight ranges from 20–35 g. During soil preparation generous incorporation of organic manure (about 25–35 t/ha) is required. About 1–3 kg of seed is needed per ha depending on the method of sowing. Direct sowing, which is still a common practice especially in open fields, requires larger amounts of seed. The use of transplants will result in a more uniform crop stand, if done properly. In open fields in the tropics seedlings can already be transplanted after around 7 days or at the 2-true-leaf stage, but in cooler areas or for greenhouse production much older transplants of up to 33 days are used. When direct sown, cucumbers are planted on hills, 90–120 cm apart, with several seeds per hill and thinned to 2–3 plants, or they are sown in rows 1–2 m apart and thinned to 30 cm between plants. When planted as a ground crop the wider distances are used, whereas for trellised crops closer planting can be applied. Cucumber cultivated for pickles is planted closer, up to 250,000 plants/ha.
Diseases and pests
Many diseases and pests can affect cucumber in all stages of development. Leaf diseases that can result in serious damage are the fungal diseases downy mildew (Pseudoperonospora cubensis), powdery mildew (Erysiphe cichoracearum and Sphaerotheca fuliginea), anthracnose (Colletotrichum lagenarium), target leaf spot (Corynespora cassiicola) and gummy stem blight (Didymella bryoniae), as well as the bacterial disease angular leaf spot (Pseudomonas lachrymans). Anthracnose also causes symptoms on fruits. Good air circulation, for example through trellising, reduces the incidence of these diseases to some extent. Spraying of systemic fungicides such as benomyl (Benlate) or metalaxyl (Ridomil) can reduce spread; they can be alternated with broad spectrum fungicides such as copper oxychloride (Vitigran Blue) or mancozeb (Dithane). Other wilting in cucumber may be caused by soilborne Fusarium wilt (Fusarium oxysporum f. sp. cucumerinum), or bacterial wilt (Erwinia tracheiphila), which is spread by cucumber beetles. In protected cultivation in temperate countries, especially Japan and Korea, grafting of cucumber on Cucurbita ficifolia Bouché or Cucurbita maxima Duchesne × Cucurbita moschata Duchesne rootstock is often practised to avoid soilborne diseases such as root rot caused by the fungi Phomopsis sclerotioides and Fusarium oxysporum; no experience with grafting in tropical Africa has been reported. Cucumber is susceptible to damping off, resulting in seedling death soon after emergence; it occurs more often when the soil is poorly drained, and can be caused by several fungi, e.g. Pythium spp. or Phytophthora spp., some of which can also cause root rot in older plants.
Fruit damage can be caused by scab (Cladosporium cucumerinum), a fungus that also attacks the leaves of susceptible cultivars, by bacterial soft rot (Erwinia), phytophthora fruit rot (Phytophthora capsici) and belly rot (Rhizoctonia solani). Resistance to scab is widely available; to prevent soft rot and other rotting of fruits, fruits should be handled with care especially during harvest to prevent damage as much as possible. Wounds on fruits are often the starting points of infection. Belly rot is soilborne and infects the fruits at the place where they touch the soil; preventing contact for example through the use of mulch or trellis systems can prevent this disease. Other fungal diseases observed in tropical Africa (Côte d’Ivoire) are Alternaria sp., Cercospora citrullina, Choanephora cucurbitarum, Myrothecium roridum,Oidium tabaci and Sclerotium rolfsii.
Commonly found viruses that can cause considerable yield losses in cucumber in the tropics are the aphid-borne cucumber mosaic virus (CMV), zucchini yellow mosaic virus (ZYMV), and papaya ringspot virus (PRSV), and a range of whitefly transmitted viruses that cause yellowing, such as cucumber vein yellowing virus (CVYV) and cucumber yellows virus (CYV). Another important virus is cucumber green mottle mosaic virus (CGMMV), which is highly seed transmitted. Special care must be taken not to grow seeds produced on infected plants; CGMMV can be easily spread mechanically, but it is unknown whether there is an insect or other vector.
Root-knot nematodes (Meloidogyne spp.) can severely affect plant growth resulting in stunting or wilting, thereby reducing yields.
A general recommendation is to grow cucumber only on sites where no other cucurbits have been grown for a number of years, to prevent soilborne diseases. Several of the diseases mentioned, such as angular leaf spot, scab, anthracnose, and phytophthora can be seedborne. Use of disease free seed or seed treated with chemicals can prevent early disease infection or insect attack and will reduce risk levels considerably. For most leaf diseases and viruses, resistant cultivars are available; using the relevant ones is a good way to minimize problems.
Aphids, whitefly and thrips are insects that can cause major problems, mainly because they act as vectors for viruses or diseases. General insect damage may be caused by beetles, leaf miners and leaf hoppers. The melon worm or pyralid moth (Diaphania hyalinata) and red spider mites (Tetranychus spp.) may cause much damage to the leaves, and fruit flies (Dacus cucurbitae) may cause fruit rotting. Non-bitter cultivars are more susceptible to damage by spider mites than bitter ones. The use of natural insect enemies is a more environmentally friendly method than spraying chemicals against pests, but until now it has mainly or exclusively been practised in protected cultivation of cucumber.
Cucumber fruits for fresh consumption are harvested before they are fully mature; depending on the type this can be 1–2 weeks after flowering. The moment of first harvest is 40–60 days after sowing, depending on climate and cultivar. Harvesting is done every other day to every few days. For pickling types, immature fruits of several stages are harvested. Cucumber fruits for the fresh market are harvested by hand, but pickling types are also harvested mechanically all in a single harvest, especially on the large fields in the United States. For seed production, the fruits are allowed to mature on the plant.
In 2002 average world yield for cucumber reached 18 t/ha, but the range is very wide. For Africa few data are available; estimates for DR Congo and Ghana are 4 and 10 t/ha respectively. In tropical Asia, countries such as Thailand, Indonesia and India have an estimated average yield of just below 10 t/ha. Hybrid cultivars in Thailand yield over 100 t/ha. The European Union as a whole produces an average of 90 t/ha, but under protected conditions in greenhouses this can be even higher, mainly because the crop’s life cycle is extended considerably.
Handling after harvest
Cucumber fruits should be treated with care as they are sensitive to transportation damage. The maximum storage period is about 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 reduces moisture loss. In tropical countries, fruits will usually keep an acceptable marketable quality for around 5 days unless they are stored under cool conditions. After that they become soft and lose their crispy texture, and they can become yellowish.
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), Russian Federation (N.I. Vavilov Institute of Plant Industry, St Petersburg), United States (NCRPIS, Iowa State University, Ames; NSSL, USDA-ARS Colorado State University, Colorado).
Genetically, cucumber is one of the best known vegetable species and a great deal of work on breeding has been done. The first hybrid, the slicer ‘Burpee Hybrid’, was released in 1945. Gynoecious sex expression was found in a Korean cultivar. Since then, the development of hybrid, gynoecious and parthenocarpic cultivars has led to extremely high yields, especially in cucumber for fresh consumption cultivated in greenhouses. Breeding of disease- and pest -resistant cultivars, combined with better cultivation practices, has led to more than threefold increases in the yield of pickling cucumber over the past 60 years.
For tropical Africa, breeding work should aim at producing suitable cultivars for hot and humid conditions, with the necessary disease tolerances. The French company Technisem focuses on breeding for the tropics, mainly for West Africa, with experimental stations in e.g. Senegal, Mali, Benin and Cameroon under the name Tropicasem. For cucumber, the common open-pollinated slicer cultivars are sold, as well as improved hybrids in slicer, Beit Alpha, and pickling cucumber types. Depending on type preference, climate and disease problems, various options are available. The F1 hybrid ‘Tokyo’ (slicer) is popular in West Africa. It tolerates hot and humid conditions, and has tolerance to downy mildew and CMV. Another, also heat tolerant, gynoecious hybrid is ‘Olympic’, which in addition to downy mildew and CMV has tolerance to powdery mildew and angular leaf spot. The pickling cucumber hybrid ‘Antilla’ is tolerant to heat, as well as to anthracnose, downy and powdery mildew. ‘Arizona F1’ is a less heat tolerant pickler, but adds angular leaf spot and CMV tolerance. The Beit Alpha type ‘F1 Basma’ has tolerance to both mildews, and to CMV and WMV viruses. The hybrid ‘Excel’ has a less vigorous plant and is parthenocarpic; it is especially suited for greenhouse growing.
Cucumber cultivars from East-West Seed Company, developed in South-East Asia, are also adapted to hot and humid conditions. Available cultivars for Africa in the slicer type are the F1 hybrids ‘Kande’ and ‘Kosey’, which have strong vigour and tolerance to downy mildew; ‘Kosey’ has tolerance to ZYMV and PRSV.
Studies have shown that the genetic base within cultivated cucumber is rather narrow. Genebank accessions from various locations are however found to be genetically diverse, and often different from the commercial germplasm. More use of this material, as well as hybridization with related wild taxa might be promising to obtain new desirable characteristics. Combinations with Cucumis sativus var. hardwickii are made to increase branching and fruit set, especially in pickling cucumber cultivars. Interspecific crosses with Cucumis hystrix Chakrav. (2n = 24) have been attempted for quite some time. Cucumis hystrix is rather similar to cucumber and especially interesting because of its resistance to nematodes. After embryo rescue techniques and chromosome doubling, an amphidiploid (2n = 38) was obtained, which is now being further developed to try to obtain lines directly crossable with Cucumis sativus.
Cucumber is quite important in tropical Africa, and is becoming increasingly so because it is an easy to prepare vegetable and suited for sale in supermarkets and the big city markets. Moreover, cultivars are becoming available that are more adapted to the climatic conditions prevailing in tropical Africa, and that also include the relevant disease tolerances.
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Sources of illustration
• Gildemacher, B.H. & Jansen, G.J., 1993. Cucumis sativus L. In: Siemonsma, J.S. & Kasem Piluek (Editors). Plant Resources of South-East Asia No 8. Vegetables. Pudoc Scientific Publishers, Wageningen, Netherlands. pp. 157–160.
Correct citation of this article:
van Luijk, M.N., 2004. Cucumis sativus L. In: Grubben, G.J.H. & Denton, O.A. (Editors). PROTA 2: Vegetables/Légumes. [CD-Rom]. PROTA, Wageningen, Netherlands.
1, flowering and fruiting shoot; 2, female flower in longitudinal section; 3, fruit.
fruit with dried corolla