Prota 2: Vegetables/Légumes
2n = 40
Courgette, zucchini, summer squash, vegetable marrow, pumpkin (En). Courgette, courge, citrouille (Fr). Abobrinha, aboborinha, abóbora (Po). Mboga (Sw).
Origin and geographic distribution
The centre of origin of Cucurbita pepo is Mexico, where it was domesticated at least 5000 years ago. It is sometimes believed that it was domesticated on separate occasions in Mexico and the United States as data from archaeological research and molecular studies suggest that two lineages of domesticated taxa exist in Cucurbita pepo. It was introduced in Europe with other Cucurbita species during the 16th century. Cucurbita pepo is less heat resistant than Cucurbita moschata Duchesne, and for that reason less appropriate for tropical Africa, yet it is grown on a limited scale in all countries. It is traditionally more important in francophone than in anglophone countries and is mainly grown in the vicinity of big cities, especially for European and Lebanese customers.
The immature fruits, called courgette, zucchini or summer squash, are the main product of Cucurbita pepo. They are eaten as a vegetable, either boiled or fried or stuffed. Mature fruits, called winter squash or pumpkin, are used peeled and cooked like the fruits of Cucurbita maxima Duchesne, or following the Anglo-Saxon tradition, prepared as pumpkin pie. In West Africa the fruits are used in soups and with couscous. Gem squashes, small globular fruits popular in southern Africa, are cooked whole or cut in half and their flesh is scooped out and eaten. The young leaves and shoots are used as a potherb e.g. in south-western Nigeria, but in general the leaves of Cucurbita moschata are preferred, being less coarse. Male flowers of courgette are sometimes used to make fritters. ‘Vegetable spaghetti’ cultivars are a speciality; when cooked the flesh of mature fruits resolves into thin strands which look like spaghetti. Cucurbita pepo seeds are edible in the same way as those of other cucurbits, either raw or roasted. Pumpkin seed powder is used in China and the United States as an ingredient of salad dressings and in baked products. The seed oil is used as salad oil in Europe, and in India for cooking and lighting. The seed is becoming popular for its medicinal properties including the prevention of kidney stones. In Africa the pulp is used as a poultice to treat burns and inflammations and as a cooling compress to treat headache and neuralgia; it has also been applied to tumours and corns. Seeds are eaten as an anthelmintic. In Mauritius an infusion of the seeds is used internally to treat hypertension and prostate complaints, and externally to treat erysipelas.
The fruit pulp has been used to dehair and soften hides in tanning. In Western countries special cultivars are grown for the nicely shaped and coloured fruits (‘coloquintes’). The fruits of these ornamental cultivars have a hard rind and are not edible. Pumpkins are sometimes grown for animal feed.
Production and international trade
International statistics on production and trade rarely distinguish between Cucurbita pepo and other Cucurbita species; this especially affects information on tropical Africa, where Cucurbita pepo is less important than Cucurbita moschata or Cucurbita maxima. FAO statistics for 2002 estimate world production of pumpkins, squashes and gourds at 17.7 million t from 1.4 million ha. China is by far the most important producer (4 million t, mainly Benincasa), followed by India (3.5 million t), Ukraine (0.9 million t) and the United States (750,000 t). For tropical Africa substantial production is reported in Cameroon (122,000 t), Rwanda (210,000 t) and Sudan (68,000 t). During winter there is some export of courgette from East Africa to western Europe and occasionally to the Arab states. Countries in northern Africa, e.g. Morocco, also export courgette to Europe.
The nutritional composition of Cucurbita pepo fruits varies somewhat with type and degree of maturity. Zucchini is highest in water content and lowest in calories, winter squash lowest in water and highest in energy; summer squash, pattypan and other types eaten unripe are similar to zucchini although somewhat lower in water and higher in energy and nutrients; pumpkin is similar to winter squash. Types with yellow to pink fruit flesh are rich in vitamin A.
The composition of zucchini per 100 g edible portion (raw, 95% as purchased) is: water 95.3 g, energy 59 kJ (14 kcal), protein 1.2 g, fat 0.14 g, carbohydrate 2.9 g, dietary fibre 1.2 g, Ca 15 mg, Mg 22 mg, P 32 mg, Fe 0.4 mg, Zn 0.2 mg, vitamin A 340 IU, thiamin 0.07 mg, riboflavin 0.03 mg, niacin 0.4 mg, folate 22 μg, ascorbic acid 9.0 mg. The composition of winter squash per 100 g edible portion (raw, 71% as purchased) is: water 88.7 g, energy 155 kJ (37 kcal), protein 1.5 g, fat 0.2 g, carbohydrate 8.8 g, dietary fibre 1.5 g, Ca 31 mg, Mg 21 mg, P 32 mg, Fe 0.6 mg, Zn 0.13 mg, vitamin A 4060 IU, thiamin 0.10 mg, riboflavin 0.03, niacin 0.8 mg, folate 22 μg, ascorbic acid 12.3 mg. The composition of pumpkin leaves (Cucurbita sp.) per 100 g edible portion (raw, 61% as purchased) is: water 92.9 g, energy 80 kJ (19 kcal), protein 3.2 g, fat 0.4 g, carbohydrate 2.3 g, Ca 39 mg, Mg 38 mg, P 104 mg, Fe 2.2 mg, vitamin A 1942 IU, thiamin 0.09 mg, riboflavin 0.13 mg, niacin 0.9 mg, ascorbic acid 11 mg. The composition of pumpkin and squash seed kernels per 100 g edible portion (raw, 74% as purchased) is: water 6.9 g, energy 2265 kJ (541 kcal), protein 24.5 g, fat 45.8 g, carbohydrate 17.8 g, dietary fibre 3.9 g, Ca 43 mg, Mg 535 mg, P 1174 mg, Fe 14.9 mg, Zn 7.5 mg, vitamin A 380 IU, thiamin 0.21 mg, riboflavin 0.32 mg, niacin 1.7 mg, folate 58 μg, ascorbic acid 1.9 mg (USDA, 2002).
Fruits of Cucurbita pepo, especially ornamental forms, may contain bitter compounds; cucurbitacins B, D, E, G and I and the glycoside of cucurbitacin E have been recorded. Seeds (as reported from Eritrea) are rich in oil (about 35%) and contain protein 38%, carbohydrate 37% and α-tocopherols. The oil contains linoleic acid 47%, oleic acid 29%, palmitic acid 13.5% and stearic acid 8%. Seed extracts showed insecticidal activities against mosquitoes and flies, and reduction of arterial tension in chickens. The ribosome -inactivating protein pepocin has been isolated from Cucurbita pepo fruits.
Adulterations and substitutes
Cultivars of Cucurbita ficifolia Bouché, Cucurbita maxima and Cucurbita moschata are used for the same purposes as Cucurbita pepo.
Annual, scandent herb, climbing by lateral, 3–4-branched tendrils, strongly branched, or with bushy habit and then often without tendrils; stems angular and often grooved, prickly hairy, often rooting at nodes. Leaves alternate, simple, without stipules; petiole 9–24 cm long, grooved; blade broadly ovate to triangular in outline, distinctly palmately 5–7-lobed, (10–)20–35 cm in diameter, deeply cordate at base, margins toothed, bristly hairy, often with white markings, 3–5-veined from the base. Flowers solitary, unisexual, regular, 5-merous, large, c. 10 cm in diameter, lemon yellow to golden yellow; sepals free, subulate to linear, 1–3 cm long; corolla campanulate, with erect to spreading lobes; male flowers long-pedicelled, with 3 stamens, filaments free, anthers usually connivent into a long twisted body; female flowers shortly pedicelled, with inferior, rounded to ellipsoid, 1-celled ovary, style thick, stigmas 3, 2-lobed. Fruit a large, globose to ovoid, obovoid, cushion-shaped or cylindrical berry, weighing up to 50 kg when mature, with a wide range of colours, with small, raised, wartlike spots or smooth, sometimes deeply grooved; flesh whitish to yellow or orange, many-seeded; fruit stalk pentagonal in section, not enlarged at apex. Seeds obovoid, flattened, 1–1.5 cm × 0.5–1 cm, usually white or tawny, surface smooth to somewhat rough, margin prominent. Seedling with epigeal germination.
Other botanical information
Principal features distinguishing Cucurbita pepo from other cultivated Cucurbita species are more deeply lobed leaves with silvery markings, prickly hairy stems and leaves and fruit stalk hard and pentagonal in cross-section.
Supposedly wild populations of Cucurbita pepo are known from northern Mexico (subsp. fraterna (L.H.Bailey) D.S.Decker) and eastern United States (subsp. ovifera (L.) D.S.Decker var. ozarkana D.S.Decker and var. texana (Scheele) Filov). These are all considered candidates for the progenitor of cultivated Cucurbita pepo, which has been divided into 2 taxa, subsp. pepo and subsp. ovifera var. ovifera (L.) Harz.
Several cultivar classifications have been proposed, but none has been widely accepted. Mediterranean type cultivars called courgette or zucchini, grown for the immature cylindrical fruits, are most important for tropical Africa. The American or English types, known as vegetable marrow, summer squash, cocozelle, crookneck and straightneck are also grown for their young fruits, whereas pumpkin or winter squash, acorn types and also local African cultivars (old introductions) are grown for the mature fruits.
Modern courgette cultivars are mostly characterized by a bushy growth type. Fruits of these cultivars are mostly elongate, but some are spherical (e.g. ‘Courgette Ronde de Nice’) or flattened and star-like (scalloped summer squash, pattypan or pâtisson). Coussa types, popular in the Middle East, are eaten when nearly mature; they are often stuffed with meat, spices and rice. Vegetable marrow and vegetable spaghetti cultivars are vigorous trailing plants. Gem squash is popular in southern Africa (Malawi, Zambia, Zimbabwe, South Africa). Some cultivars produce naked kernels, an interesting character if edible seed production is wanted.
Growth and development
Seeds germinate 5–7 days after sowing, or earlier if the seed-coat is carefully split or peeled. Plants develop an extensive fibrous root system and their growth is indeterminate. Under favourable conditions stems may grow up to 15 m long and root at the nodes. Many modern cultivars of courgette have a bushy habit characterized by short internodes and sparse or no branching. Flowering starts 30–40 days after emergence of the seedling, and is more or less continuous. Pollination is by insects, mainly bees and wasps. The first immature fruits can be harvested 50–60 days after germination. Mature fruits can be harvested after 90–100 days. Under cool temperatures (nights 10°C, days 20°C) parthenocarpic fruit set may take place.
Cucurbita pepo tolerates monthly average day temperatures of 18–28°C, but growth is best when day temperatures are between 24°C and 29°C and night temperatures between 16°C and 24°C, as found at high altitudes in East Africa or at higher latitudes. Production is mostly restricted to the beginning of the dry season, when temperatures are relatively low and the pressure of aphids less intense.
Cucurbita pepo behaves as day-neutral. It is drought tolerant, but requires about 2.5 cm water per week for good production. It prefers fertile, well-drained soils of pH 5.6–8.0. Aluminium and manganese toxicity in acid soils must be corrected by liming. In bush cultivars heavy rains (more than 40 mm in one day) quickly induce symptoms of waterlogging and splitting of the stem, which finally breaks; since there are no axillary buds, these plants are lost. For this reason, and also because of its higher susceptibility to diseases and slower growth rate at high temperatures, Cucurbita pepo is less adapted to tropical lowlands than Cucurbita moschata, especially during the rainy season.
Growth and productivity of Cucurbita pepo plants respond very well to large applications of organic matter (farm manure or compost), which need not be fully decomposed (NH3 emissions are well tolerated). The organic matter should preferably be incorporated in the planting hole or furrow, in amounts of 50–70 t/ha. The crop also responds well to a complementary application of mineral fertilizer, e.g. 150 kg N, 150 kg P and 300 kg K, one half before planting, the other half 30 days later. Placement of bee hives in the field during flowering often improves pollination and yield.
Propagation and planting
All Cucurbita pepo types are grown from seed. Trailing plants may be propagated by cuttings, but this is not done in practice. Several seeds of courgette or pumpkin are sown directly in small hills; for bush cultivars only one plant per hill is left. Seeds are placed about 2.5 cm deep. For bush cultivars 40,000 plants/ha are planted in double rows, on beds 1.2 m wide, or on equidistant hills 50 cm apart. Trailing cultivars should be sown at wide spacing with 5000–10,000 plants/ha because they cover the soil surface for several metres around. Growing seedlings in a nursery and transplanting is recommended when costly F1 seeds are used.
Diseases and pests
Cucurbita pepo is more susceptible to diseases present in the humid lowland tropics than Cucurbita moschata. The principal leaf disease is powdery mildew, caused by Erysiphe cichoracearum (or especially in dryer conditions Sphaerotheca fuliginea). Alternaria or Ulocladium spp. can sometimes cause necrotic leaf spots. Downy mildew (Pseudoperonospora cubensis), very destructive on cucumber and muskmelon, induces only localized small yellow lesions, except in Japan, where a virulent strain was described on Cucurbita spp. Didymella bryoniae causes leaf spot mostly on senescent petioles only. Temperatures in the lowland are higher than optimal for the development of anthracnose (Colletotrichum lagenarium) and scab (Cladosporium cucumerinum), but these fungi of leaves and fruits may occur at higher elevations. A number of other fungi can attack the young fruits. Wet rot (Choanephora cucurbitacearum) first invades the corolla, then the blossom-end of the fruit. Pythium aphanidermatum and Phytophthora capsici invade the fruits directly from the soil, the zoospores or conidia being splashed on the fruits by heavy rain. Direct contact with the soil can also cause Rhizoctonia solani or Sclerotium rolfsii fruit rots. Plastic mulch may give good control of these soil-linked diseases, provided water can freely drain off from the mulch. Roots and stem bases of Cucurbita pepo may be invaded by Pythium aphanidermatum, Phytophthora capsici, Rhizoctonia solani and occasionally by the seedborne Fusarium solani f.sp. cucurbitae. The most important root diseases are caused by root-knot nematodes (Meloidogyne spp.), against which manuring with organic matter under the plants is a good control measure.
Several viruses can infect Cucurbita pepo. The most important in the lowland tropics is the papaya ringspot potyvirus-W (PRSV-W), also called watermelon mosaic virus-1 (WMV1). Cucurbit beetles (Epilachna, Diabrotica, Acalymma spp.) are vectors of the seedborne squash mosaic virus (SqMV). The cucumber mosaic virus (CMV), watermelon mosaic potyvirus-2 (WMV2) and zucchini yellow mosaic potyvirus (ZYMV) are noxious viruses in subtropical countries, but are rarely observed in the tropics. Several whitefly-transmitted viruses attack Cucurbita pepo in temperate and subtropical regions, but have not been observed in tropical Africa.
Direct insect damage may be caused by Aphis gossypii, Epilachna spp. and other beetles, Bemisia argentifolia (synonym: Bemisia tabaci strain B), pickle worm (Diaphania nitidalis) and melon worm (Diaphania hyalinata, synonym: Margaronia hyalinata). Fruit flies (Dacus cucurbitae) cause serious losses in West Africa. Spider mites (Tetranychus spp.) can invade the leaves when day temperatures are higher than 30°C.
Courgette fruits are best harvested at a commercial size of 20–25 cm, long before the seeds differentiate from the flesh. At that stage the fruits have reached about one quarter of their final size. This may start 55–60 days after sowing. Gem squash is ready for harvesting once the outer skin starts hardening but before the seeds have matured. At that stage they are about 6 cm in diameter. The plot should be visited every day since fruits enlarge very quickly. The harvest period may last 30–40 days. Pumpkin cultivars grown for mature fruits are harvested once over at the early maturity stage.
Bush cultivars produce 5–8 fruits per plant, trailing cultivars many more. F1 hybrid courgette cultivars grown under optimal cultural practices, such as adequate organic and mineral fertilizing, regular irrigation, adequate control of diseases and absence of heavy rains, may yield up to 80 t/ha. In tropical Africa, an average yield level is 20 t/ha.
Handling after harvest
Immature fruits are very susceptible to damage and must be carefully handled and put into baskets or crates coated with paper or plastic. They cannot be kept longer than 5–6 days at temperatures of 25–35°C. Optimum storage temperature is 10°C, with a storage life of 20–25 days. Larger fruits for family use (40–50 cm long for courgette or vegetable marrow) can be kept one month or more at 25°C. Mature fruits can be stored for several months. The pulp may be cut into chips or strips and dried for later use in soups.
Important collections of Cucurbita pepo are preserved in a number of institutes in the world, e.g. Institute of Crop Germplasm Resources (CAAS), Beijing, China (390 accessions), Genebank Department, Vegetable Section Olomouc, RICP Prague, Czech Republic (380), Universidad de San Carlos (FA-USAC), Guatemala City, Guatemala (475), N.I. Vavilov All-Russian Scientific Research Institute of Plant Industry, St. Petersburg, Russian Federation (325), Banco de Germoplasma de Horticolas, Zaragoza, Spain (350) and North Central Regional Plant Introduction Station, USDA-ARS, Ames, IA, United States (860).
Cucurbita pepo is naturally cross-pollinated but self-compatible. Inbreeding does not induce significant loss of vigour. Traditional cultivars offered by seed companies are true inbred lines; they offer an easy start for development of F1 hybrids, which yield 50–100% more than open-pollinated cultivars. F1 seed is obtained either by hand pollination, or by planting both parents in the field side by side, the female one developed by 2-chloroethyl-phosphonic acid sprays. Commercial hybrids belong to the bush type. F1 hybrids between bush and trailing cultivars were tried in the West Indies. They give robust and highly productive plants with stems 1–1.5 m long, less susceptible to breakage after heavy rains.
Interspecific hybridization is possible with Cucurbita maxima and Cucurbita moschata, but the progeny is not fertile. Genes can be transferred to vegetable cultivars from any cultivated type of Cucurbita pepo, including small-fruited cultivars grown as ornamentals, as well as from closely related wild taxa (e.g. var. texana). Interesting characters such as powdery mildew and virus resistances have been transferred to Cucurbita pepo from wild Cucurbita species. Commercial hybrids with powdery mildew resistance are appearing in seed catalogues.
In tropical Africa old trailing pumpkin cultivars of Cucurbita pepo will be replaced by Cucurbita moschata, more resistant to tropical conditions and diseases. Courgette is becoming increasingly popular. The availability of cultivars, possibly F1 hybrids, accumulating resistance to powdery mildew and viruses, lower susceptibility to stem breaking and resistance to high temperatures would make production easier for the local market. Prospects for export production in tropical African countries during the winter to Europe are not favourable as they would have to compete with countries in northern Africa (e.g. Morocco) and Spain (Andalusia).
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Correct citation of this article:
Messiaen, C.-M. & Fagbayide, J.A., 2004. Cucurbita pepo L. In: Grubben, G.J.H. & Denton, O.A. (Editors). PROTA 2: Vegetables/Légumes. [CD-Rom]. PROTA, Wageningen, Netherlands.
1, flowering and fruiting branch (courgette); 2, fruit (gem squash); 3, seed.
Redrawn and adapted by Iskak Syamsudin
flowering and fruiting plant
plant with young fruit