Cucurbita (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Cucurbita L.

Protologue: Sp. pl.: 1010 (1753); Gen. pl. ed. 5: 441 (1754).

Family: Cucurbitaceae

Chromosome number: x= 10, 2n= 40

Major species and synonyms

• Cucurbita ficifolia Bouché - see separate article.

• Cucurbita maxima Duchesne ex Lamk, Encycl. 2: 151 (1786).

• Cucurbita mixta Pangalo, Bull. Appl. Bot., Leningrad 23(3): 258 (1930), synonym: C. argyrosperma Bailey (1948).

• Cucurbita moschata (Duchesne ex Lamk) Duchesne ex Poiret, Dict. sci. nat. 11: 234 (1818), synonym: C. pepo L. var. moschata Lamk (1786).

• Cucurbita pepo L., Sp. pl.: 1010 (1753), synonyms: C. fastuosa Salisb. (1796), C. subverrucosa Willd. (1805), C. esculenta S.F. Gray (1821).

Vernacular names

• Pumpkin, winter squash, summer squash, marrow, cushaw, gourd (En)
• Courge, potiron, courgette (Fr)
• Indonesia: waluh, labu, labu merah
• Malaysia: labu merah, labu parang
• Papua New Guinea: pamkin
• Philippines: kalabasa
• Cambodia: lo-pëu
• Laos: f'ak kh'am, f'ak th'oong, 'ü'
• Thailand: fak-thong (central), namtao farang (peninsular)
• Vietnam: bí dỏ, bí ngô.

Note: all these names may refer to any of the cultivated Cucurbita species. There is no clear discriminating vernacular nomenclature. See under "Uses" for culinary differences.

Origin and geographic distribution

The genus Cucurbita, comprising about 25 species, is of New World origin. Central Mexico is considered the centre of origin of C. pepo, C. moschata and C. mixta, and southern Peru, Bolivia and northern Argentina the centre of origin of C. maxima . Archaeological evidence for the association of cultivated Cucurbita with man date back to about 8000 BC. Wild forms have never been found. C. pepo mainly spread in northern direction (United States), C. moschata and C. mixta spread both north (United States) and south (Central and northern South America), whereas C. maxima remained confined to South America. After the discovery of the New World, Cucurbita species were introduced into the Old World, and secondary centres of diversity developed, mainly in Asia. There is little information on the relative importance of the 4 species in South-East Asia, but C. moschata seems to be the most common, due to its adaptation to the lowland tropics.

Uses

Fruits, leaves and flowers of all 4 species are used as vegetable, and their seeds are consumed roasted as a snack food. There are numerous types and cultivars which differ greatly in composition and therefore in their suitability for certain culinary uses. The common names "pumpkin" and "squash" have no botanical significance, but should be used in a strictly culinary sense. "Pumpkin" is the edible fruit of any of the Cucurbita species, utilized in the ripe stage for pies or as fodder; the flesh is somewhat coarse and rather strongly flavoured for use as a table vegetable. In contrast, "squash" is the edible fruit of any of the Cucurbita species, utilized as a table vegetable; the flesh is fine-grained and mild-flavoured, and therefore also suitable for baking. "Summer squash" applies to immature fruits (mainly C. pepo), "winter squash" to mature fruits (all 4 species), the term "winter" being used in the sense that the fruit may be stored for later use. The term "marrow" (mainly used in Great Britain) is used for mature fruits of C. pepo and C. maxima, served boiled or stewed. The name "cushaw" is confined to mature fruits of C. mixta used for baking or fodder.

Immature and mature fruits of C. moschata in particular are used in South-East Asia as a blanched, steamed or fried vegetable and as an ingredient of soups. Various desserts are made from the fruits: steamed flesh with grated coconut and sugar, crisps made from steamed meshed flesh mixed with cassava flour, pumpkin custard, pumpkin pudding, pumpkin in coconut milk and sweet pumpkin paste.

Ornamental gourds are cultivars of C. pepo with small, bitter and inedible fruits in many shapes, sizes and colours. The potential of the seeds as a source of vegetable fat and protein has not been fully exploited. Fresh seeds have been reported to be used as a vermifuge, and seed decoctions as diuretic and to reduce fevers.

Production and international trade

World production of pumpkin and squash in 1988 is estimated at 6 346 000 t. In South-East Asia, where they are produced for local markets, production is estimated at 217 000 t.

Properties

The edible portion of pumpkin and winter squash (mature fruits) varies from 60-85%. They are good sources of vitamine A. Per 100 g edible portion, they contain: water 85-91 g, protein 0.8-2.0 g, fat 0.1-0.5 g, carbohydrates 3.3-11.0 g, vitamin A 340-7800 IU, vitamin B₁ 0.07-0.14 mg, vitamin B₂ 0.01-0.04 mg, niacin 0.5-1.2 mg, vitamin C 6-21 mg, Ca 14-48 mg, Fe 70 mg, Mg 16-34 mg, P 21-38 mg. The energy value is 85-170 kJ/100 g.

Summer squash (immature fruits of C. pepo ) is slightly less nutritious because it contains more water, but it has less waste. The seed kernels contain 40-50% oil and 30% protein.

Pumpkins and squashes contain cholinesterase inhibitors, and summer squash has been reported to contain glycosides called cucurbitacins, causing bitterness.

The 1000-seed weight is about 80 g for C. moschata, and 200 g for C. maxima, C. mixta and C. pepo.

Description

• Monoecious annual or short-lived perennial scandent herbs.
• Stem long-running or short and bushy, more or less scabrous, soft to hard, round to angular, often rooting at the nodes.
• Tendrils branched.
• Leaves simple, alternate, long petiolate; leaf-blade broadly cordate to triangular in outline, shallowly to deeply lobed, often with whitish blotches, more or less rigid and scabrous.
• Flowers solitary, large, showy, lemon yellow to deep orange; calyx and corolla campanulate; staminate flowers on long pedicels, stamens 3, anthers usually connivent into a long twisted body, filaments partly free; pistillate flowers on short pedicels, with ovary oblong or discoid, unilocular and style thick with 3 two-lobed stigmas.
• Fruit a pepo; fruit stalk soft to hard, round to angular, thickened with soft to hard cork, enlarged or not at point of attachment of the fruit.
• Seeds numerous, flattened, usually white or tawny, sometimes dark-coloured.

• C. maxima. Vine or rarely bush. Stem soft and round. Leaves neither rigid nor prickly, nearly orbicular in outline, serrate, not or only shallowly lobed, but with a deep sinus at the base. Corolla lobes curved outwards. Fruit stalk soft, spongy, nearly cylindrical, strongly thickened by soft cork, not enlarged at the point of attachment of the fruit.

• C. mixta. Vine. Stem hard, 5-angled, grooved. Leaves softly hairy or glabrous, not harsh, large, broadly cordate, shallowly to moderately lobed. Fruit stalk hard, strongly thickened by hard cork, not enlarged at fruit attachment.

• C. moschata. Vine. Stem hard and angular. Leaves softly hairy, not harsh, large, shallowly lobed. Corolla with widely spreading, mostly reflexed lobes. Fruit stalk hard, smoothly grooved, enlarged at fruit attachment.

• C. pepo. Vine or bush. Stem hard and angular. Leaves prickly through spiculate bristles, more or less rigid, broadly triangular, deeply and acutely lobed. Corolla with erect or spreading lobes. Fruit stalk hard, sharply 5-angled, grooved, not enlarged at fruit attachment.

Growth and development

Germination is epigeal. Seeds germinate in about one week from sowing. They have extensive fibrous root systems and indeterminate growth habit. Under suitable conditions, they will continue to grow indefinitely when the trailing stems are permitted to root at the nodes. Vines may reach a length of more than 15 m. This does not apply to the bushy cultivars of C. pepo and C. maxima, which have short, semi-erect stems, due to short internodes.

Flowering is more or less continuous, the ratio of male to female flowers being influenced by growing conditions. Pollination is effected by insects, mainly bees, so they are predominantly cross-pollinated.

Squashes grown for the immature fruits produce the first harvest 7-8 weeks after planting and continue bearing for several months; those grown for mature fruits take 3-4 months until harvesting. The four species described here are all cultivated as annuals.

Other botanical information

There is some confusion about the identity of the cultivated Cucurbita species. The fact that all species are often indicated by the same vernacular names (pumpkin and/or squash) contributes considerably to this confusion; if a certain species is meant, it is necessary to add the scientific name to the vernacular.

The great variability of most species, especially visible in their fruits, has led to numerous subspecific classifications. However, it is preferable to develop classifications directly based on cultivar characteristics below the species level.

• C. maxima. Some proposed cultivar groups are: Mammuth (synonym: C. maxima ssp. maxima convar. maxima), Banana (synonym: C. maxima ssp. maxima convar. bananina Grebenscikov), Hubbard (synonym: C. maxima ssp. maxima convar. hubbardina Grebenscikov), Turban (synonym: C. maxima ssp. maxima convar. turbaniformis (Roem.) Alef).

• C. mixta. Botanically it has been long included in C. moschata, but sterility barriers are effective enough to maintain its identity. Genetically it seems closest to C. pepo. It is not of such ancient cultivation as C. maxima and C. pepo. Cultivars include "Cushaw", "Japanese Pie", "Silverseed Gourd".

• C. moschata. The species most widely grown throughout the tropics, Cultivars include "Butternut", "Kentucky Field", "Sugar", "Winter Crookneck".

• C. pepo. Some proposed cultivar groups are (for the edible forms): Pumpkin, Scallop, Acorn, Crookneck, Straightneck, Vegetable Marrow, Cocozelle and Zucchini. The inedible ornamental forms could be grouped in cv. group Ornamental Gourd (synonyms: C. ovifera L., C. pepo var. ovifera Alefeld, C. pepo ssp. pepo convar. microcarpina Grebenscikov). Another subclassification of C. pepo divides the cultivated forms into two groups: the longicaules group sensu Grebenscikov with running or climbing stems and the brevicaules group sensu Grebenscikov with non-running, bushy growth.

C. texana A. Gray is a wild species occurring in the United States (Texas) and is considered as the archetype of C. pepo; sometimes it is classified as a taxon within C. pepo (e.g. C. pepo ssp. texana (Scheele) Filov).

Ecology

Pumpkins and squashes are grown in the tropics from the lowlands up to 1500 m altitude. They are warm season crops adapted to monthly mean temperatures of 18-27 °C. C. maxima is the most tolerant of low temperatures, C. moschata and C. mixta the least, with C. pepo in an intermediate position. C. maxima and C. pepo have long been cultivated in temperate regions.

All 4 species are relatively insensitive to photoperiod, although both photoperiod and temperature influence the ratio of male to female flowers (long days and high temperatures favouring male sex expression).

Pumpkins and squashes are not very demanding with respect to soil requirements. They can be cultivated on almost any fertile, well-drained soil with a neutral or slightly acid reaction (pH 5.5-7). They are drought-tolerant, requiring relatively little water, and are sensitive to waterlogging. Excessive humidity is harmful because of the development of leaf diseases, so none of the species does well in the humid tropics.

Propagation and planting

Pumpkins and squashes are grown from seed. They can be grown from cuttings if required, as they root at the nodes, but this method is not used in commercial practice. Seeds may be sown in containers and transplanted to the field when they are 10 cm high. Direct-seeding of 2-3 seeds per hill is commonly practised. Trailing types are planted at distances of 2-3 m either way; the seed requirement is 2-3 kg/ha. The bushy types (mainly C. pepo) are planted closer, e.g. plants spaced 60-120 cm in rows 1-1.5 m apart; the seed requirement is 3 kg/ha for pumpkin and 7 kg/ha for summer squash. Plant densities vary from 5000 plants/ha for the long-running trailing forms to 20 000 plants/ha for the bushy types.

Husbandry

In South-East Asia pumpkins and squashes are often planted in home gardens or mixed with field crops such as maize. Sole cropping is sometimes used for commercial production. The bushy types are mainly restricted to commercial gardens.

They grow well on organic matter and are often encountered on compost or refuse heaps. They respond well to side dressings of liquid manure.

It is recommended to split-apply N 100 kg/ha, P 40 kg/ha and K 80 kg/ha, during the vegetative phase.

Other cultural practices to improve growth and development are the removal of growing tips to check growth, and the bagging of fruits in paper to protect against fruit fly and other pests. Fruit setting may be stimulated by manual pollination, but this practice is not very common.

Diseases and pests

Anthracnose caused by Colletotrichum lagenarium is the most destructive disease. It causes defoliation and lesions on the fruits. Other diseases, mainly affecting the leaves and stems, are powdery mildew (Erysiphe cichoracearum), downy mildew (Pseudoperonospora cubensis, scab (Cladosporium cucumerinum), and leaf-spot (Alternaria cucumerina). Choanephora cucurbitarum causes wet rot of fruits. Important virus diseases are cucumber mosaic (CMV), watermelon mosaic (WMV-2), papaya ring spot (PRSV-W), zucchini yellow mosaic (ZYMV) and squash leaf curl (SLCV).

The leaf-feeding Epilachna beetles are a serious problem for Cucurbita growers. Other troublesome pests are the squash vine borer Melittia satyriniformis and the pickle worm Diaphania nitidalis, apart from aphids, fruit flies, and various leaf beetles.

Harvesting

The summer squashes (mainly C. pepo), from which the immature fruit is used as a fresh vegetable, develop very rapidly. The first marketable fruits can be harvested 50-60 days after planting, or 2-6 days after anthesis of the female flower. During the harvest season the plants are visited 2-3 times per week.

Winter squashes are picked when mature in a once-over harvest or in several rounds, about 90-120 days after planting.

Yield

Crop yields for summer squash (immature fruits) are 7-12 t/ha, whereas 20-25 t/ha are normal yields for winter squash (mature fruits). The number of mature fruits harvested per plant is usually low, and the weight of individual fruits varies widely from 1-15 kg.

Winter squash (the baking types) and pumpkins are considered to be among the most efficient of vegetable crops when evaluated on nutritional yield in relation to land area and labour needed. Summer squash scores much lower in this respect.

Indicative figures for seed yield of C. pepo are 400-1500 kg/ha. A valuable source of oil and protein is thus neglected if the seeds are left unutilized. In seed production, isolation between fields of different Cucurbita species is recommended, not only for reason of purity but also for obtaining maximum yields (pollen of other species may cause reduced fruit set or parthenocarpic fruits).

Handling after harvest

Mature fruits of winter squash and pumpkin can be cured (healing of wounded tissue by suberization) in the sun, or under controlled conditions of 27-29 °C and 80-85% relative humidity for 10 days. Properly cured, the mature fruits can be stored at 10-13°C and 70-75% relative humidity for up to 6 months without serious deterioration. Chilling injury may occur at temperatures below 10°C. The flesh is often dried in strips for later use in soups and stews. Pumpkins are as a rule canned for the bakery trade. Summer squash can be kept for up to 14 days when stored at 7-10 °C and 85-95% relative humidity.

Genetic resources

Cucurbita spp. are well represented in the cucurbit germplasm collections of many institutions all over the world. Important base collections are maintained by the National Seed Storage Laboratory (NSSL), Fort Collins, Colorado, United States, and by the Vavilov Institute of Plant Industry (VIR), Petersburg, Russia.

In South-East Asia, the largest Cucurbita collection is maintained by the National Plant Genetic Resources Laboratory (NPGRL), Institute of Plant Breeding, Los Baños, the Philippines. C. moschata is the dominant species. Relatively little attention has been given to the tropical types, and with the introduction of modern cultivars, ancient tropical landraces are certainly in danger of disappearing.

Breeding

Squashes and pumpkins are entomophilous and although self-compatible, they are naturally cross-pollinated. Inbreeding causes little loss of vigour, whereas a considerable degree of heterosis has been observed.

Considerable breeding work has been done in the United States and Europe, and many cultivars and types have been developed, mainly in C. maxima and C. pepo . The Zucchini cultivar group of C. pepo is most advanced in combining horticulturally valuable characteristics such as open bushy growth habit (facilitating repeated harvesting), smoothness of foliage, and intense coloration.

High-yielding hybrid cultivars are now becoming popular. Several small-fruited cultivars, generally known as Japanese pumpkins, have been developed more recently in Japan. They have excellent culinary and storage properties.

No natural interspecific hybrids between the cultivated Cucurbita species have ever been observed. Crosses, however, can be obtained with varying degrees of difficulty. There is a potential for gene flow through backcrosses or the development of new amphidiploid crops. Results of interspecific hybridization suggest that the sterility barriers are genic rather than the result of a lack of chromosomal homology, which means that heterozygosity improves the chances of obtaining interspecific hybrids.

About 30 genes known to control qualitative characters have been described in the cultivated Cucurbita species. Desirable traits are available in related wild species, such as powdery mildew resistance in C. lundelliana Bailey.

Prospects

The cultivated Cucurbita species make valuable contributions to the food resources of South-East Asia and will continue to do so in the future. Because relatively little attention has been given to the tropical types, germplasm collection of South-East Asian landraces deserves priority. Besides development of improved vegetable cultivars, attention should also be paid to the potential of the seed as a source of vegetable fat and protein.

Literature

• Decker, D.S., 1988. Origin(s), evolution, and systematics of Cucurbita pepo (Cucurbitaceae). Economic Botany 42: 4-15.
• Herklots, G.A.C., 1972. Vegetables in South-East Asia. George Allen & Unwin, London, United Kingdom. pp. 276-296.
• Paris, H.S., 1989. Historical records, origins, and development of the edible cultivar groups of Cucurbita pepo (Cucurbitaceae). Economic Botany 43: 423-443.
• Singh, A.K., 1979. Cucurbitaceae and polyploidy. Cytologia 44: 897-905.
• Tisbe, V.O., Deanon Jr, J.R. & Bantoc Jr, G.B., 1967. The cucurbits. In: Knott, J.E. & Deanon Jr, J.R. (Editors): Vegetable production in South-East Asia. University of the Philippines Press, Los Baños, the Philippines. pp. 138-166.
• Whitaker, T.W. & Bemis, W.P., 1975. Origin and evolution of the cultivated Cucurbita. Bulletin of the Torrey Botanical Club 102: 362-368.
• Whitaker, T.W. & Bohn, G.W., 1950. The taxonomy, genetics, production and uses of the cultivated species of Cucurbita. Economic Botany 4: 52-81.
• Whitaker, T.W. & Robinson, R.W., 1986. Squash breeding. In: Bassett, M.J. (Editor): Breeding vegetable crops. Avi Publishing Company, Westport, Connecticut, United States. pp. 209-242.

Authors

• E.A. Widjaja & S. Sukprakarn