Cucumis melo (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Cucumis melo L.

Protologue: Sp. pl.: 1011 (1753).

Family: Cucurbitaceae

Chromosome number: 2n= 24

Synonyms

• C. melo L. var. agrestis Naudin (1859),
• C. melo L. var. cultus Kurz (1877).

Vernacular names

• Melon, musk melon, cantaloupe (En)
• Melon (Fr).
• Indonesia: blewah, semangka londo
• Malaysia: bluwak
• Papua New Guinea: melon
• Philippines: milon (Tagalog), itimon (Ilocano), atimon (Bisaya)
• Cambodia: trâsâk sröö'w
• Laos: tèèng laay, tèèng suk
• Thailand: taeng-thai (central), taeng-lai (central)
• Vietnam: dưa bở, dưa hồng.

Origin and geographic distribution

Melon probably originated in eastern and north-eastern Africa where wild forms still occur. It reached the Mediterranean region some 2000 years ago and was subsequently introduced into Asia. Important secondary centres of genetic diversity developed in Spain, Iran, Uzbekistan, Afghanistan, India, China and Japan. Melon is now distributed worldwide.

Uses

Mature fruits of most melon cultivars are consumed fresh for the juicy and sweet-tasting flesh. The pulp can also be mixed with water and sugar, or sometimes with milk, and served as a refreshing drink. Immature fruits of certain types are also used as a fresh, cooked or pickled vegetable. The seeds are eaten after roasting; they contain an edible oil.

Production and international trade

Annual world production is about 9 million t (700 000 ha). Major melon-producing countries are China and Turkey (150 000 ha each), India (100 000 ha), Spain (70 000 ha), United States (42 000 ha), Romania (30 000 ha), Japan (18 000 ha), Italy (17 000 ha), France (16 000 ha), Taiwan (9 000 ha), Australia (3 000 ha).

Melon is a typical fruit vegetable of the dry and warm subtropical and temperate climates. In tropical Asia it is more a luxury crop for urban markets, grown in the drier lowlands and highlands. Statistics on production are incomplete for these countries, but it is generally a minor crop, except in the Philippines (ca. 2000 ha).

Each country has its own specific local melon cultivars (landraces) and most of the crop is sold to local markets. Production for export markets has developed in Mediterranean countries, United States, Australia, Taiwan and Japan, using F₁ hybrid cultivars of the musk melon type in particular, with long shelf-life characteristics.

Properties

Melon is generally low in protein and rich in sugars, vitamins and minerals. The edible portion (45-80% of the mature fruit) contains per 100 g: water 87-92 g, protein 0.6-1.2 g, fat 0.1-0.2 g, carbohydrates (mainly sugars) 6-15 g, vitamin A 500-4200 IU, vitamin B₁ 0.06 mg, vitamin B₂ 0.02 mg, niacin 0.4-0.9 mg, vitamin C 6-60 mg, K 130-330 mg, Ca 5-18 mg, Fe 0.2-0.6 mg, Mg 8-17 mg, P 7-57 mg. The energy value is 75-220 kJ/100 g. The edible seed kernel contains approximately 46% of a yellow oil and 36% protein. The weight of 1000 seeds is (8-)25-35 g.

Description

• A variable, climbing, creeping or trailing, herbaceous, hairy, annual, andromonoecious or monoecious vine.
• Root system large, mostly distributed in the top 30-40 cm of the soil, a few roots descending to 1 m depth.
• Stem ridged or striate, 1.5-3 m long.
• Leaves simple, alternate; leaf-blade orbicular or ovate to reniform, 3-15(-20) cm in diameter, angular or shallowly palmately 5-7-lobed, base cordate, margins shallowly sinuate-toothed, surfaces hairy; petiole 4-10 cm long; tendrils unbranched.
• Flowers axillary, either staminate and clustered (2-4 together), or pistillate or hermaphrodite and solitary, 1.2-3.0 cm in diameter, yellow, on short, 0.5-3 cm long, stout pedicels; calyx 5-lobed, 6-8 mm long; corolla deeply 5-partite, 2 cm long, lobes suborbicular; stamens 3, of which 2 double 2-thecous and 1 single 1-thecous, free, connectives of anthers prolonged; pistil with inferior ovary, 3-5 placentas, united style and 3-5 stigmas; nectaries at base of style and stamens.
• Fruit a pepo, very variable in size and shape, globular, ovoid or oblongoid, smooth or furrowed; rind smooth to rough and reticulate, white, green, yellowish-green, yellow, yellowish-brown, speckled yellow or orange with green or yellow background; flesh yellow, pink, orange, green or white; fruit weight is 0.4-2.2 kg.
• Seeds numerous (300-500 per fruit), compressed elliptical, 5-12 mm × 2-7 mm × 1-1.5 mm, whitish or buff, smooth.

Growth and development

Melon seed will remain viable for at least 5 years when stored dry (moisture content 6%) at temperatures below 18 °C. Germination is epigeal and seedlings appear within 4-8 days after sowing. The first true leaf appears 5-6 days after unfolding of the cotyledons. The first 2-4 axillary buds on the main stem produce vigorous primary stems which check the growth of the main stem. The first clusters of male flowers appear on the 5th-12th node of primary branches, while hermaphrodite or female flowers appear on secondary laterals, formed from the 14th node of primary stems onwards. Flowers are open for one day only and pollination is effected by insects, mostly bees. The fruit is a heavy sink for assimilates and minerals and usually only 3-6 out of 30-100 female/hermaphrodite flowers per plant will develop into mature fruits. The fruit development curve is sigmoid with maximum growth (for most musk melons) at 10-40 days after flowering; maturation with little further expansion occurs during the last 10 days when sugars accumulate in the fruit flesh and the net tissue on the fruit surface develops. Upon ripening, the fruit softens and fruity aromatic essences are exuded by the fruit. Fruits mature 90-120 days after sowing.

Other botanical information

Melon is a highly polymorphic species with many different cultivars developed over time to meet local taste and preference. For modern market gardening the following main types or cultivar groups can be distinguished.

Sweet melon types used as fruit:

• Musk Melon (var. reticulatus Naudin): fruit globular (1-1.8 kg); rind strongly reticulate, sometimes furrowed, yellowish-green with orange flesh (Italo-American) or rind finely reticulate to smooth, yellowish-green with light green flesh (Japanese, Mediterranean-Galia); high sugar content (10-15%) and aromatic; good for shipping;

• Cantaloupe Melon (var. cantalupensis Naudin; convar. melo ): fruit globular to slightly ovoid (1.2-1.8 kg); rind smooth or reticulate, ribbed, greyish-green with orange flesh (French "Charantais"); high sugar content and very rich flavour; limited storability; mainly grown in western Europe and the United States;

• Winter Melon (var. inodorus Naudin; convar. zard (Pang.) Grebenscikov): fruit ovoid (1.5-2.5 kg); late maturing; rind smooth, often striped or splashed, grey, green or yellow in colour; flesh firm, white or light green (e.g. "Casaba", "Honeydew"); high sugar content but little flavour; good storage quality; mainly grown in Iran, Central Asia and Afghanistan, but also in Spain and Japan;

• Chinese Hami: fruit ovoid to oblong (1.5-2.0 kg); rind yellowish to light green, slightly reticulate; flesh crisp, light orange to pink; very sweet (14% sugar); good shelf life; adapted to cool climates;

• Oriental Sweet Melon: fruit small, globular to ovoid (0.4-0.6 kg); rind smooth, pale green to yellow with white, crisp flesh; very sweet but little flavour; adapted to hot and humid climates; seeds are small (1000-seed weight 8-10 g).

Non-sweet melon types used as vegetable:

• Snake Melon (var. flexuosus Naudin; convar. flexuosus (L.) Grebenscikov): fruit long, slender, with smooth rind; used immature as cucumber, mainly in Afghanistan, Iran and the Commonwealth of Independent States;

• Oriental Pickling Melon (var. conomon Makino; convar. conomon (Thunberg) Grebenscikov): fruit small, elongated like cucumber; mainly used in India, China, Japan and South-East Asia; in Indonesia the young green fruits ("ketimun krai") are consumed in the same way as cucumber, although they have a flat taste and little flavour; the mature fruits ("ketimun poan") are oval-cylindrical and have a typical rind, which is smooth, yellow with white longitudinal striping; they may become very big (weighing more than 5 kg) and are used for the preparation of candy or eaten with ice and sugar as a delicacy;

• Garden Melon (var. chito Naudin): fruit small, smooth, mottled; used for pickles and as ornamental, mainly in southern Europe and the United States;

• Pomegranate Melon (var. dudaim Naudin; convar. dudaim (L.) Grebenscikov): fruit small, globular, pubescent; mainly in south-western Asia, Transkaukasia and northern Africa; also used as ornamental and odoriferous fruit.

Imported F₁ hybrid cultivars are becoming popular and are replacing local materials. Popular cultivars in Indonesia are "Jade Dew" and "Honeydew" of the Winter Melon type, "Sky Rocket" of the Musk Melon type, and "Hales Best" of the Cantaloupe type.

Ecology

Melon requires warm and dry weather with plenty of sunshine for growth and production. The optimum temperature range is 18-28 °C, growth being severely retarded below 12 °C. Plants are killed instantly by frost. Melon is grown from moderate elevations up to about 1000 m altitude; in Java between 300 and 800 m above sea-level. High humidity will reduce growth, adversely affect fruit quality and encourage leaf diseases. Melon grows best on deep, well-drained and thoroughly cultivated fertile loamy soils with pH 6-7. Melons are often grown with furrow or drip irrigation.

Propagation and planting

Melon is usually direct-seeded: 2-3 seeds, sown 2-4 cm deep on mounds or ridges, later thinned to one plant. Spacing is 50-75 cm within and 150-200 cm between the rows, giving a density of 10 000-15 000 plants per ha. Alternatively, seedlings are raised in polythene pots or in soil blocks and transplanted carefully to the field when 4 weeks old, taking care not to damage the root system. Seed rates per ha are 1.5-2 kg for direct-seeded melon and 0.5 kg for the transplant method.

Husbandry

Melon can be grown in normal upland conditions, provided that it is rotated with non-cucurbit crops to avoid soilborne diseases and nematodes, or in a paddy field immediately after harvesting the rice crop. The upland soil should be ploughed, harrowed and rotovated to attain a well-pulverized and well-levelled soil. The rice field requires minimum tillage to prevent loss of residual moisture and soil compaction. Irrigation under upland conditions should be frequent, since plants have a high demand for water until the fruits have reached maturity.

Fertilizer requirements depend on crop performance and nutrient status of the soil. Removal of nutrients in a harvest of 20 t/ha of fruits is: N 60-120 kg, P₂O₅ 20-40 kg, K₂O 120-140 kg, CaO 100-140 kg and MgO 20-60 kg. Melon responds well to organic manures applied at 25-30 t/ha. A complete fertilizer should be applied before sowing/planting, followed by regular applications of liquid fertilizer during the growing season.

Mulching is one of the well-established practices in the production of melon. In subtropical areas, black, transparent or silver-painted polyethylene sheets are commonly used not only to control weeds but also to raise or lower the soil temperature. In the tropics, common mulching materials used are rice straw and rice hulls. In areas where mulching materials are not available, weeding is necessary until the plants start vining. Hand hoeing or pulling of large weeds is often practised.

Various methods of pruning primary and secondary stems are applied to regulate vegetative growth and fruit set (3-5 per plant).

Diseases and pests

There are a number of important diseases. Fusarium wilt (Fusariumoxysporum f.sp. melonis) can be effectively prevented only by resistant cultivars (races 0, 1, 2 and 1-2). Powdery mildew (Sphaerotheca fuliginea and Erysiphe cichoracearum) can be controlled by fungicides, but modern F₁ hybrids have high tolerance of most races. Downy mildew (Pseudoperonospora cubensis) is important in hot and humid climates and can be controlled by fungicides; polygenically controlled resistance is available in certain Indian accessions. Gummy stem blight (Dydimella bryoniae, formerly Mycosphaerella citrullina) is also a disease in humid and hot conditions. Anthracnose (Glomerella cingulata, formerly Colletotrichum lagenarium) can be controlled by seed treatment, crop rotation and fungicides. Damping-off (Pythium sp. and Rhizoctonia sp.) has to be prevented by treating seed with fungicides (e.g. thiram). Bacterial soft rot (Erwinia tracheiphila) is controlled by removing affected plants and by eliminating the vector (the striped and spotted cucumber beetle) with insecticide sprays. Angular leaf-spot (Pseudomonas syringae) has been reported on melon in Indonesia. Cucumber mosaic virus (CMV), watermelon mosaic virus (WMV-2) and zucchini yellow mosaic virus (ZYMV), all three transmitted by aphids, in particular Aphis gossipii, affect melon; there are various sources of resistance to these three viruses and also to the vector A. gossipii. Other virus diseases in melon are papaya ring spot (PRSV, aphid transmitted), melon necrotic spot (MNSV, transmitted by the soil fungus Olpidium sp.) and curly top (transmitted by leafhoppers).

Pests in melon are thrips (Thrips palmi and Frankiniella spp.), spider mite (Tetranychus urticae), aphids (Aphis gossipii), melon fruit fly (Dacus cucurbitae), cucumber beetles (Diabrotica spp.), leaf folder (Diaphania indica), leaf feeder (Aulacophora similis) and the fly Bactrocera cucurbitae, which is especially active in the humid tropics and causes young fruits to drop by tunnelling in the pedicel. Farmers usually control these pests with insecticides. However, indiscrimate use of insecticides only aggravates the pest problems by destroying useful parasitic insects.

Root knot nematodes (Meloidogyne spp.) can be a serious problem when melons are grown without proper crop rotation; control by wide-spectrum soil fumigants can be effective, but it is expensive and hazardous to the environment.

Harvesting

Cantaloupe and musk melon tend to separate from the pedicel at the base of the fruit at maturity due to the formation of an abscission layer. This is called "full slip". Harvesting occurs usually at the "half slip" stage. Winter and Chinese Hami melons do not form an abscission layer and maturity is indicated by colour change, e.g. from green to yellow.

Yield

Averaging 13 t/ha of fresh fruits, but ranging from 5-30 t/ha depending on cultivar and cultural practices. Seed yields are about 300-500 kg/ha for open-pollinated and 100-200 kg/ha for hybrid cultivars.

Handling after harvest

Musk melons for storage should be predominantly green in colour (sugar content more than 10%) and cooled to 10-15 °C immediately after harvesting to retard ripening. Storage for 10-15 days at 3-4 °C (90% relative humidity) is possible, but lower temperatures can cause chilling injury. "Honeydew", other winter melons and Chinese Hami melons can be stored at 10-15 °C for longer periods, some cultivars up to 90 days. Heavily netted melons (e.g. "American Western Shipper") are relatively resistant to handling and transport.

Genetic resources

The genetic diversity within C. melo is fairly well preserved in germplasm collections of universities, horticultural institutes and gene banks in the United States (USDA, Georgia and New York), Spain (INIA), France (INRA), Italy (Bari), Egypt, Israel, India, Japan (NIAS), China, CIS (VIR) and other countries. These could be complemented by further collection of germplasm in the secondary centres of genetic diversity in Afghanistan, Pakistan, India and China. In the Philippines, 105 accessions are being maintained at the National Plant Genetic Resources Laboratory, Institute of Plant Breeding, Los Baños.

Breeding

Much of the varietal improvement in melon is based on mass and line selection in open-pollinated populations. However, these are now rapidly giving way to F₁ hybrid cultivars, especially in Europe, United States, Japan and Taiwan. Pure-line development in melon is easy, as there is practically no inbreeding depression after repeated selfing. On the other hand, there is also little hybrid vigour in hybrids between inbred lines. The main advantages of F₁ hybrids are, however, uniformity of plant and fruit type and combination of favourable characters of different melon types in one genotype: fruit quality (round shape, good flavour, high sugar content, small seed cavity), long shelf life, adaptation to more humid climates and especially resistance to diseases and pests.

Most cultivars are andromonoecious and F₁ hybrid seed production requires emasculation of the hermaphrodite flowers followed by hand pollination. Monoecious plant types would enable hybrid seed production with bee pollination, as the female line can be temporarily induced to become gynoecious (only female flowers) by sprays with ethrel. However, the change to monoecious F₁hybrids is slowed down by the fact that monoecy in melons is linked to elongated shape and large size of the fruits, while the aim of most breeding programmes is round and compact fruits. However, in smooth-skinned "Charentais" and Italian musk melons, monoecious F₁ hybrids are now becoming increasingly common. In South-East Asia, melon improvement is still in its initial stage.

Prospects

Melon is well-liked by most people and the importance of this crop would increase further, including in South-East Asia, with better adaptation to hot and humid growing conditions. Another factor limiting melon production is the multitude of diseases (viruses in particular) and pests. However, new techniques from cellular (protoplast fusion) and molecular (genetic transformation, DNA markers) biology are now within reach of the melon breeders. This will open prospects of exploiting germplasm from other Cucumis species for disease and pest resistance and other characters, not available through conventional interspecific hybridization.

Literature

• Odet, J. (Editor), 1991. Le melon. Ctifl, France. 293 pp.
• Pitrat, M. & Risser, G., 1992. Le melon. In: Gallais, A. & Bannerot, H. (Editors): Amélioration des espèces végétales cultivées [Improvement of cultivated plant species]. Institut National de la Recherche Agronomique (INRA), Paris, France. pp. 448-459.
• Purseglove, J.W., 1968. Tropical crops. Dicotyledons 1. Longman, London, United Kingdom. pp. 110-113.
• Shinohara, S. (Editor), 1984. Vegetable seed production technology of Japan. Shinohara's Authorized Agricultural Consulting Engineer Office, Tokyo, Japan. Vol. 1. pp. 361-394.
• Tindall, H.D., 1983. Vegetables in the tropics. MacMillan, London, United Kingdom. pp. 156-159.
• Whitaker, T.W. & Davis, G.N., 1962. Cucurbits: botany, cultivation and utilization. Leonard Hill, London, United Kingdom. 250 pp.
• Yamaguchi, M., 1983. World vegetables: principles, production and nutritive values. Avi Publishing Company, Westport, Connecticut, United States. pp. 322-327.

Authors

M.M. Paje & H.A.M. van der Vossen