1.0 Introduction
Watermelons ( Citrullis vulgaris ) refer to both fruit and plant of a vine-like (climber and trailer) herb originally from southern Africa and one of the most common types of melon are a member of the cucurbit family, which also includes rock-melons, honeydew melons, cucumbers, pumpkins, squash, zucchini and other gourds. Common in fruit platters or as a refreshing desert at a picnic, watermelons are available in a wide range of sizes and shapes.
This flowering plant produces a special type of fruit known by botanists as a pepo, which has a thick rind (exocarp) and fleshy center (mesocarp and endocarp); pepos are derived from an inferior ovary and are characteristic of the Cucurbitaceae. The watermelon fruit, loosely considered a type of melon (although not in the genus Cucumis), has a smooth exterior rind (green, yellow and sometimes white) and a juicy, sweet, usually red, but sometimes orange, yellow, or pink interior flesh. Dark red fleshed, black seeded varieties are the most popular on the market place. Yellow fleshed (champagne) melons and small mini melons also find a ready market. "Seedless" melons, although more difficult to grow, have become popular in the market.
• Name and Botany
1.1.1 Scientific
Kingdom: Plantae
Division: Magnoliophyta
Class: Magnoliopsida
Order: Cucurbitales
Family: Cucurbitaceae
Scientific name: Citrullus lanatus
Synonyms: Citrullus vulgaris
Genus: Citrullus
Species: lanatus
1.1.2 Common Names
English: Watermelon
Bahasa Melayu: Tembikai; Semangka; Mendikai
Mandarin: Xigua
Tamil: Kumati palam
Indonesian: Semangka; Cimangko (Indonesia), Watesan (Java).
Tagalog ( Philippines ): Pakwan
Vietnamese: Doa haau
Afrikaans: Waatlemoen.
Arabic: Battikh, Bateekh, Betteakh (Egypt).
Bengali: Taramuj.
Bulgarian: Dinia.
Chinese: Xi gua ( Cantonese Si koa), Shi yong xi gua, Choei koa, Ts'ing teng koa, Han koa, Hia koa.
Croatian: Lubenica.
Czech: Lubenice meloun.
Danish: Vandmelon.
Dutch: Watermeloen.
Finnish: Vesimeloni, Arpuusi.
French: Melon d'eau, Pasteque.
German: Wassemelone (East Germany), Wassermelone, Gewohnliche Wassermelone, Wasserzitrulle, Wasser-melone.
Greek: Karpusi, Karpouzia (Cyprus).
Gujarati: Tarabuucha.
Hebrew: Avatiach, Avatiach pashut.
Hindi: Kharbuza ( kharmuja), Tarabuuza (Tarbooz, Tarbuj, Tarbuz, Tarmuj).
Hungarian: Gorogdinnye.
Italian: Anguria, Cocomero, Melone d'acqua, Pastecca.
Japanese: Suika, Suika, Shokuyou suika (Shokuyo suika), Shokuyou suika, Shokuyou suika.
Khmer: 'oo'w llok.
Korean: Su bak (Soo bahk).
Laotian: Moo, Teeng moo.
Macedonian: Lubenica.
Marathi: Tarabuuja.
Nepalese: Tarabuujaa (Tarbuja).
Norwegian: Vannmelon.
Persian: Raqqi
Polish: Arbuz, Kawon.
Portuguese: Melancia, Melancia.
Pujabi: Tarabuuja.
Romanian: Pepene verde.
Russian: Arbuz, Arbuz stolovyj.
Serbian: Lubenitsa.
Slovenian: Lubenice.
Spanish: Sandia (Spain), Melon de agua (Cuba), Albudeca (?).
Sundanese: Samangka.
Swahili: Mtango, Mtikiti.
Swedish: Vattenmelon.
Thai: Taeng chin (Peninsular Thailand), Taeng moh (Central Thailand), Matao (Northern Thailand).
Turkish: Karpuz.
Ukranian: Kavun.
1.1.3 General Biology
Watermelon belongs to the Cucurbitaceae or gourd family. It is a trailing annual with stems, as long as 400 cm and chayote. The roots are shallow (40-50 cm) and extensive (60-90 cm), with taproot and many lateral roots.
Watermelon is a warm season crop and is not chill-resistant. It requires a long growing season in the subtropics, but fast growing in the tropical regions. Flowering and fruit development are promoted by high light intensity and high temperature.
Leaf: Leaves are ovate (oval but broader towards the base) to obovate (oval but broader at the apex), 8-20 cm long, scabrid (rough to touch) and deeply pinnatified. The lobes are pinnately divided inti three or four pairs of lobes (see picture below).
A closeup of a watermelon leaf, flower and fruitlet
Stem: The stems are hairy, rounded to angular in cross-section, and have branched tendrils at each node. The stems are highly branched and long (up to 400 cm). The tendrils are pinnately divided into three or four pairs of lobes.
Flowers and sex expression: Watermelons bear separate male and female flowers on the same plant (monoecious). The flowers are unisexual, solitary, axillary and pedicillate. The pedicel of male flower is slender and 12-30 cm long; the female flower pedicel is slightly stouter.
Female flower: Calyx and corolla as in male. Staminodes 3, tounge-shaped or represented by setae. Ovary is ovoid, pubescent, with 3 placentas and many ovules; style short, columnar; stigmas 3, thick and kidney-shaped (Dayer 1975). Only female flowers set fruit. Bees are necessary for pollen transfer pollen.
Male flower: Calyx 5-lobed; tube campanulate; corolla 5-lobed; lobes ovate-oblong, glandular-hairy or setose outside. Stamen 3 or 4, one anther 1-thecous; thecae bent; connective flat and broad; inserted at base of calyx tube. Pistil is absent (Dayer 1975).
Watermelon flowers are small, 4-5 cm across, sulphur yellow in color, and less showy than other cucurbits. A few older varieties and accessions collected from the wild are andromonoecious, i.e having staminate and hermaphrodite flowers. Flowering begins at about eight weeks after seeding, with the production of staminate flowers and later followed by the production of pistillate flowers. In some varieties hermaphrodite flowers develop after the production of staminate flowers.
Most varieties have a ratio of 7:1 staminate to perfect or pistillate flower. There are some varieties with a ratio of 4:1. There is no advantage of andromonoecious sex expression because even the perfect flowers must be cross-pollinated to set fruit. For successful seedless watermelon production, bees are especially important as seedless varieties do not produce pollen. The pollinator variety is planted in alternate or every third row, or as every third plant in the row. Use a distinctly different variety as pollinator in order to easily distinguish seedless fruit. Icebox varieties used as pollinators result in early yields; picnic varieties used as pollinators result in greater total yields. Icebox varieties usually flower 7-10 days earlier than picnic varieties, so delay icebox pollinator planting.
Fruit: The fruit consists of a firm outer rind, a layer of white inner rind flesh of 0.5-1.4 cm thick, and an interior colored edible pulp embedded with seeds (seedy types). The fruit is round to oblong. The skin is smooth with color ranging from yellow, orange, light green to almost black, either solid or striped with a paler green or marbled. The flesh may be white, cream yellow, pale red, red or dark red. The edible part of the fruit is the endocarp (placenta), which contrasts with muskmelon (Cucumis melo), where the edible part of the fruit is the mesocarp. Fruit weight is usually 415 kg. But in Asia, smaller fruit in the range of 1-4 kg is popular. Fruit rind varies from thin to thick and from brittle to tough.
Seed: The seeds are embedded in the edible pulp, small in size (4-6 cm), long and flattened (Stone 1970). Seed color can be white, tan, brown, black, red, green, or mottled.
1.2 Taxonomy and species relationship
Watermelon has 22 chromosomes in the diploid form. The genus Citrullus belongs to the sub-tribe Benincasinae . Other members of similar genera in Cucurbitaceae are Acanthosicyos and Eureiandra whilst those with 22 chromosomes include Gymnopetalum, Lagenaria, Momordica, Trichosanthes and Melothria . The genus Citrullis has now been revised to include C. lanatus, C. ecirrhosus, C. colocynthis, and C. rehmii.