Watermelon

Citrullus lanatus

1. Identification and origin

Watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai], belonging to the Cucurbitaceae family, is a species native to sub-Saharan Africa, with evidence of domestication more than 4,000 years ago in the Sahel region and the Nile valley. The species was subsequently spread to the Mediterranean, Asia and the Americas. It includes various varietal groups, from large and elongated fruits to mini, seedless (triploid) types and cultivars with yellow or orange flesh.

2. Economic importance

Watermelon is one of the most produced and consumed fruits in the world, standing out for its high water content, sweet flavour and refreshing value. It is consumed fresh, in juices, salads and processed products. The main producers include China, Turkey, India, Iran, Brazil, the United States and Spain. The international market values fruits with high sweetness (°Brix), skin resistant to transport and absence of seeds.

3. Botanical characterisation

An annual herbaceous plant, creeping or climbing, with long, branched stems. The leaves are large, deeply lobed and rough to the touch. The flowers are unisexual, yellow, with predominantly entomophilous pollination. The fruit is a large berry (pepo), with thick skin, juicy flesh and numerous seeds (except in triploid cultivars). The root system is deep and well adapted to dry soils, conferring moderate tolerance to drought.

4. Soil and climate requirements

Watermelon adapts to hot climates, with ideal temperatures between 22–32 °C. It is sensitive to cold and does not tolerate frosts. It prefers light, well-drained soils, of sandy to sandy-loam texture, with a pH between 6.0 and 7.5. It requires high light and regular irrigation, especially in the fruiting phase, avoiding waterlogging. Efficient pollination is essential for good fruiting, with the use of beehives being common.

5. Main pests

• Whitefly (Bemisia tabaci): Honeydew, sooty mould and transmission of viruses.
• Aphids (Aphis gossypii, Myzus persicae): Sap sucking and transmission of viruses.
• Thrips (Frankliniella occidentalis, Thrips tabaci): Damage to leaves and flowers.
• Mites (Tetranychus urticae): Chlorosis and fine webs in dry conditions.
• Caterpillars (Noctuidae): Defoliation and damage to shoots.
• Nematodes (Meloidogyne spp., Pratylenchus spp.): Root galls and reduction of vigour.

6. Main diseases

• Downy mildew (Pseudoperonospora cubensis): Angular spots and leaf necrosis.
• Powdery mildew (Podosphaera xanthii, Erysiphe cichoracearum): White coating and reduction of photosynthesis.
• Anthracnose (Colletotrichum orbiculare): Leaf lesions and rots in fruits.
• Fusarium wilt (Fusarium oxysporum f. sp. niveum): Vascular wilting and death of plants.
• Gummy stem blight (Didymella bryoniae): Cankers on stems and rots in fruits.
• Viruses (WMV, ZYMV, CMV): Mosaics, deformations and reduction of production.

7. General crop management

It includes the choice of cultivars adapted to the local climate, sowing in well-drained soils, crop rotation to reduce pressure from diseases and nematodes, weed control, regular irrigation without waterlogging and monitoring of downy mildew, powdery mildew and whitefly. Pollination should be ensured with beehives. Harvesting is carried out when the fruit presents a hollow sound to the touch, drying of the peduncle and a change of colour in the area of contact with the soil.

Bibliographic references

• EPPO Global Database. Citrullus lanatus – pests and diseases.
• CABI Invasive Species Compendium. Citrullus lanatus – datasheets.
• Robinson, R. W., & Decker‑Walters, D. S. (1997). Cucurbits. CAB International.
• Wehner, T. C. (2008). Watermelon. In: Prohens, J., & Nuez, F. (Eds.), Vegetables II. Springer.
• FAO (2019). Production statistics of watermelon.