Grapefruit

Citrus × paradisi

1. Identification and origin

The grapefruit tree (Citrus × paradisi Macfad.) is a hybrid species of the Rutaceae family, resulting from the natural cross between Citrus maxima (Burm.) Merr. (pomelo) and Citrus sinensis (L.) Osbeck (sweet orange). The hybrid is thought to have arisen in the 18th century in the Caribbean, later spreading to subtropical citrus-producing regions. It is cultivated mainly for fresh consumption and for the juice industry.

2. Economic importance

Grapefruit has significant commercial value in international markets, especially in the United States, Israel, South Africa and some Mediterranean countries. It is appreciated for its characteristic sour-bitter flavour and its high content of vitamin C, antioxidants and bioactive compounds. Production is intended for fresh consumption, juices, concentrates and the food industry. In Portugal, the crop is a minor but growing one in citrus farms of the Algarve and Alentejo.

3. Botanical characterisation

The grapefruit tree is a medium-sized tree, 4–6 m tall, with a rounded and dense canopy. The leaves are simple, leathery, with a winged petiole. The flowers are white, aromatic, hermaphrodite, grouped in axillary inflorescences. The fruit is a large hesperidium, with thick rind, segmented pulp and variable colouring (yellow, pink or red). The root system is deep, sensitive to root asphyxiation and salinity.

4. Soil and climate requirements

The grapefruit tree adapts to hot subtropical climates, with optimal temperatures between 20 and 30 °C. It is sensitive to frost and cold winds. It prefers well-drained soils of medium texture, with a pH between 6.0 and 7.5. The crop requires good light and regular water availability, avoiding waterlogging. The pink/red colouring of the fruits is favoured by moderate thermal ranges.

5. Main pests

• Fruit fly (Ceratitis capitata) — perforations and deterioration of the fruits
• Citrus mealybug (Planococcus citri) — sap sucking, honeydew and sooty mould
• Black aphid (Aphis spiraecola) — sap sucking and transmission of viral diseases
• Citrus leafminer (Phyllocnistis citrella) — mines in young leaves and reduction in vigour
• Mites (Panonychus citri, Tetranychus urticae) — discolouration and leaf fall
• Thrips (Scirtothrips aurantii) — damage to young leaves and scars on the fruits

6. Main diseases

• Citrus canker (Xanthomonas citri subsp. citri) — corky lesions and fruit fall
• Citrus black spot (Phyllosticta citricarpa) — necrotic spots and commercial loss
• Root rots (Phytophthora nicotianae, P. citrophthora) — decline and death of plants
• Citrus tristeza virus (CTV) — chlorosis, decline and incompatibility with sensitive rootstocks
• Anthracnose (Colletotrichum gloeosporioides) — leaf necrosis and post-harvest rot

7. General crop management

Management of the grapefruit tree is based on the choice of rootstocks adapted to the soil and tolerant to soil diseases. Formation and cleaning pruning improves ventilation and reduces pest pressure. Monitoring of fruit fly, mealybugs and leafminer is essential. Irrigation must be regular, avoiding waterlogging. Balanced fertilisation, with attention to boron and magnesium, favours fruit quality. Harvesting is carried out when the fruits reach colouring and a content of soluble solids suited to the market.

Bibliographic references

• EPPO Global Database – Citrus × paradisi, Citrus maxima, Citrus sinensis
• CABI – Crop Protection Compendium – Citrus × paradisi
• Spiegel‑Roy, P., & Goldschmidt, E. E. (1996). Biology of Citrus. Cambridge University Press.
• Talon, M., Caruso, M., & Gmitter, F. G. (2020). The Genus Citrus. Woodhead Publishing.
• Ladaniya, M. S. (2008). Citrus Fruit: Biology, Technology and Evaluation. Academic Press.