Lemon

Citrus limon

1. Identification and origin

The lemon tree [Citrus limon (L.) Osbeck], belonging to the Rutaceae family, is a subtropical fruit tree resulting from ancient hybridisation between species of the genus Citrus, probably involving Citrus medica L. and Citrus aurantium L.. Its origin dates back to Southeast Asia, having been spread to the Mediterranean basin during Antiquity and subsequently to other regions of the world.

2. Economic importance

The lemon is one of the most produced citrus fruits globally, with great importance in the food, pharmaceutical and cosmetic industries. The fruits are used fresh, in juices, preserves, pastry and beverages. The essential oil of the peel is widely valued. The main producers include India, Mexico, Argentina, Spain, Turkey and the United States. In Portugal, production is concentrated mainly in the Algarve and Ribatejo.

3. Botanical characterisation

A small to medium-sized tree (3–6 m), evergreen, with a rounded crown and frequently thorny branches. The leaves are simple, ovate, glossy, with a short petiole. The flowers, white and aromatic, can appear throughout the year, although with greater intensity in spring. The fruit is a modified berry (hesperidium), with a yellow peel rich in oil glands, acidic pulp and variable seeds. The root system is sensitive to waterlogging.

4. Soil and climate requirements

It prefers subtropical and Mediterranean climates, with mild winters and hot summers. It is more sensitive to cold than other Citrus species, suffering damage below –2 °C. It requires well-drained soils, of medium texture, with a pH between 5.5 and 7.0. Regular watering is essential, especially during fruiting. Strong winds can cause fruit drop and damage to the branches.

5. Main pests

• Fruit fly (Ceratitis capitata): direct damage to the fruits.
• Cotton mealybug (Planococcus citri): honeydew and sooty mould.
• Black aphid (Aphis spiraecola): leaf curling and virus transmission.
• Citrus leafminer (Phyllocnistis citrella): galleries in young leaves and reduction of vigour.
• Nematodes (Tylenchulus semipenetrans, Meloidogyne spp.): root decline and reduction of production.

6. Main diseases

• Citrus canker (Xanthomonas citri subsp. citri): corky lesions and fruit drop.
• Root rots (Phytophthora spp.): gummosis, wilting and death of plants.
• Black spot (Phyllosticta citricarpa): lesions on the fruits and commercial loss.
• Citrus tristeza virus (CTV): rapid decline in sensitive rootstocks.
• Alternaria brown spot (Alternaria alternata): leaf necrosis and fruit drop in susceptible cultivars.

7. General crop management

This includes the choice of rootstocks adapted to the soil and climate, planting in well-drained locations, regular watering without waterlogging, balanced fertilisation and formative pruning to improve air circulation. The monitoring of fruit fly, citrus leafminer and Phytophthora is essential. Harvesting should be carried out when the fruits reach a suitable colouration and firmness, avoiding mechanical damage.

Bibliographic references

• EPPO Global Database. Citrus limon – pests and diseases.
• CABI Invasive Species Compendium. Citrus limon – datasheets.
• Davies, F. S., & Albrigo, L. G. (1994). Citrus. CAB International.
• Spiegel‑Roy, P., & Goldschmidt, E. E. (1996). Biology of Citrus. Cambridge University Press.
• Ladaniya, M. S. (2008). Citrus Fruit: Biology, Technology and Evaluation. Academic Press.