Cultivation

With some exceptions, all citrus plants are sensitive to frost and are unable to tolerate temperatures that are more than a few degrees below zero. They are cultivated in temperate and sub-tropical regions, including areas of the USA, South America, South Africa, Australia and the Mediterranean countries. Losses through pests and weeds are estimated to represent a proportion of 20 per cent of the potential harvest.

Mandarins and clementines are cultivated most often and are followed by oranges, lemons and grapefruits.

Utilisation

Most citrus fruits are consumed raw or are processed into

• juice, preserves, fruit preparations, marmalade

Gene technology: aims of research and development

Agronomic traits

Resistance to pests

• Insect resistance to aphids, achieved through the transfer of lectin genes from the snowdrop plant; lectins are compounds that are produced naturally by plants as a defence against insects.

Resistance to pathogens

• resistance to fungi

• resistance to viruses

• resistance to bacteria

Field trials with GM citrus trees