The Spanish citrus industry

Citrus have a long history in Spain. Citrons were introduced by the Romans during the V century, sour oranges,lemons, and pummelos by the Arabs during the X and XI centuries, the first sweet oranges by the Genovesetraders during the XV century and then higher quality varieties by the Portuguese in the XVI century, themandarins during the XIX century, and finally, grapefruits from U.S.A. in the early XX century. Initially citruswere used as ornamental plants and for medicinal purposes, and after introduction of sweet oranges alsofor direct consumption at very local scale. Commercial plantings and exports of fresh fruit to other Europeancountries started at the end of the XVIII century. In the past, the Spanish citrus industry has been conditioned by diseases. The first important problem appearedat the end of the XIX century, when about 4,000 ha of citrus were grown as seedlings or grafted on sweetorange, lemon, citron and sour orange rootstocks. Observations published in 1892 indicated that trees weredying from a disease, much later identified as Phytophthora root rot. In 10-15 years all trees in commercialplantings died, except those grafted on sour orange, which is tolerant to this pathogen. Consequently, allnew plantings were established on sour orange rootstock, which has an excellent horticultural behavior andis tolerant to most biotic and abiotic stresses. Indeed most citrus growing countries followed the Spanishexample and sour orange became the predominant citrus rootstock worldwide. Later this created a seriousproblem due to its high susceptibility to decline induced by Citrus tristeza virus (CTV). In the period 1910-1930 new higher quality cultivars were imported from different countries that wereused for new plantings and also to change old cultivars by topworking. Evidence indicates that many of theimported cultivars were affected by viruses, including CTV, and viroids that spread throughout the country. The first CTV outbreak in Spain was recorded in