LIBRO-CONGRESO-CITRUS

PC01
The Spanish citrus industry
Luis Navarro
Instituto Valenciano de Investigaciones Agrarias (IVIA). E-mail: lnavarro@ivia.es. Moncada, Valencia, Spain
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 Genovese
traders during the XV century and then higher quality varieties by the Portuguese in the XVI century, the
mandarins during the XIX century, and finally, grapefruits from U.S.A. in the early XX century. Initially citrus
were used as ornamental plants and for medicinal purposes, and after introduction of sweet oranges also
for direct consumption at very local scale. Commercial plantings and exports of fresh fruit to other European
countries started at the end of the XVIII century.
In the past, the Spanish citrus industry has been conditioned by diseases. The first important problem appeared
at the end of the XIX century, when about 4,000 ha of citrus were grown as seedlings or grafted on sweet
orange, lemon, citron and sour orange rootstocks. Observations published in 1892 indicated that trees were
dying from a disease, much later identified as Phytophthora root rot. In 10-15 years all trees in commercial
plantings died, except those grafted on sour orange, which is tolerant to this pathogen. Consequently, all
new plantings were established on sour orange rootstock, which has an excellent horticultural behavior and
is tolerant to most biotic and abiotic stresses. Indeed most citrus growing countries followed the Spanish
example and sour orange became the predominant citrus rootstock worldwide. Later this created a serious
problem 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 were
used for new plantings and also to change old cultivars by topworking. Evidence indicates that many of the
imported cultivars were affected by viruses, including CTV, and viroids that spread throughout the country.
The first CTV outbreak in Spain was recorded in 1957, and since then it has produced the death of more
than 44 million trees of sweet oranges and mandarins grafted on sour orange. At the end of the 1960’s the
total surface of citrus was about 210,000 ha and citrus exports were the main source of foreign currency
for the country. The risk of a socio-economic disaster caused by CTV was so high that the Government set
up very severe rules to reduce losses produced by the virus. The use of sour orange was prohibited in new
plantings and propagation of plants at citrus nurseries was strictly regulated, leading to a drastic reduction in
its number from thousands to nine.
Early surveys and indexing disclosed that other virus and virus-like diseases were widespread in all Spanish
cultivars. Psorosis, impietratura, and concave gum were producing important damage. Exocortis infected all
cultivars and consequently, Troyer citrange, the best tristeza-tolerant rootstock under the Spanish growing
conditions, could not be used for propagation. It was estimated that in addition to tristeza, other virus and
virus-like diseases produced losses estimated at 10-25% of the total production.
In the early 1970s graft-transmissible pathogens were the major limitation for the development and even
for maintenance the Spanish citrus industry. It became evident that control of virus and virus-like diseases
required the use of pathogen-free cultivars grafted on tristeza tolerant rootstocks. Since all the Spanish
cultivars were infected, the first step was to recover healthy plants from those cultivars. The development
of shoot-tip grafting in vitro (STG) to recover healthy citrus plants allowed in 1975 to set up a program with
the objectives of recovering pathogen-free plants from all cultivars grown in Spain, establishing a germplasm
bank with pathogen-free plants, and releasing pathogen-free budwood to nurseries through a mandatory
certification program. Later, in 1983, a new quarantine procedure based on STG was developed and legislation
was changed to allow the safe importation of citrus budwood. Thus, introduction of genotypes for commercial
and scientific purposes was included as an additional objective of the program.
Today the germplasm bank has more than 600 accessions protected in screenhouses that are the initial
material used by all nurseries to produce plants under the certification program. Nurseries started to sell
certified plants originated in the Program in 1982 and until now they have sold about 140 million plants,
representing more than 97% of the Spanish citrus industry.
XII INTERNATIONAL CITRUS CONGRESS 2012 - 3