Maintaining Malta's protected zone for the Citrus Tristeza virus and its importance for Maltese Citriculture

Abstract

Citrus Tristeza Virus (CTV) is the worst viral disease affecting citrus trees. It infects all citrus species and varieties and has caused severe damage to citrus industries. The virus occurs worldwide throughout citrus cultivating regions including the Mediterranean region. CTV causes severe symptoms including quick decline of citrus species grafted on sour orange (Citrus. aurantium L.), which has led to great losses of citrus trees in countries like Spain and South America. The disease is spread through grafting infected germplasm and by aphid vectors. Prior to the accession of Malta with the European Union (EU), surveys were carried out for the presence of this virus in the Maltese Islands due to the importance of citrus for Maltese agriculture. These surveys revealed a significant general absence of the virus from citrus orchards. This paved the way for obtaining a protected zone for preventing the introduction of the virus from other EU countries where the virus is present. The most efficient aphid vector of CTV - Toxoptera citricida Kirkaldy (which was accidentally introduced in the Mediterranean (Spain and Portugal) in 200212003 (EPPO, 2006), is still not present in Malta, however other aphid vectors of CTV including Aphis gossypii Glover, Aphis spiraecola Patch and Toxoptera aurantii Fonsc. are present in Malta (Dept. of Plant Health- Diagnosis and Control Unit (DCU), 2008 pers. comm.). Despite the absence of CTV on local citrus, the virus was encountered on traded citrus originating in other EU countries. Eventually CTV was also encountered on local citrus in two isolated foci, both of which were eradicated by the Department of Plant Health. Maintaining the protected zone protects Maltese citriculture including the right of Maltese Member State to prevent citrus fruit with leaves and peduncles from entering the Maltese Islands. However the absence of a source of local certified citrus allows the introduction of citrus from neighbouring EU countries which are not protected zones for the virus so the full benefits of Malta being a protected zone for the virus are still not being fulfilled . Annual monitoring of local citrus proves to be essential for controlling any new isolated foci of infection and for maintaining the protected zone.