Current situation of Citrus tristeza closterovirus in Italy
Italy has been free for some time from Citrus tristeza closterovirus (CTV – EPPO A2 list), but recently, outbreaks were reported in 3 separate areas in the south of the country:
- in Cassibile (province of Syracusa, Sicilia) on Fortune mandarin (Citrus reticulata); see also EPPO RS 2003/071;
- in Massafra (province of Taranto, Puglia) on sweet orange (C. sinensis ‘Navelina’);
- in Belpasso (province of Catania, Sicilia) on sweet orange (C. sinensis ‘Tarocco’).
In all cases, infected plants were grafted on sour orange rootstocks (C. aurantium). Isolates from Cassibile and Massafra were mild, whereas isolates from Belpasso induced severe symptoms, such as dwarfing and dieback of trees, small leaves with interveinal chlorosis, small and elongated fruits, and root death. Genetic variation of the 3 CTV populations was studied with molecular tools (single strand conformation polymorphism (SSCP) and nucleotide sequence analysis of CTV gene p20). All isolates from the same area presented the same SSCP patterns, and these patterns differed from one area to another. Isolates from Massafra and Cassibile showed more than 99% nucleotide identity with a mild isolate from Spain, and 92 % similarity with the Belpasso isolates. The latter were similar (more than 99% similarity) to severe isolates from California (US) and Japan. These results suggested that there had been at least 2 independent introductions to Italy, probably by imports of CTV-infected material. The fact that virus populations were homogeneous within each area also suggested that CTV is naturally and rapidly spread by aphids. The need for eradication and containment programmes is underlined.
Sources
Davino S, Rubio L, Davino M (2005) Molecular analysis suggests that recent Citrus tristeza virus outbreaks in Italy were originated by at least two independent introductions.
European Journal of Plant Pathology, 111(3), 289-293.