Outbreak of Citrus tristeza virus in Calabria, Italy
In Italy, during testing for breeding purposes in a large citrus orchard at Rosarno (province of Reggio di Calabria, Calabria), a large number of mandarin trees (satsumas: Citrus unshiu and mandarins: C. reticulata cv. ‘Fortune’) showed symptoms of tristeza. A high percentage of mandarin trees were already dead. All trees were grafted on sour orange (C. aurantium). Samples were collected from approximately 100 trees and were tested for Citrus tristeza virus (Closterovirus, CTV – EPPO A2 list) by DAS-ELISA, DTBIA and PCR. As a result, 20 trees were found infected by CTV. It was also found that the Calabrese isolate was almost identical to a Spanish isolate (98% sequence similarity) but was slightly different from isolates previously found at Cassibile (Province of Siracusa, Sicilia) on the same mandarin cultivar ‘Fortune’ (see EPPO RS 2005/089). Field infections of CTV had been reported in Calabria since 1983 on a few plants that had been illegally imported, but the present outbreak concerns hundreds of trees. In addition, the infected plants have not been imported from abroad but produced in Italy. The authors considered that the present situation in Calabria was alarming and proposed the following measures: immediate eradication of this CTV outbreak; surveys in nurseries, use of certified plants grafted onto tolerant rootstocks when establishing new orchards; typing of CTV strains present in Calabria. It was stressed that the recent introduction of Toxoptera citridicus, the most efficient aphid vector of CTV, into parts of Portugal and Spain was of concern to Italy and that surveillance programmes on aphids should be carried out. Finally, experiments on tolerant rootstocks which could replace the susceptible C. aurantium should be intensified.
The situation of Citrus tristeza virus in Italy can be described as follows: Present, 4 outbreaks have been reported in Puglia (province of Taranto), Calabria (province of Reggio di Calabria) and Sicilia (provinces of Syracusa and Catania), under official control.
Sources
Caruso A, Davino S, Sorrentino G, Agosteo GE, Davino M (2006) Gravi infezioni del virus della ‘tristeza’ degli agrumi (CTV) mettono a rischio l’agrumicoltura calabrese. Informatore Fitopatologico no. 7/8, 5-6.