Assessment of Citrus tristeza virus (CTV) incidence in Calabria, southern Italy: results of a three-years survey

Since 2006 a survey on Citrus tristeza virus (CTV) has been carried out in Calabria, southern Italy, to determine the occurrence of the virus, to evaluate its incidence, to identify and characterize the virus strains, and to monitor the aphid vector populations. Citrus samples were collected from nurseries and orchards located in the five provinces of the region. The virus was not detected in the citrus-growing areas of Catanzaro (CZ) or Crotone (KR), whereas it was found in three orchards in Cosenza (CS), three in Vibo Valentia (VV) and twelve citrus plantings in Reggio Calabria (RC). The highest infection percentages occurred in citrus orchards close to fields already infected with CTV. Infections were detected not only in foreign cultivars, but also in local cultivars such as 'Comune' clementine, 'Moro', 'Ovale' and 'Tarocco' sweet orange, suggesting that CTV was transmitted by aphids. CTV occurred in only a few plantlets sampled in two citrus nurseries located near the main areas already infected. Serological differentiation of several CTV field isolates revealed that the mild strains were prevalent. Aphis gossypii (Glover) and A. spiraecola Patch (= A. citricola Van der Goot) were the most frequent aphids in the orchards, whereas Toxoptera aurantii (Boyer de Foscoulombe) and Myzus persicae (Sulzer) occurred with low incidence. The absence of T. citricidus (Kirkaldy) was confirmed.