Occurrence of the T36 Genotype of Citrus tristeza virus in Citrus Orchards in Sicily, Italy

Abstract

Recent phylogenetic studies have shown that different lineages representing mild and virulent Citrus tristeza virus (CTV) isolates have been present in Italy for a long time. The genetic structure of CTV population, based on p23 and p27 genes sequences, highlighted two main clusters referred to as T30 and VT-like, as confirmed by the full genomes sequences of two representative isolates SG29 (KC748392) and Bau282 (KC748391) (Licciardello et al. 2015). On the basis of risk analyses, regulatory measures have been outlined, including the recommendation to replace sour orange (C. aurantium) with tolerant rootstocks and to monitor the spread and the presence (if any) of different isolates not controlled by the change of rootstock. In 2014, during a large survey covering more than 25,000 ha in eastern Sicily, a subset of 249 alemow (C. macrophylla) seedlings, which are the preferred host of many citrus aphid species, was tested for the presence of CTV by DAS-ELISA (Agdia, Elkhart, IN). A subset of 57 alemow seedlings infected by CTV, randomly selected, was transferred in a safe climate controlled greenhouse and grown to observe symptoms.