Characterization of Additional Citrus tristeza virus Isolates in a Highly Infected Citrus Area of Sicily

Abstract

In recent years, Citrus tristeza virus (CTV) has often been reported in Italy. Interestingly enough, despite the wide use of sour orange rootstock the typical inverse pitting commonly associated with CTV infection has only been reported on trees derived from introduced budsticks of citrus varieties, and recently on some 30 yr-old Sanguinello sweet orange trees. Recently, thousands trees of different varieties at distant locations were examined for inverse pitting without success. Preliminary studies showed that the isolate of CTV infecting two representative Sanguinello orange trees was different from other CTV isolates found close to this area which do not induce inverse pitting. All the sources indexed on Mexican lime seedlings showed typical vein clearing after only 10 days, whereas only sour orange, sweet orange and grapefruit inoculated with the Sanguinello sources showed stunting, yellowing, small and/or cupped leaves and vein corking to different degrees. The gene coding for p23 was amplified and the nucleotide sequences were determined in both directions. BLAST analysis showed a nucleotide identity of 99% with seedling yellow strains like BaraoB, Val- CB and C271-2. Results confirm that more than a single introduction of CTV could have occurred in Italy over the years.