Biological and molecular characterization of a distinct Citrus tristeza virus isolate originating from a lemon tree in Greece

A Citrus tristeza virus (CTV) isolate (L192GR) naturally occurring in lemon trees of more than 100 years old in Greece was fully characterized. Virus-derived small interfering RNAs, induced by Dicer processing of dsRNAs formed during RNA virus replication, were isolated and used as targets for sequencing. Next-generation high-throughput sequencing using the Ion Torrent platform was performed. A total of 432 632 sequences, 94·05% of which corresponded to L192GR, were determined. Subsequent bioinformatics analysis enabled the determination of the full-length 19 251 nt genome of the L192GR isolate (GenBank no. KC262793). Comparative analysis of complete genomes revealed molecular homology with CTV-VT isolate FS2-2 from Florida (GenBank no. EU937519) with 98·2% nucleotide sequence identity. Recombination events were detected in L192GR and they probably contribute to its unique characteristics. Specifically, although most isolates of the CTV-VT group induce the seedling yellows syndrome and react positively with the monoclonal antibody MCA13, which is typically associated with severe CTV isolates, the MCA13-positive L192GR gave very mild or even no symptoms in the seedling yellows indicator plants. Furthermore, experimental aphid transmissibility studies revealed a poor transmission efficiency of 20%. This is the first report of a CTV isolate originating from a lemon tree being fully characterized at biological, serological and molecular levels. The present study further confirms that, when the goal is the risk assessment associated with a new pathogen or isolate in a particular area, molecular data have to be combined with the biological properties of the pathogen.