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.