Status of potato viruses in Tunisia and molecular characterization of Tunisian Potato Virus X (PVX) isolates

Three hundred and eighteen symptomatic potato samples were collected from the main potato growing provinces of Tunisia, in main and late season crops (respectively spring and autumn 2013). Double antibody sandwich ELISA (DAS-ELISA) was used to assess the presence of the five most common potato viruses [ Potato virus A (PVA), Potato virus X (PVX), Potato virus Y (PVY), Potato leafroll virus (PLRV) and Potato virus S (PVS)]. According to ELISA results, the highest overall percentage of infected samples was observed in the late season (84.5%), in comparison to the main season (30.7%). PVY was dominant in all infected plots with detection rates ranging from 20% in the North region (main season) to 100% in Cap Bon (late season). PLRV was the second most detected virus, with 4.3% distributed in the North West and Sahel during the main season, but was not detected in the late season. PVX was found with even lower detection rates of 0.6% and 1.3% in main and late seasons, respectively. No infection by PVA or PVS was detected in these two periods. Positive PVX detection results were confirmed by Reverse Transcription PCR using total RNA extracted from infected leaves. The near-complete nucleotide sequences of three PVX isolates were determined using an Illumina MiSeq sequencer. Phylogenetic analyses on full genome sequences or on coat protein (CP) gene sequences show that Tunisian PVX isolates belong to low diversity clade I.