Occurrence of Potato Viruses in Syria and the Molecular Detection and Characterization of Syrian Potato virus S Isolates

Potato virus Y (PVY) is the main potato virus in Syria but no information is available on the prevalence of other potato viruses. A survey was conducted by ELISA using specific antibodies to nine potato viruses. PVY, Potato virus S (PVS), Cucumber mosaic virus and Potato leafroll virus were detected with infection rates of 54.2, 8.4, 3.7 and 0.9%, respectively. The overall virus infection rate was as high as 72.9% in ware potato fields. A preliminary characterization was carried out on PVS isolates. Syrian PVS isolates infected Chenopodium amaranticolor only locally and therefore were classified as PVSO. Phylogenetic analysis of the coat protein gene showed that PVS comprised two main clusters, cluster-O and cluster-A, which contained the ordinary and Andean strains respectively. Cluster-O was separated into two subclusters, O1 and O2. Two Syrian PVS isolates, PVS3-5 and PVS6-2, fell into the O1 subcluster. PVS3-5 coat protein, however, shared the highest nucleotide identity with European isolates of the O1 subcluster, whereas PVS6-2 was closely related to Asian isolates of the same subcluster. Owing to the high incidence of PVY and PVS in Syria, a duplex reverse-transcription PCR was developed to detect these two viruses in a single PCR.