Strain characterization of potato virus S isolates from Tasmania, Australia

Potato virus S (PVS) is prevalent within potato (Solanum tuberosum) production worldwide. Traditionally, PVS has been split into two strains, Ordinary (PVS^O) and Andean (PVS^A), based on reaction in herbaceous indicator species such as Chenopodium quinoa. However, recent research has identified further strain designations, such as PVS^O-CS (Ordinary and Chenopodium systemic). Forty-four isolates of PVS were collected from potato seed lines in different geographical regions within Tasmania, Australia. Isolates were initially characterized by reactions in C. quinoa. Nineteen isolates were characterized as PVS^O, based on the development of local lesions and serological detection in inoculated leaves only. Three isolates were identified as PVS^A-like, based on local lesion development in inoculated leaves, mild mottling or chlorotic spots on noninoculated leaves, and serological detection in both inoculated and noninoculated leaves. Thirteen isolates produced no symptoms, and were detected serologically in inoculated leaves only (PVS^O-like). Four isolates produced no symptoms but were detected serologically in both inoculated and noninoculated leaves (PVS^A-like). Five isolates produced symptoms in inoculated leaves only but were detected serologically in both inoculated and noninoculated leaves (also PVS^A-like). The ability of isolates to infect tomato has also been used as a criterion to assist in PVS strain differentiation. A subsample of isolates (n = 16) was unable to infect tomato 'Grosse Lisse'. Seventeen isolates representative of these groupings based on reactions in C. quinoa were also characterized by coat-protein sequencing. Phylogenetic comparisons suggested that all isolates were PVS^O rather than PVS^A. Therefore, whereas some of these PVS isolates were systemic in C. quinoa, findings from this study suggest that they were not PVS^A, and that only PVS^O and PVS^O-CS isolates are present in Tasmania. The implications of this finding for disease management are discussed.