Abstract
During a survey for detection of PVS in potato fields in Northern Khorasan province, some tubers from the plants which have been already marked and showing mosaic, rugosity, undulation on leaf margins, little leaf and slightly vein deepening, were collected in Bodjunrd region, Also, some tubers from potato fields of Mashhad, Chenaran, Ghoochan, Faruj and Shirvan regions were randomly collected. These tubers maintained in 40C until their dormancy broken, and then grown at greenhouse conditions. On the base of reaction of differential hosts a few plants have been infected with PVS. In host range studies infected sap from one of potato plants, infected Nicotiana debneyi Domin. and Lycopersicon esculentum L.cv. early urbana 111 Systematically, It also developed chlorotic local lesions on Chenopodium amaranticolor Costa & Reyn. And C. quinoa Wild as well, but Datura stramonium L., Phaseolus vulgaris L. var. red kidney. and Capsicum frutescens L. did not show any symptoms in this study. The virus indentifed as PVS on the basis of differential host reactions. The isolate was propagated on N. debneyi and purification was carried out according to Hammond & Lawson procedure (1988) with some modification. The antiserum was provided against partially purified virus. Serological tests including double diffusion in agar and ELISA were performed. Electron microscopy showed intact filamentus particle of virus measuring 629 nm (57000x). To determine infection percent of PVS in Bodjnord region, 200 plants were randomly collected and ELISA tests have been used. The results showed the infection rate of 15.5 percent in Bodjnurd region.

Key words: potato Virus S , purification, Antiserum ELISA, Electron microscopy.