Determination of the races of potato virus X and its host rang in Karaj, Damavand and Ardabil, Iran.

Potato virus x (PVX) is found commonly in potato-growing areas, worldwide. It is an economically important virus which causes losses in tuber yield of approximate 5 to 15 percent. In a 2 year survey, potato leaf and tuber samples were collected from various fields in Damavand and Karaj. The initial isolations from potato were made by mechanical inoculation first to Gomphrena globosa L. and later to Dartura stramonium L. It was not transmitted by 2 species of Cuscuta but transmitted mechamically. The isolates were inoculated to Nicotiana glutinosa L. in which they were maintained throughout the work. Sap from infected N. glutinosa was ineffective after dilution to 10-6, after 10 minutes at 70 degrees C and after 10 weeks at room temperature. The virus had filamentous and slightly flexuous particles with a normal length of about 490-500 nm and 12 nm width. According to the symptoms, TIP results and serological comparisons, the compared isolates showed no difference and they belong to XN group. In order to estimate disease incidence, 773 tubers from Damavand area were tested and compared with that in Ardabil area. Disease incidence in Damavand ranged from 1.1-20.9 percent and was lower than disease incidence in Ardabil. In 8 genera of collected weeds from fields of potato and tomato samples by using test plants and serological methods, they didn't show existence of the potato virus x.