Spotted wilt of potato. I. The field disease and studies of the causal virus

Abstract

The symptoms of spotted wilt on potato (variety Up to Date) are described in detail. The strain content of the field virus is analysed by inoculation to differential hosts, and by comparison with the symptoms produced by five purified virus strains. Potato is a selective host for the Ringspot strain. The virus affecting potato in the field lacks the Tip Blight strain and so differs in strain composition from the type commonly occurring in tomatoes. It is shown that the Tip Blight strain is unable to become systemic in potato, but that it is not a filtering action by potato that gives rise to the abbreviated complex lacking the Tip Blight strain. There is evidence of a synergism of strains of spotted-wilt virus since although the Mild and Very Mild strains are present in the naturally occurring potato virus together with the dominant Ringspot strain, they are unable to invade potato when in pure form. It is suggested that the virus affecting potato in the field be designated "potato type spotted wilt" to differentiate it from the type containing Tip Blight strain.