Evidence and characterization of a virus of St John's Wort (Hypericum perfora tum L.)

Abstract

Vein yellows, necrotic leaf spots and growth inhibition were observed on St John's wort plants (Hypericum perforatum L.) growing in a field in northern Thuringia. A virus was isolated from diseased plants and mechanically transmitted to several species of the genera Antirrhinum, Chenopodium, Cucurbita, Datura, Gomphrena, Lathyrus, Malva, Nicotiana, Ocimum, Petunia, Phaseolus and Spinacia. After retransmitting the virus to H. perforatum it developed symptoms similar to those observed in the field and was reisolated from experimentally infected H. perforatum plants. High concentrations of the virus were found in Nicotiana clevelandii Gray and N. occidentalis Wheeler. The thermal inactivation point was 52°C. The virus remained infectious in frozen and dried leaves of N. clevelandii for at least 3 months, but lost its infectivity in crude sap of N. clevelandii plants already after 3 days, in crude sap of H. perforatum plants even after 1 day. The virus has isometric particles with a diameter of 27 nm. It is highly immunogenic and an antiserum was produced with a titre of 1/2 048. The virus is serologically not identical or related with 10 other viruses investigated. It is not transmissible by the aphid species Myzus persicae (Sulz.), but it seems easily transmissible by leaf contact and by cutting of leaves or stalks. The contents of valuable active compounds in diseased plants differ partly from those in healthy plants. According to the first preliminary studies different varieties of St John's wort respond the virus infection in a distinct manner.