Investigation of carnation viruses

SUMMARY Carnation ringspot virus (CRSV) was isolated from twenty‐three carnation cultivars, was readily transmitted by grafting and sap‐rubbing inoculation, and was spread among carnations by handling. CRSV was cultured in Nicotiana clevelandii or carnation and assayed in Chenopodium amaranticolor ; Gomphrena globosa was the best diagnostic indicator plant. CRSV was not transmitted by Myzus persicae or through seed of Dianthus barbatus . The virus infected sixty‐two out of ninety‐six plant species tested, but carnation is the only plant likely to be a virus source for commercial stocks. The concentration of CRSV decreased greatly in the terminal 1–2 mm. of the carnation shoot apex and, unlike carnation mottle, CRSV was not detected in the meristem dome; it was, however, present in some first leaf primordia. Clones free from the virus were obtained by aseptic culture of excised meristem‐tips, but more easily by growing infected carnations at 38–40d̀ C. for 4 weeks, followed by striking small cuttings or culturing meristem‐tips. N. clevelandii sap was infective after dilution to 1/100,000, heating for 10 min. to 85d̀ C. but not 90d̀ C., and storage for 16 days at 20d̀ C. or 3 months at 0d̀ C. Purified and concentrated preparations of CRSV from carnation, D. barbatus or N. clevelandii were highly infective, contained polyhedral particles about 29 mμ diameter, were antigenic, and produced a specific light‐scattering zone in density‐gradient centrifugation. The S 20 , w at infinite dilution was 140. CRSV shares many in vitro properties with eleven other viruses having similar particle shape, but it was not serologically related to any of them.