Some hosts and properties of dahlia mosaic virus

Dahlia mosaic virus (DMV) infected twenty-five of the eighty-five plant species from four of eighteen families inoculated, but only dahlias were found naturally infected. DMV infected fourteen members of the Solanaceae, Amaranthaceae and Chenopodiaceae, and eleven of twenty-nine Compositae. Verbesina encelioides was the best plant for diagnosis, assay and source of virus. Systemically infected hosts contained ovoid intracellular inclusions 2–5–10 μm in diameter which were shown by electron microscopy to consist of a finely granular, vacuolated matrix containing numerous virus particles. V. encelioides sap was sometimes infective after dilution to 1/2000 but not 1/3000, after heating for 10 min to 75 °C but not 80 °C, and after 4 days at 18 °C or 32 days at 2 °C. Sap from infected dahlia, Zinnia elegans or Ageratum houstonianum rapidly became non-infective, but extracts made with 0·05 M sodium thioglycollate or 0·03 M sodium diethyldithiocarbamate remained infective for 24–48 h at 18 °C. Some purified preparations remained infective for up to 3 years at 2 °C. DMV was best purified from V. encelioides by one or more cycles of differential centrifugation, followed by density-gradient centrifugation and further concentration. Composition, molarity, and pH of the extracting buffer had little effect on yield of virus. Best yields were obtained from extracts stored with 8-5% (v/v) n-butanol at 2 °C for 10–14 days. Purified preparations were infective at dilutions up to 1/5000, had ultraviolet absorption spectra typical of a nucleoprotein (Å 260/280 = 1·47), probably contained DNA, and had a single sedimenting component having isometric particles c. 50 nm in diameter with a sedimentation coefficient of 254 S. The cryptogram of DMV is (D)/*:*/(16):S/S:S/Ap. DMV is serologically closely related to cauliflower mosaic virus, but the viruses are distinct pathogens. The two viruses have similar properties, size, shape and other characteristics, and together with at least three others form a small but apparently homogeneous group of aphid-borne viruses.