Some properties of chrysanthemum stunt, a virus with the characteristics of an uncoated ribonucleic acid

Grafting to virus-free Mistletoe chrysanthemums was the most reliable method of detecting the chrysanthemum stunt agent, but specific light and temperature conditions were required for the diagnostic ‘measles’ symptoms to develop. Although stunt agent was highly infectious, leaf-rubbing inoculations with chrysanthemum sap gave erratic results. Colorimetric and electrophoretic tests were unreliable for indexing chrysanthemums. Stunt agent infected eight of twenty-nine species in the family Compositae, but none of 116 species in forty-seven other families. Stunt spread rapidly by foliage contact and by handling plants, but dipping the hands in 2% trisodium orthophosphate when handling plants increased the amount of spread. Stunt agent was not transmitted by four species of aphids, the glasshouse redspider mite, dodder (Cuscuta campestris) or through chrysanthemum seed. Stunt agent withstood 10 min at c. 98 °C and dilution to 10^-4, was not pelleted by ultracentrifugation, and was inactivated by RNase in weak, but not strong, buffer, suggestive of an uncoated RNA ‘viroid’. Partially purified preparations were made by homogenizing frozen chrysanthemum leaves in 0.5 m phosphate buffer with antioxidant at c. 2 °C, and clarification by n-but-anol and chloroform, followed by centrifugation. Highly infective RNA was precipitated from the supernant fluid by 2.5 vol. cold ethanol, and resuspended in a small volume of buffer. The u.v. absorption spectra of infective preparations and the u.v. absorbance profiles of density-gradients, were very similar to those of preparations from healthy chrysanthemum. Infective partially purified preparations of stunt agent withstood exposure to 2% formaldehyde or tri-sodium orthophosphate, u.v. irradiation, and sonication. Stunt preparations contained no virus particles recognizable by electron microscopy, gave no distinct peak on analytical ultracentrifugation, and did not consistently contain any specific antigen. Although similar to the ‘viroids’ potato spindle tuber and citrus exocortis, stunt agent did not infect Citrus limon, Gynura aurantiaca or tomato.