Isolation, purification and characterization of the virus causing St. Augustine Decline

Abstract

The virus causing St. Augustine Decline (SAD) was purified by differential centrifugation in phosphate buffer, filtered through charcoal and celite, millipore filtered to 0.2 u and then centrifuged on sucrose density gradients. The sucrose density gradient centrifugations yielded one clear zone which produced one Schlieren peak with a sedimentation constant of 102 S and was highly infectious. The virus particles were polyhedral in shape when shadowed and negatively stained. The individual particles had a mean diameter of 24 nm. Ultraviolet absorption determinations on purified preparations yielded a 280:260 value of 0.76. The thermal inactivation point of the virus in crude extract was 60 C and that of the purified virus was 56 0. The dilution end point of the virus was 10⁻⁴ in crude extract and 10⁻⁵ for purified virus. The longevity was not reduced by storage at -20 C but was proportionately reduced at 8 C and 25 C. A potassium phosphate buffer (pH 7.4) was found to best preserve infectivity. A host range study of Panicum sp., Setaria sp. and Pennisetum sp. millets indicated that Setaria italica Strain-R cultivar was the better assay host. Serological tests using the Ouchterlony Agar Double Diffusion technique proved a strong relationship with another polyhedral plant virus, Panicum Mosaic Virus. The name St. Augustine Decline strain of Panicum Mosaic Virus is proposed for the virus that causes St. Augustine Decline.