Purification and serology of an apple mosaic virus.

Abstract

Abstract Preparations of a virus isolated from apple petals by inoculating cucumber seedlings formed two light-scattering zones in sucrose density gradient centrifugation and two peaks, corresponding to S values of 88 and 117, in the analytical ultracentrifuge. Electron micrographs revealed spherical particles the sizes of which showed a bimodal frequency distribution. Two populations were obtained by density gradient centrifugation: the smaller particles, corresponding to the upper band, had diameters with a modal value in the range 25.4–26.3 mμ and were not infective. The larger ones with a modal diameter of 28.7–29.6 mμ were associated with the lower band and were highly infective. Both populations were serologically identical. Antiserum prepared against this apple virus reacted with spur formation in double-diffusion tests with necrotic ringspot virus (NRSV) isolated from plum and cherry, but at a lower titer than with the homologous virus. Other characteristics, including host range, symptomatology, and thermal inactivation point, distinguish the apple virus isolate from previously described strains of NRSV. This is believed to be the first report of the natural occurrence of NRSV in the Pomoideae; electron microscopy and serological tests with petal extracts from apple trees with and without mosaic indicate that this virus is responsible for the common apple mosaic syndrome.