The Sedimentation Rate of Potato Yellow-Dwarf Virus

BLACK et al. (1948) have published electron micrographs of bodies believed to represent the New York variety of potato yellow-dwarf virus (Aureogenus vastans (H) Black) (Holmes 1948). The photographs showed bodies in several different extracts of infected plants of Nicotiana rustica L., but not in corresponding preparations from healthy plants. Similar bodies were found in concentrates from plants infected with the New Jersey variety of the virus (var. agalliae Black). These bodies were larger than, and of a different character from, those of plant viruses hitherto examined in the electron microscope. The present study was undertaken to obtain evidence that might more closely identify these bodies with the virus, to ascertain if the sedimentation rate of the virus activity was consistent with the size of the bodies, and to determine the sedimentation constant of this active virus in order to use it in further attempts at purification. At the same time, the experiments were designed and carried out in the expectation that they might serve as a guide to later work with other plant viruses with long incubation periods in their leaf- hopper vectors, particularly the wound-tumor virus (Aureogenus magnivena Black). Potato yellow- dwarf virus is the easiest member of this group to work with because it is the only one that has been readily transmitted mechanically from plant to plant. It produces many primary lesions on inoculated susceptible leaves of N. rustica and, therefore, unlike the other viruses of the group, can be subjected to a convenient and roughly quantitative bioassay