COMPARATIVE STUDIES IN POTATO VIRUS DISEASES

This paper is an account of an investigation into the identity of a hitherto undescribed mosaic disease of President potato. Both a mild and a severe form of the disease were observed, but both forms were characterized by a yellow mottling not found in the previously reported potato mosaics.The mild form of the disease has been shown to be caused by a single virus, while the severe form is due to a combination of this virus and one of the vein-banding" group. Because of the yellow color associated with the symptoms produced on a number of host plants, the name "yellow mottle" is proposed for the newly described virus.The "yellow mottle" virus of President mosaic has been compared with the "mottle" and "ringspot" viruses from rugose mosaic, both as to behavior under certain physical and chemical tests and with respect to the symptomatological reaction of a number of solanaceous host plants.Tabulated results of the differential property studies are given, and descriptions of the symptoms caused by each of the three viruses on eight different host plants are presented.From these studies it is concluded that the newly described "yellow mottle" virus is distinct from both "mottle" and "ringspot", but it is closely related to the "X-virus" or "latent virus" group.