On the composite nature of certain potato virus diseases of the mosaic group as revealed by the use of plant indicators and selective methods of transmission

Abstract In 1928 some experiments by the writer (1929) on the transmission of a potato mosaic virus to tobacco revealed the curious fact that needle and aphis (Myzus persicæ) inoculation respectively, from the same mosaic-affected potato plant, produced in tobacco symptoms characteristic of the mode of transmis­sion. This phenomenon was the first definite evidence of the composite nature of potato mosaic diseases, although its exact significance was not at first realised. The following year a parallel set of experiments, carried out with the potato virus disease known as “crinkle,” revealed the same phenomenon, i. e., the production in tobacco of symptoms characteristic of the method of infection (1930a). In this case, however, although the disease produced in tobacco from the crinkle potato by the aphis Myzus persicæ was similar to that produced by the aphis in the first set of experiments with mosaic potato, the parallel symptoms arising in tobacco by needle inoculation from the two sources were not identical. Valleau and Johnson (1930) also showed that the American potato disease known as “rugose mosaic,” probably the same disease as the above-mentioned crinkle, contained two viruses, one of which they refer to as “veinbanding.” This is apparently identical with the disease produced in tobacco by the aphis in the writer’s experiments. The other virus they call the “healthy potato virus,” which is similar to that shown by James Johnson (1925) to be almost universally present in American potatoes. In 1931 the writer published a short account of the results achieved in four years’ study of the composite nature of potato mosaic viruses, outlining the technique of virus isolation from a complex in the living plant, which is more fully described in the present paper. Later Koch (1931) published a statement of the results of work carried on in James Johnson’s laboratory on rugose mosaic of potato, which appears to confirm the writer’s findings with “crinkle.”