1959 Volume 24 Issue 5 Pages 287-295
1. This paper deals with the host range, properties, purification, and electron microscopy of the radish P virus. In a preliminary survey of the viruses of Japanese radish mosaic disease complex in the suburbs of Tokyo, made jointly with Mr. Yasuo Komuro, it was found, that besides the cucumber mosaic virus, three other viruses, which we have termed P, Q, and R, are involved. These viruses occur either singly, or as combinations of two, three, and four. While the virus Q is apparently distinct, both the viruses P and R are considered to belong, in the conventional taxonomy, to the turnip mosaic virus group. There are, however, some indications that these two viruses are rather related remotely with each other. Most of the experiments reported here, unless otherwise stated, were made using a virus isolate P0, which was isolated in May 1956, from a mosaic radish plant in Matsudo, Chiba Prefecture, and was maintained in a greenhouse, by successive juice inoculations on turnip plants.
2. Host range. (Mosaic, or mottle): Brassica rapa var. glabra, B. rapa var. pervidis, B. juncea (two subvarieties), B. nigra, B. campestris, Raphanus sativus var. acanthiformis (five subvarieties), Matthiola incana, Spinacia oleracea (subvariety Ujo), Chrysanthemum coronarium, and Petunia hybrida.
(Symptomless carriers): B. oleracea var. capitata (subvariety Yoshin), and B. napus.
(Necrotic local lesions on inoculated leaves): Gomphrena globosa, and Chenopodium album.
(Not susceptible): N. tabacum (subvariety Bright yellow), N. glutinosa, Vigna sesquipedalis, Vicia faba, Cucumis sativus, Beta vulgaris var. flavescens, Datura stramonium, Lycopersicum esculentum, Zinnia elegans, Brassica oleracea var. capitata (subvariety Hachigatsudori), B. oleracea var. botrytis, and Spinacia oleracea (subvariety Nihon). N. glutinosa was found to be infected by the P virus, when inoculated together with cucumber mosaic virus.
3. Properties. Dilution end-point in extracted leaf juice was 1:2000∼1:5000. Thermal inactivation point was between 55 and 60°C, in 10 minutes treatment. Longevity of the virus in crude juice was between 4 and 7 days at 25∼26°C, but this period became much longer, when a little KCN was added to the leaf juice. In a frozen-dried preparation of leaf juice, the virus still retained infectivity after 23 months.
4. Aphid transmission. The P virus is readily transmitted by the aphid, Myzus persicae, except for the particular virus isolate P0, which has been maintained in a greenhouse for more than two years by successive juice inoculation. Although this isolate P0 was found not transmissible by the aphid, a sub-isolate P'0, which was derived from the same source as P0 but which had been kept in a frozen-dried juice preparation, was found to be transmissible by the aphid.
5. Purification. Attempts were made to obtain a purified virus preparation, using diseased turnip (subvariety Kanamachikokabu) or petunia leaves. The final procedure adopted was as follows: (freezing and thawing of leaf tissues or juice) → combined procedures of repeated salting-out by ammonium sulfate and differential centrifuging → (treatment with chloroform). The final product was almost colorless, and the yield was about 10∼15mg per 100ml leaf juice. This purified virus preparation diluted to (2∼3)×107 (dry weight basis) was still capable of infecting 20 per cent of inoculated turnip plants.
6. Electron microscopy. Examination of the purified virus preparation revealed the presence of sinuous rod-shaped particles, of about 12∼13mμ in width, with the most frequent length of 650∼700mμ. The preparation was found to be almost free of other particulate matter.