This paper deals with the host range, properties, purification, and electron-microscopy of the radish R virus (RRV). Virus isolates “Miyahara 5” and “Kurayoshi 2” were used in the experiments. For comparison, radish P virus (RPV), isolates “P₀” and “Chikugo 10”, were also used.
1. The host range of RRV isolate “Miyahara 5” was almost similar to that of RPV isolate “P₀”, except that “Miyahara 5” produced local lesions on the inoculated leaves of tobacco, subvar. Bright Yellow, and broad bean. In crude juice from diseased turnip leaf infected with the isolate “Miyahara 5”, the dilution end-point was 1:1, 000∼1:10, 000; the thermal inactivation point was between 50∼55°C for 10 minutes treatment, and the longevity of the virus was between 2∼3 days at 250°C.
2. Virus purification was attempted by procedures, similar to those adopted in the case of RPV. Electron-micrographs showed that final preparations consist mostly of small and apparently spheroidal particles 12∼13mμ in diameter, and a small varying proportion of long and short sinuous rod-like particles 12∼13mμ in width. Particles having a length of 650∼750mμ which are characteristic of RPV and other viruses belonging to the turnip mosaic virus group, could be found only in very small quantities.
3. These quasi-purified preparations of RRV showed UV absorption curves having no peak, but a plateau, in the vicinity of 260mμ. There was also no maximum absorption at 280mμ. Purified preparations of RPV, on the other hand, showed a maximum absorption at 260mμ, the absorption curve being similar to that of tobacco mosaic virus.
4. Infectivity of diseased turnip leaf juice was usually much lower in RRV than in RPV. Using the complement fixation test, concentrations of virus antigen in the juice were found to be about equal in both viruses.
5. It is considered that the spheroidal particles observed in the electron-micrographs may be a product of disintegration of longer virus particles. These spheroidal particles probably are devoid of infectivity, but retain antigenicity. In crude juice freshly obtained from diseased leaves, most of the virus antigen seems to be already in the form of spheroidal particles, because in the case of RRV, reaction of the crude juice with antiserum always produced dense particulate precipitates, instead of bulky floccular precipitates produced in the case of RPV.
6. RRV could readily be transmitted by the aphid, Myzus persicae, from diseased turnips to healthy radishes.
7. The virus retained infectivity in frozen-dried turnip juice preparations after 31 months.