An investigation was made to determine the conditions for transmission of the mosaic virus of Japanese radish by its vector, Myzus persicae SULZ. Single non-viruliferous aphids acquired the virus in a time of 5 minutes feeding on the mosaic plants, and viruliferous aphids caused infection of healthy plants by feeding for 5 minutes. The aphids were able to acquire and transmit mosaic virus within as short a period as 30 minuts. Therefore, it seems improbable that the virus can have incubation period in its vector. The aphids retained the ability to transmit the virus for 3 hours when held in vitro after removal from diseased plants, but lost after 5 hours. This period is in accord with the length of time the virus is destroyed by drying. Viruliferous aphids ceased to be infective within 30 minutes feeding on healthy plants or within 1 hour feeing on immune plant (tobacco). When the aphids were previously starved for 1 hour, fed for 5 minutes on the source of virus and then transfered immediately to the healthy plants, the efficiency of vector was much increased. Inoculations with the extract of macerated aphids collected from mosaic plants failed to cause infection. No evidence of any direct transmission of the virus from viruliferous parent aphids to their progeny was obtained. The evidence mentioned above indicates that the mosaic virus of Japanese radish in question falls under the so-called non-persistent virus.
(1) In Tokyo omitopsis olivac a IMAZEKI et AOSHIMA, nov. comb. was found to be fruiting at the beginning of July once a year. (2) The basidiospore has not any swellings in the germinating process, but has a germination tube in one side. (3) They germinate at the temperature from 13°C to 40°C. The optimum temperature for the germination is about 33°C. (4) The possibility of overwintering of the basidiospores is very little. (5) The direct sunlight in June in Tokyo is very harmfull for the germination of basidiospores. (6) The high temperature at the time of exposure in direct sunlight does not influence directly on the germination of basidiospores.
Germination of the conidia of the rice blast fungus, Piricularia Oryzae, in the water drops on the leaves of rice plants, treated with Cephalothecin, an antibiotic substance obtained from culture filtrate of Cephalothecium sp., was inhibited in proportion to the concentration of the solution. The treatment with Cephalothecin solution was made either by soaking the rice seeds for 3 days or by immersing the roots of rice seedlings for 12 hours. A tendency of reduction in percentage of appressorium formation was also recognized. As a result of inoculation, the number of infections on the leaves of rice seedlings previously treated with Cephalothecin was significantly less than on non-treated. The retardation in germination of conidia and appressorium formation prior to the penetration may be of primary significance for the lowering of infections. The fact that the actual number of the lesions was less than the calculated number of penetrated conidia per 1cm length of leaf, suggests that the treatment may also influence the development of the fungus within the host plant after penetration. The macerated powder of dried mycelium of Cephalothecium showed the similar effect upon the germination of conidia in the water drop on the rice plants.
The snow-blight diseases of winter cereals caus ed by three or four fungi (Typhula, Fusarium, Pythium and Sclerotinia) are widely distributed in Hokkaido, the Tohoku and Hokuriku districts in Japan. The present paper deals with the pathological changes in leaf-sheath cells of wheats in the course of snow-cover. Osmotic pressure of the epidermal cells in leaf-sheath under snow was periodically estimated by plasmolytic method, and the cell permeability (both to water and urea) was also estimated by the end-plasmolytic method (SCARTH, 1939). Osmotic value was always higher in the hardy varieties than in the less hardy, but its seasonal changes under snow were not recognized. Both water and urea permeability were tend to decrease gradually under snow and they increased after snow-melt. As to the cell permeability and wheat varities having different snow-resistance, the authors could not find any correlation between them. The authors consider the decreased permeability to be a factor of physiological weakness of wheat under snow. At present the experiments are in progress on the changes of protoplasmic viscosity under snow in relation to the infection of snow-blight fungi.