On the Influence of Sunlight upon the Incubation Period and the Development of the Blast Disease and the Helminthosporium Disease of the Rice Plant

Abstract

1. The writer has made an investigation on the influence of sunlight upon the incubation period and the development of the blast disease as well as the Hclminthosporium disease of the rice plant.2. In the experiments, four groups of the potted rice plants were used. The plants in the first group were exposed to the sunlight both before and after the time of inoculation. In the second group, they were exposed only before the inoculation and shaded with a single sheet of black cotton cloth after they had been taken out from the inoculation chamber until the disease developed. In the third group, they were shaded several days before the inoculation and exposed thereafter to the sunlight. The plants in the fourth group were shaded throughout the experiment.3. The results of the experiments on the blast disease showed that the mean incubation period shortened and the disease increased more or less on the plants shaded before the time of inoculation, without relating to the light condition after inoculation. From the results of the above experiments it seems to be probable that shading in some degrees before inoculation affects the causal fungus advantageously.4. The mean incubation period shortened more or less on the plants shaded after the time of inoculation without relating to the light condition before inoculation. However, the disease decreased on the plants shaded before the inoculation. These results may indicate that the excessive shading affects the causal fungus disadvantageously.5. From the results of experiments, the writer recognized the Helminthosporium disease of the rice plant to show almost identical tendencies with those given by the blast disease.