1. The present paper deals with the morphology and pathogenicity of Sclerotium Oryzae-sativae SAWADA collected from Southern China. 2. The size of sclerotia of the fungus produced on potato decoction agar was somewhat diverse according to the localities. It was 266.60-1666.25×266.60-1199.70μ (Mean 741.981±12.674μ in length, 585.354±8.295μ in width) for the “Amoy” (_??__??_) culture strain, 333.25-1732.90×266.60-1466.30μ (Mean 784.137±13.060μ in length, 572.520±8.635μ in width) for the “Tankuei-t'sun” (_??__??__??_) culture strain, and 266.60-1466.30×266.60-1333.30μ (Mean 731.317±14.193μ in length, 547.696±9.327μ in widtn) for the “Fui Sha Wai” (_??__??__??_) culture strain. 3. The size of constituent cells of the sclerotia was 11.10-28.86×11.10-26.64μ (Mean 20.468±0;357μ in length, 17.716±0.341μ in width) for the “Amoy” (_??__??_) culture strain, 11.10-24.42×11.10-22.20μ (Mean 18.559±0.366μ in length, 16.583±0.357 in width) for the “Tan-kuei-T'sun” (_??__??__??_) culture strain and 13.32-28.86×11.10-28.86μ (Mean 20.091±0.366μ in length, 17.227±0.333 in width) for the “Fui Sha Wai” (_??__??__??_) culture strain. 4. The pathogenicity of the fungus to the leaf sheath of rice plant (Miisinriki variety) differed according to the culture strains. Among these culture strains tested, the “Fui Sha Wei” (_??__??__??_) culture strain was the strongest and the “Amoy” (_??__??_) and the “Tan-kuei-t'sun” (_??__??__??_) culture strains were second to it. In comparison to the “Amoy” culture strain, the “Tan-kuei-t'sun” culture strain was somewhat weaker in the pathogenicity.
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.
The writer observed the relation of root pests to black rot of sweet potato root-tubers in the field. The results are summarized as follows:- 1. Black rot fungus invades the root-tuber mostly from the eaten cavity caused by various root pests: for example, Cylas formicarius, Colasposoma oberthuri etc., which are the common pests of sweet potato in Okinawa-honto. Consequently, the extermination of these pests in the field is a method of protection from black rot on sweet potato root-tuber. 2. The longer the time elapsed after the formation of eaten cavity, the more difficult is the infection by the pathogene.