STUDIES ON OVERWINTERING, PRIMARY INFECTION AND CONTROL OF RICE BLAST FUNGUS, PIRICULARIA ORYZAE

Abstract

1. The present paper is intended to report the experiments on the mode of overwintering and the primary infection of Piricularia Oryzae, the causal fungus of the blast disease of rice plants.2. The conidia on any parts of the diseased rice plants or the mycelium within the tissue of the diseased spots must be considered as the principal overwintering organs of this fungus.3. In the present experiments, conidia on the diseased straw and seeds kept in dry condition at room temperature retain their vitality during more-than one year, but those kept on the soil, as well as in the barnyard manure, lost their vitality in the next spring.4. The mycelia in the diseased tissue which kept in dry condition alive far longer than the conidia under the same condition, and in the case of diseased node, the mycelia retain their vitality more than 1058 days, while those under the moist condition lost their vitality at the middle of April in the next year.5. The overwintered mycelia abundantly produce conidia on the surface of the substratum under the moist condition. The luxurious formation of conidia occurs in temperature from 18°C. to 30°C.6. The conidia which overwintered on the diseased straw, as well as those formed on the surface of the diseased tissue under the moist condition, are capable to infect the healthy rice plants. The conidia on the surface of apparently healthy seeds which taken from the diseased rice plants and the mycelia penetrated into the tissue of partially blasted-seeds give rise the wilting of rice seedlings when the seeds are planted in the next year. Thus they may serve as the most important source of the primary infection of this fungus.7. To control of the blast disease of rice plants, some treatment on the diseased straw and seeds must be needed. For the severely attacked straw, its burning or mixing to barn-yard manure and fodder is the best method. Moreover, hot water treatment is recommendable for the affected seeds.