On the Relation of Atmospheric Humidity to the Infection of the Rice Plant by Ophiobolus Miyabeanus ITO et KURIBAYASHI and to the Germination of its Conidia
1937 Volume 7 Issue 2 Pages 105-124
Details
1937 Volume 7 Issue 2 Pages 105-124
1. This paper deals with the results of the writer's experiments on the relation of relative humidity to the infection of the rice plant by Ophiobolus Miyabeanus ITO et KURIBAYASHI and also to the germination of its conidia.
2. After the drops of conidial suspension of the causal fungus sprayed on rice seedlings had dried, these seedlings were kept in desiccators, in which the air had been adjusted to the desirable constant relative humidities by means of using sulphuric acid in various concentrations. Those desiccators containing the inoculated rice seedlings were placed for 18 hours in a room controlled at 25°C., and then the seedlings were removed to a green-house bench. After 5 days, the seedlings inoculated and kept in the air of 100, 97.5, 95 and 92% in relative humidities for 18 hours showed typical lesions of the disease, while the seedlings kept at 89% for the same period remained quite healthy.
3. Small drops of conidial suspension of the fungus and pure water as controls were placed on clean slide-glasses and dried naturally at room temperature. After the drops had dried completely, these slides were placed on supports in PETRI dishes, in which the air humidity had been controlled in various degrees by means of using sulphuric acid. These dishes were kept at 25°C. for 18 hours and then the germinability of the spores in the different air-humidities was tested. The conidia on the slides kept at 92% relative humidity germinated slightly, while those kept at 89% showed no signs of germination.
4. The limitation of the relative humidity in which the disease occurs is, therefore, almost the same as in the case of the conidial-germination of its causal fungus on slide-glasses. It is quite reasonable to assume that no infection of rice seedlings by the fungus takes place in relative humidities lower than 89%, since the conidia are not able to germinate under such conditions.
5. The drying of the conidial suspensions of the causal fungus caused to reduce or retard remarkably the germinability of its conidia.
6. The new conidia were formed on the tips of germ-tubes from the conidia of the causal fungus kept at 25°C. for 18 hours in the relative humidities higher than 97.5%.
