Abstract
The effect of Piricularin (a toxic substance of Piricularia Oryzae Cav.) on the resistant activity of rice plants to the blast disease has been studied by the sheath inoculation method and the following results have been obtained.
1, The treatment of rice plants with a highly diluted Piricularin solution (1∼2μg/ml) gives rise an increase of resistant activity of the plants to the blast disease, being accompanied with the following phenomena.
The callus formation of the host's cell against the penetration hyphae is activated, and checks the invasion, and even when the invasion took place, the invaded hyphae can scarcely grow in the host's cell. The infected cell loses the ability of plasmolysis at the initial stage of infection, as usually observed on the cell of the rice plant variety which is non-susceptible to the blast disease.
2. When the plants were killed dy steam heating for 30 minutes, no difference has been observed, in the resistant ability against the growth of invasion hyphae between the plants pre-treated with highly diluted Piricularin solution and control. Considering the fact that Piricularin is very stable against the heating, these observations lead to the conclusion that the rise of the resistant ability of such a pre-treated plant must be attributable to the activated function of the host cell and not to the antifungal activity of Piricularin itself which has an inhibitory effect to the germination of the blast fungus conidia even in a more highly dilute solution as 0.5μg/ml.
This conclusion has been further supported by the observation that the treatment of the plants with a Piricularin solution of relatively high concentration (10μg/ml) causes a decrease of resistnat activity of the host's cell against the growth of invasion hyphae, being accompanied with the impediment of the cell-function.
