Abstract
The present paper deals with the results of experiments on the blast-controlling effect of several kinds of fungicides absorbed by roots of rice seedings, and the behavior of conidia of Piricularia oryzae in water drops on leaves of treated seedlings. The fungicides used in these experiments are follows: mercuric chloride, copper sulfate, phenylmercuric acetate (PMA), phenylmercuric dinaphthylmethane-disulfonate (PMF), n-trichloromethylthioterahydrophthalimide (Captan), 2, 3-dichloro-1, 4-naphthoquinone (Dichlone), tetramethylthiuramdisulfide (TMTD), and Blasticidin-S (Bl-S).
Before or after the inoculation of the causal fungus, the roots of rice seedlings, raised for 8 days, were dipped in the fungicide solutions, or spraying of fungicide was made on their leaves. All the fungicides used seemed to have an influence on the pathogenic fungus developed in tissues of the suscept, decreasing the incidence of the blast disease. There was no correlation between the grade of conidial germination in water drops on leaves and the grade of formation of lesions.
Okamoto and Yamamoto (1958) proposed that water drops on leaves of treated seedlings may act indirectly to inhibit the conidial germination. In the present investigation, however, conidia in water drops on leaves of treated seedlings seemed to contact directly with the fungicide exuded through epidermis. It is likely that the inhibition of conidial germination is attributable to direct action of fungicide, but not to indirect one.
