Abstract
In the present paper, the inhibitory activities of some antibiotics and fungicides, such as Antipiriculin-A (Antimycin-A, AP), Blastmycin (BM), and phenyl mercuric acetate (PMA), against different growing stages of P. oryzae were studied. The results obtained are as follows:
(1) Inhibition to spore germination. Under an adequate condition of temperature and moisture, 20∼30per cent spores of the fungus germinated within 6 hours and 80∼90per cent germinated 24 hours after incubation. All chemicals prevented comparatively the germination in the early stage of incubation, whereas these activity became feeble 24 hours after incubation. Among the chemicals tested, PMA showed to be the most effective and the crystalline antibiotics, AP and BM, did not show so much effect, probably because of their lower solubility in water. However, one of the solubilized antibiotics (e. g. AP-emulsion) showed satisfactorily the same inhibitory effect as did PMA.
(2) Inhibition to growing mycelium. When the chemicals was added into flasks, in which mycelia of the fungus had been inoculated, a remarkable inhibition to mycelial growth was observed. However, the addition of chemicals at the stationary growth phase could not obtain the inhibitory activity except the addition of AP-emulsion. AP-emulsion not only prevented the mycelial growth, but also lysed the mycelial content.
(3) Inhibition to sporulation. Spore suspension of the fungus was inoculated in Petri dish containing agar medium and was incubated at 27°C. When the vegetative mycelia were grown, the chemicals were added by spraying them on mycelia. No chemicals showed the inhibitory effect against the sporulation of the fungus.
(4) The clinical concentration of growth inhibition. Using the agar dilution method, PMA was found to prevent the growth of the fungus at 0.05mcg/ml and AP-emulsion at 0.1mcg/ml. It is supposed, therefore, that the satisfatory effect against the rice blast fungus may be obtained by AP-emulsion spray in the field test.
