1. In the vicinity of Kyoto I have isolated two species of Pythium from water. They were identified with
Pythium aphanidermatum (EDS.) FITZP. having strong pathogenicity on various plants and with
P. monospermum FITZP. having no pathogenicity on living plants respectively.
2. Both fungi have some similar physiological characters. The optimum temperature for the growth of the mycelium of both fungi seems to lie at 34-36°C. They belong to the high temperature group in genus Pythium.
3. Using the corn meal agar, the relation of pH value of culture media to the mycelial growth of the two fungi was studied. The results show that the optimum hydrogen-ion concentration for the growth of P.
aphanidermatum was pH6.0 and for P.
monospermum was pH7.0. They grow vigorously at pH9.0 yet, but there is no growth at pH4.0.
4. When artificially inoculated,
Pythium aphanidermatum forced to show the damping-off of seedlings of
Cucumis sativus, Cucurbita pepo, Solanum lycopersicum, S. Melongena, Hibiscus Manihot, Pharbitus Nil, Vicia Faba f. ascendens etc. Pythium monospermum, however, did not show any injurious effect on the plants tested. Phaseolus vulgaris and Oryza sativa, when artificially inoculated with both fungi, did not show any significant symptoms. Cucurbita Pepo and Vicia Faba are more resistant than the other host plants tested.
8. As above-stated, the seedlings of Phaseolus vulgaris and Oryza sativa showed no definite symptoms, when inoculated with both fungi. The germinating seeds, however, were much affected by the laboratory conditions.
6. Generally high moisture content of soil increases the susceptibility of seedlings to fungal attack.
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