稻熱病菌分生胞子の低温に對する抵抗力に就きて

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The cnidia of Piricularia Oryzae, the rice blast fungus, produced on the leaves of the rice plant by the natural as well as the artificial ingection, were kept in the refrigerator, where the temperature had been controlled at various degrees below zero constantly. After previously determined intervals some tubes containing the conidia were taken out from the refrigertor and their viability was tested. The germinability of the conidia, constantly kept at -4℃ to -6℃ under dry condition, diminished gradually according to the duration of refrigeration. However, 20% or more of the tested conidia survived even at 50th to 60th day, and 14% at 81st day. 10 to 30% of the conidia kept at-10℃ constamly under the same comdition as in the previous experiment, survived until 75th day. Comparing the results of the above two experiments, the writer noticed that the germinability of the conidia kept at-10℃ seems to be a little lower, especially iin the beginning of refrigeration, than those kept at -4゜to -6℃, The effect of those different temperatures to the conidia was, however, quite indistinguishable in the later period of the experiments. The percentage of germination and the lenght of period, in which they keep their vitality, were almost the same. From the above results, it is cleare that the power of resistance to low temperatures in the conidia of the fungus in question is remarkably strong as compared with the urediniospores of cereal rusts. In the next experiment a suspension was prepared, using the conidia produced on the artificial media, and was kept in the refrigerator controlled at -10℃. After 24 to 25 days the writer tested their vitality and found that 1 to 2 % of the conidia germinated. However, after 31 days no germinated conidia could be seen. The results of this experiment show that the power of resistance in the conidia to low temperatures is greater under dry condition than under wet condition. In the fourth experiment, the influence of temperatures on the viability of the conidia, by which their frozen suspension is thawed, was thested. After exposed to -10℃ for 24 hours, the frozen suspensions were kept for one and half hours in thrree different incubators, each controlled at 16℃, 28℃ and 40℃ respectively. According to the temperatures percentage of the germinated conidia was considerably different. Namely, the germinabillity of the conidia in the suspension thawed at -40℃ was worst, while those treated at 16℃ showed the best. Within the limits of temperatures, between 16゜ to 40℃, the higher the temperature is, at which the suspension of conidia has been thawed, the lower percentage of germination they become to show. Accodingly it is clearly recognized that the vitality of the frozen conidia of the present fungus is less injured when the suspension is thawed slowly at lower temperatures than when the suspension is thawed slowly at lower temperatures than when thawed rapidly at higher temperatures.
日本植物病理学会の論文
1935-12-25

稻熱病菌分生胞子の低温に對する抵抗力に就きて

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