稲白葉枯病

1.A bacteriophage specific to Xanthomonas oryzae which causes the leafblight of rice was isolated from the diseased leaf and from the paddy soil in our laboratory last year. The biological and physiological characters of the bacteriophage has been studied. 2. Xanthomonas oxyzae isolates collected from various places in Japan were tested on their sensitiveness against the bacteriophage. Three isolates out of 25 were found not to be affected by the phage. 3. The inactivation temperature of the bacteriophage was determined by planting technique. It was found that this phage was inactivated at 53～54℃ for 10 min. in distilled water(pH5.8). This is neary equal to thermal death point of the host bacteria. The inactivation temperature was variable by the kind of solution. In Britton and Robinson’s buffer solution (pH 7), the phage was inactivated at 54℃ for 10 min., while in potato broth semi-artificial medium, the thermal inactivation point was 58℃. 4. The decrease of activity of the phage due to pH value of the solution was determined by the same technique. In the potato broth semi-artificial medium, the velocity of decrease of activity was slower than that in the buffer solution under the same pH value and the same temperature. When temperature is kept at 30℃, the decrease of activity of the phage is sooner than at 5℃. In general, the phage is comparatively stable under the condition of pH rainging from 5 to 11.