1) The bath water seed disinfection method, which is widely used in Japan for the control of loose smut of wheat, Ustilago tritici, is as follows: After temperature of the bath water has risen to 45° or 46°C., the oven fire is put out. Wheat seed in a package is suspended in the hot water in a container with a slightly opened lid for about ten hours until the water temperature descends down to about 25°C. 2) Present experiments were carried out to ascertain the rate of decrease of water temperature under above stated method with bath-tubs of several different structures and water depths, and the time required for seed soaking for the control of loose smut of wheat. Three kinds of bath-tubs were used, namely, a mortar-tub, directly, heated with side oven, an iron-tub directly heated from below, and the common wooden-tub directly heated with side oven. Each of them had about 300 liters capacity. Wheat seed which had been inoculated with the fungus by the partial vacuum method of Oort was used. 3) The results obtained were as follows: i) The rate of temperature decrease at a definite time was proportional to the temperature of bath water at that time. ii) In case when the quantity of water was larger the rate of temperature decrease was smaller. iii) When the initial temperature of hot water was kept between 46°C. to 50°C., and the bath-tubs were filled with water, the difference of the rate of temperature fall due to the structure of bath-tubs was not so great as to disturb the practical use of the bath water soaking method. iv) It was found that five hours' soaking was sufficient for the control of the loose smut of wheat in case the initial temperature was kept at 46°C. v) No ill-effect for the germination of wheat seed was found when the initial temperature of bath water was kept at 46°C. and the fire was put out, even if the seed was soaked for ten hours.
This paper deals with the changes in the respiration of leaf tissues infected by Piricularia oryzae. Rice varieties, Aiti-asahi (susceptible) and Kanto 53 (resistant) were used. Leaf lesions occurring on these varieties were classified into 5 types as shown diagramatically in Fig. 1. Lesions of the types 3, 4 and 5 were used for the experiments. Types 4 and represent the lesions on the susceptible var5ety and type 3 represents the lesion on the resistant variety. From each lesion, the central necrotic area is removed and a marginal zone of about 3mm width was taken as the material for measurement of the respiration rate. If the tissue is resistant, the respiration is stimulated to some extent, not exeeding over two times as that of non-infected tissue, while f the tissue is susceptible, the respiration is stimulated up to 4 to 5 times. The RQ gives usually 0.8 in the healthy, and 0.9 in the infected tissues. The diminution of Pasteur effect (shown by QairCo2/QN2Co2) is remarkeble in the susceptible tissue, but in the resistant tissue it is not affected. The respiration of resistant tissue is inhibited by 10-25 per cent by such metal enzyme inhibitors as NaN3, 8-hydroxyquinoline, and salicylaldoxime, while, that of susceptible tissue is not affected, suggesting that flavoprotein enzyme works as terminal oxidase in the infected tissue, in place of metal protein enzymes. The above mentioned change of terminal oxidase system in the infected tissue is probable because it is already known that P. oryzae produces two toxins, α-picolinic acid. and piricularin and that these are inhibitory to metal enzymes (Tamari et al.). The writers consider that the main cause of unusual stimulation of respiration and the diminution of Pasteur effect in susceptible tissue is the change of terminal oxidase, from metal protein to flavoprotein.
The faculty to produce fusaric acid in culture which is toxic to plant living cell was investigated by using the 25 strains belonging to 6 sgecies of the genus Fusarium. In F. oxysporum and F. maniliforme all the forma specialis were positive, but the other four Fusaria employed in the present experiment were negative. It might give an interesting problem in the study of pathological wilt-mechanism in pinat, that all the Fusarium belonging to oxysporum and moniliforme, have the faculty of fusaric acid production and then cause a systemic fusariose as wilting or damping off of host plant Moreover, application of investigating the faculty to produce such specific metabolite as fusaric acid in culture will be help in studying species relationship in Fusaria.