On the hot bath water treatment of wheat seed for the control of loose smut, Ustilago tritici Rostrup

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.