Establishment of a Pre-Drying Methods for Hot Water Disinfection of Rice Seeds at a High Temperature

: The tolerance to high temperature during the treatment for disinfection in rice seeds is strengthened by reducing their water contents to below 10% before the hot water disinfection treatment. Pre-drying treatment prevents the reduction in germinability of the seeds disinfected with hot water at 65ºC for 10 minutes, which is a method used to effectively control several seed-borne diseases. We examined the conditions for pre-drying of seeds using a heating dryer for improving the germinability after the disinfection treatment. The seeds of Nipponbare were dried at 40 – 60ºC for 2 – 72 hours. A higher temperature was more effective for drying. When the seeds were dried at 40ºC, 12 hours of treatment was required to reduce the water content to below 10%. Thereafter, the water content rapidly decreased to around 8% by further heating, but the speed of decrease dropped and the values remained above 7% in the seeds dried for 24 hours at 50ºC. The germinability was not changed by further decrease in water content to less than 7%. In some cases, the seeds dried at 60ºC for 72 hours had lower germinability. Moreover, experimental results using Koshihikari showed that the seeds with a water content reduced to below 9.5% by pre-drying had a germination rate of more than 90%, even after the seeds were disinfected with hot water at 72ºC for 10 min. Taken together, we concluded that pre-drying to a water content of 7 – 9.5% in seeds at 40 – 50ºC for 12 – 24 hours is the most useful method for pre-drying the seeds of Nipponbare and Koshihikari before the hot-water disinfection treatment.