Pathum Thani 1 rice has after ripening period about 4 weeks which affect the post-harvest process during seed production that requires germination test values for the further decision. Therefore, the main objective of this study is tracking its after ripening period under the particular temperature and relative humidity (RH) during storage, including the dormancy breaking methods of the Pathum Thani 1 rice seeds. Completely randomized design was used. Treatments were divided into 5 treatments as follows, T1: storing the raw rice seed at 20% RH. T2: storing the brown rice seed at 20% RH. T3: storing the rice seed at 100% RH. T4: storing the brown rice seed at 100% RH. All of this seed was stored at 15 degree Celsius, and T5: the raw rice seed was stored at 50 degree Celsius for 5 days. All samples of rice seed were tested via germination and vigor tests under the rules of International Seed Testing Association (ISTA) at 0, 1, 3 and 7 months after storage. The results showed that storage raw rice seed in a cool-dry condition (T1) could maintain germination for 7 months. T5, taking raw rice seed at 50 degree Celsius for 5 days, was percentage germination after storing for 0, 1, 3 and 7 months as 91.75, 98.00, 97.75 and 97.00 percent, respectively, which are significantly higher than the other methods (p<0.05). T5 also provided high vigor seed after performing when compared to other methods. This is concluded by the fact that T5's seed has a higher radicle emergence speed. This showed that T5 is a reliable method to break the natural dormancy of the Pathum Thani 1 rice seed. The T5's treated seed was highest percentage germination and vigor during storage for 7 months.
