Effect of Humidification and Hardening Treatment on Seed Germination of Rice

To find out the effects of humidification and hardening of rice (Oryza sativa L. cv. Ilpumbyeo) seeds on the germination, both normal and artificially aged seeds with 60% germination rate were humidified at 40, 60, and 80% RHs and $25^{\circ}C$ for five weeks or hydrated for 6, 12, 18, and 24 hours at $25^{\circ}C$ from one to five cycles for hardening. Relative humidity and duration of humidification did not affect the germination rate of normal seeds, while reduced the time to get 50% germination rate ($T_{50}$) by 1.0～1.6 days compared to that of normal seeds at $25^{\circ}C$. Aged seeds humidified at 40 and 60% RHs did not affect the germination rate and $T_{50}$ regardless of relative humidity and duration of treatment, while at 80% RH, the germination rate decreased and $T_{50}$ increased significantly with the duration of humidification. Hardening of normal seeds reduced $T_{50}$ by 0.7～1.1 days without changes in the germination rate. However, the germination rate and $T_{50}$ of aged seeds soaked in water for 6, 12, and 18 hours were similar regardless of soaking/drying cycles, while hardening of artificially aged seeds with 1～4 cycles in 24 hours soaking increased the germination rate by 11-16% and reduced $T_{50}$ by 1.4～2.0 days.