水稻秧苗耐寒性之研究 II.低溫處理前後溫度對耐寒性之影響

Abstract

Eight rice varieties were used as experimental materials to study the effects of air temperatures (30/25℃ or 20/15℃) before and after low temperature treatment (10/10℃) on the cold tolerance of rice seedlings. The duration for pre- and post-low temperature treatment was 1 and 2 weeks, respectively. Seedlings at 3.5-4 leaf age were subjected to 10℃ of low temperature treatment for 9 days. The light intensity was 270μEm^(-2)s^(-1) for 12 hrs per day in the growth chabmers. The air temperatures before and after the low temperature treatment did affect the growth rate of rice seedlings in terms of seedling height. In general, seedlings under higher temperature at pre-treatment stage showed higher growth rate and the rate was maintained throughout the low temperature treatment period. Seedlings under lower temperature at pre-treatment stage, however, tended to have higher growth rate at the post treatment stage. Results also showed that the treatment of 10℃ for 9 days was adequate to reveal the varietal differences in conductivity of cell leakage, especially for pre- 30/25℃ treatment to show a higher and wider range of conductivity. A similar result was also obtained on fresh leaf weight. Based on the data of survival rate, which were read two weeks after low temperature treatment, rice seedlings under high temperature (30/25℃) at the pre-treatment stage tended to have lower survival rate for semi-cold tolerant and cold sensitive varieties, especially with the low temperature (20/15℃) at post-treatment stage. However, rice seedlings under pre-30/25℃ and post-20/15℃ treatment showed the highest survival rate among the 4 treatments. In addition, the result from variance analysis revealed that the variety×treatment interaction reached the 1% significant level. Cold tolerant varieties such as HOW 4 and USSR No. 45 had little variation under different treatments. The semi-cold-tolerant varieties and cold sensitive varieties, however, had a relatively low survival rate if the air temperature at the pre-treatment satage was high, hut the survival rate was higher if the air temperature at the pre-treatment stage was low. Regression analysis between conductivity of cell leakge and survival rate, and fresh leaf weight and survival rate indicated that both conductivity of cell leakage and fresh leaf weight, measured at the 9th day of low temperature treatment, can be used as indicators for screening the cold tolerant rice varieties at seedling stage.