Abstract
The effects of low temperature at the seedling stage on the growth of some indica and japonica varieties were examined. Five varieties, three indica and two japonica, were used. Seedlings were kept at normal temperature (20°C) until the third leaf blade was fully emerged. Then they were exposed to 8, 10, 12 or 14°C for 3, 6, 9 or 12 days. The increase on leaf area, top dry weight and number of roots during the treatment period was suppressed with the decrease of temperature and the increase of treatment period, in both indica and japonica varieties. The content of chlorophyll also decreased with the decrease of temperature and the increase of treatment period, and this tendency was remarkable in indica. After transplanted to the paddy field, the top dry weight, leaf age, the number of stem and the number of roots increased. The leaf age increased more rapidly, the severer the low-temperature treatment, and finally recovered to the control level in both indica and japonica varieties. On the other hand, the top dry weight, the number of roots and the number of stem increased more slowly, the severer the low-temperature treatment, and this tendency was remarkable in indica. The number of productive culms also showed a similer response to a low-temperature treatment. It was considered that the difference in the recovery of growing after transplanting to the paddy field between indica and japonica varieties was caused by the difference in the recovery of the root activity and photosynthetic activity after the low-temperature treatment.
