Abstract
Ripening characters were compared between the japonica and the improved semi-dwart high-yielding indica varieties. The results obtained are as follows: 1. At the heading stage, there was a tendency that improved indica varieties had more spikelets per m2. Especially, the receptive capacity (sink) of dry matter per m2, which is represented by the number of spikelets per m2 × weight of a hull, was larger in improved indica than in japonica varieties. 2. Improved indica varieties had smaller LAI (source) irrespective of growth duration not only in early variety group but also in middle and late variety group. 3. Accordingly, there was a tendency that improved indica varieties had smaller leaf area per spikelet at the heading stage. In addition, their hull size was large considering leaf area per spikelet, resulting in lower ripening percentage. As a result, there was no significant difference in yield between improved indica and japonica varletles. 4. There was no correlation between grain weight and leaf area per spikelet at the heading stage, but was a high positive correlation between grain and hull weight. 5. At the heading stage, among the varieties whose nitrogen contents in leaf blade were almost same, the improved indica varieties showed lower starch and higher sugar contents in culm and leaf sheath than japonica varieties. 6. Among the japonica varieties, the very early varieties whose yields were low had smaller LAI at the heading stage considering their number of spikelets per m2.
