k Weon Seo

Studies on the Characters of the Improved Semi-Dwarf, High-Yieding Indica Rice Varieties : I. Characters of the ripening from the viewpoint of sink, source, and reserve carbohyrates

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.

Role of the Hull in the Ripening of Rice Plant : IX. Physiological characteristics of hulls of unclosed and wounded spikelets, and relationship between hull and kernel development

Physiological activities of hulls of unclosed and wounded spikelets were compared with those of normal one during ripening. The results are as follows : 1. In the checking at early and middle stage of ripening, fresh weight, percentage of water content and chlorophyll content were lower in hulls of unclosed and wounded spikelets than in those of normal one. And respiratory and photosynthetic activities were also lower in these. 2. Increase in dry weight of hulls and kernels was lower in these spikelets, of which physiological activity declined. 3. There was a negative correlation between degree of damage on spikelets by Typhoon and dry weights of hull and kernel. From these results, it was demonstrated that decline in physiological activity of hull of spikelet cause to decline in sink activity, i.e., pumping up carbohydrates from leaf and stem.