| Budget Amount *help |
¥3,400,000 (Direct Cost: ¥3,400,000)
Fiscal Year 1998: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1997: ¥2,700,000 (Direct Cost: ¥2,700,000)
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| Research Abstract |
Rice yields are primarily water=limited under upland and rainfed lowland conditions. A rice cultivar "Suweon", which is a high yielding Japonicax lndicahybrid lowland cultivar, showed high yield under upland conditions even in a year which had a dry growing period. This cultivar had a higher leaf photosynthetic rate and a higher dry matter production rate than upland cultivars in Japan under the same soil drying conditions. The leaf water potential decreased similarly among cultivars tested. Thus "Suweon" had a high drought tolerant ability. This cultivar could continue photosynthesis under the mild water stress conditions with relatively small decrease in the stomatal conductance, and had a tendency to possess higher sugar concentration during the day time. This high sugar concentration decreased leaf osmotic potential and maintain high turgar under the low leaf water potential during soil drying. In order to examine the relation of a root activity and leaf physiology under the water stress conditions, the bleeding rates which reflect a root activity were compared. The bleeding rates decreased with decreasing soil water content and the decreasing tendency was almost the same among the cultivars tested. In addition, the cytokinins in the bleeding sap, zeatine riboside and dihydrozeatineriboside concentration were not different significantly among cultivars. Conjugated cytokinins, a large cytokinin fruction of rice plant should be determined further. Under the upland field conditions, some cultivars which had a high dry matter production after healing, had a tendency of higher bleeding rate and slower leaf senescence. In these cultivars, the numbers of seminal roots increased after healing. Wheatear the formation of new seminal roots is important for maintaining a high activity of the whole root system will be one of the future research challenges to improve drought resistance and high yielding of upland rice production.
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