Maintenence of the Grain Growth in Rice (oryza sativa L.) Subject to Water Stress during the Early Grain Filling

The glain growth of rice was found to be highly tolerant to water stress during the poriod of rapid starch seposition, despie of a large reduction in the total dry-matter production. The objective of this study was to examine whether the water stress in the earlier stage of grain growth when the process of cell division and expansion is predominant affects the growth of endosporm as well as final agrain yield per plant. Rice plants (Oryza sativa L. cv. Nipponbare) were grows in 4-liter pots under outdoors conditions. Twenty plants were grown in each pot in which the soil was submerged till ears emerged. All tellers removed as they appeared, only the main culm being kept growing. After the ear emergence, the amount of water applied to 15 pots was reduced for 10 day period inpose the development of defictis in plants (dry treatment 1) Water application was also reduced for another 15 pots between 5 days and 14 days after ear emergence (dry treatment 2). The remaining pots continued to be waterd as before (control). Pots of bith dry treatments were well watered as control after 10 days drying poriod. At intervals during the stress and recovery cycle, the relative water content (RWC) was monitored on the flag leaves between 1300 and 1500 h. During the period between 9 days and 13 days after ear emergence, the measurements of diffusion resistance 9 were taken late in the morning on the flag leaves. The number of spikelets at flowering was noted every day for eavh ear. Plants were harvested at both the being and the end of treatments and at maturity to determani the dry weights of grain, leaf and others. Leaf areas were also determined on these occasions. At the end of dry treatment, the grains which had formed the aleuron, and their dry weight and volume were measured individually.