Effect of Water Stress on Grain Filling in Rice

Water stress, by affecting the rate of grain filling, decreased yield per panicle of rice by 29–40% in the small-seeded variety IR747(L) and by 19–32% in the large-seeded variety PP6R-13-12-3. It had little effect on the duration of grain filling. High nitrogen level increased culm+sheath and leaf blade weights substantially in both varieties, but decreased starch concentrations (determined for IR747(L) only) at flowering in the culm+sheath significantly. Relatively more starch remained in the culm+sheath of the water-stressed plants at maturity. The balance sheet suggested that plants grown at a low nitrogen level were more dependent on “reserve starch” and that the percentage of reserve starch that went to the panicle was higher in the stressed plants than in the unstressed plants. High nitrogen level increased the nitrogen concentration in the culm+sheath at flowering by about 80%. At harvest, the concentration decreased substantially irrespective of nitrogen levels and varieties. Relatively more nitrogen remained in the culm+sheath of the water-stressed plants at maturity. High nitrogen level and water stress increased the percentage of nitrogen in the panicle significantly. In general, water stress affected IR747(L) relatively more than PP6R-13-12-3.