Effects of stepwise raising of the water level on increasing tiller number in rice plants (Oryza sativa L.)

Effects of stepwise raising of the water level on tiller emergence in rice were examined. When the plant age counted by leaf number on the main stem was 7.5, the plants were submerged to the level of the lamina joint of the 7th leaf. Thereafter, with the advancement of plant age, the water level was raised to the level of the lamina joint of the uppermost leaf. Tiller emergence was restrained during the first 13 days after the start of the deep-water treatment. Thus, the increase in tiller number per plant and the increase rate of tiller number were smaller in the deep-water plot than in the control plot during this period. However, the percentage of tillers that appeared between the 13th and 18th day after the start of the treatment was the same in both plots. This was because the increase rate of tiller number in the deep-water plot was higher than in the control plot during this period. We assume that the plants had adapted physiologically and morphologically to deep-water during this period. In the deep-water plot, tillers did not emerge from the nodes where the tillering had been restrained before the 13th day, but emerged from the upper nodes. Thus, it is clear that once the tillers failed to emerge in deep-water they could not emerge again even if the conditions for the emergence were improved thereafter.