Abstract
The effects of stepwise raising of the water level on tiller growth in rice plants were examined. When the plant age in leaf number of the main stem was 7.5, the plants were submerged to a level of the 7th leaf collar. Thereafter, as the plant's age advanced, the water level was raised to the level of the uppermost leaf collar. The length or the second tiller(T2), T3, T4, T7 in a deepwater plot was higher than in the control plot from the 6th or 18th day after the start of deepwater treatment. The response of tiller length to the treatment was similar to the main stem. Changes in age counted by the leaf numbers of T2, T3, T4 were simllar to the main stem, but the changes of T7 were not. The differences in relative tiller age between tillers(T2, T3, T4) and the main stem in the deepwater plot were smaller than in the control plot. The younger the tiller age at the start of treatment, the larger the difference in relative tiller age between the deepwater plot and the control plot. The starts of panicle differentiation in primary tillers were delayed by the treatment. In the treated plants, the starts in the primary tillers were more delayed than in the main stem. Therefore the effects of the deepwater treatment on tiller growth varied with the tiller growing stage at the beginning of treatment.
