Abstract
We carried out two types of experiments to clarify the emergence of tillers of rice plants under deep water conditions. One (Exp. 1) was to keep the water level constant during the treatment, and the other (Exp. 2) was to raise the water depth in some grades. In Exp. 1, when the water level was deep enough to submerge the leaf sheath of the fully expanded leaf of main stem at about 5.0 plant age in leaf number, the emergence of 3 rd node tiller (T 3), which was growing inside the completely submerged leaf sheath, was inhibited. Though the emergence of T 3 was inhibited, the emergence of T 4 and T 5, which were growing inside the completely submerged leaf sheath at the start of treatment, was not inhibited. There was not always a relation between the inhibition of tiller emergence and the complete submergence of the leaf sheath. In Exp. 2, the emergence of T 4, T 5 and T 6 node tiller was inhibited when the water level was deep enough to submerge the leaf sheath of the fully expanded leaf of the main stem from the platn age of about 5.2 to 10.5 in succession. From the relation between the plant age at the time of the deep water treatment and the growth response of the tiller, we concluded that the growth response of the tiller under deep water varied with the growth stage of the tiller bud ; the most sensitive growth stage of the tiller bud to the deep water was just before emergence of the tiller which had four differentiated leaves. However, at the early growth stage just as the tiller bud differentiated 2-3 leaves and at the late growth stage just as the tiller began to emerge from the leaf sheath, the tiller growth was scarcely inhibited.
