STUDIES ON INTERNODE ELONGATION IN SOYBEAN PLANTS .4. EFFECTS OF GIBBERELLIN BIOSYNTHESIS INHIBITORS ON INTERNODE ELONGATION

In order to obtain the fundamental information on chemical control of plant structure in soybean (Glycine max Merr. cv. Fukuyutaka), the effects of growth regulators on the internode elongation were examined. The chemicals used were the gibberellin biosynthesis inhibitors of AMO1618, Ancymidol, Uniconazole, Paclobutrazol and CCC. They were sprayed with different concentration solutions on the pot-grown plants at the different growth stages. When AMO1618 was sprayed at different growth stages, plant height was reduced by the application at the floral differentiation and the beginning of flowering stages, and the former was found to be more effective (Table 1, Fig. 1). Gibberellin biosynthesis inhibitor applications at floral differentiation stage inhibited the internode elongation, and Paclobutrazol and Uniconazole were most effective followed by AMO1618 and Ancymidol. However, the CCC hardly effected the vegetative growth (Table 2). When the Paclobutrazol, Uniconazole and AMO1618 were applied, the inhibition of elongation was observed on the internodes that reached at mid-phase of elongation after treatment, whereas the inhibition was found to occur on the upper internodes when Ancymidol was used (Fig. 2). On the other hand, the diameter of internodes was also reduced by the gibberellin biosynthesis inhibitor applications. These effects were observed on the internodes, which were lowered by 3 or 4 internodes from that reduced in length (Fig. 2). Though these growth regulators showed some disadvantages in plant growth, such as reduction of vegetative growth and pod elongation, it may become an useful tool to control internode elongation by the development of more useful chemicals applicable to soybean culture.