抄録
Meechanisnl of the effects of 2, 4-D on lodging resistance in rice plant was investigated experimentally. The material plants were grown on seven plots of which six were sprayed with 2, 4-D at six different stages of growth respectively, i. e. 33, 25, 23, 18, 14, and 5 days before the earing time, another plot being left untreated for control. The lodging resistance of the plant was investigated physically by measuring the weight of stem internodes, bending moment, breaking strength, etc. and also histologically by examining structural development of the stem. The results were as follows : 1. When the plants had been treated with 2, 4-D at earlier stages of growth, the lower internodes grew longer, but their upper ones shorter, the culm height as a whole becoming lower and the plant being more resistant against lodging than the control plants. On the contrary, in the plants sprayed at later stages, e. g. 23, 18 or 5 days before heading, the upper internodes grew longer and the whole culm length became higher than in the control plants, the lodging resistace being reduced. 2. Abnormally elongated internodes brouht about by spraying were more often observed on main stems and on the tillers of lower positions. It might therefore be conceivable that spraying promoted elongation of those internodes where the activity of meristematic tissues was especially vigorous just at the time of the treatment; and that it suppressed conversely the elongation of internodes which came to develope after the spray had previously been applied. It was concluded that the most suitable time for applying 2, 4-D spray on rice plants, so far as its effect on lodging resistance is concerned, be the period prior to the beginning of internode-elongation.
