抄録
In this report, breaking resistance, structures and cell wall components of lower internodes were studied in rice plants, var. Koshihikari, grown in several different environments, which implied the effects of natural lodging, heavy manuring, shading or tiller cut as described in Table 1. In the experimental plots of the natural lodging, the heavy manuring and the shading, most of the plants lodged with the breaking of spindly grown lower internodes (Table 1). The plants in the lodging plots had longer culm or longer lower internodes, smaller breaking strength, less developed EF (epidermis-cortical fiber compound) and less quantity of dry weight, lignin and ash contents per unit length of lower internodes than the plants in the unlodging control plots (Tables 1-4, Figs. 1 and 2). The plants in the heavy manuring plot had thick lower internodes in diameter as the result of favourable growth untill the tillering stage, but their value of d2t, (diameter of of internode)2 × (thickness of EF), was smaller than that in the control plot because of over-luxuriant growth in the time of internodal elongation and poor development of EF (Table 2). The lower internodes of the plants in the tiller cut plot, on the other hand, had sufficiently all the characteristics to increase the breaking resistance, namely, thick EF, thick cell wall, large diameter and large value of d2t, short length of epidermal cells and fundamental parenchyma cells, long fiber cells, and large amounts of dry matter, lignin and ash per unit length (Tables 1-4, Figs. 1 and 2). In order to develop the lower internodes with the structural characteristics indispensable to powerfull breaking resistance as shown in the plants of the tiller cut plot, it is necessary to realize the following items, (1) inhibiting the lower internodes from spindly growing by full exposure to sunlight, (2) increasing the photosynthetic ability of each tiller, and (3) increasing the amount of dry matter per unit length of lower internodes.
