水稲収量成立原理とその応用に関する作物学的研究 : 第99報 穂相による稲作診断 : (2) 苞葉の発現と発生条件

抄録

With a view to diagnosing the rice cultivation by morphological observation of adult panicles, the authors investigated the occurrence of elongated bracts at the neck-nodes of panicles and its cause. Generally speaking, the bract can clearly be recognized at the panicle initiation stage under a microscope, but they mostly degenerate in the processes of panicle developement. In few cases, however, they elongate instead of degeneration and they can clearly be observed with the naked eye at the neck-node of adult panicles. The results of the present investigation can be summarized as follows. 1. Elongated bracts at the neck-nodes can be classified from their lengths and shapes into 5 groups as shown in Fig. 1. In the present paper, however, C, D, E are taken as elongated bracts and O, A and B are considered as degenerated bracts. 2. A number of varieties (111) have been investigated on the occurrence of elongated bracts. So far as the present investigation is concerned, no specific varieties have been found which are liable to produce the elongated bracts. 3. The conditions of fertilization such as the amount of basic fertilizers, the kind of elements (N·P·K) and the time of nitrogen topdressing have had no concern with the occurrece of the elongated bracts. 4. It has firmly been confirmed that lower irrigation water - temperatures than 20∼21°C, especially lower than 16°C, during the period centering around the first bract differentiation stage (approximately 33 days before heading) have closely been connected with the occurrence of elongated bracts, but a low air-temperature itself has no effect on the occurrence. (Since the growth points of rice plants are always under the water-surf at the first bract differentiation stage under the normal rice cultivation, if only a water-temperature is high, even if an air-temperature is considerably low, the growth points are not subjected to a low temperature and then the bracts never elongate. 5. From the study of developmental anatomy it has already been clarified in the previous paper that the elongated bract is the first bract which has firstly differentiated and abnormally developed at the neck-node. Accordingly, it is quite reasonable that the occurrence of elongated bracts is closely connected with the abnormally low water-temperature at the first bract differentiation stage, though the mechanism of the occurrence is not yet clear. Anyway, the occurrence of elongated bracts means in not a few cases that the rice plant have been subjected to a considerable low water-temperature during the period centering around the first bract differentiation stage.