水稻に於ける挿秧期の早晩に依る穗の形成の品種間差異 : 昭和十四年四月九日受理

抄録

In Japan late setting have hrretofore been occasionally used to the problem of crop rotation and irrigation facilities. The authors have carried on an investigation on the behavior of late setting in the diffrent varieties of rice. In the case when the duration of growth in seed-bed is the same, the period from time of the setting of rice seedlings to heading deer as a generally as transplanting becomes later. The number of days thus decreased varies. in different varieties, being less in early varieties than in intermediate or late varieties, as shown by our experiments (Fig. 1). We may consider that there are two different stages in the course of heading, namely, the period previous to the beginning of panicle differentiation, and the subsequent development of differentiating panicle towrds the heading, and these stages are affected by the influence of environmental factors respectively. In order to ascertain which stage will be seriously affected by late setting upon heading, the present experiments were carried out, and the results are summarized as follows: (1) The material used in this study consisted of 9 varieties with different growing periods under natural conditions. 30 days seedlings were transplanted in the paddy field on June 15th, 30th, and July 15th. In the cultivation of these varieties, the authors tried with utmost care to make all the cultivating conditions as nearly uniform as possible, so that quite uniform plants were sampled out from time to time for observation. As to the differentiation of panicle, a part of main stem inclusive of the growing point was fixed by Carnoy's fluid, cut in longitudinal section in 13μ thickness, and stained with Delafield's henmatoxylin. The differentiation of the first bract (Plate 1, (II) could be esily observed by determining the number of leaves on the main stem which were marked with enamel. The authors considered the stage in question as the beginning of panicle formation. (2) The stage of panicle differentiation may be divided into 12 principal phases as shown by the photomicrographs (Plate 1, (I)-(XII)). These 12 phases were used as basis for determining the grade of differentiation of panicles sampled at each date of observation (Table 1). After the growth of panicle were visible, their lengths were measured, and the results are shown in percentage in comparison to adult panicles (Table 2, Fig. 2, Plate 2). (3) The period previous to the beginning of panicle formation (=the number of days required from setting to differentiation of the first bract) was found to vary considerably according to different varieties and date of transplanting. This period was short for early varieties but long for late ones, and the later the transplanting, the shorter the period. The effect of late setting upon the number of days mentioned was less in early maturing varieties than in others (Table 3 Fig. 3). (4) The period subsequent to the beginning of panicle formation (=the number of days extending from differentiation of the first bract to heading) was seemed to be a little shorter in early varieties than in other ones. Notwithstanding the fact that the period in question was almost equal in early varieties both in early or late setting, it was observed to be somewhat shorter after late setting in intermediate and late varieties (Table 3, Fig 3). (5) As mentioned above, the effet of late transplanting upon the period (number of days) from setting to heading was found to be less intense in early varieties than in intermediate or late ones. This is chiefly due to the fact that the late transplanting exerts less intense influence on early varieties than on late ones concerning both perirods, viz. previous and subsequent to the beginning of panicle formation, and this effect exerts a decided influence in the formeer stage.