Abstract
The number of days before heading has hitherto been used to express developmental stages of rice plants, and it is known that the number of days before heading can also been used practically in case of a definite variety grown in a definite area. However, in fact, the number of days before heading is strongly affected by many factors such as varieties, time of seeding or transplanting, cultural conditions and so on. On the other hand, the number of leaves on the main culm is also affected by the factors mentioned above. Therefore, the authors have tried to clarify the relation between the leaf number index, which is possible to express the developmental stages of young panicles of rice plants, and the number of days before heading at various stages, and the following results have beed obtained. 1. The relation between the leaf number index (LNI) and the number of days before heading (DBH) is variable with varieties, time of seeding or transplanting and cultural conditions etc. For instance, the number of days before heading corresponding to a given developmental stage (a given LNI) is larger in late varieties than in early ones, in the case of an identical seeding time. Likewise, DBH is larger in early seeding time than in late one, in case of an identical variety being used. These facts suggests that the variation in the number of days before heading corresponding to a given leaf number index might be mainly governed by the number of days from seeding to heading (DSH). 2. The number of days before heading is divided by the number of days from seeding to heading and is multiplied by 100, and then its relation to the leaf number index has been examined, so that the time difference in the number of days before heading caused by various factors may be eliminated. As a result of it, relation between leaf number index and DBH/DSH ratio shows always a definite tendency irrespective of variation caused by varieties and other factors. Accordingly, the values of DBH/DSH have been proved to be effectively used for estimating each developmental stage of young panicles in rice.
