Studies on Structure and Function on the Rice Ear : IV. Classification of ear type by number of grain on the secondary rachis-branch

[摘要] Varietal Variations in the structure of ear and the size of grain were examined on thirty-two varieties, belonging to the different ecotypes. Five types of ear were classified principally based on the differences in number of grains on the secondary rachis-branch with the nodal position of the primary rachis-branch on a rachis (Fig. 1). Ear type I: The number of grains on the secondary rachis-branch was numerous in basal position of the car and became less towards the top of car. Ear type III: The number of grains on the secondary rachis-branch was also numerous in the middle position of car. And car type V: the number of grains on the secondary rachis-branch was numerous in the upper position of ear and became less towards the basal position. Two intermediate types, i.e., ear type II and IV were set in betwen type I and III, and type III and V, respectively. Indica varieties, which had larger total number of grains per ear than others, belonged to ear type III-V. Large grain varietics, which were larger in grain size than others, belonged to ear type I-II, and japonica cultivars belongcd to ear type I-III (Table 1, Fig. 2 and 3). The primary rachis-branch was numbered acropetally. The ratio of a nodal number of the primary rachis-branch having the maximum number of grains on the secondary rachis-branch to total number of the primary rachis-branch per ear was in the range of 4.3-3.8 in type I, 3.8-2.8 in type II, 2.6-1.9 in type III, 1.9-1.6 in type IV and below 1.6 in type V (Fig. 1). In a previous paper (SASAHARA, et al., 1982), it was reported that increasing rate of car weight at the maximum increasing period was higher in indica and large grain varieties than in japonica ones. Therefore, it may be concluded that indica varieties in which the grains on the secondary rachis-branch would have recieved the effect of apical dominance due to their abundant existence in the upper position of ear, and may result in increased rate of ear dry weight. On the other hand, in large grain varieties the less grain number in the upper position of ear could be compensated by the large grain size, resulting in high increasing rate of ear dry weight similar to indica varieties.

[学科分类] 农业科学（综合）