Significance of Intra-plant Flowering Date in Soybean Seed Production : 2. Number of flowers, podding efficiency, nodal distribution of pods and yield components among different flowering dates

Abstract

To evaluate the significance of intra-plant flowering date in yielding process of soybeans, number of flowers, podding efficiency, nodal distribution of pods on the main stem and yield components originated from different flowering dates within a plant were investigated. The experiment was conducted under the field condition with six determinate, one semi-indeterminate and two indeterminate varieties. Flowering period of each variety was classified by five days interval into three to seven groups by painting a different color to a calyx. The results obtained are summarized as follows: 1. Total number of flowers per plant was widely varied among varieties. In semi-indeterminate and indeterminate types a peak of flowering was in the middle of flowering period while in determinate types most of flowering occurred in the first ten days of flowering. Podding efficiency also varied 20 to 62% among varieties. It tended to be the earlier the flowering date, the lower the abscission level, although the podding efficiency of the earliest flowering group in indeterminate types was somewhat low (Table 1 and Fig. 1). 2. Nodal distribution profiles of pods on the main stem were different among types of growth habit and among varieties of determinate types. However, most pods in the upper and middle portion of the main stem showed a tendency to be originated from the full-flowering period (Fig. 2). 3. Seed numbers per pod of the flowering groups with high podding efficiency tended to be larger and those from the later-flowered groups were small. Seventy percent and more seeds produced per plant were originated from the first ten days of flowering in determinate types and from the fifteen days in the middle of flowering period in semi-indeterminate and indeterminate types (Table 2). 4. Seed size in the flowering period described above was also larger than the other flowering period. Coefficients of variation of individual seed size were not always related to the date of flowering group, although they differed among flowering groups (Table 3). 5. As a result, the greater parts of seed yield (70-80% in early-matured variety and 90% and more in others) originated from the first ten days of flowering in determinate types and from the fifteen days in the middle of flowering period in semi-indeterminate and indeterminate types (Fig. 3). Therefore, these periods might be called effective flowering period (EFLP) for soybean seed production.