Studies on Developmental Morphology and Yield Determining Process of Soybeans : II. Developmental regularity of flower clusters and flowering habit from a viewpoint of gross morphology

Abstract

This experiment was conducted to clarify the developmental process of flower clusters produced on the leaf axils. The phytomer concept was introduced to classify both axillary racemes and a terminal raceme on each shoot of a plant. Soybean cultivar, Tachisuzunari was planted on June 25, 1979. The treatments were three levels of plant population (D1: 3, 333 plants/a, D2:1, 667 plants/a, D3:833 plants/a) and two levels of nitrogen application (N1: 0 kgN/a, N2: 0.3 kgN/a). The experimental design was 3×2factorial experiment with two replications. The results were summarized as follows: 1. Flower clusters are classified into a terminal raceme, primary racemes, secondary racemes and tertiary racemes according to developmental order on each shoot. There is a regularity of the developmental pattern of these racemes from bottom to top on the shoot. This pattern is related to the co-growing relationship which can be observed in the branching of the soybean (Fig. 1). 2. The number of terminal and primary racemes per plant is closely related to the development of branches, while the number of secondary and tertiary racemes depends upon the amount of vegetative growth (Fig. 2 and Table l). 3. First flower of primary racemes on the shoot appears at around the lowest nodes which do not produce the vegetative branch. Flowers of primary racemes appear acropetally and up to the terminal raceme. Flowering pattern of secondary racemes is the same as the primary racemes. Plant population and nitrogen application do not affect this flowering pattern in a plant (Fig. 3). 4. The number of flowers per primary raceme is not affected by plant population, while the number of flowers per secondary and tertiary racemes is affected by these treatments (Table 2). 5. There may be two critical stages in yield determining process of the soybean cultivar Tachisuzunari. One is the period during phytomer 5 to 8 visible stages, which is the transitional stage from the vegetative growth to the reproductive growth. The other is the bloom period of secondary racemes, which is the transitional stage for physiological adjustment toward the grain filling.