Significance of Intra-plant Flowering Date in Soybean Seed Production : 1. Pod and seed development among different flowering dates

Abstract

Flowering of soybean plants continues for a cosiderably long period. This experiment was conducted to make clear the significance of intra-plant flowering date in yielding process of soybeans. Characteristics of pod and seed development were investigated under the field condition with nine varieties differing in growth habit, maturity and seed size (Table 1). Flowers were distinguished by five days interval by painting a different color to a calyx. The results obtained are summarized as follows: 1. Flowering period was classified into 3 (I-III) or 4 (I-IV) groups in six determinate types, 6 (I-VI) in one semi-indeterminate and 6 or 7 (I-VII) in two indeterminate types. All flowers of the last flowering group were aborted except three determinate varieties with 3 flowering groups (Fig. 1). 2. Pod length and pod width attained their maximum values within 20 to 30 days after flowering irrespective of variety and flowering group. There were little effects of flowering date on pod width at maturity. Although thickness of pod, and length, width and thickness of seed increased until near maturity, differences in sizes of seed among flowering groups became very small during dehydration process (Fig. 2). 3. During seed filling period and at maturity, sizes of pod and seed from the last flowering group (III) tended to be small compared with those from the earlier ones (I, II) in determinate types, whereas those from the earliest (I or I, II) and the last (V or VI) flowering group tended to be small in semi-indeterminate and indeterminate types (Fig. 2). These tendencies were more clearly shown in dry weight of pod and seed (Fig. 3). 4. Sigmoid curves were obtained for seed dry matter changes of each flowering group. The slope and duration of linear phase differed among varieties and flowering groups. Rate of dry matter accumulation (RDA) of seed in a large-seeded variety was of lineal phase differed among varieties and flowering groups. Rate of dry matter generally higher than that in a small-seeded variety. In determinate types, seed from the last flowering group had low RDA or short effective filling period (EFP), whereas in semi-indeterminate or indeterminate types, the earliest-flowered seed had low RDA and the last had short EFP (Table 2).