Temporal Patterns of Flowering and Pod Set of Determinate Soybean in Response to High Temperature

Yean-Uk Kim,Beom-Seok Seo,Doug-Hwan Choi,Byun-Woo Lee,Ho-Young Ban,Junhwan Kim

doi:10.3390/agronomy10030414

Yean-Uk Kim, Beom-Seok Seo + Show 4 more

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https://doi.org/10.3390/agronomy10030414

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Abstract

Global warming is expected to affect yield-determining factors of soybean (Glycine max (L.) Merr.), including the number of flowers and pods. However, little is known about the effects of high temperature on the temporal patterns of flowering and pod set. Experiments in the temperature-controlled greenhouses were conducted to examine the temporal pattern of flowering in determinate soybean cultivar “Sinpaldalkong” and to assess the effects of high temperature on the flower number, pod-set ratio, and pod number of the early- and late-opened-flowers and their contributions to overall pod number. The experiment comprised five sowing dates in 2013–2015 and four temperature treatments, namely ambient temperature (AT), AT + 1.5 °C, AT + 3.0 °C, and AT + 5.0 °C. Flowering duration (i.e., days between the first flowering and the last flowering) was extended by higher temperature and earlier sowing. The temporal distribution of flowering showed a bimodal distribution except for the experiment with the shortest flowering duration, i.e., second sowing in 2014. More flowers were produced in the late flowering period at high temperatures; however, most of these late-opened-flowers failed to reproduce, regardless of temperature conditions, resulting in a negligible contribution to the overall pod number. For the early-opened-flowers, the number of flowers was not significantly affected by temperature, while the pod-set ratio and pod number decreased with high temperatures resulting in a decrease in the overall pod number at temperatures above 29.4 °C.

Highlights

IntroductionAmong the two main yield components (i.e., the number of seeds and seed size) of soybean (Glycine max (L.) Merr.), the number of seeds, which primarily depends on the number of pods, accounts for most of the variation in yield [1]
Among the two main yield components of soybean (Glycine max (L.) Merr.), the number of seeds, which primarily depends on the number of pods, accounts for most of the variation in yield [1]
The daily mean temperature averaged over R1–R5 (TR1–R5 ) in the ambient temperature (AT) was 27.3 ◦ C in 2013s1, 28.3 ◦ C

Summary

Introduction

Among the two main yield components (i.e., the number of seeds and seed size) of soybean (Glycine max (L.) Merr.), the number of seeds, which primarily depends on the number of pods, accounts for most of the variation in yield [1]. The temporal pattern of soybean flowering follows a bimodal distribution in a node-level [4]. The early group of flowers is on a primary raceme, while the later flowers are mostly on sub-racemes. In a plant-level, peak blooming period for a primary raceme was 4–13th day after first flowering, while that for sub-racemes (including sub-branches) was 11–21st day after first flowering in 12 cultivars [5]. Late developing flowers have higher levels of abortion compared to the early developing flowers [6,7,8] The number of pods is determined by the number of flowers and pod-set ratio; environmental conditions during the flowering and pod set period—from the beginning of flowering (R1) to the beginning of seed filling (R5)—are closely associated with the numbers of pods and seeds [2,3].

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