Abstract
Water stress is the main abiotic factor that limits soybean grain yield. We investigated eight soybean cultivars under well-watered (WW) and terminal drought stress (TDS) conditions to determine the traits associated with water saving and the relationship between water use, root morphology, canopy architecture, flower and tagged-pod number, and yield performance. Under WW conditions, the average grain yield across the new soybean cultivars was significantly higher (18.7 g plant−1 vs. 15.1 g plant−1), but significantly less water was used (36 L plant−1 vs. 47 L plant−1) than in the old soybean cultivars. Under TDS, the four old soybean cultivars failed to produce a measurable grain yield, while the new soybean cultivars Zhonghuang 30 (ZH) and Jindou 19 (J19) produced a measurable grain yield. Water stress significantly reduced the flower numbers and tagged-pod numbers; the four new soybean cultivars on average had low flower and tagged-pod numbers under WW treatment, while they had low flower but high tagged-pod numbers under TDS conditions. ZH and JD exhibited a lower branch number and leaf area under both WW and TDS conditions. Water use during the flowering and podding periods was significantly positively correlated with the flower number and the tagged-pod number under both WW and TDS conditions. Thus, the small canopy size and low root length and root surface area contributed to a water-saving mechanism in the new soybean cultivars and improved the yield under drought conditions.
Highlights
Soybean (Glycine max (L.) Merr.) yield and yield stability are constrained by drought [1]
(30.1 vs. 26.9 g plant−1 ), the average hundred-grain weight (14.9 vs. 7.9 g), and the average water use efficiency for grain yield (WUEG, 0.54 vs. 0.31) were significantly higher than the old soybean cultivars under the WW condition (Table 3)
Less water had a lower root length density www.mdpi.com/journal/agronomy and root surface area at the same soil depth but a higher grain yield than the soybean cultivars with higher water use, indicating that root morphology had evolved in the water-saving mechanism
Summary
Soybean (Glycine max (L.) Merr.) yield and yield stability are constrained by drought [1]. These yields could be further threatened by drought, as drought events are predicted to increase in the future [2]. Tremendous efforts in soybean breeding have been conducted to improve drought tolerance, with the primary goal of enhancing yield under drought. Soybean yield has been increased significantly by traditional breeding efforts, the underlying mechanisms are unclear. Previous studies showed the pattern of water extraction/use is crucial for crops growing under limited water resources [3,4]. Water shortages during flowering and/or podding stages could reduce the flower and pod number and increase pod and flower abortion, with a large impact on seed yield [5,6]
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