Water Stress during Seed Filling and Leaf Senescence in Soybean

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Abstract
Water stress during seed filling could reduce soybean [Glycine max (L.) Merr.] yield by accelerating leaf senescence and shortening the seed filling period. Greenhouse experiments were conducted to (i) evaluate the effect of water stress during seed fill on leaf senescence and (ii) determine the potential role of redistributed C and N in moderating the effect of water stress during seed fill. Soybean plants (‘McCall’, Exp. 1; ‘Elgin 87’, Exp. 2) were grown in soil‐filled pots. At the beginning of Growth Stage R6, two levels of water stress were imposed until maturity: daily waterings of 60% (moderate stress) and 30% (severe stress) of the water required to bring well‐watered pots to field capacity. Moisture stress reduced yield by reducing seed size (8–20%) in Exp. 1 and seed number (18%) and seed size (14–32%) in Exp. 2. Moisture stress accelerated leaf senescence, as shown by more rapid declines in leaf chlorophyll and N, and shortened the seed filling period in both experiments. In Exp. 2, a 50% depodding treatment was applied at the beginning of Growth Stage R6. Depodding delayed senescence and physiological maturity. Moisture stress accelerated leaf senescence and reduced seed size on the depodded plants, but the effect was less than on the nondepodded plants. Our results demonstrate that moisture stress during seed filling reduces yield by accelerating senescence and shortening the seed filling period. Increasing the source‐sink ratio may reduce the effect of moisture stress on seed size.
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