Soybean seed weight responds to increases in assimilate supply during late seed-fill phase

The understanding of source-sink dynamics during reproductive stages is essential to increase crop productivity and to describe yield component determination in eco-physiological models. Previous studies in soybean (Glycine max [L.] Merr.) evaluated the effect of changes in assimilate supply from the beginning of rapid seed growth but not at different times during the seed-filling phase or at the single-pod level. Two source-sink manipulation experiments were conducted in the greenhouse to quantify the effect of assimilate supply during the seed-filling phase on final seed weight of soybean. One pod on each node containing 3 mm seeds was marked in all plants, and pods not marked were removed at weekly intervals to avoid sink competition for assimilates. Removing pod competition on the day of marking and up to 21 days later increased final seed weight in marked pods by 25% relative to the control and by 18% when pod competition was removed 28 days after marking. Pods acquired mature color 33-35 days after marking. At 21 and 28 days after marking of individual pods, seeds had achieved 73% and 97% of their final seed weight and had 67 and 62% moisture, respectively. Our study provides new evidence that the final seed weight can still respond to increases in assimilate supply applied by the end of the seed-filling phase. These results highlight the potential to increase soybean yield through management practices and breeding efforts that extend the duration of a photosynthetically active canopy and increase assimilate supply to developing seeds during late seed-fill.