Synchronous Flowering and Fruit Set at Phloem-Isolated Nodes in Soybean
2002
Egli, D. B. | Bruening, W. P.
Much of the variation in yield of soybean [Glycine max (L.) Merr.] results from variation in seeds per unit area, but the physiological regulation of seed number is not well understood. The relationship between the timing of flower development and pod and seed number was evaluated in three greenhouse experiments with a girdled-node system. Plants (‘Elgin 87’) were grown in 3.0-L pots filled with a soil-vermiculite mixture (2:1 v/v) and the main stem below Node 7 (one-node treatment) or below Node 5 (three-node treatment) was girdled when the first flower opened at Node 7. The leaves at Nodes 5 and 6 on the three-node treatment were removed and the main stem above Node 7 was removed on all plants. All nodes in the three-node treatment flowered at the same time and the total flower production was 68% greater than on the one-node treatment. The three-node treatment produced more pods (36–94%) and more seeds (36–78%) than the one-node treatment. Girdling-induced reductions in light saturated C exchange rate (CER) during flowering and pod set were consistently greater on the one-node than on the three-node treatment. However, the three-node treatment produced more pods per unit assimilate, suggesting that the increased CER did not account for the increase in pods and seeds. The number of pods and seeds at phloem-isolated nodes responded to synchronous flowering, suggesting that the timing of flower development may play a role in determining reproductive success in soybean.
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