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Regulation of Reproductive Sink Size in Soybean (Glycine max L. Merrill)
Department of Plant and Soil Sciences
Pod and seed number is the yield componet that explains most of the environmental variation in yield in grain crops. Thus, the determination of pod and seed number is an extremely important part of the yield production process, but it is not yet well understood. This project will contribute to a better understanding of the yield production process and may increase our ability to produce higher yielding varieties.
2011 Project Description
Increasing the yield of grain crops in the future will depend on our ability to manipulate basic plant processes that determine yield and any such manipulation will require a thorough understanding of the processes involved.
Yield of all grain crops, including soybean, can be defined by its two components, the number of seeds per unit area and the average weight per seed (seed size). Environmentally induced yield fluctuations are generally a result of changes in seed number. Roughly 50% of the flowers on a soybean plant do not survive to produce mature pods containing developed seed, suggesting that the number of flowers never limits pod and seed number. Since the number of flowers on a soybean plant is partially determined by the number of nodes, the excess flower production implies that seed number and yield may not be closely related to the number of nodes.
Some agronomists, however, feel that early plantings to increase nodes per plant are a key to high yields. We tested this hypothesis by varying the number of nodes per plant (using cultivars with a range in maturity) and per unit area (several plant populations) in a field experiment in 2009,2010, and 2011. The results from 2011 are yet available, but, in 2009 and 2010, the treatments created substantial variation in nodes m-2 (~600 to 1500, but there was no relationship between the number of nodes and seeds m-2 or yield.
Our tentative results are consistent with the belief that pod and seed number in soybean is determined by canopy photosynthesis during flowering and pod set, and the number of nodes and flowers are not important. Once we complete the analysis of the data from 2011, we will make our final conclusions. Our tentative results suggest that management practices to increase the number of nodes will not lead to higher yield.