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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.
2009 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). Variation in yield must be caused by changes in either or both of these components, but environmentally induced yield fluctuations are generally a result of changes in seed number.
It is well known that seed number is determined by the level of photosynthesis during flowering and pod set, but the exact period when seed number is sensitive to the supply of photosynthate is not well defined. We conducted field experiments in 2005 to 2008 to determine the effect of reducing photosynthesis (placing shade cloth over the crop) during flowering and pod set on seed number. We found that short periods of shade (4 to 9 days) during the peak pod production period had no effect on pod number. The soybean plant could not, however, recover from 14 days of shade at the beginning of the flowering and pod set period. These results can be explained by, first, the fact that individual soybean pods can tolerate assimilate starvation for substantial periods of time (perhaps as long as 8 days) without aborting, and, secondly, by the failure of the soybean plants to increase flower and pod production when the stress is relieved.
We now know that the relatively short period of maximum pod production (less than half of the total period) in soybean does not make the plant more susceptible to environmental stress. It is clear that the soybean plant does not need a continuous high level of canopy photosynthesis (i.e., no cloudy days or dry periods) throughout the flowering and pod set period to produce high yields. Short periods of stress will not affect pod and seed numbers and therefore will not affect yield.
Egli,D.B.(2010)SOYPOD: A model of fruit set in soybean. Agronomy Journal 102:39-47.
Egli, D.B. (2010) Soybean reproductive sink size and short-term reductions in photosynthesis during flowering and pod set. Crop Science (In press).