Research Accomplishment Reports 2007

Regulation of Reproductive Sink Size in Soybean (Glycine max L. Merrill)

D.B. Egli
Department of Plant and Soil Sciences

 

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 a field experiment in 2007 to define this critical period in the yield production process. Shade cloth was removed from or placed over soybean communities at various times to increase or decrease the supply of photosynthate to the developing pods. Preliminary results after one year suggest that pod and seed number was sensitive to assimilate supply until early seed filling (the beginning of growth stage R6.0); shade applied after that time did not reduce seed number. Plants could not recover from shade stress after approximately growth stage R3.0 (early in the flowering and pod set period) since shade removal after this growth stage resulted in lower seed numbers.

These results suggest that the critical period for the determination of seed number begins at approximately growth stage R3.0 and ends at the beginning of growth stage R6.0. Additional experiments will be conducted to determine if this definition of the critical period is affected by environmental conditions (i.e., is consistent across years).

Impact

It is difficult to evaluate the impact of this work after only one experiment, but our goal is to greatly improve our understanding of the processes by which the soybean plant determines how many seeds it will produce. Since seed number is a critical yield component, a better understanding of its regulation will be helpful to plant breeders, agronomists, and crop modelers and hopefully will lead to greater production efficiencies and higher yields for soybean producers.

Publications

Egli, D.B., and Bruening, W.P. (2007). Accumulation of N and dry matter by soybean seeds with genetic differences in protein concentration. Crop Science. 47: 359-366.

Egli, D.B., and Bruening, W.P. (2007). Nitrogen accumulation and redistribution in soybean genotypes with variation in seed protein concentration. Plant Soil 301: 165-172.

Hyatt, J., Wendroth, O., Egli, D.B., and TeKrony, D.M. (2007). Soil compaction and soybean seedling emergence. Crop Science. 47: 2495-2503.

Egli, D.B., and Lee, Chad. (2007). Record yields - What have we learned? Corn and Soybean Science Newsletter. 7 (1): 2-4.

Egli, D.B. (2007). Will the dry May affect yield in 2007? Corn and Soybean Newsletter. 7(6):1-3.