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Title:   Author  item
                                            Edwards, Jode
  Submitted to: Crop Science
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 11/4/2010
                                    Publication  Date: 11/1/2011
                                    Citation: Edwards, J.W. 2011. Changes in plant morphology in response to recurrent selection in the Iowa Stiff Stalk synthetic maize population. Crop Science. 51(6):2352-2361.Interpretive Summary: Modern corn hybrids are developed by selection for agronomic performance but we still do not understand fully the extent to which selecting for high corn yield affects other phenotypic traits such as leaf angle and plant height in the corn plant. Breeders, seed dealers, and farmers may desire certain traits that may or may not be most desirable for high grain yield. The present study found that 70 years of selection for grain yield appears to have had the greatest impact on traits that influence light interception in the upper canopy. The traits affected included more upright flag leaf, smaller flag leaf, and smaller tassels. The importance of these phenotypes in this study illustrates the importance of the structure and health of the upper corn canopy for intercepting light and converting it to grain yield. The results illustrate that current practices in the corn industry that affect structure and health of the upper corn canopy should be evaluated in terms of their impacts on light interception and use in order to develop more informed recommendations for such practices. Furthermore, the work suggests a need to better understand dynamics of light interception in order to make decisions about planting densities and planting geometries that corn breeders should target in the future. In addition to illustrating the importance of light interception, this study also paves the way for future genetic studies to understand the genetic basis for changes that have occurred which will be critically important for utilizing maize germplasm resources and enabling future genetic gains.
                                Technical Abstract: The maize plant phenotype has changed a great deal through the era of hybrid maize production. Some of the observed changes, such as upright leaf angle, silking-anthsis interval, and tassel branch number, have well understood contributions to improved grain yield in modern hybrids. However, less is known formally about indirect selection responses for these phenotypes because they have not been studied in the context of recurrent selection programs in which detailed knowledge of selection programs is available. The objective of this study was to determine if recurrent selection for grain yield, grain moisture, root lodging, and stalk lodging in three testcross-based recurrent selection programs initiated in the Iowa Stiff Stalk Synthetic population has changed important plant phenotypes. Thirty synthetic populations representing a total of 29 cycles of recurrent selection in three programs in BSSS were evaluated in four Iowa locations in 2008 and 2009. Sixteen phenotypic and agronomic traits were measured. In all three programs consistent changes were observed for more traits that increase light penetration into the canopy including angle of the flag leaf, flag leaf size, and tassel branch number. These light-interception traits had the most consistent changes and appeared to have more consistent responses in the populations per se evaluated here than the agronomic traits actually selected in testcrosses in the recurrent selection programs. Reductions in plant stature and anthesis-silking interval were also observed, but the changes did not occur in all programs as consistently as light-interception related traits.


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