Changes in Plant Morphology in Response to Recurrent Selection in the Iowa Stiff Stalk Synthetic Maize Population

The maize (Zea mays L.) 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-anthesis 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 traits in the context of recurrent selection programs. The objective of this study was to determine if recurrent selection for agronomic performance in Iowa Stiff Stalk Synthetic (BSSS) population has changed important plant traits. 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. The most consistent changes observed across selection programs were for traits that increase light penetration into the canopy, including flag leaf angle, flag leaf size, and tassel branch number. Light-interception traits had more consistent responses in the populations per se evaluated here than agronomic traits selected for on a testcross basis in the recurrent selection programs. Reductions in plant stature and anthesis-silking interval were also observed, but changes were not as consistent as light-interception traits. Selection responses for morphological traits in populations per se suggested these traits may have much simpler inheritance than typically assumed for grain yield.