Selection and Adaptation to High Plant Density in the Iowa Stiff Stalk Synthetic Maize (Zea mays L.) Population

The plant density at which maize (Zea mays L.) hybrids achieve maximum grain yield has increased throughout the hybrid era, whereas grain yield on a per plant basis has increased little. Changes in grain yield, grain moisture, test weight, and stalk and root lodging have been well characterized in comparisons of commercial hybrids representing different eras of hybrid maize production but have yet to be examined in a recurrent selection program. The objective of this experiment was to determine if direct selection for grain yield and agronomic performance in the Iowa Stiff Stalk Synthetic (BSSS) population has indirectly improved adaptation to high plant density. Material from an unselected base population, BSSS, was compared to the most advanced cycles of selection from three different recurrent selection programs at seven Iowa locations in 2008 and 2009. Populations were compared at densities of 38,300, 57,400, 77,500, and 95,700 plants ha(-1). Treatments were replicated twice at each location and arranged in a split plot design. Selection produced notable improvement in adaptation to high plant density for grain yield and stalk lodging. Selection did not have large impacts on density response for root lodging, test weight, or grain moisture. Because of the improvement in density response for grain yield and stalk lodging without major negative changes in other traits, our data suggest that selection has improved adaptation to high plant density in these populations.