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

The plant density at which maize (Zea mays L.) hybrids achieve maximum grain yield has increased throughout the hybrid era while grain yield on a per plant basis has increased little. Changes in plant characteristics including flag leaf angle, anthesis-silking interval, plant height, tassel branch number, and total number of loaves have been characterized in comparisons of commercial hybrids representing different eras of hybrid maize production but have not been studied extensively in a temperate maize 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 per Se, was compared to four selected populations per se at four plant densities ranging from 38,300, to 95,700 plants ha1. Treatments were replicated twice in each of two locations in 2 yr and arranged in a split plot design with plant density as whole plot and breeding population as subplot treatment. Selected populations had reduced anthesis-silking interval and fewer tassel branches. Increasing plant density increased anthesis-silking interval in the base population whereas increasing plant density did not increase anthesis-silking interval in the most advanced populations. These results demonstrated that selected populations were better adapted to high plant density than the unselected base population. [ABSTRACT FROM AUTHOR]