| Since the 1950's, the average maize grain yield, on a per unit area basis, has risen exponentially and without a pause. Associated with this increase have been changes in shoot morphology which permit more light penetration into the canopy. Changes in plant traits including plant height, leaf number, individual leaf area, vertical leaf angle, tassel size and weight, and leaf area density distribution along the main stem have been reported in the literature; however, the response of canopy components to changes in plant density has not been examined in closed populations and at today's densities. The objective of this study was to: (i) analyze canopy traits (leaf angle / leaf area) to determine how canopy architecture has changed; (ii) determine if canopy architecture interacted with density either directly or indirectly. Materials from unselected base populations, Iowa Stiff Stalk Synthetic (BSSS) and Iowa Corn Borer Synthetic no.1, were compared to the most advanced cycles of selection at four locations near Ames, Carroll, Crawfordsville, and Keystone, IA, in 2011.;Populations were compared at six densities ranging from 3.0 to 9.5 plants m-1. Each breeding population by density combination was replicated once at each location and arranged in a split plot design. Increased densities resulted in reduced numbers of total nodes, lower ear height, shorter plant stature, smaller tassels, more upright leaf angles with smaller leaf areas at the top sector of the canopy and more horizontal leaf angles with larger leaf areas lower in the canopy. More importantly, the shape of the canopy was affected by plant height, ear height, node of attachment of the ear, and density. |
