Leaf Orientation and Yield of Maize1

The advantage of vertically oriented leaves in crop canopies has been studied with variable results. In many maize (Zea maysL.) populations there is a wide variation of leaf orientations. Nine maize inbreds visually selected for upright, intermediate, and horizontal leaf orientation were grown in 51‐cm rows at three plant densities at Iowa State University. Each inbred was evaluated for 2 years for leaf area index, light extinction coefficient (k), dry‐matter yield, and grain yield, and 1 year for leaf orientation and leaf display. We developed a new leaf orientation parameter, leaf orientation value (LOV), to account for the ability of leaves to maintain the same orientation for their entire length. This parameter was easier to measure than k, is a good indicator of leaf orientation, and could be used as a selection index for leaf orientation. Differences in dry matter yields and grain yields across leaf orientation groups agreed with expectations based on theories involving leaf orientation and leaf area index; i.e., yield advantages for genotypes with upright leaves were observed only at high leaf area indices.