Estimation, variation and importance of leaf curvature in Zea mays hybrids

Abstract

Maize leaves are curved but this curvature cannot be described by a single system of equations based on conic sections. We made comparisons of curvature between hybrids, leaf positions and planting density using measures of maximum leaf height and leaf tip:maximum leaf height ratio. With these measures a modern hybrid released in 1991 (Pioneer 3394) shows less curvature compared with hybrids released in 1963 (Pioneer 3306) and 1936 (Pioneer 307). The greater uprightness of 3394’s leaves was apparent for all leaves measured. Curvature is a plastic character. While all hybrids developed less curvature in higher density plantings the effect was greatest for 3394. 3394 had shorter, more lanceolate leaves with smaller leaf area, a lower estimated torque around the point of leaf attachment to the stem, and a significantly smaller auricle base and smaller angle between the leaf blade and auricle base. These results support suggestions that the pattern of curvature may be produced by the progression of irreversible bending during leaf development. We found no consistent relationships between differences in curvature and measurements of leaf midrib morphology or anatomy. A frequently used approach in modeling foliage area distribution by angle is to use an approximation provided by the angular distribution of an ellipsoid. We show that for leaves in this study this approach is biased and that a Richards function describes the cumulative frequency distribution of leaf area by inclination angle more effectively. The importance of an unbiased estimator is discussed in relation to the variation in photon flux density received by surfaces of different inclinations.