Kinetics of leaf extension in maize. Parameterization for two tropically adapted cultivars planted on 2 dates at Gatton

The kinetics of extension of individual leaves and component laminae and sheaths in maize were studied in two field experiments at Gatton (Australia) using two cultivars, Pioneer 3527 and Pioneer C87, in one experiment and Pioneer C87 only in the second. Destructive sampling based on non-destructive observations to ensure accurate representation of the population was used to establish timing of leaf initiation, leaf tip appearance, ligule being able to be discerned and full extension of organs. The appearance and extension of leaves were related to thermal time, calculated from temperature measured in the region of cell division and extension. Extension of leaves and sheaths was analysed using the first three phases of a four phase framework consisting of two exponential phases, rapid (linear) extension and transition to final organ length. The last phase was not examined as there were insufficient data. Final organ length was related to leaf position, and linear extension rates of leaves and laminae were linearly related to final organ length, with differing equations for upper and lower leaves. The study has proposed extensions to an existing analytical approach, and argues that regular patterns of extension of leaves and sheaths can be explained in relation to the position of the ear using a physiological approach.