Effects of Temperature and Leaf Position on Leaf Area Expansion of Kiwifruit ( Actinidia deliciosa) Shoots: Development of a Modelling Framework

Abstract

This paper describes mathematically the effects of temperature and position on the expansion of leaves along a kiwifruit ( Actinidia deliciosa) shoot, taking into account shoot morphology. The leaves were grouped into three zones along the shoot: initial cluster leaves (first zone); the rest of the leaves that were preformed during the previous season (second zone); and leaves that were initiated during the current season (third zone). After opening of the initial cluster, the leaves appeared at constant rates for each of the two temperature treatments considered. The expansion of individual leaves was modelled by a growth function with the parameters: final area; duration of the growth window; centre of the growth window (timing of expansion); and lower asymptote. Within the first two zones, the pattern of leaf expansion was affected by nodal position, with basal leaves having higher initial rates of expansion than distal leaves. The timing of expansion was linear with respect to the nodal position within each of the zones, with the slope independent of temperature for the first zone. The slopes of the timing of expansion for the second and third zones depended on temperature and were correlated for each temperature treatment. Final leaf area was a function of leaf position in the first zone and a function of timing of leaf expansion for distal leaves starting from leaf 10. Temperature had no effect on final leaf area in the first zone. For the rest of the leaves, temperature affected final leaf area indirectly, through the timing of leaf expansion. The effect of temperature on the growth window of individual leaves within the first zone was less than that for the rest of the leaves. However, simulated values for the total leaf area of shoots using the average shoot growth window showed good agreement with experimental values.