A compartment model of the effect of early-season temperatures on potential size and growth of 'Delicious' apple fruits

Abstract

A compartmental growth model was developed to describe expansion of 'Delicious' apple fruit diameter and the effect of early-season temperatures on potential size at harvest. The model was based on the assumption that growth may be described as a function of transfer between two conceptual compartments. Under this scheme, the first compartment represented all tissue contributing to the setting of potential fruit size (determined as the integral of its output) whereas the second compartment represented all other fruit tissue whose growth actualized that potential. Expansion of both compartments was assumed to have a temperature response with an optimum, whereas an aging process with an asymptotic temperature response controlled transfer to the second compartment. Model parameters were estimated by fitting to data from controlled environment experiments in which early-season temperature conditions were varied. Predicted fruit growth curves showed close agreement with measured diameter data. The results were consistent with a two-fold impact of early-season temperatures on apple fruit size: an immediate, direct effect on growth rate and an enduring effect, mediated through fruit cell number or resource allocation to young fruit, reflecting the establishment of a potential that subsequent growth actualizes.