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

A compartmental growth model was developed to describe expansion of 'Delici ous' apple fruit diameter and the effect of early-season temperatures on po tential size at harvest. The model was based on the assumption that growth may be described as a function of transfer between two conceptual compartme nts. Under this scheme, the first compartment represented all tissue contri buting to the setting of potential fruit size (determined as the integral o f its output) whereas the second compartment represented all other fruit ti ssue whose growth actualized that potential. Expansion of both compartments was assumed to have a temperature response with an optimum, whereas an agi ng process with an asymptotic temperature response controlled transfer to t he second compartment. Model parameters were estimated by fitting to data f rom controlled environment experiments in which early-season temperature co nditions were varied. Predicted fruit growth curves showed close agreement with measured diameter data. The results were consistent with a two-fold im pact 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. (C) 1999 Annals of Botany Company.