A BIOPHYSICAL MODEL OF FRUIT-GROWTH - SIMULATION OF SEASONAL AND DIURNAL DYNAMICS OF MASS

A model of fruit growth was developed, based on a biophysical represen tation of water and dry material transport, which is coupled with cell wall extension stimulated by turgor pressure. The fluxes of materials connect the growing fruit with the parent plant (by phloem and xylem transport) and with the ambient atmosphere (by respiration and transpi ration). The sugars are transported from the phloem to the fruit mesoc arp by mass flow, passive diffusion and an active (and/or facilitated) mechanism, The stages after cell division has ceased and when fruit g rowth is due mainly to cell enlargement were modelled. This enabled us to consider the fruit as a cell community with a constant number of c ells and to apply directly the equation describing the effect of hydro static pressure on the irreversible cell wall expansion elaborated ori ginally for a single cell. The model was applied to the peach [Prunus persica (L.) Batsch] fruit, Seasonal and diurnal fruit growth, express ed in terms of dry and fresh mass changes, was calculated for conditio ns of water stress with various crop loads. Simulation of the diurnal patterns of fruit fresh mass variation revealed, in agreement with obs ervations, intensive growth by night and midday fruit shrinkage, which depend on plant water status and on crop load.