Fishman, S., Dept. of Stat. and Operations Res., Agricultural Research Organization, Volcani Center, Bet Dagan 50250, Israel
Génard, M., U. Rech. en Ecophysiologie et Hort., Inst. Natl. de la Rech. Agronomique, Site Agroparc, Domaine Saint-Paul, 84914 Avignon Cedex 9, France

A model of fruit growth was developed, based on a biophysical representation 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 transpiration). The sugars are transported from the phloem to the fruit mesocarp by mass flow, passive diffusion and an active (and/or facilitated) mechanism. The stages after cell division has ceased and when fruit growth is due mainly to cell enlargement were modelled. This enabled us to consider the fruit as a cell community with a constant number of cells and to apply directly the equation describing the effect of hydrostatic pressure on the irreversible cell wall expansion elaborated originally for a single cell. The model was applied to the peach [Prunus persica (L.) Batsch] fruit. Seasonal and diurnal fruit growth, expressed in terms of dry and fresh mass changes, was calculated for conditions of water stress with various crop loads. Simulation of the diurnal patterns of fruit fresh mass variation revealed, in agreement with observations, intensive growth by night and midday fruit shrinkage, which depend on plant water status and on crop load.