Fishman, S., Department of Statistics and Operations Research, ARO, Volcani Center, 50250 Bet Dagan, Israel
Génard, M., Unité de Recherche en Ecophysiologie et Horticulture, INRA, Domaine Saint-Paul, Site Agroparc, 84914 Avignon Cedex 9, France

A theoretical framework is suggested for the description of fruit growth. The stages of fruit development are considered when cell division is finished and the fruit can be approximated by a community of growing cells; this criterion enables us to clarify the relationship among the basic mechanisms. The fruit is treated as one compartment, separated from two external compartments - the parent plant and the ambient atmosphere - by composite membranes. The composite membrane approximates a set of transport barriers, arranged both in series and in parallel, as a single barrier with combined transport characteristics. Cell growth is related to the turgor pressure exerted on the wall, by an equation based on experiments that revealed a threshold turgor pressure, below which no extension occurs. The model was applied to the calculation of seasonal and diurnal growth of the peach (Prunus persico. (L.) Batsch) fruit. The growth, as determined by dry and fresh mass dynamics, was calculated under conditions of water stress for various crop loads. The model also enables us to calculate the hydrostatic and osmotic pressures in the fruit, and to compare the contribution of xylem and phloem flows to the fruit water budget.