DRY-MATTER AND WATER IMPORT RATES IN THE TOMATO FRUIT - A MODEL INCORPORATING THE CHANGES IN SAP VISCOSITY AND OSMOTIC POTENTIAL WITH TEMPERATURE

The change in water import rate in tomato fruit was modelled by incorporating into a previously-published model the changes in sap viscosity and osmotic potential into fruit with temperature. An experimental relationship between water and dry matter import rates was used to compare the model to dry matter import rates in fruit measured by Walker and Thornley (Annals of Botany 41: 977-985, 1977) at different temperatures. The effect of temperature on the water import calculated from the model, was also compared with the effect of temperature on the fruit growth rate measured by Pearce, Grange and Hardwick (Journal of Horticultural Science 68: 1-11 and 13-23, 1993). The model accounted for a large part of these temperature effects. It was concluded that resistances in sap transfer pathways in the tomato fruit could be due to viscosity. These results supported, on the one hand, the hypothesis that the progressive decrease of water import rate during fruit growth could result partly from the progressive increase in transfer pathway length, and, on the other hand, the hypothesis that the ratio between water and dry matter import rates could depend on flow conditions in transfer pathways. The equations of the model could be used to simulate tomato fruit growth, mass and dry matter content in relation to fruit size, to nutrient solution salinity and to fruit temperature.