Modelling tomato fruit transpiration under greenhouse

Fruit transpiration may vary according to growing and climatic conditions a nd plays a significant role in fruit water balance. To better understand an d predict tomato fruit transpiration, measurements of the transpiration rat e of shaded and non-shaded fruits were carried out under a wide range of cl imatic conditions. Linear models relating transpiration and either air VPD (VPDa) or fruit-to-air VPD (VPDfr-air) were proposed and their parameters w ere identified. The best fit was always obtained when using the explicative variable VPDfr-air. The model using VPDa as variable fits moderately well in the case of shaded fruits, but is not adequate for non-shaded fruits. Va lues of cuticular conductance, g(c) deduced from our measurements appeared to depend (i) on the growth-VPD regime and (ii) on the prevailing values of VPDfr-air. Our results suggest that, as for leaf transpiration, VPD betwee n the evaporating surface and the air is the variable that drives the fruit transpiration rate, and that more realistic models could be based on the h ypothesis of a variation of g(c). vs. VPD.