This study investigates the effects of shading on the biophysical mechanisms of apple (Malus Domestica
Bork.) fruit growth by assessing how vascular and transpiration flows to/from the fruit are affected by
shading. At 30 days after full bloom, a 90% neutral shading net was applied to four trees of the cv. Gala, for
seven days, while four more trees, chemically thinned, were used as control. Fruit vascular and transpiration
flows were assessed from two days before, to the end of shading. The daily patterns of fruit relative
growth rate (RGR) and of phloem, xylem and transpiration flows were determined by continuous monitoring
of fruit diameter by automatic fruit gauges. Before shading application, no differences between the
two groups of trees selected were found for any of the parameters measured. Despite shading induced
an immediate drop in canopy photosynthesis, both fruit daily RGR and phloem flow decreased gradually,
until reaching 20% of the before treatment values after 7 days of shading. Differences in RGR and phloem
flow appeared especially during the afternoon and night, i.e. post carbon assimilation by the tree, and
fruit growth rates were higher in control trees. In the same period no, or very small differences were
found between treatments for transpiration rates, while xylem flow was affected later than phloem and
only at specific times during the day. These results suggest that the decrease in fruit growth rate under
shading should be attributed to the reduction of canopy photosynthesis, rather than to a direct effect of
shading on fruit sink strength