Testing the effect of different light environments and water shortage on apple physiological parameters and yield

The effect of different light environments on 'Imperial Gala' apple yield and several physiological parameters were evaluated in 2013 by placing over the trees nets with different levels of shading and colour (black, 20% shading, red and white, 50% shading). A fourth plot was left uncovered. Each net was combined with two irrigation treatments for 60 days before harvest: no stress and moderate stress. Irrigation was applied to achieve specific levels of water stress and was managed using midday stem water potential (mSWP) thresholds. mSWP was measured weekly from the onset of the irrigation treatments until harvest. Leaf gas exchanges were assessed three times during that period. Crop water requirements were estimated as crop coefficient values (Kc) from measurements of tree light interception three times during the season. Water stress reduced mSWP and leaf photosynthesis. Shading level and colour did not affect leaf photosynthesis but the uncovered plot had the highest Kc and the most negative mSWP (values around -1.3 MPa). The black net (20% shading) had an intermediate Kc and mSWP between trees without nets and trees with 50% of shading. The red and white nets had the same Kc and maintained mSWP around -1.0 MPa indicative of no water stress in apple. At harvest, marketable yield was higher for the shaded trees compared to uncovered trees for both irrigation treatments indicating that apple trees without nets were grown in more stressed conditions. This leads to think that under moderate water conditions before harvest net shading may be useful to maintain acceptable marketable yields. Conditioning the available light inside the orchard with the use of shading nets could be therefore a promising horticultural technique to face future challenges related to low water availability in fruit orchards.