Characterization of training system in relation to water use efficiency in apricot and kiwifruit plants

Trials were carried out in Southern Italy on apricot plants (cv. Tirynthos) trained to transverse Y and kiwifruit vines (cv. Hayward) trained to pergola. Leaf area, light availability and gas exchange measurements were performed during different times of the growing season on both orchards. In kiwifruit vines at maximum LAI (3.7), reached in July, the shaded leaves were 60% of the total. During the annual cycle, exposed leaves showed a photosynthetic rate 50 times higher than shaded ones, while transpiration rate was only twice higher. Average WUE value in exposed leaves was 20 times higher than in shaded leaves. Apricot trees reached maximum LAI (4.7) in July with 44% of the leaves exposed (> 40% of incident sunlight), 20% of intermediate leaves (20-40 % of incident sunlight ) and 36% of shaded leaves (<20% of incident sunlight). The transpiration and photosynthesis in apricot leaves showed the same behavior as in kiwifruit leaves. The exposed leaves showed a WUE 3 up to 8 times higher than that of shaded ones. Shaded leaves consume 19% and 38% of the total transpired water respectively in apricot and kiwifruit during the day and, if we consider the night respiration, they do not contribute in any way to the energy balance of the whole plant. Shaded leaves were not a source but another sink for the plant and through an appropriate choice of canopy architecture and its correct management, in particular with summer pruning, it would be possible to improve the daily carbon balance and WUE.