C. Andergassen^1,2, D.A. Hey¹, D. Pichler¹, M. Peterlin¹, M. Kelderer¹, P. Robatscher¹ and M. Tagliavini^2
1 Laimburg Research Centre, Pfatten (Vadena), Auer (Ora), Italy
² Faculty of Science and Technology, Free University of Bolzano, Bolzano, Italy

SUMMARY Pneumatic leaf removal on apple trees has become a standard practice in commercial orchards on bicolored apple cultivars. To get a better understanding of the physiological impact of this new technol-ogy on apple trees, two trials on cv. ‘Nicoter’ and ‘Rosy Glow’ were conducted in commercial orchards located in South Tyrol (Italy) in autumn 2020 and 2021. The aim was to examine the influence of sum-mer pruning, pneumatic preharvest-defoliation and their combination on light penetration and fruit quality inside the tree canopy. For this purpose, four treatments, namely untreated control (UTC), sum-mer pruning (SP), pneumatic defoliation (PD), and SP in combination with PD (SP+PD), were compared. The results showed that summer pruning causes a reduction of up to 25.6% and pneumatic defoliation up to 59.2% of the leaf area on cv. ‘Rosy Glow’ and 22.6% and 48.9%, respectively, on cv. ‘Nicoter’ com-pared with the untreated control. The light conditions insight the canopy significantly improved apply-ing summer pruning and pneumatic defoliation. Photosynthetic active radiation (PAR) measurements in 2021 showed that the effects on light penetration inside the canopy is especially high at 100–150 cm tree height, and a significant interaction of summer pruning and pneumatic defoliation could be found for ‘Rosy Glow’, with a maximum increase of 601%, compared to untreated control. On the contrary in both years, summer pruning and pneumatic defoliation significantly reduced fruit weight on cv. ‘Nico-ter’, whereas on cv. ‘Rosy Glow’ only pneumatic defoliation in 2021 decreased fruit weight. Total soluble solids content of apples in both years was affected negatively on ‘Nicoter’ by pneumatic defoliation treatment. Color index and anthocyanin content were increased significantly on fruits harvested in the inner part of the tree canopy on both varieties by summer pruning and pneumatic defoliation treat-ments. This study provides a first evidence of the physiological impact of pneumatic defoliation on ap-ple trees, obtained under real conditions. It underlines the importance of a correct use of both summer pruning and pneumatic defoliation to minimize their adverse effects. Keywords anthocyanins, fruit color, leaf area, light environment, PAR radiation, return bloom

Significance of this study What is already known on this subject? Pneumatic preharvest defoliation is a new technology for fruit color improvement in apple production. What are the new findings? Pneumatic defoliation removed leaf some 30–40% of the leaves, slightly more than summer pruning. Summer pruning and pneumatic defoliation had an additive effect, meaning that when applied together they can re-move up to 60% of the leaves and increase by 600% the light penetration. Total anthocyanins content on the fruit skin increased up to 140% compared to the untreated when pneumatic defoliation was applied. What is the expected impact on horticulture? This study shows how to improve the fruit coloration, with no or minor yield losses through summer pruning and pneumatic leaf removal.

E-mail: christian.andergassen@laimburg.it  

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Received: 7 February 2023 | Accepted: 25 June 2023 | Published: 17 October 2023 | Available online: 17 October 2023