It's great to be the King: Apple fruit development affected by the position in the cluster

Apple trees (Maus domestica Borkh.) develop an abundance of flowers and shed the majority of fruitlets in the first developmental stages. In this study the process of abscission was monitored in cultivar 'Golden Delicious' and linked with the position of fruitlets in the cluster, focusing on differences among central or king flower/fruit (K1), flowers/fruit nearest to the king flower (lower on the peduncle; L2) and flowers/fruit located at different positions near the base of the peduncle (L3-L6). Individual clusters consisted of 3-7 flowers the most frequent were clusters with 5 flowers. Abscission was biphasic with the first peak 29 days after full bloom (DAFB) and the second peak 48 DAFB. At the end of the abscission process approx. 70% of all fruitlets shredded. Fruitlets at the central position (K1) were frequently unaffected by this process and developed to fruit in 70% of the analyzed clusters. The ratio between subsisting and shedded fruitlets was the opposite for lateral positions in the cluster; approx. 70% of fruitlets abscised in the clusters with 4/5 flowers. No significant differences in the level of abscission have been observed between the lateral positions in the cluster (L2-L6). A tendency to abscission has been detected for L2 position (lateral fruitlet nearest to the king flower) in clusters consisting of 6 flowers. This was further confirmed at harvest. Fruit from the lateral position nearest K1 were smaller and firmer in comparison to K1, L3 and L4. This demonstrates the obvious dominance of the central fruit in comparison to lateral fruit, especially those nearest to the king fruit. This is particularly evident in clusters with many flowers. (C) 2015 Elsevier B.V. All rights reserved.