Hierarchy among fruitlets in the apple cluster

Apple trees (Malus domestica Borkh.) form an abundance of flowers, but not all of them develop into a fruit. Although apple trees shed the majority of fruitlets in the first developmental stages, this is not sufficient for achieving optimal commercial yield. Abscission can be stimulated or inhibited by several technological measures, thereby influencing the factors that are important for crop quality. Advanced knowledge on the natural process of abscission is crucial for the implementation of these measures. In the process of abscission all fruitlets from the cluster do not drop at the same frequency. In our study we compared the abscission potential of fruitlets at various positions along the peduncle - from the central fruitlet (position 1) to the basal one (position 6) in 6-flowered clusters. Abscission started 4 weeks after full bloom and lasted for 6 weeks. During this time more than 70% of all fruitlets abscised. Fruitlets most rarely abscised from the central position (less than 40% incidence), while the lowest positions (positions 5 and 6) dropped more than 80% of fruitlets. Interestingly, high abscission potential has been observed at the position 2 (nearest to the central position). At this position fruitlets abscised more frequently than at lower positions. The disadvantage of position 2 was further confirmed at harvest. Fruits from the lateral position nearest to the central one were smaller and firmer compared to fruits from central and lower positions 3 and 4. This demonstrates the obvious dominance of the central fruit compared to lateral fruits, especially those nearest to the king fruit.