Hierarchy and strategy: how do they affect thinning response?

In the apple, the reproductive structures are formed by corymbs carrying a central flower (that originates the fruit king) blooming first, and 4-6 lateral flowers that bloom according to a time sequence, originating the lateral fruitlets. In a normal climatic course, the king fruit grows before and at a higher rate (high hierarchy situation), thus exerting a competition for the assimilation of nutrients towards lateral fruitlets and the other growing organs (i.e., shoots and leaves). In some situations, however, these differences in growth are not so marked and both the central and lateral fruitlets grow at the same rate thus, bearing similar sizes (low hierarchy situation). In the first case, the king fruit has a low tendency to abscise and the lateral fruits are characterized by higher natural abscission, while in the second situation the probability of abscission of both the king and laterals fruitlets are similar, thus affecting also the efficacy of the chemicals thinners used. In some circumstances, a consistent reduction of the fruit load is required to meet the commercial standard fruit requirement and different chemical thinning agents can be sprayed in a sequence, especially on cultivars considered “difficult to thin”. This technique is named “strategy” in the practice.