Flower strategy and stigma performance in the apple inflorescence

Flower gathering in inflorescences promote pollinator activity and assures seed and fruit set within the inflorescence. However, in this flower social behaviour, the possible contribution of each single flower gets diluted and has been overlooked. In this work we explore stigma receptivity in the different flower types of the apple corymb, an inflorescence with clear flower positions a central or king flower and four lateral flowers, where subsequent fruit set can be followed by the position along the flower axis. Flowers were receptive in turns, first in the king flower and thereafter in lateral flowers, prolonging in this way the whole inflorescence receptivity. But a closer look at pollen performance showed that king flowers had an intense but short stigmatic receptivity, whereas lateral flowers had a more discrete but much longer stigmatic receptivity. These divergences contribute to different strategies within a single inflorescence with different advantages under different scenarios. The king flower will have an advantage under good pollination conditions, whereas lateral flowers will have a better chance under poor pollination conditions. But in any circumstance these two stigma performances provide a strategy to deal with environmental uncertainty, ensuring a minimum of fruit production per inflorescence.

► Stigmatic receptivity is different in king and lateral flowers of the apple corymb.
► King flowers show an intense and short stigmatic receptivity.
► Lateral flowers receive less pollen grains, but have a longer stigmatic receptivity.
► This different performance may have different advantage in different scenarios.
► This provides a strategy to deal with environmental uncertainty assuring fruit set.