Olive trees have very low fruit set due to intense fruitlet abscission. To determine the reasons for this shedding, we simultaneously monitored the reproductive processes and fruit population dynamics in 'Arbequina' trees growing under controlled conditions. Although low pollen adhesion in undersized pistils may limit fruit set, ovule penetration by pollen tubes was observed in 60% of flowers prior to the onset of abscission; nevertheless 96% of the initial pistil population abscised. Most of the abscission occurred during the first two weeks after bloom and affected primarily smaller pistils, both unfertilized and fertilized; only a small percentage of pistils reaching 3-4 times their initial size were shed. Ovule degeneration was often observed in unfertilized flowers prior their abscission, but there was no evident cause for shedding of the fertilized flowers. The results suggest that rapid ovule and ovary growth following fertilization required an increased nutrient supply causing competition among the developing fruitlets. Such competition for nutrients triggers selective abortion of smaller, less competitive fruitlets.

Peer reviewed