Detachment force and natural abscission in ripening olive fruits in southern Spain

• Fruit detachment force in olive is highly variable among individual measurements. • Its average values are cultivar-dependent and they seldom decrease with ripening. • The fruit-pedicel junction is the main abscission zone irrespective of the cultivar. • Natural fruit abscission dynamics depend on fruit load, water status and cultivar. • Natural abscission does not seem to be related with fruit detachment force. Variations in detachment force (FDF) and natural abscission (NA) during ripening are critical for the efficient harvesting of olive trees, but their dynamics are still poorly understood. In this study, we measured the variations of FDF and NA in a three-year experiment with eight olive cultivars, exploring the impacts of fruit load and water status on these processes. In general, rather stable values of FDF were observed in most cultivars and seasons with huge variability among individual FDF measurements (from close to nil to around 1 kg or even more in all cultivars). Yet, the data revealed significant cultivar differences, with ‘Arbequina’ (0.35±0.005 kg) and ‘Hojiblanca’ (0.61±0.006 kg) showing the lowest and highest average values, respectively, and negligible effects of fruit load and water status on FDF. Likewise, they confirmed that the fruit-pedicel junction represents the primary abscission zone for all the cultivars examined (72.5% on overall average). Natural abscission accelerated as ripening progressed, with different values at harvest among years. Our results show that the probability of losing a significant number of fruits before a given date depends to some extent on the genotype and fruit load (the higher the load, the later the abscission). Water stress reduced fruit shed, which was not related to a higher FDF or to a lower fruit mass. The data of this experiment shows that indexes based on relative fruit load at tree level would be probably more useful than those based on retention force for decision making over harvest time.