Influence of antioxidative enzymes, phytohormones and pigments in alternate bearing of three olive cultivars

The olive tree (Olea europaea. L), is a characteristic species of the Mediterranean landscape. This species is widely known for its strong tendency for alternate bearing which severely affects the fruit yield from year to year. This phenomenon is widespread throughout many prennial trees and shrubs, but is not universal. Prennial fruit crops initiate flower buds for next season's crop in the current season, and for most deciduous fruit species, the alternation of large and small crops is caused by competition between the current season's crop and the coming season's flower buds. Despite its agricultural importance, how the developing crop influences the following year's return bloom and yield is not fully understood. This study was carried out in an olive orchard (Olea europaea L., cultivars Chemlali, Koroneiki and Arbosana) located in Sfax, Tunisia, during two consecutive years (2014-2015). Crop load alternation provoked good fruit and oil productions in the ON year (2014), followed by low crops in the OFF year (2015). For all the three cultivars, leaves and fruits of olive plants in the OFF year generally showed reduced pigments, decreased enzymatic and non-enzymatic antioxidant defences, and their abscisic acid (ABA) homeostasis was disrupted. All the studied factors can interact in determining the alternation of high and low crop load in olive tree and its effects on fruit/ oil yield and plant physiological status.