Drought-Induced Changes in Morphology and Phenology of Olive Trees (Olea europaea L.)

The olive tree (Olea europaea L.), a cornerstone of Mediterranean agriculture, is widely recognized for its inherent drought tolerance. However, the increasing frequency and intensity of water deficit events driven by climate change are challenging its growth, productivity, and long-term sustainability. This review synthesizes current knowledge on the morphological and phenological adaptations of olive trees to water stress. In fact, under drought conditions, olive trees develop a suite of structural and anatomical adjustments that collectively enhance water-use efficiency and help maintain plant water status. These adjustments include reduced leaf area, thickened cuticles, mesophyll rearrangements, remodeling of xylem vessel architecture, and reinforced root systems. These morpho-anatomical responses influence phenology, through changes in the timing and duration of key phenological stages, leading to reduced flower induction, lower flowering intensity, decreased fruit set, and overall lower yields, while the most pronounced effects are observed in sensitive cultivars. Among all stages, flowering is the most vulnerable to water deficit, while pit hardening and fruit development show comparatively more tolerance. The combination of morphological, anatomical, and phenological responses could provide a mechanistic elucidation of drought tolerance variability within olive cultivars. Understanding this interplay is likely to offer valuable criteria in selecting and breeding resistant varieties, thus ensuring productive and sustainable olive cultivation under increasingly severe climatic conditions.