Olive trees are considered among the most resilient crops in Mediterranean basin. However, prolonged water stress may adversely affect plant productivity and quality of fruits and oil. Therefore, it is essential to design new agronomic strategies to improve plant water stress tolerance and secure yield and product stability of this important agricultural crop. Under water deficit, plants cope with serious threats, and melatonin (MEL), as a versatile signaling biomolecule, can play a crucial role in morphological and physiological modifications of plants able to enhance drought stress tolerance. In this view, the current research aimed at elucidating the potential beneficial role of exogenous foliar application of MEL (0 and 100 µM) to Sevillana and Roughani olive cultivars under different water stress levels (100%, 75%, and 50% ET). In particular, the morphological, physiological and biochemical changes occurring in leaves treated with or without MEL and the quality of fruits and oil were discussed. A decrease of electrolyte leakage (EL) and malondialdehyde (MDA) content as well as an increase of relative water content (RWC) in MEL-sprayed leaves of drought stress trees were observed. The application of MEL was also associated with higher K⁺ to Na⁺ ratio, Ca²⁺ content, phenolic and soluble carbohydrates contents and a lower decline chlorophyll (Chl) levels. MEL-treated leaves also showed higher catalase (CAT) and peroxidase (POD) activities, responsible for scavenging reactive oxygen species (ROS) generated during drought stress in a severity-dependent manner. MEL-foliar application enhanced the oil content and yield in the olive fruits in both cultivars compared to the untreated ones. Since MEL was also able to exert a beneficial effect on both Sevillana and Roughani cultivar trees by improving their crop water productivity (WPc) under water deficit, it can be considered an effective eco-friendly candidate to minimize the detrimental consequences of water stress.

橄榄树被认为是地中海盆地最具弹性的作物之一。然而，长期的水分胁迫可能会对植物生产力和水果和油的质量产生不利影响。因此，设计新的农艺策略以提高植物对水分胁迫的耐受性并确保这种重要农作物的产量和产品稳定性至关重要。在缺水条件下，植物应对严重威胁，而褪黑激素（MEL）作为一种多功能的信号生物分子，可以在增强干旱胁迫的植物形态和生理改变中发挥关键作用宽容。鉴于此，目前的研究旨在阐明在不同水分胁迫水平（100%、75% 和 50% ET）下，外源叶面喷施 MEL（0 和 100 µM）对 Sevillana 和 Roughani 橄榄品种的潜在有益作用。特别是讨论了用或不用 MEL 处理的叶片的形态、生理和生化变化以及果实和油的质量。观察到在干旱胁迫树的 MEL 喷洒叶片中电解质泄漏 (EL) 和丙二醛 (MDA) 含量降低以及相对水分含量 (RWC) 增加。MEL 的应用还与较高的 K ⁺与 Na⁺比、Ca²⁺含量，酚类和可溶性碳水化合物含量和较低的叶绿素（Chl）水平下降。MEL 处理的叶片还表现出较高的过氧化氢酶 (CAT) 和过氧化物酶(POD) 活性，它们负责以严重程度依赖的方式清除干旱胁迫期间产生的活性氧 (ROS)。与未经处理的品种相比，叶面喷施 MEL 提高了两个品种橄榄果实的含油量和产量。由于 MEL 还能够通过提高缺水情况下的作物水分生产力 (WPc) 对 Sevillana 和 Roughani 品种树产生有益影响，因此它可以被认为是一种有效的环保候选者，可以最大限度地减少水分胁迫的不利后果。