The purpose of this study was to address the influence of melatonin foliar application on the flowering and fruit formation of olive cultivars of Sevillana and Roughani at the Dalaho Olive Research Station conditions of Kermanshah province. The experiment was conducted in a randomized complete block design in a factorial arrangement and three factors (MEL concentration, irrigation regime and olive cultivar) with 3 replicates and implemented in the crop year 2021-2022. The trees were sprayed with melatonin [0 (as a control), 50 and 100 µM] before flowering and during rapid fruit growth (two growth stages) on leaves. Irrigation treatments included 100% (control), 75 and 50% evapotranspiration. In order to investigate the state of flowering and fruit formation of olive cultivars under drought stress and melatonin foliar application, flower and fruit formation were recorded. Statistical analysis of variance and comparison of averages was done by Duncan for multiple comparisons between pairs of treatment as a post-hoc test. The results showed that flower traits and fruit formation were significant under the impact of variety, various levels of melatonin and irrigation regime at the probability level of 1%. The decrease in the amount of irrigation water affected flower characteristics and fruit formation. Melatonin foliar spraying improved the condition of flowering and fruit formation in Sevillana and Roughani cultivars.
