Lilium (lily) is known as an important cut flower whose quality and ornamental value may be negatively affected by deficit irrigation (DI); however, the adverse effects of DI could be alleviated by exogenous application of 24-epibrassinolide (EBR). Therefore, we conducted the present research to study the effects of different levels of soil water content (SWC) [100% (full irrigation), 75% (low DI), 50% (moderate DI), and 25% (severe DI)] and foliar spray of EBR (0.0, 0.75 and 1.5 μM) on certain morpho-physiological characteristics of Lilium “Fangio” (LA hybrid, Longiflorum x Asiatic). Different levels of DI were observed to alter lily’s morphological characteristics, affecting biochemical and physiological indices. Severe DI reduced plant height (11.11%), pedicel length (33.51%), and flower number (13.57%) while it increased the accumulation of proline (115.78%), electrolyte leakage (EL; 79.68%), and malondialdehyde (MDA; 40.35%) content. It also increased the water use efficiency (WUE; 135.59%) and saved water (66.7%). Foliar application of EBR significantly decreased the content of MDA (32.87%), on top of enhancing proline content (37.03%) and WUE (20.25%). The application of EBR (1.5 μM) on water stressed lily plants resulted in the improvement of chlorophyll content (41.46%) and activities of antioxidant enzymes (CAT and APX). Our results confirmed that applying irrigation at 75% SWC could reduce water inputs without affecting the ornamental value of lily. Overall, lily showed a moderate level of tolerance to water deficit by various mechanisms, such as a decrease of morphological parameters, maintenance of physiological function, an increase in WUE, and accumulation of osmolytes and enzymatic antioxidants. It could be concluded that severe water stress has to be avoided throughout the growing season of lilies, and if a foliar spray of EBR is used for the modulation and alleviation of the detrimental effects of drought stress, only moderate deficits are acceptable.
