Foliar Biostimulants Mitigate Water‐Deficit Effects on Morphophysiological Traits of Tobacco ( Nicotiana tabacum L.)

This study evaluated whether foliar‐applied biostimulants can mitigate water‐deficit stress in tobacco ( Nicotiana tabacum L.) and improve several morphophysiological traits associated with drought tolerance under reduced irrigation. A comparative evaluation of three biostimulants—FitoMas‐E, Quitomax, and EM‐50—was conducted under graded water‐deficit conditions (100%, 75%, 50%, and 25% of the established irrigation norm), providing new insights into their relative effectiveness in tobacco. Tobacco plants grown in brown sialitic carbonate soil were evaluated using a split‐plot design with irrigation treatments and foliar biostimulant applications. Morphological and physiological parameters assessed included leaf area, leaf area index (LAI), leaf expansion rate (LER), biomass accumulation, membrane stability index (MSI), chlorophyll content, relative water content (RWC), and dry weight (DW). Water deficit significantly reduced leaf growth, biomass accumulation, chlorophyll content, and membrane stability. However, foliar biostimulant application improved plant performance under all irrigation regimes. Under severe water deficit (25% irrigation), Quitomax increased leaf area by up to 97.21%, MSI by 43.01%, and DW by 133.33% compared with untreated plants. FitoMas‐E showed the strongest effect on growth and plant water status, increasing LAI and LER by up to 189.47% and 214.81%, respectively, while improving RWC by 63.99% under water‐limited conditions. EM‐50 significantly increased chlorophyll b concentration by up to 144.06%, while no significant effect was observed for chlorophyll a . These findings demonstrate that foliar biostimulants partially alleviate drought‐induced damage in tobacco and improve drought tolerance, with effectiveness varying depending on the evaluated morphophysiological trait.