Differential efficacy of TiO₂ nanoparticle application methods in mitigating water deficit stress in sugar beet (Beta...

This two-year field study (2022-2024) evaluated the efficacy of various application methods for titanium dioxide nanoparticles (TiO₂-NPs) in mitigating water-deficit stress in sugar beet (Beta vulgaris L. cv. Dena). A split-plot design in a randomized complete block arrangement with three replications was employed. Main plots consisted of two irrigation regimes: normal (60 mm evaporation) and deficit (120 mm evaporation). Subplots included four TiO₂-NPs treatments: control, seed priming, soil application, and foliar spray. Physiological, biochemical, and yield parameters were assessed. Water deficit stress significantly reduced chlorophyll content, relative water content (RWC), stomatal conductance, auxin (IAA), cytokinin (CK), root yield (RY), and sugar yield (SY), while increasing proline, abscisic acid (ABA), carotenoids, antioxidant enzyme activities (CAT, SOD, APX), and malondialdehyde (MDA). Among the TiO₂-NPs application treatments, foliar application increased chlorophyll a content by 14.59% and 13.89%, SC by 2.89% and 11.30%, and SY by 26.33% and 32.89%, respectively, compared to the priming and soil application treatments. Under water deficit conditins the foliar application of TiO₂-NPs increased RWC by 5.23% and 16.44%, stomatal conductance by 3.80% and 14.03%, IAA by 8.26% and 31.27%, CK by 6.17% and 35.81%, CAT activity by 4.42% and 14.89%, SOD activity by 24.20% and 20.92%, APX activity by 9.45% and 48.64%, and RY by 23.59% and 22.21 respectively, compared to the priming and soil application treatments. It also reduced MDA content by 17.24% and 8.68%, respectively. The lowest Integrated Biomarker Response (IBRv2) was observed for the foliar spray of TiO₂-NPs treatment. The impact on RY (I value) was least negative with foliar application (I = -0.14) compared to the control (I = -2.46), and other treatments. For MDA, a significant increase under water deficit (I = 2.20 for control) was notably reduced with foliar application (I = -0.05), seed priming (I = 0.76), and soil application (I = 1.65). It is concluded that foliar application of TiO₂-NPs is the superior strategy for enhancing drought tolerance in sugar beet.