Integrated Biomarker Response Version 2 (IBRv2)-Assisted Examination to Scrutinize Foliar Application of Jasmonic Acid (JA) and Zinc Oxide Nanoparticles (ZnO NPs) Toward Mitigating Drought Stress in Sugar Beet

Foliar application effects of jasmonic acid (JA) and zinc oxide nanoparticles (ZnO NPs) was examined to mitigate water stress consequences on the Iranian monogerm sugar beet cultivar of “Shokofa,” the most popular cultivar in Iran. The experiment was designed using a split-plot layout based on a Randomized Complete Block Design (RCBD) with four replications over two growing seasons (2021–2023). The main plot consisted of three irrigation levels [50%, 75%, and 100% of irrigation water requirement (IWR)], while the sub-plot contained foliar application treatments (Control, JA, and ZnO NPs). Integrated Biomarker Response version 2 (IBRv2) was calculated twice for the sugar beet plants grown under 75% and 50% IWR and sprayed with distilled water (control), JA, and ZnO NPs, with the “100% IWR + Control” treatment serving as the reference site. Foliar application of ZnO NPs and JA under the 50% IWR caused increases in beta-glycine, sugar content, and the activities of antioxidant enzymes. The IBRv2 values for the first round were similar (18.245, 18.575, and 19.549), while for the second round, the lowest value (20.330) was obtained for the “50% IWR + JA” treatment, suggesting that JA may have a stronger moderating effect during severe drought stress conditions compared to the “50% IWR + ZnO NPs” and “50% IWR + Control” treatments. These findings demonstrated that foliar application of both stimulators could improve root yield, provoke the antioxidant enzymes’ activities, and growth promotion of sugar beet under water stress condition.