Integrated Structural, Physiological, and Molecular Assessment of Sugar Beet Infested by Scrobipalpa ocellatella Under Field Conditions

Background: The beet moth, Scrobipalpa ocellatella Boyd, 1858 (Lep.: Gelechiidae), is an increasingly important pest whose climate-driven expansion threatens sugar beet (Beta vulgaris L.) production in Europe. This study aimed to characterize the structural, physiological, biochemical, and molecular responses of sugar beet to infestation. Methods: Plants were analysed using computed tomography (CT), SPAD and NDVI measurements, HPLC-based sugar analysis, FRAP and MDA assays, and RT-qPCR of antioxidant-related genes. Results: CT imaging enabled non-destructive detection of larvae (mean length: 7.32 ± 0.73 mm) and pest-induced cavities (982.20 ± 316.04 mm3). SPAD did not differ significantly among treatments, whereas NDVI was consistently reduced in infested plants, declining from 0.648 ± 0.031 in non-infested plants to 0.593 ± 0.038 in infested-treated plants and 0.611 ± 0.021 in infested-untreated plants at the first sampling. Infestation induced pronounced oxidative stress, with FRAP increasing from 14.102 ± 0.943 to 25.471 ± 0.922 µg AA eq g−1 FW and MDA from 558.065 ± 21.819 to 1325.806 ± 16.762 nmol g−1 FW in untreated infested plants. Antioxidant gene expression was significantly upregulated, particularly for SOD, CAT, APX, DHAR, MDAR, and GPX. Conclusions: S. ocellatella infestation triggered coordinated oxidative stress responses in sugar beet, while CT and NDVI proved useful for early damage detection.