The Impact of Different Biostimulants on Physiological Aspects of Tomato in a Pot ExperimentFathi Hussien, Saeed Safwat (Avtor) Urbanek Krajnc, Andreja (Mentor) Lešnik, Mario (Komentor) Senekovič, Jan (Komentor) Amalgerolhydrogen peroxideplant biostimulantsSolanum lycopersicum L.spectral reflectance indicestannintomatoTrichodermaTomatoes (Solanum lycopersicum L.) are sensitive to photothermal and drought stress during the summer growing season, particularly under warm outdoor conditions and elevated irradiance. Plant biostimulants are increasingly proposed to support physiological stability under such conditions. However, biostimulant performance is known to depend on cultivar, treatment type, environmental context, and the physiological parameters measured. Comparative evidence across contrasting biostimulant families also remains limited. This master's thesis evaluated the physiological responses of two tomato cultivars, 'Optima' and 'Sfinge F1 500', to treatments with hydrogen peroxide (H₂O₂)-, tannin-based treatments, Trichoderma-based treatments and treatments with commercially available plant extract-based Amalgerol products together with a water-treated control. The experiment was carried out in pots during the 2025 growing season at the Faculty of Agriculture and Life Sciences, University of Maribor. Leaf spectral reflectance was measured non-destructively using PolyPen RP 410 on four sampling dates between 19 June and 30 July 2025. The measured indices included five chlorophyll-related indices, Normalised Difference Vegetation Index (NDVI), Modified Chlorophyll Absorption in Reflectance Index 1 (MCARI1), Modified Chlorophyll Absorption in Reflectance Index (MCARI), Carter Index 1 (Ctr1), and Carter Index 2 (Ctr2), and five pigment- or stress-related indices, Structure Insensitive Pigment Index (SIPI), Anthocyanin Reflectance Index 1 (ARI1), Anthocyanin Reflectance Index 2 (ARI2), Carotenoid Reflectance Index 1 (CRI1), and Carotenoid Reflectance Index 2 (CRI2). One-way and two-way ANOVA were used to evaluate treatment, cultivar, and Treatment × Cultivar interaction effects. The treatment effects strengthened over time and were most evident on 30 July, when all five chlorophyll-related indices differed significantly among treatments. Amalgerol-based treatments were most consistently associated with maintained NDVI and MCARI values during the mid-June to July sampling period, supporting better maintenance or recovery of leaf greenness and chlorophyll-related reflectance. Tannin- and peroxide-based treatments were associated with selected changes in pigment- and stress-related indices. Overall, no single biostimulant was consistently superior across all indices and dates, but Amalgerol-based treatments showed comparatively consistent responses in selected chlorophyll-related indices. Significant Treatment × Cultivar interactions were detected for MCARI1 (19 June) and NDVI (30 July), confirming cultivar-dependent differences in the expression of treatment effects. The hypotheses were partially supported overall, with the clearest support observed for the temporal hypothesis. Spectral reflectance also proved a useful non-destructive indicator for comparing biostimulant programmes across the season.S. Hussien20262026-03-23 14:41:55Magistrsko delo/naloga97593UDK: 635.64:577.17(043)COBISS_ID: 286369539sl