Heat stress effects on physiological, biochemical and fruit quality traits of tomato (Solanum lycopersicum L.) genotypes at the late fruit maturation stage

Heat stress during late fruit maturation can impair physiological efficiency and fruit quality in tomato (Solanum lycopersicum L.). The present study evaluated 12 genotypes under natural field heat stress conditions (maximum temperature 36–38 °C) during the late fruit maturation stage using a randomised complete block design (RCBD) with five replicates. Gas exchange parameters, chlorophyll fluorescence (Fv/Fm), pigment composition, membrane thermostability, proline accumulation and fruit quality attributes were quantified and analysed using ANOVA (p ≤0.05). Significant genotypic variation was observed in net photosynthetic rate (1.08–21.01 µmol m-2 s-1), Fv/Fm (0.424–0.662), electrolyte leakage (EL; 76.59–99.15 %) and carotenoid retention. Genotypes VRT 101 A, EC 538380 and EC 620438 maintained comparatively higher photosynthetic performance and membrane stability, whereas EC 620-1, INDAM 2102, EC 620568 and EC 620419 exhibited superior fruit quality retention, including higher lycopene (up to 0.522 mg 100 mL-1), β-carotene and total soluble solids (TSS). Sensitive genotypes showed reduced photosynthetic efficiency and higher membrane injury under prolonged exposure to elevated temperatures. The findings highlight genotype-dependent heat tolerance strategies and identify physiological and biochemical markers useful for selection under terminal heat stress conditions.