https://doi.org/10.37229/fsa.fjh.2026.07.10

Heat stress poses a major challenge to tomato plants as global warm temperatures continue to rise and its negative effects on plants performance (physiological, bio-chemical and productivity). This research assessed and evaluated the response of tomato plants “Alisa hybrid” to natural heat stress using some bio-stimulants as foliar treatments during the late summer seasons of 2024 and 2025 at a vegetables private farm in Mansoura district, Dakhlia Governorate, Egypt in clay soil conditions and using drip irrigation system. Eight treatments were applied in a complete randomized block design system with three replicates included Brassinolide at 250 ppm, Glutathione at 200 ppm, Methyl jasmonate at 100 ppm, Melatonin at 150 ppm, Glycine betaine at 2 g/L, Spirulina at 2.5%, Jasmonic acid at 100 ppm plus the control treatment (spraying only water). The findings revealed that most of studied parameters significantly reduced as a result of heat stress conditions in both seasons, while exogenous application of all mentioned substances improved plants performance. Melatonin application significantly mitigated heat stress effects and recorded maximum plant growth, chemical contents, enzymes activity, phyto-pigments and hormones as well as yield and quality followed by glycine betaine treatment in most cases. This mitigation effect by applied treatments is likely attributable to stimulate nutrients uptake and osmotic adjustment in tomato plants. Also, these results highlight the vital role of either melatonin or other foliar substances for improving productivity of tomato plants under heat stress conditions.