关键词: 芝麻, 高温胁迫, 褪黑素, 盛花期, 光合特性, 品质, 产量

Abstract: To investigate the alleviating effect of exogenous melatonin（MT）on sesame plants under high‐temperature stress and to enhance their thermotolerance，the cultivar Shangzhi 196 was used as the test material，with natural climate growth as the control（CK）.During the full‐bloom stage under high‐temperature stress，sesame leaves were sprayed with melatonin solution at concentrations of 0（MT0），100（MT100），150（MT150），200（MT200），and 250 mg/L（MT250）.The study examined the agronomic traits，photosynthetic and chlorophyll fluorescence characteristics，antioxidant enzyme activities，quality and yield‐related traits under different treatments.The results showed that high‐temperature stress during the full‐bloom stage（MT0）significantly reduced plant height and fruit axis length by 8.15% and 15.09%，respectively，compared with CK，while increased yellow tip length by 21.11%.The number of capsules per plant，seeds per capsule，1 000‐seed weight，and yield decreased significantly by 18.22%，24.93%，8.60%，and 12.53%，respectively. Leaf net photosynthetic rate（Pn），stomatal conductance（Gs），and transpiration rate（Tr）were significantly reduced，and the photosystem Ⅱ（PSⅡ）reaction center was damaged. Additionally，seed moisture content increased by 4.54%，while oil and protein contents decreased by 0.28% and 0.75%，respectively. Exogenous melatonin application significantly increased the number of capsules per plant and seeds per capsule，while reduced yellow tip length.Leaf SPAD value，Pn，Gs，and Tr were significantly enhanced，whereas intercellular CO_₂ concentration（Ci）decreased.The maximum quantum efficiency of PSⅡ（Fv/Fm），actual photochemical efficiency of PSⅡ（ΦPSⅡ），and photochemical quenching coefficient（qP） increased significantly，while minimal fluorescence（Fo）decreased. Additionally，exogenous MT application significantly enhanced the activities of peroxidase（POD），superoxide dismutase（SOD），and catalase（CAT）in sesame leaves，while markedly reduced the malondialdehyde（MDA） content. Concurrently，both the grain water content and protein content decreased，accompanied by a significant increase in yield.Principal component analysis revealed that the high‐temperature tolerance of sesame followed the order of MT200 > MT150 > MT250 > MT100 > MT0，indicating that exogenous melatonin alleviated growth inhibition under high‐temperature stress，with the 200 mg/L treatment（MT200）exhibiting the best mitigation effect.Under MT200 treatment，SOD，POD and CAT activities increased by 24.36%，22.72%，and 22.42%，respectively，compared to MT0.Oil content increased by 1.06%，while moisture and protein contents decreased by 3.47% and 1.30%，respectively.Yield improved by 11.75%.In conclusion，exogenous melatonin application positively enhanced thermotolerance of sesame during the full‐bloom stage by protecting chloroplast structural stability and regulating antioxidant pathways，thereby mitigating high‐temperature‐induced damage.The optimal concentration for foliar spraying was determined to be 200 mg/L.

Key words: Sesame, High‐temperature stress, Melatonin, Full‐bloom stage, Photosynthetic characteristics, Quality, Yield