Effects of exogenous hormones on leaf photosynthetic performance and fruit quality of Cabernet Sauvignon grape under high temperature stress

【Objective】To study the effects of exogenous spraying of melatonin（MT）and 2,4-epibrassinolide（EBR） on photosynthetic performance and fruit quality of Cabernet Sauvignon grape under high temperature stress，which provided theoretical basis for enhancing the photosynthetic performance of wine grapes，improving fruit quality and enhancing high temperature resistance.【Method】Using wine grape Cabernet Sauvignon as the test material，four treatments were set up，namely，spraying distilled water（control，CK）at natural temperature，high temperature treatment（H treatment），high temperature+MT（150 μmol/L）treatment（H+MT treatment），high temperature+EBR（0.6 mg/L）treatment （He+EBR treatment）. The effects of MT and EBR on photosynthetic performance parameters and fruit quality of Cabernet Sauvignon grape were measured and analyzed. The correlation between fructose and anthocyanins was also analyzed.【Result】H treatment reduced the content of photosynthetic pigments，H+MT and H+EBR treatments were effective in mitigating the damage caused by high temperature to chlorophyll a，chlorophyll b and carotenoids. 91 d after anthesis，compared to H treatment，leaf chlorophyll a significantly increased by 41.73% in H+MT treatment（P<0.05，the same below），at the same time，the net photosynthetic rate（P_n）significantly increased by 18.98%，P_n increased by 8.76% in H+EBR treatment. 115 d after anthesis，compared to H treatment，transpiration rate（T_r）significantly increased by 23.68% in H+ MT treatment，the reducing sugar content significantly increased by 11.82%. During the fruit harvesting period，H+MT treatment significantly mitigated the effect of high temperature stress on soluble solids，total soluble sugar，anthocyanin， total phenols and tannin contents. 67 d after anthesis，the anthocyanin content of grape leaves significantly increased by 64.91% in H+MT treatment and 36.39% in H+EBR treatment，significant positive correlation between fruit sugar fractions and anthocyanosides was observed.【Conclusion】Spraying MT and EBR at high temperature can alleviate the effects of high temperature on leaf photosynthetic performance and fruit quality，the effects of H+MT treatment were fine.