Effects of exogenous brassinolide on photosynthetic characteristics and fruit quality of Merlot grape

【Objective】 To study effects of 2,4-epibrassinolide （EBR）on photosynthetic characteristics and fruit quality of grapes，so as to provide theoretical reference for improving grape photosynthetic efficiency and fruit quality and application of brassinolide compounds on wine grape.【Method】 Merlot wine grapes were taken as test material，spraying different concentrations of EBR（0.2，0.4 and 0.6 mg/L）and the grapes sprayed with water were taken as CK to study effects of EBR on photosynthesis and fruit quality of the grapes.【Result】 The results showed that every EBR treatment raise transpiration rate and stomatal conductance in fruit expansion stage，color-changing stage and maturing stage.Among them，0.4 mg/L EBR had better effect and during fruit expansion stage，it increased average value of transpiration rate and stomatal conductance by 69.59% and 20.87%，respectively compared with the control.Both 0.2 and 0.4 mg/L EBR could increase net photosynthetic rate and in fruit expansion stage，the average net photosynthetic rate of 0.2 and 0.4 mg/L EBR treatments increased by 24.05% and 18.38%，respectively，but that of 0.6 mg/L EBR group decreased by 3.56%.At 40 d after flowering，0.2 and 0.4 mg/L EBR treatments significantly increased Rubisco enzyme activity（P<0.05，the same below），which increased by 21.74% and 31.30% compared to CK.However，0.6 mg/L EBR treatment inhibited Rubisco enzyme activity which decreased by 36.90%.0.4 mg/L EBR had a good effect on improving the correlation between net photosynthetic rate and various photosynthetic pigments，and net photosynthetic rate was significantly correlated with the content of chlorophyll a，chlorophyll b and chlorophyll ab，and net photosynthetic rate was extremely significantly correlated with carotenoid content（P<0.01）.In the maturing stage，0.2 mg/L EBR treatment could promote the accumulation of soluble total sugar and reducing sugar，reaching 203.32 and 170.37 mg/g respectively.All treatments could significantly reduce the content of titratable acid，tannins and total phenols.Among them，0.4 mg/L EBR treatment could reduce the content of tannins and total phenols，reaching 7.59 and 5.26 mg/g respectively.All treatments could promote the fruit to complete color change in advance.【Conclusion】 0.6 mg/L EBR affects photosynthetic rate by reducing Rubisco enzyme activity and photosynthetic pigment content in the early stage of treatment.0.4 mg/L EBR improves plant photosynthesis and Merlot grape fruit quality by increasing photosynthetic rate，Rubisco enzyme activity and photosynthetic pigment content.