Effect Of Exogenous Melatonin And Brassinolides Treatment On Photosynthesis And Fruit Quality Of ’Cabernet Sauvignon’ Grapes Under Heat Stress

The "greenhouse effect" caused by the increase in atmospheric CO2 concentration is increasing the temperature of the atmosphere,the continuous high temperature environment has seriously affected the yield and quality of wine grape.Exogenous hormones can alleviate the damage of adversity to plants,promote fruit quality.Therefore,in this study,the wine grape ’Cabernet Sauvignon’ was used as the test material,150μmol·L-1MLT and 0.6 mg·L-1EBR is sprayed on the marked grapes one week before veraison(55 days after anthesis),MRM-Model 2420 infrared radiator(Kallo electronics Inc,Pennsylvania,USA)was used to increase the temperature,making the temperature rise by 5±0.5 degrees,distilled water spraying was used as control,the effects of exogenous spraying 150μmol·L-1MLT and 0.6 mg·L-1EBR on photosynthesis and fruit quality of Cabernet Sauvignon ’ grape under high temperature stress were studied,the results of the study are as follows:1.Effect of 150μmol·L-1MLT and 0.6 mg·L-1EBR on grape growth under high temperature stress.High temperatures reduced the length and stem thickness of new shoots,spraying 150μmol·L-1MLT and 0.6 mg·L-1EBR at high temperature increased new shoot length,stem thickness,longitudinal and transverse fruit diameter;79 days after anthesis,the new tip length increased by 42.33%after spraying 150 μmol·L-1MLT at high temperature compared to high temperature,stem thickness increased by 5.85%after spraying 150 μmol·L-1MLT at high temperature compared with high temperature,fruit transverse diameter increased by 7.08%after spraying 150 μmol·L-1MLT at high temperature compared to high temperature,the new tip length increased by 15.7%after spraying 0.6 mg·L-1EBR at high temperature compared to high temperature,stem thickness increased by 5.26%after spraying 0.6 mg·L-1EBR at high temperature compared to high temperature,fruit cross diameter increased by 6.19%after spraying 0.6 mg·L-1EBR at high temperature compared to high temperature,this indicates that spraying 150 μmol·L-1MLT with 0.6 mg·L-1EBR under high temperature has a mitigating effect on the growth of grapes under high temperature.2.Effects of 150 μmol·L-1MLT and 0.6 mg·L-1EBR on photosynthetic characteristics of grape leaves.High temperatures reduced chlorophyll a,chlorophyll b,carotenoids spraying 150 μmol·L-1MLT and 0.6 mg·L-1 EBR at high temperature alleviated the damage to chlorophyll a,chlorophyll b and carotenoids caused by high temperature stress;91 and 115d days after anthesis,net photosynthetic rate(Pn)increased by 18.98%and 27.27%after spraying 150 μmol·L-1MLT at high temperature compared to high temperature,net photosynthetic rate(Pn)increased by 8.76%and 13.78%after spraying 0.6 mg·L-1EBR at high temperature compared to high temperature;115 days after anthesis,the transpiration rate(Tr)increased by 23.68%after spraying 150 μmol·L-1MLT at high temperature compared to high temperature,the maximum photochemical efficiency(Fv/Fm)increased by 5.23%after spraying 150μmol·L-1MLT at high temperature compared with high temperature,the actual quantum yield(YII)after spraying 150 μmol·L-1MLT at high temperature increased by 12.98%compared to high temperature,transpiration rate(Tr)increased by 13.16%after spraying 0.6 mg·L-1EBR at high temperature compared to high temperature,the maximum photochemical efficiency(Fv/Fm)increased by 3.83%after spraying 0.6 mg·L-1EBR at high temperature compared to high temperature,the actual quantum yield(YII)after spraying 0.6 mg·L-1EBR at high temperature increased by 10.21%compared to high temperature;Intercellular CO2 concentration(Ci)was reduced by spraying 150 μmol·L-1MLT at temperature,increased photosynthetic capacity of leaves;high temperatures significantly reduced the potential photochemical activity(Fv/Fo)and electron transfer efficiency(ETR),high-temperature spraying of 150 μmol·L-1MLT reduces photosynthetic organ damage caused by high-temperature stress,the effect is remarkable.3.Effect of 150 μmoI·L-1MLT and 0.6 mg·L-1EBR on antioxidant indexes in grapes.Spraying 150μmol·L-1MLT and 0.6 mg·L-1EBR could increase the activities of SOD and CAT and the content of reduced glutathione under high temperature,reduction of malondialdehyde content;among them,SOD at 67 day after anthesis,spraying 150 μmol·L-1MLT increased 44.72%compared to CK,spraying 0.6 mg·L-1EBR increased 28.88%compared to CK,the spraying of 150 μmol·L-1MLT at high temperature increased 41.16%compared to high temperature,spraying 0.6 mg·L-1EBR at high temperature increased 28.99%compared to high temperature.4.Effect of 150 μmol·L-1MLT and 0.6 mg·L-1EBR on grape fruit quality.Spraying 150μmol·L-1MLT at high temperature can mitigate the effect of high temperature on fruit quality;67 days after anthesis,the anthocyanin content increased by 22.61%after spraying 150 μmol·L-1MLT compared with CK,the anthocyanin content increased by 64.91%after spraying 150 μmol·L-1MLT at high temperature compared to high temperature,the anthocyanin content increased by 36.39%after spraying 0.6 mg·L-1EBR at high temperature compared to high temperature,the best results were obtained by spraying 150 μmol·L-1MLT treatment.