Response of Tomato Sugar and Acid Metabolism and Fruit Quality under Different High Temperature and Relative Humidity Conditions

The combined stress of high temperature and high relative air humidity is one of the most serious agrometeorological disasters that restricts the production capacity of protected agriculture.However,there is little information about the precise interaction between them on tomato fruit quality.The objectives of this study were to explore the effects of the combined stress of high temperature and relative humidity on the sugar and acid metabolism and fruit quality of tomato fruits,and to determine the best relative air humidity for fruit quality under high temperature environments.Four temperature treatments(32℃,35℃,38℃,41℃),three relative air humidity(50%,70%,90%)and four duration(3,6,9,12 d)orthogonal experiments were conducted,with 28℃,50%as control.The results showed that under high temperature and relative air humidity,the activity of sucrose metabolizing enzymes in young tomato fruits changed,which reduced fruits soluble sugar content;in addition,enzyme activities involved phosphopyruvate carboxylase(PEPC),mitochondria aconitase(MDH)and citrate synthetase(CS)increased which increased the content of organic acids(especially malic acid).Eventually,vitamin C,total sugar and sugar-acid ratio decreased significantly,while the titratable acid increased,resulting in a decrease in fruit flavor quality and nutritional quality in ripe fruit.Specifically,a temperature of 32℃and a relative air humidity of 70%were the best cultivation conditions for tomato reproductive growth period under high temperature.Our results indicating that fruit quality reduced under high temperature at the flowering stage,while increasing the relative air humidity to 70%could alleviate this negative effect.Our results are benefit to better understand the interaction between microclimate parameters under specific climatic conditions in the greenhouse environment and their impact on tomato flavor quality.