Effect of Low-Light Stress on Sugar and Acid Accumulation during Fruit Development and Ripening of Sweet Cherry

In the production process of sweet cherry, there are unreasonable planting densities and tree shape selections. With increasing tree age, the crown of the tree continues to expand and the tree body is prone to canopy closure, which leads to the inability to efficiently use space and light energy. Low-light has become a major limiting factor in the quality of sweet cherry. Therefore, we analyzed the changes of various physiological indicators and the transcriptome of ‘Hongdeng’ sweet cherry under shading treatment in this study to investigate the effects of low-light stress on the photosynthetic characteristics of sweet cherry leaves and fruit physiology and biochemistry. The results showed that shading significantly reduces the light capture capacity of leaves, damages the photosystem, reduces carbon assimilation capacity, and consumes the majority of the captured light energy as photochemical energy, thereby restricting the growth and development of leaves and reducing the accumulation of nutrients in fruits. Shading significantly reduced fruit weight, sugar content, and vitamin C content at maturity and significantly increased acid content. Transcriptomic data demonstrated that low-light stress produces a large number of differential genes related to carbon metabolism, organic acid metabolism, and stress resistance, thereby suggesting that low-light stress may affect the expression of these related genes and inclusions in the fruit. The results of this study will provide theoretical and technical support for the physiological response mechanism of low-light tolerance in sweet cherry, the selection and breeding of low-light tolerant sweet cherry varieties, and the cultivation of sweet cherry in facilities.