Effect of Foliar Calcium Fertilization on Fruit Quality, Cell Wall Enzyme Activity and Expression of Key Genes in Chinese Cherry

Chinese cherries are early flowering and early fruiting, with both edible and ornamental values. This study aims to explore the effects of pre-harvest spraying with different concentrations of CaCl2, amino acid calcium, and sugar alcohol calcium on the quality of Chinese cherry and the expression of genes related to cell wall softening. The goal is to identify suitable calcium-based agents for pre-harvest spraying on Chinese cherry. The results of the study demonstrated that all three exogenous calcium treatments significantly increased the mineral content compared to the control group. Moreover, these treatments also led to a significant increase in various fruit quality parameters such as hundred fruit weight, firmness, soluble solid, soluble sugar, titratable, vitamin C, soluble protein, β-Carotene content and superoxide dismutase, peroxidase activities. Additionally, they were found to effectively reduce rot rate, polyphenol oxidase activity, malondialdehyde content and relative conductivity. The activity of pectin methylesterase, polygalacturonase, cellulase and β-galactose was reduced by amino acid calcium and sugar alcohol calcium. All three types of exogenous calcium down-regulated the expression of PME and ChCaBP1. Additionally, amino acid calcium and sugar alcohol calcium decreased the expression of PG, Cx, and BGal. Exogenous calcium reduces the size of stomata in the fruit epidermis, leading to a decrease in both fruit respiration rate and transpiration. Of the three calcium preparations, amino acid calcium and sugar alcohol calcium were more effective than CaCl2, with 0.12 g·L−1sugar alcohol calcium and 0.06 g·L−1 amino acid calcium being the most effective.