Exogenous Methyl Jasmonate Effects of Sugar, Acid, and Calcium Accumulation During Fruit Development in Prunus humilis Bunge

Prunus humilis is rich in various minerals, organic acids, proteins, and carbohydrates, but its sour taste limits fresh consumption and industry growth. Methyl jasmonate, a plant growth regulator known to enhance fruit quality, has been studied in other fruits, but research on its effects on P. humilis has not yet been reported. This experiment used the P. humilis cultivar ‘Nongda No. 4’ as the material. During the fruit development stages (the pre-young fruit stage and pre-coloring and enlargement stage), the fruiting branches were sprayed with a 20 mg/L methyl jasmonate solution four times. The results indicate that exogenous methyl jasmonate increases the content of various sugar components in P. humilis fruits throughout their development, with a particularly strong effect in the later stages of fruit development. It effectively reduces the content of malic acid and citric acid in these later stages while significantly enhancing flavor-related attributes such as the sweetness, sugar–acid ratio, and sweetness–acid ratio. Moreover, methyl jasmonate markedly promoted the accumulation of different forms of calcium in the fruit. Specifically, at the fully ripe stage, the total sugar content increased significantly by 18.64% (p < 0.05), the total acid content decreased by 15.95% (p < 0.05), and the total calcium content increased by 55.98% (p < 0.05). Correlation and principal component analyses revealed that sugars, acids, and calcium are closely linked in P. humilis, and exogenous treatment with methyl jasmonate effectively improved the overall quality score of sugars, acids, and calcium in the fruit throughout its development. In conclusion, exogenous methyl jasmonate can effectively improve the sugar–acid quality, flavor, and calcium content of P. humilis fruits. This provides a theoretical foundation for cultivation management, quality enhancement, and the breeding of fresh-eating cultivars.