Magnesium's impact on fruit quality of loquat: Insights into sugar and acid dynamics

The flavor and taste of loquat fruits are influenced by soluble sugars (fructose, glucose, and sucrose) and organic acids, with malic acid being crucial. This study explored the effect of foliar magnesium sulfate (MgSO4) application on the sugar -acid profile and associated physiological and molecular factors in loquat fruits. Varied concentrations of MgSO4 (1 %, 2 %, 3 %) and a control (water spray) were tested. The application of 2 % MgSO4 notably enhanced fruit weight and size, increased the sugar -acid ratio by 5.58 -fold, elevated total soluble solids by 53.81 %, and reduced titratable acidity by 72.45 %. The increase in fructose and glucose (by 107.20 % and 77.50 %, respectively) and decrease in malic acid (by 43.65 %) were significant with 2 % MgSO4 treatment. Enzymatic and gene expression analyses revealed significant upregulation of SPS, SS, HK, and FK activities, and corresponding genes, particularly with 2 % MgSO4, while PEPC activity and its associated genes were downregulated. The study also identified a positive correlation of NAD-MDH with malic acid content and varied expression of NAD-ME and NAD-MDH genes, indicating their roles in malic acid biosynthesis. These findings demonstrate that MgSO4 application substantially modified the enzymatic and genetic profile related to sugar and acid metabolism in loquats, leading to improved fruit quality with higher sugar content and reduced acidity. This study offers valuable insights for enhancing loquat fruit quality through magnesium -based horticultural practices.