Canopy management combined with ethylene application enhances acidity and phenolic accumulation of Marselan grapes in Ningxia

Abstract

Warm climate in Ningxia wine region commonly triggers excessive sugar accumulation, low organic acid and inadequate secondary metabolite synthesis in Marselan grapes, deteriorating grape and wine quality. This two-year field trial was carried out to explore whether combined canopy height management and ethephon spraying could balance berry sugar-acid composition and promote phenolic accumulation. Three canopy heights (0.9, 1.2, 1.5 m) and two ethephon concentrations (300, 600 mg/L) were set with single and combined treatments. Results indicate that all three canopy height treatments reduced sugar content and increased acid content in grape fruit. Fruit treated with ethylene exhibited higher total phenolic content. Compared with control, independent 1.2 m canopy cut soluble sugar by 10%–11% and elevated titratable acid by 13%–14%. Single 300 mg/L ethephon increased berry total phenolics by 10%-23% and total anthocyanins by 10%–17%. The combination of 1.2 m canopy plus 300 mg/L ethephon reduced fruit sugar-acid ratio by around 14%, and increased total phenolics, tannins and flavanols by 11%–46%; meanwhile, contents of multiple monomeric anthocyanins and phenolic compounds in finished wine were significantly improved. In conclusion, 1.2 m canopy matched with 300 mg/L ethephon is an effective cultivation strategy to fix high-sugar low-acid problems and enhance phenolic richness for warm-climate Marselan production.