Deficit Irrigation and Preharvest Chitosan Sprays Enhance Fruit Quality and Postharvest Performance in Peach

Water scarcity in Mediterranean environments has driven the search for sustainable strategies to improve water-use efficiency while maintaining fruit quality. This study evaluated the combined effect of sustained deficit irrigation and preharvest chitosan sprays on fruit quality, bioactive compounds, mineral composition, and postharvest behaviour in two late-season peach cultivars (“Tiétar” and “Duero”) grown under semi-arid Mediterranean conditions. Sustained deficit irrigation was applied throughout the season, together with preharvest chitosan applications during fruit development, to assess individual and interactive effects. Deficit irrigation caused only slight reductions in fruit size while increasing total soluble solids (TSS) concentration and the maturity index (TSS/titratable acidity). Chitosan application increased fruit firmness and modified titratable acidity depending on the irrigation regime (full irrigation or deficit irrigation). The combined treatment (chitosan + deficit irrigation) promoted the accumulation of phenolic compounds and antioxidant activity, particularly in “Tiétar”, increased calcium and iron contents, and showed a longer shelf life. These results indicate that integrating deficit irrigation with preharvest chitosan sprays can mitigate the impact of water scarcity while improving functional and postharvest quality of peaches under Mediterranean conditions.