Effect of irrigation practices upon yield and fruit quality of four grapefruit (Citrus paradisi Mac.) cultivars

Two strategies of irrigation were applied during the phase of fruit growth in 30-year-old grapefruit trees (Citrus paradisi Mac.) of four varieties (cv. Marsh SRA 8, cv. Shambar SRA 22, cv. Frost Marsh, cv. Ruby). For the first strategy (T1), the trees were irrigated every week at 100% crop evapotranspiration (ETc), while for the second strategy (T2) at 60% ETc. At harvest time, tree yield was estimated along with fruit quality and water productivity. T1 strategy significantly increased the tree yield, the fruit weight and the juice content. Although an increase in water productivity (crop yield/total water use) was achieved during the water stress experiment for three out of the four varieties. The main effect of the T2 strategy was a significant increase of qualitative (commercial and nutritional) attributes like total soluble solids (TSS), citric acid, ascorbic acid (Vitamin C) and phenolic content. In addition, strategy T2 increased the maturation index and the fruits had sweeter flavor for two varieties. These results lead to the conclusion that in mature grapefruit trees, optimal irrigation practice provided better fruit yield, while water stress practices favor the accumulation of specific nutritional elements and improve specific fruit quality parameters, especially for cv. Ruby.