Influence of deficit irrigation timing on the fruit quality of grapefruit (Citrus paradisi Mac.).

The irrigation necessities for grapefruit production are very high. Due to the scarcity of water resources, growers use deficit irrigation (DI) - which could affect the fruit quality. Different DI strategies were studied: Control (irrigated at 100% ETc) and T1, T2 and T3 (50% ETc at phases I, II and III of fruit growth, respectively). Strategy T1 only delayed external maturation depending on the duration of the water stress. High water stress in T2 delayed fruit maturation, increased acidity and reduced the sugar concentration. Under T2, trees suffering moderate water stress showed increased flavonoid and phenolic contents but decreased lycopene levels. External maturation was delayed in T3 when severe stress occurred during the first part of phase III. Strategy T3 advanced internal ripening when moderate water stress occurred during the first 40 days of phase III, increasing sugar accumulation, promoted by the high acidity of the fruits. Moderate water stress also increased β-carotene, flavonoids and phenolics levels.