‘Star Ruby’ grapefruit and ‘Clemenules’ mandarin trees show different physiological and agronomic responses to irrigation with saline water

The aim of this experiment was to evaluate the effects of saline water irrigation in two citrus species, ‘Clemenules’ mandarin (CLM) and ‘Star Ruby’ grapefruit (SR), both grafted on ‘Cleopatra’ mandarin (a rootstock considered as a Cl− excluder, but a Na+ non-excluder). The experiment was carried out over 3 years (2008–2010) in the IMIDA experimental orchard located at Torre Pacheco (Murcia), using 15-year-old trees irrigated with water of two salinity levels: 0 and 40 mM NaCl. Our data indicate different physiological and agronomic responses of the two citrus species (CLM and SR). The higher salt tolerance observed in CLM was due to the lower accumulation of Cl− in leaves and the greater reduction in vegetative growth with no effect on the quantity or quality of yield. Further, the quality of yield was improved due to the increase in total soluble solids and acidity, since the quality of the juice of CLM fruits is negatively affected in semi-arid regions by lower acidity levels. However, in SR, a high leaf Cl− concentration reduced both vegetative growth and yield and affected fruit quality negatively by increasing the titratable acidity. The increase in the acidity in SR fruits due to salinity translated into a delay of the ripening process, since more time was required to reach optimal levels for the fresh market. Thus, based on these results, we recommend the use of salt-tolerant species such as ‘Clemenules’ mandarin grafted on ‘Cleopatra’ mandarin for semi-arid regions, where the only irrigation water available is saline.