Partial rootzone drying and regulated deficit irrigation can be used as water-saving strategies without compromising fruit yield and quality in tropically grown sweet orange

We examined the effects of partial rootzone drying (PRD) and regulated deficit irrigation (RDI) on some physiological and agronomical traits in tropically grown sweet orange (Citrus sinensis (L.) Osbeck). Seven different irrigation strategies were applied over three consecutive years and compared regarding their effects on leaf gas exchange, vegetative growth, fruit yield and quality and gene expression of fruit quality-related genes. Stomatal conductance and leaf temperature were significantly affected by the different irrigation treatments and seasonal variations in the atmospheric vapour pressure deficit and air temperature. Both PRD treatments (with alternation of the irrigation side every 15 and 30 days) significantly increased the irrigation water use efficiency by 41–56% compared to the full irrigation treatment. RDI treatments induced a significant upregulation of genes related to the citrate metabolism and carotenoid biosynthesis. Trees exposed to PRD with alternation of the irrigation side at every 15 days, as well as to RDI at the fruit ripening stage, showed values of yield, productive efficiency, fruit mass, length and size, juice yield and ratio between soluble solids and titratable acidity similar to those of the full irrigation treatment. Therefore, PRD and RDI can be viable water saving irrigation strategies for sweet orange production in tropical conditions.