Effects of Deficit Irrigation and Growth Regulators on Physio-Biochemical Changes, Yield, Fruit Quality and Water Productivity in Pomegranate (Punica granatum) Growing in Shallow Basaltic Soils

Abstract

A field study was conducted (2021–2022) that evaluated the effects of deficit irrigation (DI) strategies [60% and 80% of crop evapotranspiration (ETc)] and plant growth regulators [PGRs; salicylic acid (SA) and naphthalene acetic acid (NAA)] on fruit yield, water use efficiency (WUE) and physiological responses of pomegranate grown in shallow basaltic soils. Irrigation at 80% ETc combined with SA and NAA significantly increased fruit yield by 32% and 40% and improved WUE by 65% and 75% under DI and partial root-zone drying (PRD), respectively. PRD outperformed DI, producing 8.56% higher yield and 6.25% higher WUE at the same irrigation level without PGRs. Physiological parameters such as the relative water content, membrane stability index (MSI), normalized difference vegetation index, photosystem II efficiency, chlorophyll content and photosynthetic rate were strongly correlated with fruit yield (r = 0.90–0.97). Under stress conditions, SA application increased the photosynthetic rate and MSI while reducing the leaf surface temperature by 6%, 8% and 2%, respectively, compared with those of untreated plants. Foliar application of SA (300 ppm) + NAA (45 ppm) under DI-80 or PRD-80 enhanced water productivity and fruit yield in pomegranates in challenging soil conditions in semiarid regions.