Genotype performance, biochemical and anatomical response of two mango rootstocks to glycine betaine and algae extract under salinity stress

Abstract Background Salinity is a major abiotic constraint limiting mango (Mangifera indica L.) production, particularly in arid and semi-arid regions. This study evaluated the effects of foliar application of glycine betaine (GB) and algae extract (AE) on the growth, physiological, biochemical, and anatomical responses of two mango rootstocks, Sokkary and Gahrawy, irrigated with tap water, 1500 ppm, or 3000 ppm seawater. Results Salinity significantly reduced plant height, stem diameter, leaf area, chlorophyll content, and the K⁺/Na⁺ ratio, while increasing malondialdehyde (MDA), hydrogen peroxide (H₂O₂), and antioxidant enzyme activities. At 3000 ppm, untreated plants reached only 24–25 cm in height, whereas GB application in Gahrawy and AE application in Sokkary substantially alleviated this inhibition, restoring height to 42.25 and 40.00 cm, respectively. Gahrawy exhibited greater intrinsic salinity tolerance, with higher K⁺ retention (2.174%), endogenous glycine betaine (2.91 µmol g⁻¹ DW), and antioxidant capacity (40.23% DPPH scavenging). In contrast, Sokkary responded more strongly to biostimulant application, particularly GB under severe salinity. GB improved osmotic adjustment, ion homeostasis, and chlorophyll stability, increasing plant height to 50.0 cm in Gahrawy at 1500 ppm and reducing leaf Na⁺ accumulation by up to 51% at 3000 ppm. AE enhanced antioxidant activity (53.0% DPPH scavenging), leaf expansion, and vascular development. Anatomical analyses revealed genotype-specific structural adaptations associated with salinity tolerance. Conclusions Salinity tolerance depended on the interaction among genotype, salinity level, and biostimulant treatment. GB and AE effectively alleviated salt-induced damage through complementary physiological and anatomical mechanisms, supporting their use as sustainable strategies to improve mango nursery production under saline conditions.