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Abstract

Salinity is one of the major environmental restrictions to development and esthetic value of landscape plants in arid and semi-arid climates. Nerium oleander L., commonly known as oleander, is a frequently utilized woody plant in urban landscaping due to its drought and mild salt tolerance; however, long-term exposure to saline environments adversely impacts plant development, photosynthetic efficiency and metabolic activities. Recently, chitosan oligosaccharides (COS) have emerged as potential biostimulants able to improve plant tolerance to abiotic stressors via control of antioxidant defencedefence mechanisms and ion homeostasis. Their application has been investigated predominantly in agricultural and horticultural crops, while information regarding ornamental woody species remains scarce. The current research was undertaken to investigate the efficacy of foliar application of COS to alleviate salt stress in Oleander. Plants were treated with 0 or 100 mM NaCl and sprayed with COS at 0, 50, 100 or 200 mg L-1. Salinity considerably decreased plant height, biomass accumulation, concentration of chlorophyll and K+/Na+ ratio and dramatically increased malondialdehyde (MDA) and hydrogen peroxide (H2O2) levels. Application of COS, particularly at 100 mg L⁻¹ significantly enhanced the growth performance, elevated the chlorophyll content, stimulated the activities of superoxide dismutase, catalase and ascorbate peroxidase, raised the proline accumulation and reduced the oxidative damage. COS-treated plants showed less Na+ buildup and greater K+ concentrations than the untreated salt stressed plants. Results showed that COS successfully mitigated the adverse effect of salinity stress through enhancement of antioxidant defencedefence and ionic homeostasis. Results support the potential use of COS as a bio-friendly biostimulant for sustainable cultivation of Oleander in salt-affected soils and urban environments

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