Foliar application of 5-aminolevulinic acid improves the salt tolerance in sunflower (Helianthus annuus L.) by enhancing the morphological attributes and antioxidant defense mechanism

Salinity is among the main abiotic stresses affecting crop growth and productivity in many regions across the globe. This study aimed to assess the potential of foliar application of 5-aminolevulinic acid (ALA) in improving the salt tolerance in sunflower under an arid climate. The experiment comprised of two sunflower hybrids (Parsun and NK-Senji), foliage sprayed with five levels of ALA (control, 25, 50, 75, and 100 mg L⁻¹), under two soil salinity levels (control, 40, and 80 mM NaCl). The results revealed improved plant height, number of leaves, stem diameter, and dry biomass traits in sunflower hybrid ‘NK-Senji’, while foliar applied ALA at 75 mg L⁻¹ was more useful for improvement in these traits under both growth environments, but the effect was more prominent under saline conditions. Improvement in yield and morphological traits in sunflower due to foliage application of ALA was attributed to an improvement in chlorophyll contents and increased actions of catalase, peroxidase, and superoxidase dismutase. It is concluded that foliar applied ALA at 75 mg L⁻¹ in sunflower hybrid ‘NK-Senji’ is advantageous for improving the sunflower yield in saline soils.