FOLIAR APPLICATION OF SALICYLIC ACID AND SEAWEED EXTRACT MODIFIES LEAFLET ANATOMY OF YOUNG DATE PALM TREES (PHOENIX DACTYLIFERA L. CV. KHADRAWI)

Abstract

The effects of foliar biostimulants on leaflet tissue organisation in date palm remain poorly documented. A field experiment in Salah al-Din, Iraq, evaluated three monthly foliar sprays of salicylic acid (SA; 50, 100 and 150 mg L⁻¹) combined factorially with a seaweed extract (SW; 1, 2 and 3 mL L⁻¹), plus an untreated control, on 19 leaflet anatomical traits of five-year-old Phoenix dactylifera L. cv. Khadrawi palms. All SA × SW combinations increased stomatal density on the abaxial (+32.1%) and adaxial (+30.7%) surfaces (P ≤ 0.001) without reducing stomatal length, raising the stomatal pore area index by 32.7–44.4%. Treated palms also had thicker adaxial and abaxial cuticles (+55.6%), a thicker adaxial epidermis (+13.9%), wider vascular bundles (+27.5%) and thicker phloem fibre caps (+9.6%). SA concentration governed the stomatal and epidermal responses: 150 mg L⁻¹ raised total stomatal density to 580 mm⁻², above 50 and 100 mg L⁻¹ (P = 0.014), and gave the thickest adaxial epidermis (P = 0.047). SW concentration mainly affected adaxial cuticle thickness (P = 0.008), and vascular bundle size depended on the SA × SW combination. Principal component analysis (56.3% of the variation on two axes) and a composite anatomical index ranked SA 150 mg L⁻¹ + SW 1 mL L⁻¹ (T7) first and SA 150 mg L⁻¹ + SW 3 mL L⁻¹ (T9) second. Foliar SA at 150 mg L⁻¹ with seaweed extract therefore promotes a denser stomatal apparatus, a reinforced dermal system and larger vascular bundles, traits linked to greater gas-exchange capacity and resilience.